README

Name
    ngx_lua - Embed the power of Lua into Nginx

    *This module is not distributed with the Nginx source.* See the
    installation instructions.

Status
    This module is under active development and is production ready.

Version
    This document describes ngx_lua v0.3.1rc38
    (<https://github.com/chaoslawful/lua-nginx-module/tags>) released on 2
    December 2011.

Synopsis
        # set search paths for pure Lua external libraries (';;' is the default path):
        lua_package_path '/foo/bar/?.lua;/blah/?.lua;;';

        # set search paths for Lua external libraries written in C (can also use ';;'):
        lua_package_cpath '/bar/baz/?.so;/blah/blah/?.so;;';

        server {
            location /inline_concat {
                # MIME type determined by default_type:
                default_type 'text/plain';

                set $a "hello";
                set $b "world";
                # inline lua script
                set_by_lua $res "return ngx.arg[1]..ngx.arg[2]" $a $b;
                echo $res;
            }

            location /rel_file_concat {
                set $a "foo";
                set $b "bar";
                # script path relative to nginx prefix
                # $ngx_prefix/conf/concat.lua contents:
                #
                #    return ngx.arg[1]..ngx.arg[2]
                #
                set_by_lua_file $res conf/concat.lua $a $b;
                echo $res;
            }

            location /abs_file_concat {
                set $a "fee";
                set $b "baz";
                # absolute script path not modified
                set_by_lua_file $res /usr/nginx/conf/concat.lua $a $b;
                echo $res;
            }

            location /lua_content {
                # MIME type determined by default_type:
                default_type 'text/plain';

                content_by_lua "ngx.say('Hello,world!')"
            }

             location /nginx_var {
                # MIME type determined by default_type:
                default_type 'text/plain';

                # try access /nginx_var?a=hello,world
                content_by_lua "ngx.print(ngx.var['arg_a'], '\\n')";
            }

            location /request_body {
                 # force reading request body (default off)
                 lua_need_request_body on;
                 client_max_body_size 50k;
                 client_body_buffer_size 50k;

                 content_by_lua 'ngx.print(ngx.var.request_body)';
            }

            # transparent non-blocking I/O in Lua via subrequests
            location /lua {
                # MIME type determined by default_type:
                default_type 'text/plain';

                content_by_lua '
                    local res = ngx.location.capture("/some_other_location")
                    if res.status == 200 then
                        ngx.print(res.body)
                    end';
            }

            # GET /recur?num=5
            location /recur {
                # MIME type determined by default_type:
                default_type 'text/plain';

                content_by_lua '
                   local num = tonumber(ngx.var.arg_num) or 0

                   if num > 50 then
                       ngx.say("num too big")
                       return
                   end

                   ngx.say("num is: ", num)

                   if num > 0 then
                       res = ngx.location.capture("/recur?num=" .. tostring(num - 1))
                       ngx.print("status=", res.status, " ")
                       ngx.print("body=", res.body)
                   else
                       ngx.say("end")
                   end
                   ';
            }

            location /foo {
                rewrite_by_lua '
                    res = ngx.location.capture("/memc",
                        { args = { cmd = 'incr', key = ngx.var.uri } }
                    )
                ';

                proxy_pass http://blah.blah.com;
            }

            location /blah {
                access_by_lua '
                    local res = ngx.location.capture("/auth")

                    if res.status == ngx.HTTP_OK then
                        return
                    end

                    if res.status == ngx.HTTP_FORBIDDEN then
                        ngx.exit(res.status)
                    end

                    ngx.exit(ngx.HTTP_INTERNAL_SERVER_ERROR)
                ';

                # proxy_pass/fastcgi_pass/postgres_pass/...
            }

            location /mixed {
                rewrite_by_lua_file /path/to/rewrite.lua;
                access_by_lua_file /path/to/access.lua;
                content_by_lua_file /path/to/content.lua;
            }

            # use nginx var in code path
            # WARN: contents in nginx var must be carefully filtered,
            # otherwise there'll be great security risk!
            location ~ ^/app/(.+) {
                    content_by_lua_file /path/to/lua/app/root/$1.lua;
            }

            location / {
               lua_need_request_body on;

               client_max_body_size 100k;
               client_body_buffer_size 100k;

               access_by_lua '
                   -- check the client IP addr is in our black list
                   if ngx.var.remote_addr == "132.5.72.3" then
                       ngx.exit(ngx.HTTP_FORBIDDEN)
                   end

                   -- check if the request body contains bad words
                   if ngx.var.request_body and
                            string.match(ngx.var.request_body, "fsck")
                   then
                       return ngx.redirect("/terms_of_use.html")
                   end

                   -- tests passed
               ';

               # proxy_pass/fastcgi_pass/etc settings
            }
        }

Description
    This module embeds the Lua interpreter or LuaJIT into the nginx core and
    integrates the powerful Lua threads (aka Lua coroutines) into the nginx
    event model by means of nginx subrequests.

    Unlike Apache's mod_lua
    (<http://httpd.apache.org/docs/2.3/mod/mod_lua.html>) and Lighttpd's
    mod_magnet (<http://redmine.lighttpd.net/wiki/1/Docs:ModMagnet>), Lua
    code written atop this module can be *100% non-blocking* on network
    traffic as long as you use the ngx.location.capture or
    ngx.location.capture_multi interfaces to let the nginx core do all your
    requests to mysql, postgresql, memcached, redis, upstream http web
    services, and etc etc etc (see [[HttpDrizzleModule]], ngx_postgres
    (<http://github.com/FRiCKLE/ngx_postgres/>), [[HttpMemcModule]],
    [[HttpRedis2Module]] and [[HttpProxyModule]] modules for details).

    The Lua interpreter instance is shared across all the requests in a
    single nginx worker process.

    Request contexts are isolated from each other by means of Lua
    (lightweight) threads (aka Lua coroutines). And Lua modules loaded are
    persistent on the nginx worker process level. So the memory footprint is
    quite small even when your nginx worker process is handling 10K requests
    at the same time.

Directives
  lua_code_cache
    syntax: *lua_code_cache on | off*

    default: *lua_code_cache on*

    context: *main, server, location, location if*

    Enable or disable the Lua code cache for set_by_lua_file,
    content_by_lua_file, rewrite_by_lua_file, and access_by_lua_file, and
    also force Lua module reloading on a per-request basis.

    The Lua files referenced in set_by_lua_file, content_by_lua_file,
    access_by_lua_file, and rewrite_by_lua_file will not be cached at all,
    and Lua's "package.loaded" table will be cleared at the entry point of
    every request (such that Lua modules will not be cached either). With
    this in place, developers can follow the PHP way, i.e.,
    edit-and-refresh.

    Please note however, that Lua code inlined into nginx.conf such as those
    specified by set_by_lua, content_by_lua, access_by_lua, and
    rewrite_by_lua will *always* be cached because only the Nginx config
    file parser can correctly parse the "nginx.conf" file and the only ways
    to to reload the config file are to send a "HUP" signal or to restart
    Nginx.

    The ngx_lua module currently does not support the "stat" mode like
    Apache's "mod_lua" does but this is planned for implementation in the
    future.

    Disabling the Lua code cache is strongly discouraged for production use
    and should only be used during development as it has a significant
    impact on overall performance. In addition, race conditions when
    reloading Lua modules are common for concurrent requests when the code
    cache is disabled.

  lua_regex_cache_max_entries
    syntax: *lua_regex_cache_max_entries <num>*

    default: *lua_regex_cache_max_entries 1024*

    context: *http*

    Specifies the maximum number of entries allowed in the worker process
    level compiled regex cache.

    The regular expressions used in ngx.re.match, ngx.re.gmatch, ngx.re.sub,
    and ngx.re.gsub will be cached within this cache if the regex option "o"
    (i.e., compile-once flag) is specified.

    The default number of entries allowed is 1024 and when this limit is
    reached, new regexes will not be cached (as if the "o" option was not
    specified) and there will be one, and only one, warning in the
    "error.log" file:

        2011/08/27 23:18:26 [warn] 31997#0: *1 lua exceeding regex cache max entries (1024), ...

    You should not activate the "o" option for regexes (and/or "replace"
    string arguments for ngx.re.sub and ngx.re.gsub) that are generated *on
    the fly* and give rise to infinite variations to avoid hitting the
    specified limit.

  lua_package_path
    syntax: *lua_package_path <lua-style-path-str>*

    default: *The content of LUA_PATH environ variable or Lua's compiled-in
    defaults.*

    context: *main*

    Sets the Lua module search path used by scripts specified by set_by_lua,
    content_by_lua and others. The path string is in standard Lua path form,
    and ";;" can be used to stand for the original path.

  lua_package_cpath
    syntax: *lua_package_cpath <lua-style-cpath-str>*

    default: *The content of LUA_CPATH environ variable or Lua's compiled-in
    defaults.*

    context: *main*

    Sets the Lua C-module search path used by scripts specified by
    set_by_lua, content_by_lua and others. The cpath string is in standard
    Lua cpath form, and ";;" can be used to stand for the original cpath.

  set_by_lua
    syntax: *set_by_lua $res <lua-script-str> [$arg1 $arg2 ...]*

    context: *main, server, location, server if, location if*

    phase: *rewrite*

    Execute user code specified by "<lua-script-str>" with input arguments
    "$arg1 $arg2 ...", and set the script's return value to $res in string
    form. In "<lua-script-str>" code the input arguments can be retrieved
    from "ngx.arg" table (index starts from 1 and increased sequentially).

    set_by_lua directive is designed to execute short, fast running code
    blocks. The Nginx event loop is blocked during code execution and time
    consuming code sequences should be avoided.

    Note that set_by_lua can only output a value to a single Nginx variable
    at a time but a workaround is possible by using the ngx.var.VARIABLE
    interface. For example,

        location /foo {
            set $diff ''; # we have to predefine the $diff variable here

            set_by_lua $sum '
                local a = 32
                local b = 56

                ngx.var.diff = a - b;  -- write to $diff directly
                return a + b;          -- return the $sum value normally
            ';

            echo "sum = $sum, diff = $diff";
        }

    This directive can be freely mixed with all the directives of
    [[HttpRewriteModule]], [[HttpSetMiscModule]], and
    [[HttpArrayVarModule]]. All of these directives will run in exactly the
    same order that they are written in the config file. For example,

        set $foo 32;
        set_by_lua $bar 'tonumber(ngx.var.foo) + 1';
        set $baz "bar: $bar";  # $baz == "bar: 33"

    This directive requires the ngx_devel_kit
    (<https://github.com/simpl/ngx_devel_kit>) module.

  set_by_lua_file
    syntax: *set_by_lua_file $res <path-to-lua-script> [$arg1 $arg2 ...]*

    context: *main, server, location, server if, location if*

    phase: *rewrite*

    Basically the same as set_by_lua, except the code to be executed is in
    the file specified by "<path-lua-script>".

    When the Lua code cache is on (default state), the user code is loaded
    once at the first request and cached and the Nginx config must be
    reloaded each time you modify the lua code file. You can temporarily
    disable the Lua code cache during development by switching
    lua_code_cache "off" in your "nginx.conf" to avoid reloading Nginx.

    This directive requires the ngx_devel_kit
    (<https://github.com/simpl/ngx_devel_kit>) module.

  content_by_lua
    syntax: *content_by_lua <lua-script-str>*

    context: *location, location if*

    phase: *content*

    Acts as a "content handler" and executes lua code string specified in
    "<lua-script-str>" for every request. The lua code may call predefined
    APIs to generate response content and is executed in a new spawned
    coroutine in an independent global environment (i.e. a sandbox).

    Do not use this directive and other content handler directives in a same
    location. For example, this directive and the proxy_pass directive
    should not be used in the same location.

  content_by_lua_file
    syntax: *content_by_lua_file <path-to-lua-script>*

    context: *location, location if*

    phase: *content*

    Same as content_by_lua, except the code to be executed is in the file
    specified by "<path-lua-script>".

    Nginx variables can be used in "<path-to-lua-script>" string to provide
    flexibility. This however carries some risks and is not ordinarily
    recommended.

    When the Lua code cache is on (default state), the user code is loaded
    once at the first request and cached and the Nginx config must be
    reloaded each time you modify the lua code file. You can temporarily
    disable the Lua code cache during development by switching
    lua_code_cache "off" in your "nginx.conf" to avoid reloading Nginx.

  rewrite_by_lua
    syntax: *rewrite_by_lua <lua-script-str>*

    context: *http, server, location, location if*

    phase: *post-rewrite*

    Acts as a rewrite phase handler and executes lua code string specified
    in "<lua-script-str>" for every request. The lua code may call
    predefined APIs to generate response content and is executed in a new
    spawned coroutine in an independent global environment (i.e. a sandbox).

    This directive uses exactly the same mechamism as content_by_lua so all
    the nginx APIs defined there are also available here.

    Note that this handler always runs *after* the standard
    [[HttpRewriteModule]]. So the following will work as expected:

       location /foo {
           set $a 12; # create and initialize $a
           set $b ""; # create and initialize $b
           rewrite_by_lua 'ngx.var.b = tonumber(ngx.var.a) + 1';
           echo "res = $b";
       }

    because "set $a 12" and "set $b """ run *before* rewrite_by_lua.

    On the other hand, the following will not work as expected:

        ?  location /foo {
        ?      set $a 12; # create and initialize $a
        ?      set $b ''; # create and initialize $b
        ?      rewrite_by_lua 'ngx.var.b = tonumber(ngx.var.a) + 1';
        ?      if ($b = '13') {
        ?         rewrite ^ /bar redirect;
        ?         break;
        ?      }
        ?
        ?      echo "res = $b";
        ?  }

    because "if" runs *before* rewrite_by_lua even if it is put after
    rewrite_by_lua in the config.

    The right way of doing this is as follows:

        location /foo {
            set $a 12; # create and initialize $a
            set $b ''; # create and initialize $b
            rewrite_by_lua '
                ngx.var.b = tonumber(ngx.var.a) + 1
                if tonumber(ngx.var.b) == 13 then
                    return ngx.redirect("/bar");
                end
            ';

            echo "res = $b";
        }

    It is worth mentioning that, the "ngx_eval" module can be approximately
    implemented by rewrite_by_lua. For example,

        location / {
            eval $res {
                proxy_pass http://foo.com/check-spam;
            }

            if ($res = 'spam') {
                rewrite ^ /terms-of-use.html redirect;
            }

            fastcgi_pass ...;
        }

    can be implemented in terms of "ngx_lua" like this

        location = /check-spam {
            internal;
            proxy_pass http://foo.com/check-spam;
        }

        location / {
            rewrite_by_lua '
                local res = ngx.location.capture("/check-spam")
                if res.body == "spam" then
                    ngx.redirect("/terms-of-use.html")
                end
            ';

            fastcgi_pass ...;
        }

    Just as any other rewrite phase handlers, rewrite_by_lua also runs in
    subrequests.

    Note that when calling "ngx.exit(ngx.OK)" within a rewrite_by_lua
    handler, the nginx request processing control flow will still continue
    to the content handler. To terminate the current request from within a
    rewrite_by_lua handler, calling ngx.exit with status >= 200
    ("ngx.HTTP_OK") and status < 300 ("ngx.HTTP_SPECIAL_RESPONSE") for
    successful quits and "ngx.exit(ngx.HTTP_INTERNAL_SERVER_ERROR)" (or its
    friends) for failures.

    If the [[HttpRewriteModule]]'s rewrite directive is used to change the
    URI and initiate location re-lookups (internal redirections), then any
    rewrite_by_lua or rewrite_by_lua_file code sequences within the current
    location will not be executed. For example,

        location /foo {
            rewrite ^ /bar;
            rewrite_by_lua 'ngx.exit(503)';
        }
        location /bar {
            ...
        }

    Here the Lua code "ngx.exit(503)" will never run. This will be the case
    if "rewrite ^ /bar last" is used as this will similarly initiate an
    internal redirection. If the "break" modifier is used instead, there
    will be no internal rediction and the rewrite_by_lua code will be
    executed.

  rewrite_by_lua_file
    syntax: *rewrite_by_lua_file <path-to-lua-script>*

    context: *http, server, location, location if*

    phase: *post-rewrite*

    Same as rewrite_by_lua, except the code to be executed is in the file
    specified by "<path-lua-script>".

    Nginx variables can be used in "<path-to-lua-script>" string to provide
    flexibility. This however carries some risks and is not ordinarily
    recommended.

    When the Lua code cache is on (default state), the user code is loaded
    once at the first request and cached and the Nginx config must be
    reloaded each time you modify the Lua source file. You can temporarily
    disable the Lua code cache during development by switching
    lua_code_cache "off" in your "nginx.conf" to avoid reloading Nginx.

  access_by_lua
    syntax: *access_by_lua <lua-script-str>*

    context: *http, server, location, location if*

    phase: *post-access*

    Acts as an access phase handler and executes lua code string specified
    in "<lua-script-str>" for every request. The user code may call
    predefined APIs to generate response content.

    This directive uses exactly the same mechanism as content_by_lua so all
    the nginx APIs defined there are also available here.

    Note that this handler always runs *after* the standard
    [[HttpAccessModule]]. So the following will work as expected:

        location / {
            deny    192.168.1.1;
            allow   192.168.1.0/24;
            allow   10.1.1.0/16;
            deny    all;

            access_by_lua '
                local res = ngx.location.capture("/mysql", { ... })
                ...
            ';

            # proxy_pass/fastcgi_pass/...
        }

    That is, if a client address appears in the blacklist, then we do not
    have to bother sending a MySQL query to do more advanced authentication
    in access_by_lua.

    It is worth mentioning that, the "ngx_auth_request" module can be
    approximately implemented by access_by_lua. For example,

        location / {
            auth_request /auth;

            # proxy_pass/fastcgi_pass/postgres_pass/...
        }

    can be implemented in terms of "ngx_lua" like this

        location / {
            access_by_lua '
                local res = ngx.location.capture("/auth")

                if res.status == ngx.HTTP_OK then
                    return
                end

                if res.status == ngx.HTTP_FORBIDDEN then
                    ngx.exit(res.status)
                end

                ngx.exit(ngx.HTTP_INTERNAL_SERVER_ERROR)
            ';

            # proxy_pass/fastcgi_pass/postgres_pass/...
        }

    Just as any other access phase handlers, access_by_lua will *not* run in
    subrequests.

    Note that when calling "ngx.exit(ngx.OK)" within a access_by_lua
    handler, the nginx request processing control flow will still continue
    to the content handler. To terminate the current request from within a
    access_by_lua handler, calling ngx.exit with status >= 200
    ("ngx.HTTP_OK") and status < 300 ("ngx.HTTP_SPECIAL_RESPONSE") for
    successful quits and "ngx.exit(ngx.HTTP_INTERNAL_SERVER_ERROR)" (or its
    friends) for failures.

  access_by_lua_file
    syntax: *access_by_lua_file <path-to-lua-script>*

    context: *http, server, location, location if*

    phase: *post-access*

    Same as access_by_lua, except the code to be executed is in the file
    specified by "<path-lua-script>".

    Nginx variables can be used in "<path-to-lua-script>" string to provide
    flexibility. This however carries some risks and is not ordinarily
    recommended.

    When the Lua code cache is on (default state), the user code is loaded
    once at the first request and cached and the Nginx config must be
    reloaded each time you modify the lua code file. You can temporarily
    disable the Lua code cache during development by switching
    lua_code_cache "off" in your "nginx.conf" to avoid reloading Nginx.

  header_filter_by_lua
    syntax: *header_filter_by_lua <lua-script-str>*

    context: *http, server, location, location if*

    phase: *output-header-filter*

    Uses Lua code specified in "<lua-script-str>" to define an output header
    filter. Note that the following Nginx Lua APIs are currently disabled
    within this context:

    *   Output API (e.g., ngx.say and ngx.send_headers)

    *   Control APIs (e.g., ngx.exit)

    *   Subrequest APIs (e.g., ngx.location.capture and
        ngx.location.capture_multi)

    Here is an example of overriding a response header (or adding one if
    absent) in our Lua header filter:

        location / {
            proxy_pass http://mybackend;
            header_filter_by_lua 'ngx.header.Foo = "blah"';
        }

    This directive was first introduced in the "v0.2.1rc20" release.

  header_filter_by_lua_file
    syntax: *header_filter_by_lua_file <path-to-lua-script-file>*

    context: *http, server, location, location if*

    phase: *output-header-filter*

    Use Lua code defined in a separate file specified by
    "<path-to-lua-script-file>" to define an output header filter.

    This is very much like header_filter_by_lua except that it loads Lua
    code from an external Lua source file.

    This directive was first introduced in the "v0.2.1rc20" release.

  lua_need_request_body
    syntax: *lua_need_request_body <on | off>*

    default: *off*

    context: *main | server | location*

    phase: *depends on usage*

    Determines whether to force reading of the request body data before
    running rewrite/access/access_by_lua* or not. The Nginx core does not
    read the client request body by default and if you need the request body
    then you must turn this directive "on" or call the ngx.req.read_body
    function from within your Lua code.

    To read the request body data within the $request_body variable,
    client_body_buffer_size must have the same value as
    client_max_body_size. Because when the content length exceeds
    client_body_buffer_size but less than client_max_body_size, Nginx will
    automatically buffer the data into a temporary file on the disk, which
    will lead to empty value in the $request_body variable.

    If the current location includes rewrite_by_lua or rewrite_by_lua_file
    directives, then the request body will be read just before the
    rewrite_by_lua or rewrite_by_lua_file code is run (and also at the
    "rewrite" phase). Similarly, if only content_by_lua is specified, the
    request body will not be read until the content handler's Lua code is
    about to run (i.e., the request body will be read during the content
    phase).

    It is recommended however, to use the ngx.req.read_body and
    ngx.req.discard_body functions for finer control over the request body
    reading process instead.

    This also applies to access_by_lua and access_by_lua_file.

  lua_shared_dict
    syntax: *lua_shared_dict <name> <size>*

    default: *no*

    context: *main*

    phase: *depends on usage*

    Declares a shared memory zone, "<name>", to serve as storage for the
    shm-based Lua dictionary "ngx.shared.<name>".

    The "<size>" argument accepts size units such as "k" and "m":

        http {
            lua_shared_dict dogs 10m;
            ...
        }

    See ngx.shared.DICT for details.

    This directive was first introduced in the "v0.3.1rc22" release.

Nginx API for Lua
  General Considerations
    The Nginx API exposed to the Lua land is provided in the form of two
    standard packages "ngx" and "ndk". These packages are in the default
    global scope within "ngx_lua" and can also be introduced to external Lua
    modules by using the package.seeall
    (<http://www.lua.org/manual/5.1/manual.html#pdf-package.seeall>) option:

        module("my_module", package.seeall)

        function say(a) ngx.say(a) end

    Alternatively, they can be imported external Lua modules by using file
    scoped local Lua variables:

        local ngx = ngx
        module("my_module")

        function say(a) ngx.say(a) end

    It is also possible to directly require the packages:

        local ngx = require "ngx"
        local ndk = require "ndk"

    The ability to require these packages was introduced in the "v0.2.1rc19"
    release.

    Network I/O operations in user code should only be done through Nginx
    API calls as the Nginx event loop may be blocked and performance may
    drop off dramatically otherwise. Minor disk file operations may be done
    via Lua's standard "io" and "file" libraries but these should be avoided
    wherever possible as these also block the Nginx process. Delegating all
    network and disk I/O operations to Nginx subrequests (via the
    ngx.location.capture method and its friends) is strongly recommended for
    maximum performance.

  ngx.arg
    syntax: *val = ngx.arg[index]*

    context: *set_by_lua**

    Index the input arguments to the set_by_lua and set_by_lua_file
    directives:

        value = ngx.arg[n]

    Here is an example

        location /foo {
            set $a 32;
            set $b 56;

            set_by_lua $res
                'return tonumber(ngx.arg[1]) + tonumber(ngx.arg[2])'
                $a $b;

            echo $sum;
        }

    that outputs 88, the sum of 32 and 56.

  ngx.var.VARIABLE
    syntax: *ngx.var.VAR_NAME*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua** value = ngx.var.some_nginx_variable_name
    ngx.var.some_nginx_variable_name = value Note that you can only write to
    nginx variables that are already defined. For example:

        location /foo {
            set $my_var ''; # this line is required to create $my_var at config time
            content_by_lua '
                ngx.var.my_var = 123;
                ...
            ';
        }

    That is, nginx variables cannot be created on-the-fly.

    Some special nginx variables like $args and $limit_rate can be assigned
    a value, some are not, like $arg_PARAMETER.

    Nginx regex group capturing variables $1, $2, $3, and etc, can be read
    by this interface as well, by writing "ngx.var[1]", "ngx.var[2]",
    "ngx.var[3]", and etc.

    Setting "nil" values to "ngx.var.Foo" will effectively make Nginx
    variable $Foo undefined. For instance,

        ngx.var.args = nil

  Core constants
    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

      ngx.OK (0)
      ngx.ERROR (-1)
      ngx.AGAIN (-2)
      ngx.DONE (-4)

    They take the same values of "NGX_OK", "NGX_AGAIN", "NGX_DONE",
    "NGX_ERROR", and etc. But now only ngx.exit only take two of these
    values, i.e., "NGX_OK" and "NGX_ERROR".

  HTTP method constants
    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

      ngx.HTTP_GET
      ngx.HTTP_HEAD
      ngx.HTTP_PUT
      ngx.HTTP_POST
      ngx.HTTP_DELETE

    These constants are usually used in ngx.location.catpure and
    ngx.location.capture_multi method calls.

  HTTP status constants
    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

      value = ngx.HTTP_OK (200)
      value = ngx.HTTP_CREATED (201)
      value = ngx.HTTP_SPECIAL_RESPONSE (300)
      value = ngx.HTTP_MOVED_PERMANENTLY (301)
      value = ngx.HTTP_MOVED_TEMPORARILY (302)
      value = ngx.HTTP_SEE_OTHER (303)
      value = ngx.HTTP_NOT_MODIFIED (304)
      value = ngx.HTTP_BAD_REQUEST (400)
      value = ngx.HTTP_UNAUTHORIZED (401)
      value = ngx.HTTP_FORBIDDEN (403)
      value = ngx.HTTP_NOT_FOUND (404)
      value = ngx.HTTP_NOT_ALLOWED (405)
      value = ngx.HTTP_GONE (410)
      value = ngx.HTTP_INTERNAL_SERVER_ERROR (500)
      value = ngx.HTTP_METHOD_NOT_IMPLEMENTED (501)
      value = ngx.HTTP_SERVICE_UNAVAILABLE (503)
      value = ngx.HTTP_GATEWAY_TIMEOUT (504) (first added in the v0.3.1rc38 release)

  Nginx log level constants
    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

      ngx.STDERR
      ngx.EMERG
      ngx.ALERT
      ngx.CRIT
      ngx.ERR
      ngx.WARN
      ngx.NOTICE
      ngx.INFO
      ngx.DEBUG

    These constants are usually used by the ngx.log method.

  print
    syntax: *print(...)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Emit args concatenated to nginx's "error.log" file, with log level
    "ngx.NOTICE" and prefix "lua print: ".

    It is equivalent to

        ngx.log(ngx.NOTICE, 'lua print: ', a, b, ...)

    Lua "nil" arguments are accepted and result in literal "nil", and Lua
    booleans result in "true" or "false".

  ngx.ctx
    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    This table can be used to store per-request context data for Lua
    programmers.

    This table has a liftime identical to the current request (just like
    Nginx variables). Consider the following example,

        location /test {
            rewrite_by_lua '
                ngx.say("foo = ", ngx.ctx.foo)
                ngx.ctx.foo = 76
            ';
            access_by_lua '
                ngx.ctx.foo = ngx.ctx.foo + 3
            ';
            content_by_lua '
                ngx.say(ngx.ctx.foo)
            ';
        }

    Then "GET /test" will yield the output

        foo = nil
        79

    That is, the "ngx.ctx.foo" entry persists across the rewrite, access,
    and content phases of a request.

    Also, every request has its own copy, include subrequests, for example:

        location /sub {
            content_by_lua '
                ngx.say("sub pre: ", ngx.ctx.blah)
                ngx.ctx.blah = 32
                ngx.say("sub post: ", ngx.ctx.blah)
            ';
        }

        location /main {
            content_by_lua '
                ngx.ctx.blah = 73
                ngx.say("main pre: ", ngx.ctx.blah)
                local res = ngx.location.capture("/sub")
                ngx.print(res.body)
                ngx.say("main post: ", ngx.ctx.blah)
            ';
        }

    Then "GET /main" will give the output

        main pre: 73
        sub pre: nil
        sub post: 32
        main post: 73

    We can see that modification of the "ngx.ctx.blah" entry in the
    subrequest does not affect the one in its parent request. They do have
    two separate versions of "ngx.ctx.blah" per se.

    Internal redirection will destroy the original request's "ngx.ctx" data
    (if any) and the new request will have an emptied "ngx.ctx" table. For
    instance,

        location /new {
            content_by_lua '
                ngx.say(ngx.ctx.foo)
            ';
        }

        location /orig {
            content_by_lua '
                ngx.ctx.foo = "hello"
                ngx.exec("/new")
            ';
        }

    Then "GET /orig" will give you

        nil

    rather than the original "hello" value.

    Arbitrary data values can be inserted into this "matic" table, including
    Lua closures and nested tables. You can also register your own meta
    methods with it.

    Overriding "ngx.ctx" with a new Lua table is also supported, for
    example,

        ngx.ctx = { foo = 32, bar = 54 }

  ngx.location.capture
    syntax: *res = ngx.location.capture(uri, options?)*

    context: *rewrite_by_lua*, access_by_lua*, content_by_lua**

    Issue a synchronous but still non-blocking *Nginx Subrequest* using
    "uri".

    Nginx subrequests provide a powerful way to make non-blocking internal
    requests to other locations configured with disk file directory or *any*
    other nginx C modules like "ngx_proxy", "ngx_fastcgi", "ngx_memc",
    "ngx_postgres", "ngx_drizzle", and even "ngx_lua" itself and etc etc
    etc.

    Also note that subrequests just mimic the HTTP interface but there is
    *no* extra HTTP/TCP traffic *nor* IPC involved. Everything works
    internally, efficiently, on the C level.

    Subrequests are completely different from HTTP 301/302 redirection (via
    ngx.redirect) and internal redirection (via ngx.exec).

    Here is a basic example:

        res = ngx.location.capture(uri)

    Returns a Lua table with three slots ("res.status", "res.header", and
    "res.body").

    "res.header" holds all the response headers of the subrequest and it is
    a normal Lua table. For multi-value response headers, the value is a Lua
    (array) table that holds all the values in the order that they appear.
    For instance, if the subrequest response headers contains the following
    lines:

        Set-Cookie: a=3
        Set-Cookie: foo=bar
        Set-Cookie: baz=blah

    Then "res.header["Set-Cookie"]" will be evaluted to the table value
    "{"a=3", "foo=bar", "baz=blah"}".

    URI query strings can be concatenated to URI itself, for instance,

        res = ngx.location.capture('/foo/bar?a=3&b=4')

    Named locations like @foo are not allowed due to a limitation in the
    nginx core. Use normal locations combined with the "internal" directive
    to prepare internal-only locations.

    An optional option table can be fed as the second argument, which
    support the options:

    *   "method" specify the subrequest's request method, which only accepts
        constants like "ngx.HTTP_POST". =item *

        "body" specify the subrequest's request body (string value only).
        =item *

        "args" specify the subrequest's URI query arguments (both string
        value and Lua tables are accepted) =item *

        "ctx" specify a Lua table to be the ngx.ctx table for the
        subrequest. It can be the current request's ngx.ctx table, which
        effectively make the parent and its subrequest to share exactly the
        same context table. This option was first introduced in the
        "v0.3.1rc25" release. =item *

        "vars" take a Lua table which holds the values to set the specified
        Nginx variables in the subrequest as this option's value. This
        option was first introduced in the "v0.3.1rc31" release. =item *

        "copy_all_vars" specify whether to copy over all the Nginx variable
        values of the current request to the subrequest in question.
        modifications of the nginx variables in the subrequest will not
        affect the current (parent) request. This option was first
        introduced in the "v0.3.1rc31" release. =item *

        "share_all_vars" specify whether to share all the Nginx variables of
        the subrequest with the current (parent) request. modifications of
        the Nginx variables in the subrequest will affect the current
        (parent) request.

    Issuing a POST subrequest, for example, can be done as follows

        res = ngx.location.capture(
            '/foo/bar',
            { method = ngx.HTTP_POST, body = 'hello, world' }
        )

    See HTTP method constants methods other than POST. The "method" option
    is "ngx.HTTP_GET" by default.

    The "args" option can specify extra URI arguments, for instance,

        ngx.location.capture('/foo?a=1',
            { args = { b = 3, c = ':' } }
        )

    is equivalent to

        ngx.location.capture('/foo?a=1&b=3&c=%3a')

    that is, this method will automatically escape argument keys and values
    according to URI rules and concatenating them together into a complete
    query string. The format for the Lua table passed as the "args" argument
    is identical to the format used in the ngx.encode_args method.

    The "args" option can also take plain query strings:

        ngx.location.capture('/foo?a=1',
            { args = 'b=3&c=%3a' } }
        )

    This is functionally identical to the previous examples.

    The "share_all_vars" option controls whether to share nginx variables
    among the current request and new subrequests. If this option is set to
    "true", then the current request and associated subrequests will share
    the same Nginx variable scope. Hence, changes to Nginx variables made by
    a subrequest will affect the current request.

    Care should be taken in using this option as variable scope sharing can
    have unexpected side effects. The "args", "vars", or "copy_all_vars"
    options are generally preferable instead.

    This option is set to "false" by default

        location /other {
            set $dog "$dog world";                  
            echo "$uri dog: $dog";                    
        }                                     

        location /lua {
            set $dog 'hello';
            content_by_lua '
                res = ngx.location.capture("/other",
                    { share_all_vars = true });

                ngx.print(res.body)
                ngx.say(ngx.var.uri, ": ", ngx.var.dog)
            ';  
        }

    Accessing location "/lua" gives

        /other dog: hello world
        /lua: hello world

    The "copy_all_vars" option provides a copy of the parent request's Nginx
    variables to subrequests when such subrequests are issued. Changes made
    to these variables by such subrequests will not affect the parent
    request or any other subrequests sharing the parent request's variables.

        location /other {
            set $dog "$dog world";
            echo "$uri dog: $dog";
        }

        location /lua {
            set $dog 'hello';
            content_by_lua '
                res = ngx.location.capture("/other",
                    { copy_all_vars = true });

                ngx.print(res.body)
                ngx.say(ngx.var.uri, ": ", ngx.var.dog)
            ';
        }

    Request "GET /lua" will give the output

        /other dog: hello world
        /lua: hello

    Note that if both "share_all_vars" and "copy_all_vars" are set to true,
    then the variable scope will be shared.

    In addition to the two settings above, it is possible to specify values
    for variables in the subrequest using the "vars" option. These variables
    are set after the sharing or copying of variables has been evaluated,
    and provides a more efficient method of passing specific values to a
    subrequest over encoding them as URL arguments and unescaping them in
    the Nginx config file.

        location /other {
            content_by_lua '
                ngx.say("dog = ", ngx.var.dog)
                ngx.say("cat = ", ngx.var.cat)
            ';
        }

        location /lua {
            set $dog '';
            set $cat '';
            content_by_lua '
                res = ngx.location.capture("/other",
                    { vars = { dog = "hello", cat = 32 }});

                ngx.print(res.body)
            ';
        }

    Accessing "/lua" will yield the output

        dog = hello
        cat = 32

    The "ctx" option can be used to specify a custom Lua table to serve as
    the ngx.ctx table for the subrequest.

        location /sub {
            content_by_lua '                          
                ngx.ctx.foo = "bar";                  
            ';
        }   
        location /lua {
            content_by_lua '
                local ctx = {}                        
                res = ngx.location.capture("/sub", { ctx = ctx })

                ngx.say(ctx.foo);
                ngx.say(ngx.ctx.foo);                 
            ';                                        
        }

    Then request "GET /lua" gives

        bar                                               
        nil

    It is also possible to use this "ctx" option to share the same ngx.ctx
    table between the current (parent) request and the subrequest:

        location /sub {
            content_by_lua '
                ngx.ctx.foo = "bar";
            ';
        }
        location /lua {
            content_by_lua '
                res = ngx.location.capture("/sub", { ctx = ngx.ctx })
                ngx.say(ngx.ctx.foo);
            ';
        }

    Request "GET /lua" yields the output

        bar

    Note that, by default, subrequests issued by ngx.location.capture
    inherit all the request headers of the current request. This may have
    unexpected side effects on the subrequest responses. For example, when
    you are using the standard "ngx_proxy" module to serve your subrequests,
    then an "Accept-Encoding: gzip" header in your main request may result
    in gzipped responses that your Lua code will not able to handle
    properly. So always set proxy_pass_request_headers "off" in your
    subrequest location to ignore the original request headers.

    Please also refer to restrictions on capturing locations that include
    Echo Module directives.

  ngx.location.capture_multi
    syntax: *res1, res2, ... = ngx.location.capture_multi({ {uri, options?},
    {uri, options?}, ... })*

    context: *rewrite_by_lua*, access_by_lua*, content_by_lua**

    Just like ngx.location.capture, but supports multiple subrequests
    running in parallel.

    This function issue several parallel subrequests specified by the input
    table, and returns their results in the same order. For example,

        res1, res2, res3 = ngx.location.capture_multi{
            { "/foo", { args = "a=3&b=4" } },
            { "/bar" },
            { "/baz", { method = ngx.HTTP_POST, body = "hello" } },
        }

        if res1.status == ngx.HTTP_OK then
            ...
        end

        if res2.body == "BLAH" then
            ...
        end

    This function will not return until all the subrequests terminate. The
    total latency is the longest latency of the subrequests, instead of
    their sum.

    When you do not know how many subrequests you want to issue in advance,
    you can use Lua tables for both requests and responses. For instance,

        -- construct the requests table
        local reqs = {}
        table.insert(reqs, { "/mysql" })
        table.insert(reqs, { "/postgres" })
        table.insert(reqs, { "/redis" })
        table.insert(reqs, { "/memcached" })

        -- issue all the requests at once and wait until they all return
        local resps = { ngx.location.capture_multi(reqs) }

        -- loop over the responses table
        for i, resp in ipairs(resps) do
            -- process the response table "resp"
        end

    The ngx.location.capture function is just a special form of this
    function. Logically speaking, the ngx.location.capture can be
    implemented like this

        ngx.location.capture =
            function (uri, args)
                return ngx.location.capture_multi({ {uri, args} })
            end

    Please also refer to restrictions on capturing locations that include
    Echo Module directives.

  ngx.status
    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Read and write the current request's response status. This should be
    called before sending out the response headers.

        ngx.status = ngx.HTTP_CREATED
        status = ngx.status

  ngx.header.HEADER
    syntax: *ngx.header.HEADER = VALUE*

    syntax: *value = ngx.header.HEADER*

    context: *rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    When assigning to "ngx.header.HEADER" will set, add, or clear the
    current request's response header named "HEADER". Underscores ("_") in
    the header names will be replaced by dashes ("-") and the header names
    will be matched case-insensitively.

        -- equivalent to ngx.header["Content-Type"] = 'text/plain'
        ngx.header.content_type = 'text/plain';

        ngx.header["X-My-Header"] = 'blah blah';

    Multi-value headers can be set this way:

        ngx.header['Set-Cookie'] = {'a=32; path=/', 'b=4; path=/'}

    will yield

        Set-Cookie: a=32; path=/
        Set-Cookie: b=4; path=/

    in the response headers. Only array-like tables are accepted.

    Note that, for those standard headers that only accepts a single value,
    like "Content-Type", only the last element in the (array) table will
    take effect. So

        ngx.header.content_type = {'a', 'b'}

    is equivalent to

        ngx.header.content_type = 'b'

    Setting a slot to "nil" effectively removes it from the response
    headers:

        ngx.header["X-My-Header"] = nil;

    same does assigning an empty table:

        ngx.header["X-My-Header"] = {};

    Setting "ngx.header.HEADER" after sending out response headers (either
    explicitly with ngx.send_headers or implicitly with ngx.print and its
    friends) will throw out a Lua exception.

    Reading "ngx.header.HEADER" will return the value of the response header
    named "HEADER". Underscores ("_") in the header names will also be
    replaced by dashes ("-") and the header names will be matched
    case-insensitively. If the response header is not present at all, "nil"
    will be returned.

    This is particularly useful in the context of filter_header_by_lua and
    filter_header_by_lua_file, for example,

        location /test {
            set $footer '';

            proxy_pass http://some-backend;

            header_filter_by_lua '
                if ngx.header["X-My-Header"] == "blah" then
                    ngx.var.footer = "some value"
                end
            ';

            echo_after_body $footer;
        }

    For multi-value headers, all of the values of header will be collected
    in order and returned as a Lua table. For example, response headers

        Foo: bar
        Foo: baz

    will result in

        {"bar", "baz"}

    to be returned when reading "ngx.header.Foo".

    Note that "ngx.header" is not a normal Lua table so you cannot iterate
    through it using Lua's "ipairs" function.

    For reading *request* headers, use the ngx.req.get_headers function
    instead.

  ngx.req.set_uri
    syntax: *ngx.req.set_uri(uri, jump?)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Rewrite the current request's (parsed) URI by the "uri" argument. The
    "uri" argument must be a Lua string and cannot be of zero length, or a
    Lua exception will be thrown.

    The optional boolean "jump" argument can trigger location rematch (or
    location jump) as [[HttpRewriteModule]]'s rewrite directive, that is,
    when "jump" is "true" (default to "false"), this function will never
    return and it will tell Nginx to try re-searching locations with the new
    URI value at the later "post-rewrite" phase and jumping to the new
    location. Location jump will not be triggered otherwise, and only the
    current request's URI will be modified, which is also the default
    behavior. This function will return but with no returned values when the
    "jump" argument is "false" or absent altogether.

    For example, the following nginx config snippet

        rewrite ^ /foo last;

    can be coded in Lua like this:

        ngx.req.set_uri("/foo", true)

    Similarly, Nginx config

        rewrite ^ /foo break;

    can be coded in Lua as

        ngx.req.set_uri("/foo", false)

    or equivalently,

        ngx.req.set_uri("/foo")

    The "jump" can only be set to "true" in rewrite_by_lua and
    rewrite_by_lua_file. Use of jump in other contexts is prohibited and
    will throw out a Lua exception.

    A more sophisticated example involving regex substitutions is as follows

        location /test {
            rewrite_by_lua '
                local uri = ngx.re.sub(ngx.var.uri, "^/test/(.*)", "$1", "o")
                ngx.req.set_uri(uri)
            ';
            proxy_pass http://my_backend;
        }

    which is functionally equivalent to

        location /test {
            rewrite ^/test/(.*) /$1 break;
            proxy_pass http://my_backend;
        }

    Note that you cannot use this interface to rewrite URI arguments, and
    you need to use ngx.req.set_uri_args for that. For instance, Nginx
    config

        rewrite ^ /foo?a=3? last;

    can be coded as

        ngx.req.set_uri_args("a=3")
        ngx.req.set_uri("/foo", true)

    or

        ngx.req.set_uri_args({a = 3})
        ngx.req.set_uri("/foo", true)

    This interface was first introduced in the "v0.3.1rc14" release.

  ngx.req.set_uri_args
    syntax: *ngx.req.set_uri_args(args)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Rewrite the current request's URI query arguments by the "args"
    argument. The "args" argument can be either a Lua string, as in

        ngx.req.set_uri_args("a=3&b=hello%20world")

    or a Lua table holding the query arguments' key-value pairs, as in

        ngx.req.set_uri_args({ a = 3, b = "hello world" })

    where in the latter case, this method will automatically escape argument
    keys and values according to the URI escaping rule.

    This interface was first introduced in the "v0.3.1rc13" release.

    See also ngx.req.set_uri.

  ngx.req.get_uri_args
    syntax: *args = ngx.req.get_uri_args()*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Returns a Lua table holds all of the current request's request URL query
    arguments.

    Here is an example,

        location = /test {
            content_by_lua '
                local args = ngx.req.get_uri_args()
                for key, val in pairs(args) do
                    if type(val) == "table" then
                        ngx.say(key, ": ", table.concat(val, ", "))
                    else
                        ngx.say(key, ": ", val)
                    end
                end
            ';
        }

    Then "GET /test?foo=bar&bar=baz&bar=blah" will yield the response body

        foo: bar
        bar: baz, blah

    Multiple occurrences of an argument key will result in a table value
    holding all of the values for that key in order.

    Keys and values will be automatically unescaped according to URI
    escaping rules. For example, in the above settings, "GET
    /test?a%20b=1%61+2" will yield the output

        a b: 1a 2

    Arguments without the "=<value>" parts are treated as boolean arguments.
    For example, "GET /test?foo&bar" will yield the outputs

        foo: true
        bar: true

    That is, they will take Lua boolean values "true". However, they're
    different from arguments taking empty string values. For example, "GET
    /test?foo=&bar=" will give something like

        foo: 
        bar:

    Empty key arguments are discarded, for instance, "GET
    /test?=hello&=world" will yield empty outputs.

    Updating query arguments via the nginx variable $args (or "ngx.var.args"
    in Lua) at runtime are also supported:

        ngx.var.args = "a=3&b=42"
        local args = ngx.req.get_uri_args()

    Here the "args" table will always look like

        {a = 3, b = 42}

    regardless of the actual request query string.

  ngx.req.get_post_args
    syntax: *ngx.req.get_post_args()*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Returns a Lua table holds all of the current request's POST query
    arguments (of the MIME type "application/x-www-form-urlencoded"). It is
    required to read the request body first by calling ngx.req.read_body or
    to turn on the lua_need_request_body directive, or a Lua exception will
    be thrown.

    Here is an example,

        location = /test {
            content_by_lua '
                ngx.req.read_body()
                local args = ngx.req.get_post_args()
                for key, val in pairs(args) do
                    if type(val) == "table" then
                        ngx.say(key, ": ", table.concat(val, ", "))
                    else
                        ngx.say(key, ": ", val)
                    end
                end
            ';
        }

    Then

        # Post request with the body 'foo=bar&bar=baz&bar=blah'
        $ curl --data 'foo=bar&bar=baz&bar=blah' localhost/test

    will yield the response body like

        foo: bar
        bar: baz, blah

    Multiple occurrences of an argument key will result in a table value
    holding all of the values for that key in order.

    Keys and values will be automatically unescaped according to URI
    escaping rules. For example, in the above settings,

        # POST request with body 'a%20b=1%61+2'
        $ curl -d 'a%20b=1%61+2' localhost/test

    will yield the output

        a b: 1a 2

    Arguments without the "=<value>" parts are treated as boolean arguments.
    For example, "GET /test?foo&bar" will yield the outputs

        foo: true
        bar: true

    That is, they will take Lua boolean values "true". However, they're
    different from arguments taking empty string values. For example, "POST
    /test" with request body "foo=&bar=" will give something like

        foo: 
        bar:

    Empty key arguments are discarded, for instance, "POST /test" with body
    "=hello&=world" will yield empty outputs.

  ngx.req.get_headers
    syntax: *headers = ngx.req.get_headers()*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Returns a Lua table holds all of the current request's request headers.

    Here is an example,

        local h = ngx.req.get_headers()
        for k, v in pairs(h) do
            ...
        end

    To read an individual header:

        ngx.say("Host: ", ngx.req.get_headers()["Host"])

    For multiple instances of request headers like

        Foo: foo
        Foo: bar
        Foo: baz

    the value of "ngx.req.get_headers()["Foo"]" will be a Lua (array) table
    like this:

        {"foo", "bar", "baz"}

    Another way to read individual request headers is to use
    "ngx.var.http_HEADER", that is, nginx's standard $http_HEADER variables.

  ngx.req.set_header
    syntax: *ngx.req.set_header(header_name, header_value)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Set the current request's request header named "header_name" to value
    "header_value", overriding any existing ones. None of the current
    request's subrequests will be affected.

    Here is an example of setting the "Content-Length" header:

        ngx.req.set_header("Content-Type", "text/css")

    The "header_value" can take an array list of values, for example,

        ngx.req.set_header("Foo", {"a", "abc"})

    will produce two new request headers:

        Foo: a
        Foo: abc

    and old "Foo" headers will be overridden if there is any.

    When the "header_value" argument is "nil", the request header will be
    removed. So

        ngx.req.set_header("X-Foo", nil)

    is equivalent to

        ngx.req.clear_header("X-Foo")

  ngx.req.read_body
    syntax: *ngx.req.read_body()*

    context: *rewrite_by_lua*, access_by_lua*, content_by_lua**

    Read the client request body synchronously but still non-blockingly.

    If the request body is already read previously by turning on
    lua_need_request_body or by using other modules, then this function is a
    no-op and returns immediately.

    If the request body has already been explicitly discarded, either by
    this module's ngx.req.discard_body or other modules, this function is a
    no-op and returns immediately.

    In case of errors, like connection errors while reading the data, this
    method will throw out a Lua exception *or* terminate the current request
    with the 500 status code immediately.

    You can later either retrieve the request body data via
    ngx.req.get_body_data or retrieve the temporary file name for the body
    data cached to disk via ngx.req.get_body_file, depending on

    1.  whether the current request body is already exceeding your
        client_body_buffer_size,

    2.  and whether you have turned on client_body_in_file_only.

    In case that you do not want to read the request body and the current
    request may have a request body, then it is crucial to use the
    ngx.req.discard_body function to explicitly discard the request body, or
    you'll break HTTP 1.1 keepalive and HTTP 1.1 pipelining.

    Here is a small example:

        ngx.req.read_body()
        local args = ngx.req.get_post_args()

    This function was first introduced in the "v0.3.1rc17" release.

  ngx.req.discard_body
    syntax: *ngx.req.discard_body()*

    context: *rewrite_by_lua*, access_by_lua*, content_by_lua**

    Explicitly discard the request body, i.e., read the data on the
    connection and throw it away immediately. Please note that, simply
    ignoring request body is not the right way to discard it, you need to
    call this function, or you'll break things under HTTP 1.1 keepalive or
    HTTP 1.1 pipelining.

    This function is an asynchronous call and returns immediately.

    If the request body has already been read, this function does nothing
    and returns immediately.

    This function was first introduced in the "v0.3.1rc17" release.

    See also ngx.req.read_body.

  ngx.req.get_body_data
    syntax: *data = ngx.req.get_body_data()*

    context: *rewrite_by_lua*, access_by_lua*, content_by_lua**

    Retrieves the in-memory request body data. It returns a Lua string
    rather than a Lua table holding all the parsed query arguments. If you
    want the latter, use ngx.req.get_post_args instead.

    This function returns "nil" if

    1.  the request body has not been read,

    2.  the request body has been read into disk temporary files,

    3.  or the request body has zero size.

    If the request body has not been read yet, call ngx.req.read_body first
    (or turned on lua_need_request_body to force this module to read the
    request body automatically, but this is not recommended).

    If the request body has been read into disk files, try calling the
    ngx.req.get_body_file function instead.

    In case that you want to enforce in-memory request bodies, try setting
    client_body_buffer_size to the same size value in client_max_body_size.

    Note that calling this function instead of using "ngx.var.request_body"
    or "ngx.var.echo_request-body" is more efficient because it can save one
    dynamic memory allocation and one data copy.

    This function was first introduced in the "v0.3.1rc17" release.

    See also ngx.req.get_body_file.

  ngx.req.get_body_file
    syntax: *file_name = ngx.req.get_body_file()*

    context: *rewrite_by_lua*, access_by_lua*, content_by_lua**

    Retrieves the file name for the in-file request body data. Returns "nil"
    if the request body has not been read or has been read into memory.

    The returned file is read only and is usually cleaned up automatically
    by Nginx's memory pool. It should not be modified, renamed, or removed
    by your own Lua code.

    If the request body has not been read yet, call ngx.req.read_body first
    (or turned on lua_need_request_body to force this module to read the
    request body automatically, but this is not recommended).

    If the request body has been read into memory, try calling the
    ngx.req.get_body_data function instead.

    In case that you want to enforce in-file request bodies, try turning on
    client_body_in_file_only.

    This function was first introduced in the "v0.3.1rc17" release.

    See also ngx.req.get_body_data.

  ngx.req.set_body_data
    syntax: *ngx.req.set_body_data(data)*

    context: *rewrite_by_lua*, access_by_lua*, content_by_lua**

    Set the current request's request body using the in-memory data
    specified by the "data" argument.

    If the current request's request body has not been read, then it will be
    properly discarded. When the current request's request body has been
    read into memory or buffered into a disk file, then the old request
    body's memory will be freed or the disk file will be cleaned up
    immediately, respectively.

    This function requires patching the Nginx core to function properly
    because the Nginx core does not allow modifying request bodies by the
    current design. Here is a patch for Nginx 1.0.9:
    nginx-1.0.9-allow_request_body_updating.patch
    (<https://github.com/agentzh/ngx_openresty/blob/master/patches/nginx-1.0
    .9-allow_request_body_updating.patch>), and this patch should be applied
    cleanly to other releases of Nginx as well.

    If you're using ngx_openresty (<http://openresty.org/>) 1.0.8.17+, then
    you've already had this patch applied.

    This function was first introduced in the "v0.3.1rc18" release.

    See also ngx.req.set_body_file.

  ngx.req.set_body_file
    syntax: *ngx.req.set_body_file(file_name, auto_clean?)*

    context: *rewrite_by_lua*, access_by_lua*, content_by_lua**

    Set the current request's request body using the in-file data specified
    by the "file_name" argument.

    If the optional "auto_clean" argument is given a "true" value, then this
    file will be automatically removed at request completion or the next
    time this function or ngx.req.set_body_data are called in the same
    request. The "auto_clean" is default to "false".

    You must ensure that the file specified by the "file_name" argument
    exists and is readable by an Nginx worker process by setting its
    permission properly. Otherwise a Lua exception will be thrown.

    If the current request's request body has not been read, then it will be
    properly discarded. When the current request's request body has been
    read into memory or buffered into a disk file, then the old request
    body's memory will be freed or the disk file will be cleaned up
    immediately, respectively.

    This function requires patching the Nginx core to function properly
    because the Nginx core does not allow modifying request bodies by the
    current design. Here is a patch for Nginx 1.0.9:
    nginx-1.0.9-allow_request_body_updating.patch
    (<https://github.com/agentzh/ngx_openresty/blob/master/patches/nginx-1.0
    .9-allow_request_body_updating.patch>), and this patch should be applied
    cleanly to other releases of Nginx as well.

    If you're using ngx_openresty (<http://openresty.org/>) 1.0.8.17+, then
    you've already had this patch applied.

    This function was first introduced in the "v0.3.1rc18" release.

    See also ngx.req.set_body_data.

  ngx.req.clear_header
    syntax: *ngx.req.clear_header(header_name)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Clear the current request's request header named "header_name". None of
    the current request's subrequests will be affected.

  ngx.exec
    syntax: *ngx.exec(uri, args?)*

    context: *rewrite_by_lua*, access_by_lua*, content_by_lua**

    Does an internal redirect to "uri" with "args".

        ngx.exec('/some-location');
        ngx.exec('/some-location', 'a=3&b=5&c=6');
        ngx.exec('/some-location?a=3&b=5', 'c=6');

    Named locations are also supported, but query strings are ignored. For
    example,

        location /foo {
            content_by_lua '
                ngx.exec("@bar");
            ';
        }

        location @bar {
            ...
        }

    The optional second "args" can be used to specify extra URI query
    arguments, for example:

        ngx.exec("/foo", "a=3&b=hello%20world")

    Alternatively, you can pass a Lua table for the "args" argument and let
    ngx_lua do URI escaping and string concatenation automatically for you,
    for instance,

        ngx.exec("/foo", { a = 3, b = "hello world" })

    The result is exactly the same as the previous example. The format for
    the Lua table passed as the "args" argument is identical to the format
    used in the ngx.encode_args method.

    Note that this is very different from ngx.redirect in that it is just an
    internal redirect and no new HTTP traffic is involved.

    This method never returns.

    This method *must* be called before ngx.send_headers or explicit
    response body outputs by either ngx.print or ngx.say.

    This method is very much like the echo_exec directive in
    [[HttpEchoModule]].

  ngx.redirect
    syntax: *ngx.redirect(uri, status?)*

    context: *rewrite_by_lua*, access_by_lua*, content_by_lua**

    Issue an "HTTP 301<code> or <code>302" redirection to "uri".

    The optional "status" parameter specifies whether 301 or 302 to be used.
    It is 302 ("ngx.HTTP_MOVED_TEMPORARILY") by default.

    Here is an example assuming the current server name is "localhost" and
    that it is listening on Port 1984:

        return ngx.redirect("/foo")

    which is equivalent to

        return ngx.redirect("http://localhost:1984/foo", ngx.HTTP_MOVED_TEMPORARILY)

    We can also use the numberical code directly as the second "status"
    argument:

        return ngx.redirect("/foo", 301)

    This method *must* be called before ngx.send_headers or explicit
    response body outputs by either ngx.print or ngx.say.

    This method never returns.

    This method is very much like the rewrite directive with the "redirect"
    modifier in the standard [[HttpRewriteModule]], for example, this
    "nginx.conf" snippet

        rewrite ^ /foo? redirect;  # nginx config

    is equivalent to the following Lua code

        return ngx.redirect('/foo');  -- lua code

    while

        rewrite ^ /foo? permanent;  # nginx config

    is equivalent to

        return ngx.redirect('/foo', ngx.HTTP_MOVED_PERMANENTLY)  -- Lua code

    URI arguments can be specified as well, for example:

        return ngx.redirect('/foo?a=3&b=4')

  ngx.send_headers
    syntax: *ngx.send_headers()*

    context: *rewrite_by_lua*, access_by_lua*, content_by_lua**

    Explicitly send out the response headers.

    Usually you do not have to send headers yourself. "ngx_lua" will
    automatically send out headers right before you output contents via
    ngx.say or ngx.print.

    Headers will also be sent automatically when content_by_lua exits
    normally.

  ngx.headers_sent
    syntax: *value = ngx.headers_sent*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Returns "true" if the response headers have been sent (by ngx_lua), and
    "false" otherwise.

    This API was first introduced in ngx_lua v0.3.1rc6.

  ngx.print
    syntax: *ngx.print(...)*

    context: *rewrite_by_lua*, access_by_lua*, content_by_lua**

    Emit arguments concatenated to the HTTP client (as response body). If
    response headers have not been sent yet, this function will first send
    the headers out, and then output the body data.

    Lua "nil" value will result in outputing "nil", and Lua boolean values
    will emit literal "true" or "false", accordingly.

    Also, nested arrays of strings are also allowed. The elements in the
    arrays will be sent one by one. For example

        local table = {
            "hello, ",
            {"world: ", true, " or ", false,
                {": ", nil}}
        }
        ngx.print(table)

    will yield the output

        hello, world: true or false: nil

    Non-array table arguments will cause a Lua exception to be thrown.

    This is an asynchronous call, that is, this function will return
    immediately without waiting for all the data has actually been written
    into the system send buffer. If you want to wait for the data to be
    flushed before proceeding, you should call "ngx.flush(true)" right after
    this call. See ngx.flush for more details.

  ngx.say
    syntax: *ngx.say(...)*

    context: *rewrite_by_lua*, access_by_lua*, content_by_lua**

    Just as ngx.print but also emit a trailing newline.

  ngx.log
    syntax: *ngx.log(log_level, ...)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Log arguments concatenated to error.log with the given logging level.

    Lua "nil" arguments are accepted and result in literal "nil", and Lua
    booleans result in literal "true" or "false" outputs.

    The "log_level" argument can take constants like "ngx.ERR" and
    "ngx.WARN". Check out Nginx log level constants for details.

  ngx.flush
    syntax: *ngx.flush(wait?)*

    context: *rewrite_by_lua*, access_by_lua*, content_by_lua**

    Flushing the response outputs. This operation has no effect in HTTP 1.0
    buffering output mode. See HTTP 1.0 support.

    By default, this function is an asynchronous call, that is, it returns
    immediately without waiting for the ouptuts to be actually flushed into
    the system send buffer.

    This function takes an optional boolean "wait" argument. When it is
    given "true" (which is default to "false"), this function becomes a
    synchronous call, that is, it will not return until all the outputs have
    actually been flushed into the system send buffer or the send_timeout
    setting has expired. Note that, even in the synchronous mode, this
    function still works nonblockingly (thanks to the Lua coroutine
    mechanism!).

    Synchronous flushing is very useful for streaming output in Lua.

    The "wait" argument was first introduced in the "v0.3.1rc34" release.

  ngx.exit
    syntax: *ngx.exit(status)*

    context: *rewrite_by_lua*, access_by_lua*, content_by_lua**

    When "status >= 200" (i.e., "ngx.HTTP_OK" and above), it will interrupt
    the execution of the current request and return status code to nginx.

    When "status == 0" (i.e., "ngx.OK"), it will only quit the current phase
    handler (or the content handler if the content_by_lua directive is used)
    and continue to run laster phases (if any) for the current request.

    The "status" argument can be "ngx.OK", "ngx.ERROR",
    "ngx.HTTP_NOT_FOUND", "ngx.HTTP_MOVED_TEMPORARILY", or other HTTP status
    constants.

    To return an error page with custom contents, use code snippets like
    this:

        ngx.status = ngx.HTTP_GONE
        ngx.say("This is our own content")
        -- to cause quit the whole request rather than the current phase handler
        ngx.exit(ngx.HTTP_OK)

    The effect in action:

        $ curl -i http://localhost/test
        HTTP/1.1 410 Gone
        Server: nginx/1.0.6
        Date: Thu, 15 Sep 2011 00:51:48 GMT
        Content-Type: text/plain
        Transfer-Encoding: chunked
        Connection: keep-alive

        This is our own content

    Number literals can be used directly as the argument, for instance,

        ngx.exit(501)

  ngx.eof
    syntax: *ngx.eof()*

    context: *rewrite_by_lua*, access_by_lua*, content_by_lua**

    Explicitly specify the end of the response output stream.

  ngx.escape_uri
    syntax: *newstr = ngx.escape_uri(str)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Escape "str" as a URI component.

  ngx.unescape_uri
    syntax: *newstr = ngx.unescape_uri(str)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Unescape "str" as an escaped URI component.

    For example,

        ngx.say(ngx.unescape_uri("b%20r56+7"))

    gives the output

        b r56 7

  ngx.encode_args
    syntax: *str = ngx.encode_args(table)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Encode the Lua table to a query args string according to the URI encoded
    rules.

    For example,

        ngx.encode_args({foo = 3, ["b r"] = "hello world"})

    yields

        foo=3&b%20r=hello%20world

    The table keys must be Lua strings.

    Multi-value query args are also supported. Just use a Lua table for the
    arg's value, for example:

        ngx.encode_args({baz = {32, "hello"}})

    gives

        baz=32&baz=hello

    If the value table is empty and the effect is equivalent to the "nil"
    value.

    Boolean argument values are also supported, for instance,

        ngx.encode_args({a = true, b = 1})

    yields

        a&b=1

    If the argument value is "false", then the effect is equivalent to the
    "nil" value.

    This method was first introduced in the "v0.3.1rc27" release.

  ngx.encode_base64
    syntax: *newstr = ngx.encode_base64(str)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Encode "str" to a base64 digest.

  ngx.decode_base64
    syntax: *newstr = ngx.decode_base64(str)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Decodes the "str" argument as a base64 digest to the raw form. Returns
    "nil" if "str" is not well formed.

  ngx.crc32_short
    syntax: *intval = ngx.crc32_short(str)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Calculates the CRC-32 (Cyclic Redundancy Code) digest for the "str"
    argument.

    This method performs better on relatively short "str" inputs (i.e., less
    than 30 ~ 60 bytes), as compared to ngx.crc32_long. The result is
    exactly the same as ngx.crc32_long.

    Behind the scene, it is just a thin wrapper around the "ngx_crc32_short"
    function defined in the Nginx core.

    This API was first introduced in the "v0.3.1rc8" release.

  ngx.crc32_long
    syntax: *intval = ngx.crc32_long(str)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Calculates the CRC-32 (Cyclic Redundancy Code) digest for the "str"
    argument.

    This method performs better on relatively long "str" inputs (i.e.,
    longer than 30 ~ 60 bytes), as compared to ngx.crc32_short. The result
    is exactly the same as ngx.crc32_short.

    Behind the scene, it is just a thin wrapper around the "ngx_crc32_long"
    function defined in the Nginx core.

    This API was first introduced in the "v0.3.1rc8" release.

  ngx.hmac_sha1
    syntax: *digest = ngx.hmac_sha1(secret_key, str)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Computes the HMAC-SHA1 (<http://en.wikipedia.org/wiki/HMAC>) digest of
    the argument "str" and turns the result using the secret key
    "<secret_key>".

    The raw binary form of the "HMAC-SHA1" digest will be generated, use
    ngx.encode_base64, for example, to encode the result to a textual
    representation if desired.

    For example,

        local key = "thisisverysecretstuff"
        local src = "some string we want to sign"
        local digest = ngx.hmac_sha1(key, src)
        ngx.say(ngx.encode_base64(digest))

    yields the output

        R/pvxzHC4NLtj7S+kXFg/NePTmk=

    This API requires the OpenSSL library enabled in your Nignx build
    (usually by passing the "--with-http_ssl_module" option to the
    "./configure" script).

    This function was first introduced in the "v0.3.1rc29" release.

  ngx.md5
    syntax: *digest = ngx.md5(str)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Returns the hexadecimal representation of the MD5 digest of the "str"
    argument.

    For example,

        location = /md5 {
            content_by_lua 'ngx.say(ngx.md5("hello"))';
        }

    yields the output

        5d41402abc4b2a76b9719d911017c592

    See also ngx.md5_bin if you want the raw binary MD5 digest.

  ngx.md5_bin
    syntax: *digest = ngx.md5_bin(str)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Returns the binary form of the MD5 digest of the "str" argument.

    See also ngx.md5 if you want the hexadecimal form of the MD5 digest.

  ngx.today
    syntax: *str = ngx.today()*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Returns current date (in the format "yyyy-mm-dd") from the nginx cached
    time (no syscall involved unlike Lua's date library).

    This is the local time.

  ngx.time
    syntax: *secs = ngx.time()*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Returns the elapsed seconds from the epoch for the current timestamp
    from the nginx cached time (no syscall involved unlike Lua's date
    library).

    You can enforce updating the Nginx time cache by calling ngx.update_time
    first.

  ngx.now
    syntax: *secs = ngx.now()*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Returns a floating-point number for the elapsed time in seconds
    (including microseconds as the decimal part) from the epoch for the
    current timestamp from the nginx cached time (no syscall involved unlike
    Lua's date library).

    You can use the standard Nginx directive timer_resolution to adjust the
    accuracy or forcibly updating the Nginx time cache by calling
    ngx.update_time first.

    This API was first introduced in "v0.3.1rc32".

  ngx.update_time
    syntax: *ngx.update_time()*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Forcibly updating the Nginx current time cache. This call involves a
    syscall and thus has some overhead, so do not abuse it.

    This API was first introduced in "v0.3.1rc32".

  ngx.localtime
    syntax: *str = ngx.localtime()*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Returns the current timestamp (in the format "yyyy-mm-dd hh:mm:ss") of
    the nginx cached time (no syscall involved unlike Lua's os.date
    (<http://www.lua.org/manual/5.1/manual.html#pdf-os.date>) function).

    This is the local time.

  ngx.utctime
    syntax: *str = ngx.utctime()*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Returns the current timestamp (in the format "yyyy-mm-dd hh:mm:ss") of
    the nginx cached time (no syscall involved unlike Lua's os.date
    (<http://www.lua.org/manual/5.1/manual.html#pdf-os.date>) function).

    This is the UTC time.

  ngx.cookie_time
    syntax: *str = ngx.cookie_time(sec)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Returns a formated string can be used as the cookie expiration time. The
    parameter "sec" is the timestamp in seconds (like those returned from
    ngx.time).

        ngx.say(ngx.cookie_time(1290079655))
            -- yields "Thu, 18-Nov-10 11:27:35 GMT"

  ngx.http_time
    syntax: *str = ngx.http_time(sec)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Returns a formated string can be used as the http header time (for
    example, being used in "Last-Modified" header). The parameter "sec" is
    the timestamp in seconds (like those returned from ngx.time).

        ngx.say(ngx.http_time(1290079655))
            -- yields "Thu, 18 Nov 10 11:27:35 GMT"

  ngx.parse_http_time
    syntax: *sec = ngx.parse_http_time(str)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Parse the http time string (as returned by ngx.http_time) into seconds.
    Returns the seconds or "nil" if the input string is in bad forms.

        local time = ngx.parse_http_time("Thu, 18 Nov 10 11:27:35 GMT")
        if time == nil then
            ...
        end

  ngx.is_subrequest
    syntax: *value = ngx.is_subrequest*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Returns "true" if the current request is an nginx subrequest, or "false"
    otherwise.

  ngx.re.match
    syntax: *captures = ngx.re.match(subject, regex, options?, ctx?)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Matches the "subject" string using the Perl-compatible regular
    expression "regex" with the optional "options".

    Only the first occurrence of the match is returned, or "nil" if no match
    is found. In case of fatal errors, like seeing bad "UTF-8" sequences in
    "UTF-8" mode, a Lua exception will be raised.

    When a match is found, a Lua table "captures" is returned, where
    "captures[0]" holds the whole substring being matched, and "captures[1]"
    holds the first parenthesized subpattern's capturing, "captures[2]" the
    second, and so on.

        local m = ngx.re.match("hello, 1234", "[0-9]+")
        -- m[0] == "1234"

        local m = ngx.re.match("hello, 1234", "([0-9])[0-9]+")
        -- m[0] == "1234"
        -- m[1] == "1"

    Unmatched subpatterns will have "nil" values in their "captures" table
    fields.

        local m = ngx.re.match("hello, world", "(world)|(hello)")
        -- m[0] == "hello"
        -- m[1] == nil
        -- m[2] == "hello"

    You can also specify "options" to control how the match will be
    performed. The following option characters are supported:

        a             anchored mode (only match from the beginning)

        d             enable the DFA mode (or the longest token match semantics).
                      this requires PCRE 6.0+ or else a Lua exception will be thrown.
                      first introduced in ngx_lua v0.3.1rc30.

        i             caseless mode (similar to Perl's /i modifier)

        j             enable PCRE JIT compilation, this requires PCRE 8.20+ and
                      PCRE must be built with the --enable-jit option, or it is
                      a no-op. this should always be used along with the C<o> 
                      option to gain the full performance benefit.
                      first introduced in ngx_lua v0.3.1rc30.

        m             multi-line mode (similar to Perl's /m modifier)

        o             compile-once mode (similar to Perl's /o modifer),
                      to enable the worker-process-level compiled-regex cache

        s             single-line mode (similar to Perl's /s modifier)

        u             UTF-8 mode. this requires PCRE to be built with
                      the --enable-utf8 option or else a Lua exception will be thrown.

        x             extended mode (similar to Perl's /x modifier)

    These options can be combined:

        local m = ngx.re.match("hello, world", "HEL LO", "ix")
        -- m[0] == "hello"

        local m = ngx.re.match("hello, 美好生活", "HELLO, (.{2})", "iu")
        -- m[0] == "hello, 美好"
        -- m[1] == "美好"

    The "o" option is useful for performance tuning, because the regex
    pattern in question will only be compiled once, cached in the
    worker-process level, and shared among all requests in the current Nginx
    worker process. You can tune the upper limit of the regex cache via the
    lua_regex_cache_max_entries directive.

    The optional fourth argument, "ctx", can be a Lua table holding an
    optional "pos" field. When the "pos" field in the "ctx" table argument
    is specified, "ngx.re.match" will start matching from that offset.
    Regardless of the presence of the "pos" field in the "ctx" table,
    "ngx.re.match" will always set this "pos" field to the position *after*
    the substring matched by the whole pattern in case of a successful
    match. When match fails, the "ctx" table will be left intact.

        local ctx = {}
        local m = ngx.re.match("1234, hello", "[0-9]+", "", ctx)
             -- m[0] = "1234"
             -- ctx.pos == 4

        local ctx = { pos = 2 }
        local m = ngx.re.match("1234, hello", "[0-9]+", "", ctx)
             -- m[0] = "34"
             -- ctx.pos == 4

    The "ctx" table argument combined with the "a" regex modifier can be
    used to construct a lexer atop "ngx.re.match".

    Note that, the "options" argument is not optional when the "ctx"
    argument is specified; use the empty Lua string ("") as the placeholder
    for "options" if you do not want to specify any regex options.

    This method requires the PCRE library enabled in your Nginx build.
    (Known Issue With Special PCRE Sequences).

    This feature was introduced in the "v0.2.1rc11" release.

  ngx.re.gmatch
    syntax: *iterator = ngx.re.gmatch(subject, regex, options?)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Similar to ngx.re.match, but returns a Lua iterator instead, so as to
    let the user programmer iterate all the matches over the "<subject>"
    string argument with the PCRE "regex".

    Here is a small exmple to demonstrate its basic usage:

        local iterator = ngx.re.gmatch("hello, world!", "([a-z]+)", "i")
        local m
        m = iterator()    -- m[0] == m[1] == "hello"
        m = iterator()    -- m[0] == m[1] == "world"
        m = iterator()    -- m == nil

    More often we just put it into a Lua "for" loop:

        for m in ngx.re.gmatch("hello, world!", "([a-z]+)", "i")
            ngx.say(m[0])
            ngx.say(m[1])
        end

    The optional "options" argument takes exactly the same semantics as the
    ngx.re.match method.

    The current implementation requires that the iterator returned should
    only be used in a single request. That is, one should *not* assign it to
    a variable belonging to persistent namespace like a Lua package.

    This method requires the PCRE library enabled in your Nginx build.
    (Known Issue With Special PCRE Sequences).

    This feature was first introduced in the "v0.2.1rc12" release.

  ngx.re.sub
    syntax: *newstr, n = ngx.re.sub(subject, regex, replace, options?)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Substitutes the first match of the Perl-compatible regular expression
    "regex" on the "subject" argument string with the string or function
    argument "replace". The optional "options" argument has exactly the same
    meaning as in ngx.re.match.

    This method returns the resulting new string as well as the number of
    successful substitutions, or throw out a Lua exception when an error
    occurred (syntax errors in the "<replace>" string argument, for
    example).

    When the "replace" is a string, then it is treated as a special template
    for string replacement. For example,

        local newstr, n = ngx.re.sub("hello, 1234", "([0-9])[0-9]", "[$0][$1]")
            -- newstr == "hello, [12][1]34"
            -- n == 1

    where $0 referring to the whole substring matched by the pattern and $1
    referring to the first parenthesized capturing substring.

    You can also use curly braces to disambiguate variable names from the
    background string literals:

        local newstr, n = ngx.re.sub("hello, 1234", "[0-9]", "${0}00")
            -- newstr == "hello, 10034"
            -- n == 1

    Literal dollar sign characters ("$") in the "replace" string argument
    can be escaped by another dollar sign, for instance,

        local newstr, n = ngx.re.sub("hello, 1234", "[0-9]", "$$")
            -- newstr == "hello, $234"
            -- n == 1

    Do not use backlashes to escape dollar signs; it will not work as
    expected.

    When the "replace" argument is of type "function", then it will be
    invoked with the "match table" as the argument to generate the replace
    string literal for substitution. The "match table" fed into the
    "replace" function is exactly the same as the return value of
    ngx.re.match. Here is an example:

        local func = function (m)
            return "[" .. m[0] .. "][" .. m[1] .. "]"
        end
        local newstr, n = ngx.re.sub("hello, 1234", "( [0-9] ) [0-9]", func, "x")
            -- newstr == "hello, [12][1]34"
            -- n == 1

    The dollar sign characters in the return value of the "replace" function
    argument are not special at all.

    This method requires the PCRE library enabled in your Nginx build.
    (Known Issue With Special PCRE Sequences).

    This feature was first introduced in the "v0.2.1rc13" release.

  ngx.re.gsub
    syntax: *newstr, n = ngx.re.gsub(subject, regex, replace, options?)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Just like ngx.re.sub, but does global substitution.

    Here is some examples:

        local newstr, n = ngx.re.gsub("hello, world", "([a-z])[a-z]+", "[$0,$1]", "i")
            -- newstr == "[hello,h], [world,w]"
            -- n == 2

        local func = function (m)
            return "[" .. m[0] .. "," .. m[1] .. "]"
        end
        local newstr, n = ngx.re.gsub("hello, world", "([a-z])[a-z]+", func, "i")
            -- newstr == "[hello,h], [world,w]"
            -- n == 2

    This method requires the PCRE library enabled in your Nginx build.
    (Known Issue With Special PCRE Sequences).

    This feature was first introduced in the "v0.2.1rc15" release.

  ngx.shared.DICT
    syntax: *dict = ngx.shared.DICT*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Fetching the shm-based Lua dictionary object for the shared memory zone
    named "DICT" defined by the lua_shared_dict directive.

    The resulting object "dict" has the following methods:

    *   get

    *   set

    *   add

    *   replace

    *   incr

    *   delete

    Here is an example:

        http {
            lua_shared_dict dogs 10m;
            server {
                location /set {
                    content_by_lua '
                        local dogs = ngx.shared.dogs
                        dogs:set("Jim", 8)
                        ngx.say("STORED")
                    ';
                }
                location /get {
                    content_by_lua '
                        local dogs = ngx.shared.dogs
                        ngx.say(dogs:get("Jim"))
                    ';
                }
            }
        }

    Let us test it:

        $ curl localhost/set
        STORED

        $ curl localhost/get
        8

        $ curl localhost/get
        8

    You will consistently get the output 8 when accessing "/get" regardless
    how many Nginx workers there are because the "dogs" dictionary resides
    in the shared memory and visible to *all* of the worker processes.

    The shared dictionary will retain its contents through a server config
    reload (either by sending the "HUP" signal to the Nginx process or by
    using the "-s reload" command-line option).

    The contents in the dictionary storage will be lost, however, when the
    Nginx server quits.

    This feature was first introduced in the "v0.3.1rc22" release.

  ngx.shared.DICT.get
    syntax: *value = ngx.shared.DICT:get(key)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Retrieving the value in the dictionary ngx.shared.DICT for the key
    "key". If the key does not exist or has been expired, then "nil" will be
    returned.

    The value returned will have the original data type when they were
    inserted into the dictionary, for example, Lua booleans, numbers, or
    strings.

    The first argument to this method must be the dictionary object itself,
    for example,

        local cats = ngx.shared.cats
        local value = cats.get(cats, "Marry")

    or use Lua's syntactic sugar for method calls:

        local cats = ngx.shared.cats
        local value = cats:get("Marry")

    These two forms are fundamentally equivalent.

    This feature was first introduced in the "v0.3.1rc22" release.

    See also ngx.shared.DICT.

  ngx.shared.DICT.set
    syntax: *success, err, forcible = ngx.shared.DICT:set(key, value,
    exptime?)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Unconditionally sets a key-value pair into the shm-based dictionary
    ngx.shared.DICT. Returns three values:

    *   "success": boolean value to indicate whether the key-value pair is
        stored or not.

    *   "err": textual error message, can be "no memory".

    *   "forcible": a boolean value to indicate whether other valid items
        have been removed forcibly when out of storage in the shared memory
        zone.

    The "value" argument inserted can be Lua booleans, numbers, strings, or
    "nil". Their value type will also be stored into the dictionary, thus
    you can get exactly the same data type when later retrieving the value
    out of the dictionary via the get method.

    The optional "exptime" argument specifies expiration time (in seconds)
    for the inserted key-value pair. The time resolution is 0.001 seconds.
    If the "exptime" takes the value 0 (which is the default), then the item
    will never be expired.

    When it fails to allocate memory for the current key-value item, then
    "set" will try removing existing items in the storage according to the
    Least-Recently Used (LRU) algorithm. Note that, LRU takes priority over
    expiration time here. If up to tens of existing items have been removed
    and the storage left is still insufficient (either due to the total
    capacity limit specified by lua_shared_dict or memory segmentation),
    then the "err" return value will be "no memory" and "success" will be
    "false".

    If this method succeeds in storing the current item by forcibly removing
    other not-yet-expired items in the dictionary via LRU, the "forcible"
    return value will be "true". If it stores the item without forcibly
    removing other valid items, then the return value "forcible" will be
    "false".

    The first argument to this method must be the dictionary object itself,
    for example,

        local cats = ngx.shared.cats
        local succ, err, forcible = cats.set(cats, "Marry", "it is a nice cat!")

    or use Lua's syntactic sugar for method calls:

        local cats = ngx.shared.cats
        local succ, err, forcible = cats:set("Marry", "it is a nice cat!")

    These two forms are fundamentally equivalent.

    This feature was first introduced in the "v0.3.1rc22" release.

    See also ngx.shared.DICT.

  ngx.shared.DICT.add
    syntax: *success, err, forcible = ngx.shared.DICT:add(key, value,
    exptime?)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Just like the set method, but only stores the key-value pair into the
    dictionary ngx.shared.DICT if the key does *not* exist.

    If the "key" argument already exists in the dictionary (and not expired
    for sure), the "success" return value will be "false" and the "err"
    return value will be "exists".

    This feature was first introduced in the "v0.3.1rc22" release.

    See also ngx.shared.DICT.

  ngx.shared.DICT.replace
    syntax: *success, err, forcible = ngx.shared.DICT:replace(key, value,
    exptime?)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Just like the set method, but only stores the key-value pair into the
    dictionary ngx.shared.DICT if the key *does* exist.

    If the "key" argument does *not* exist in the dictionary (or expired
    already), the "success" return value will be "false" and the "err"
    return value will be "not found".

    This feature was first introduced in the "v0.3.1rc22" release.

    See also ngx.shared.DICT.

  ngx.shared.DICT.delete
    syntax: *ngx.shared.DICT:delete(key)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Unconditionally removes the key-value pair from the shm-based dictionary
    ngx.shared.DICT.

    It is equivalent to "ngx.shared.DICT:set(key, nil)".

    This feature was first introduced in the "v0.3.1rc22" release.

    See also ngx.shared.DICT.

  ngx.shared.DICT.incr
    syntax: *newval, err = ngx.shared.DICT:incr(key, value)*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    Increments the (numerical) value for "key" in the shm-based dictionary
    ngx.shared.DICT by the step value "value". Returns the new resulting
    number if the operation is successfully completed or "nil" and an error
    message otherwise.

    The key must already exist in the dictionary, otherwise it will return
    "nil" and "not found".

    If the original value is not a valid Lua number in the dictionary, it
    will return "nil" and "not a number".

    The "value" argument can be any valid Lua numbers, like negative numbers
    or floating-point numbers.

    This feature was first introduced in the "v0.3.1rc22" release.

    See also ngx.shared.DICT.

  ndk.set_var.DIRECTIVE
    syntax: *res = ndk.set_var.DIRECTIVE_NAME*

    context: *set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,
    header_filter_by_lua**

    This mechanism allows calling other nginx C modules' directives that are
    implemented by Nginx Devel Kit
    (<https://github.com/simpl/ngx_devel_kit>) (NDK)'s set_var submodule's
    "ndk_set_var_value".

    For example, the following [[HttpSetMiscModule]] directives can be
    invoked this way:

    *   set_quote_sql_str

    *   set_quote_pgsql_str

    *   set_quote_json_str

    *   set_unescape_uri

    *   set_escape_uri

    *   set_encode_base32

    *   set_decode_base32

    *   set_encode_base64

    *   set_decode_base64

    *   set_encode_hex

    *   set_decode_hex

    *   set_sha1

    *   set_md5

    For instance,

        local res = ndk.set_var.set_escape_uri('a/b');
        -- now res == 'a%2fb'

    Similarly, the following directives provided by
    [[HttpEncryptedSessionModule]] can be invoked from within Lua too:

    *   set_encrypt_session

    *   set_decrypt_session

    This feature requires the ngx_devel_kit
    (<https://github.com/simpl/ngx_devel_kit>) module.

HTTP 1.0 support
    The HTTP 1.0 protocol does not support chunked outputs and always
    requires an explicit "Content-Length" header when the response body is
    non-empty. So when an HTTP 1.0 request is present, This module will
    automatically buffer all the outputs of user calls of ngx.say and
    ngx.print and postpone sending response headers until it sees all the
    outputs in the response body, and at that time ngx_lua can calculate the
    total length of the body and construct a proper "Content-Length" header
    for the HTTP 1.0 client.

    Note that, common HTTP benchmark tools like "ab" and "http_load" always
    issue HTTP 1.0 requests by default. To force "curl" to send HTTP 1.0
    requests, use the -0 option.

Data Sharing within an Nginx Worker
    NOTE: This mechanism behaves differently when code cache is turned off,
    and should be considered as a DIRTY TRICK. Backward compatibility is NOT
    guaranteed. Use at your own risk! We're going to design a whole new
    data-sharing mechanism.

    If you want to globally share user data among all the requests handled
    by the same nginx worker process, you can encapsulate your shared data
    into a Lua module, require the module in your code, and manipulate
    shared data through it. It works because required Lua modules are loaded
    only once, and all coroutines will share the same copy of the module.
    Note however that Lua global variables WILL NOT persist between requests
    because of the one-coroutine-per-request isolation design.

    Here is a complete small example:

        -- mydata.lua
        module("mydata", package.seeall)

        local data = {
            dog = 3,
            cat = 4,
            pig = 5,
        }

        function get_age(name)
            return data[name]
        end

    and then accessing it from your nginx.conf:

        location /lua {
            content_lua_by_lua '
                local mydata = require("mydata")
                ngx.say(mydata.get_age("dog"))
            ';
        }

    Your "mydata" module in this example will only be loaded and run on the
    first request to the location "/lua", and all those subsequent requests
    to the same nginx worker process will use the reloaded instance of the
    module as well as the same copy of the data in it, until you send a
    "HUP" signal to the nginx master process to enforce a reload.

    This data sharing technique is essential for high-performance Lua apps
    built atop this module. It is common to cache reusable data globally.

    It is worth noting that this is *per-worker* sharing, not *per-server*
    sharing. That is, when you have multiple nginx worker processes under an
    nginx master, this data sharing cannot pass process boundary. If you
    indeed need server-wide data sharing, you can

    1.  Use only a single nginx worker and a single server. This is not
        recommended when you have a multi-core CPU or multiple CPUs in a
        single machine.

    2.  Use some true backend storage like "memcached", "redis", or an RDBMS
        like "mysql".

Known Issues
  Lua Coroutine Yielding/Resuming
    *   As the module's predefined Nginx I/O API uses the coroutine
        yielding/resuming mechanism, user code should not call any Lua
        modules that use the Lua coroutine mechanism in order to prevent
        conflicts with the module's predefined Nginx API methods such as
        ngx.location.capture (Actually, coroutine modules have been masked
        off in content_by_lua directives and others). This limitation is
        significant and work is ongoing on an alternative coroutine
        implementation that can fit into the Nginx event model to address
        this. When this is done, it will be possible to use the Lua
        coroutine mechanism freely as it is in standard Lua implementations.

    *   Lua's "dofile" builtin is implemented as a C function in both Lua
        5.1 and LuaJIT 2.0 and when you call ngx.location.capture, ngx.exec,
        ngx.exit or ngx.req.read_body or similar in the file to be loaded by
        "dofile", a coroutine yield across the C function boundary will be
        initiated. This however is not allowed within ngx_lua and will
        usually result in error messages like "lua handler aborted: runtime
        error: attempt to yield across C-call boundary". To avoid this,
        define a real Lua module in your ".lua" file and use Lua's "require"
        builtin instead.

    *   Because the standard Lua 5.1 interpreter's VM is not fully
        resumable, the methods ngx.location.capture,
        ngx.location.capture_multi, ngx.redirect, ngx.exec, and ngx.exit
        cannot be used within the context of a Lua pcall()
        (<http://www.lua.org/manual/5.1/manual.html#pdf-pcall>) or xpcall()
        (<http://www.lua.org/manual/5.1/manual.html#pdf-xpcall>) when the
        standard Lua 5.1 interpreter is used; you'll get the error "attempt
        to yield across metamethod/C-call boundary". To fix this, please use
        LuaJIT 2.0 instead, because LuaJIT 2.0 supports a fully resume-able
        VM.

  Lua Variable Scope
    Care should be taken when importing modules and this form should be
    used:

            local xxx = require('xxx')

    instead of the old deprecated form: require('xxx')

    If you have to use the old form, force reload the module for every
    request by using the "package.loaded.<module>" command:
    package.loaded.xxx = nil require('xxx')

    It is recommended to always place the following piece of code at the end
    of Lua modules that use the ngx.location.capture or
    ngx.location.capture_multi directives to prevent casual use of
    module-level global variables that are shared among *all* requests:

        getmetatable(foo.bar).__newindex = function (table, key, val)
            error('Attempt to write to undeclared variable "' .. key .. '": '
                    .. debug.traceback())
        end

    Assuming your current Lua module is named "foo.bar", this will guarantee
    that local variables in module "foo.bar" functions have been declared as
    "local". It prevents undesirable race conditions while accessing such
    variables. See Data Sharing within an Nginx Worker for the reasons
    behind this.

  Locations With [[HttpEchoModule]] Directives
    The ngx.location.capture and ngx.location.capture_multi directives
    cannot capture locations that include the echo_location,
    echo_location_async, echo_subrequest, or echo_subrequest_async
    directives.

        location /foo {
            content_by_lua '
                res = ngx.location.capature("/bar")
            ';
        }
        location /bar {
            echo_location /blah;
        }
        location /blah {
            echo "Success!";
        }

        $ curl -i http://example.com/foo

    will not work as expected.

  Special PCRE Sequences
    PCRE sequences such as "\d", "\s", or "\w", require special attention
    because in string literals, the backslash character, "\", is stripped
    out by both the Lua language parser and by the Nginx config file parser
    before processing. So the following snippet will not work as expected:

        # nginx.conf
        ? location /test {
        ?     content_by_lua '
        ?         local regex = "\d+"  -- THIS IS WRONG!!
        ?         local m = ngx.re.match("hello, 1234", regex)
        ?         if m then ngx.say(m[0]) else ngx.say("not matched!") end
        ?     ';
        ? }
        # evaluates to "not matched!"

    To avoid this, you need to *double* escape the backslash:

        # nginx.conf
        location /test {
            content_by_lua '
                local regex = "\\\\d+"
                local m = ngx.re.match("hello, 1234", regex)
                if m then ngx.say(m[0]) else ngx.say("not matched!") end
            ';
        }
        # evaluates to "1234"

    Here, "\\\\d+" is stripped down to "\\d+" by the Nginx config file
    parser and this is further stripped down to "\d+" by the Lua language
    parser before running.

    Alternatively, you can present the regex pattern as a long-bracketed lua
    string literal by encasing it in "long brackets", "[[...]]", in which
    case backslashes have to only be escaped once for the Nginx config file
    parser.

        # nginx.conf
        location /test {
            content_by_lua '
                local regex = [[\\d+]]
                local m = ngx.re.match("hello, 1234", regex)
                if m then ngx.say(m[0]) else ngx.say("not matched!") end
            ';
        }
        # evaluates to "1234"

    Here, "[[\\d+]]" is stripped down to "[[\d+]]" by the Nginx config file
    parser and this is processed correctly.

    Note that you may need to use a longer from of the long bracket,
    "[=[...]=]", if the regex pattern contains "[...]" sequences. You can
    also, if you wish, use the "[=[...]=]" form as your default form and it
    may help with readability if you put a space between your long brackets
    and your regex patterns.

        # nginx.conf
        location /test {
            content_by_lua '
                local regex = [=[ [0-9]+ ]=]
                local m = ngx.re.match("hello, 1234", regex)
                if m then ngx.say(m[0]) else ngx.say("not matched!") end
            ';
        }
        # evaluates to "1234"

    An alternative approach to escaping PCRE sequences is to ensure that Lua
    code is placed in external script files and executed using the various
    *_by_lua_file directives. With this approach, the backslashes are only
    stripped by the Lua language parser and therefore only need to be
    escaped once each.

        -- test.lua
        local regex = "\\d+"
        local m = ngx.re.match("hello, 1234", regex)
        if m then ngx.say(m[0]) else ngx.say("not matched!") end
        -- evaluates to "1234"

    Within external script files, PCRE sequences presented as long-bracketed
    lua string literals do not require modification.

        -- test.lua
        local regex = [[\d+]]
        local m = ngx.re.match("hello, 1234", regex)
        if m then ngx.say(m[0]) else ngx.say("not matched!") end
        -- evaluates to "1234"

Performance
    The Lua state (aka the Lua vm instance) is shared across all the
    requests handled by a single nginx worker process to miminize memory
    use.

    On a ThinkPad T400 2.80 GHz laptop, the HelloWorld example is easy to
    achieve 28k req/sec using "http_load -p 10". In contrast, Nginx +
    php-fpm 5.2.8 + Unix Domain Socket yields 6k req/sec and Node.js
    (<http://nodejs.org/>) v0.6.1 yields 10.2k req/sec for their HelloWorld
    equivalents.

    You can get better performance when building this module with LuaJIT 2.0
    (<http://luajit.org/luajit.html>).

Typical Use Cases
    Just to name a few:

    *   Mashup'ing and processing outputs of various nginx upstream outputs
        (proxy, drizzle, postgres, redis, memcached, and etc) in Lua,

    *   doing arbitrarily complex access control and security checks in Lua
        before requests actually reach the upstream backends,

    *   manipulating response headers in an arbitrary way (by Lua)

    *   fetching backend information from external storage backends (like
        redis, memcached, mysql, postgresql) and use that information to
        choose which upstream backend to access on-the-fly,

    *   coding up arbitrarily complex web applications in a content handler
        using synchronous but still non-blocking access to the database
        backends and other storage,

    *   doing very complex URL dispatch in Lua at rewrite phase,

    *   using Lua to implement advanced caching mechanism for nginx
        subrequests and arbitrary locations.

    The possibilities are unlimited as the module allows bringing together
    various elements within Nginx as well as exposing the power of the Lua
    language to the user. The module provides the full flexibility of
    scripting while offering performance levels comparable with native C
    language programs both in terms of CPU time as well as memory footprint.
    This is particularly the case when LuaJIT 2.0 is enabled.

    Other scripting language implementations typically struggle to match
    this performance level.

Installation
    You're recommended to install this module as well as the Lua 5.1
    interpreter or LuaJIT 2.0 (with many other good stuffs) via the
    ngx_openresty bundle:

    http://openresty.org

    The installation steps are usually as simple as "./configure && make &&
    make install".

    Alternatively, you can compile this module with nginx core's source by
    hand:

    1.  Install Lua 5.1 or LuaJIT 2.0 into your system. Lua can be obtained
        freely from its project homepage (<http://www.lua.org/>). For
        Ubuntu/Debian users, just install the liblua5.1-0-dev package (or
        something like that).

    2.  Download the latest version of the release tarball of the
        ngx_devel_kit (NDK) module from lua-nginx-module file list
        (<http://github.com/simpl/ngx_devel_kit/tags>).

    3.  Download the latest version of the release tarball of this module
        from lua-nginx-module file list
        (<http://github.com/chaoslawful/lua-nginx-module/tags>).

    4.  Grab the nginx source code from nginx.org (<http://nginx.org/>), for
        example, the version 1.0.10 (see nginx compatibility), and then
        build the source with this module:

        wget 'http://nginx.org/download/nginx-1.0.10.tar.gz'
        tar -xzvf nginx-1.0.10.tar.gz
        cd nginx-1.0.10/

        # tell nginx's build system where to find lua:
        export LUA_LIB=/path/to/lua/lib
        export LUA_INC=/path/to/lua/include

        # or tell where to find LuaJIT when you want to use JIT instead
        # export LUAJIT_LIB=/path/to/luajit/lib
        # export LUAJIT_INC=/path/to/luajit/include/luajit-2.0

        # Here we assume you would install you nginx under /opt/nginx/.
        ./configure --prefix=/opt/nginx \
                --add-module=/path/to/ngx_devel_kit \
                --add-module=/path/to/lua-nginx-module

        make -j2
        make install

Compatibility
    The module is compatible with the following versions of Nginx:

    *
          1.1.x (last tested: 1.1.5)

    *
          1.0.x (last tested: 1.0.10)

    *
          0.9.x (last tested: 0.9.4)

    *
          0.8.x >= 0.8.54 (last tested: 0.8.54)

    The module may work with Nginx Versions 0.7.x and 0.8.x < 0.8.54 but
    these have not been tested.

    Nginx Versions < 0.7.0 are not compatible.

    Please consider filing a bug report if you find that any particular
    version of Nginx above Version 0.8.54 does not work with this module.

Report Bugs
    Although a lot of effort has been put into testing and code tuning,
    there must be some serious bugs lurking somewhere in this module. So
    whenever you are bitten by any quirks, please do not hesitate to

    1.  create a ticket on the issue tracking interface
        (<http://github.com/chaoslawful/lua-nginx-module/issues>) provided
        by GitHub,

    2.  or send a bug report or even patches to the nginx mailing list
        (<http://mailman.nginx.org/mailman/listinfo/nginx>).

Source Repository
    Available on github at chaoslawful/lua-nginx-module
    (<http://github.com/chaoslawful/lua-nginx-module>).

Test Suite
    To run the test suite, you also need the following dependencies:

    *   Nginx version >= 0.8.54

    *   Perl modules:

        *   test-nginx: http://github.com/agentzh/test-nginx

    *   Nginx modules:

        *   echo-nginx-module: http://github.com/agentzh/echo-nginx-module

        *   drizzle-nginx-module:
            http://github.com/chaoslawful/drizzle-nginx-module

        *   rds-json-nginx-module:
            http://github.com/agentzh/rds-json-nginx-module

        *   set-misc-nginx-module:
            http://github.com/agentzh/set-misc-nginx-module

        *   headers-more-nginx-module:
            http://github.com/agentzh/headers-more-nginx-module

        *   memc-nginx-module: http://github.com/agentzh/memc-nginx-module

        *   srcache-nginx-module:
            http://github.com/agentzh/srcache-nginx-module

        *   ngx_auth_request:
            http://mdounin.ru/hg/ngx_http_auth_request_module/

    *   C libraries:

        *   yajl: https://github.com/lloyd/yajl

    *   Lua modules:

        *   lua-yajl: https://github.com/brimworks/lua-yajl

            *   Note: the compiled module has to be placed in
                '/usr/local/lib/lua/5.1/'

    *   Applications:

        *   mysql: create database 'ngx_test', grant all privileges to user
            'ngx_test', password is 'ngx_test'

        *   memcached

    The adding order of these modules is important as the position of any
    filter module in the filtering chain determines the final output. The
    correct adding order during configuration is:

    1.  ngx_devel_kit

    2.  set-misc-nginx-module

    3.  ngx_http_auth_request_module

    4.  echo-nginx-module

    5.  memc-nginx-module

    6.  lua-nginx-module (i.e. this module)

    7.  headers-more-nginx-module

    8.  srcache-nginx-module

    9.  drizzle-nginx-module

    10. rds-json-nginx-module

TODO
    *   add "ignore_resp_headers", "ignore_resp_body", and "ignore_resp"
        options to ngx.location.capture and ngx.location.capture_multi`
        methods, to allow micro performance tuning on the user side.

    *   add directives to run lua codes when nginx stops/reloads.

    *   deal with TCP 3-second delay problem under great connection harness.

    *   add options to ngx.location.capture and ngx.location.capture_multi
        in order to share and copy a particular set of nginx variables with
        subrequests, specified by the user.

    *   add an option to ngx.location.capture and ngx.location.capture_multi
        so as to specify the ngx.ctx table for subrequests.

    *   expose nginx's shared memory facility to the Lua land.

    *   add support for multi-value arguments to [[#ngx.req.set_uri_args]]
        if its "args" argument is a Lua table.

Future Plans
    *   add the "lua_require" directive to load module into main thread's
        globals.

    *   add the "cosocket" mechamism that will emulate a common set of Lua
        socket API that will give you totally transparently non-blocking
        capability out of the box by means of a completely new upstream
        layer atop the nginx event model and no nginx subrequest overheads.

    *   add Lua code automatic time slicing support by yielding and resuming
        the Lua VM actively via Lua's debug hooks.

    *   make set_by_lua using the same mechanism as content_by_lua.

    *   add coroutine API back to the Lua land.

Changes
  v0.3.0
    New features

    *   added the header_filter_by_lua and header_filter_by_lua_file
        directives. thanks Liseen Wan (万珣新).

    *   implemented the PCRE regex API for Lua: ngx.re.match, ngx.re.gmatch,
        ngx.re.sub, and ngx.re.gsub.

    *   now we add the "ngx" and "ndk" table into "package.loaded" such that
        the user can write "local ngx = require 'ngx'" and "local ndk =
        require 'ndk'". thanks @Lance.

    *   added new directive lua_regex_cache_max_entries to control the upper
        limit of the worker-process-level compiled-regex cache enabled by
        the "o" regex option.

    *   implemented the special ngx.ctx Lua table for user programmers to
        store per-request Lua context data for their applications. thanks
        欧远宁 for suggesting this feature.

    *   now ngx.print and ngx.say allow (nested) array-like table arguments.
        the array elements in them will be sent piece by piece. this will
        avoid string concatenation for templating engines like ltp
        (<http://www.savarese.com/software/ltp/>).

    *   implemented the ngx.req.get_post_args method for fetching
        url-encoded POST query arguments from within Lua.

    *   implemented the ngx.req.get_uri_args method to fetch parsed URL
        query arguments from within Lua. thanks Bertrand Mansion (golgote).

    *   added new function ngx.parse_http_time, thanks James Hurst.

    *   now we allow Lua boolean and "nil" values in arguments to ngx.say,
        ngx.print, ngx.log and print.

    *   added support for user C macros "LUA_DEFAULT_PATH" and
        "LUA_DEFAULT_CPATH". for now we can only define them in "ngx_lua"'s
        "config" file because nginx "configure"'s "--with-cc-opt" option
        hates values with double-quotes in them. sigh. ngx_openresty
        (<http://openresty.org/>) is already using this feature to bundle
        3rd-party Lua libraries.

    Bug fixes

    *   worked-around the "stack overflow" issue while using
        "luarocks.loader" and disabling lua_code_cache, as described as
        github issue #27. thanks Patrick Crosby.

    *   fixed the "zero size buf in output" alert while combining
        lua_need_request_body on + access_by_lua/rewrite_by_lua +
        proxy_pass/fastcgi_pass. thanks Liseen Wan (万珣新).

    *   fixed issues with HTTP 1.0 HEAD requests.

    *   made setting "ngx.header.HEADER" after sending out response headers
        throw out a Lua exception to help debugging issues like github issue
        #49. thanks Bill Donahue (ikhoyo).

    *   fixed an issue regarding defining global variables in C header
        files: we should have defined the global "ngx_http_lua_exception" in
        a single compilation unit. thanks @姜大炮.

Authors
    *   chaoslawful (王晓哲) <chaoslawful at gmail dot com>

    *   Zhang "agentzh" Yichun (章亦春) <agentzh at gmail dot com>

Copyright & License
    This module is licenced under the BSD license.

    Copyright (C) 2009-2011, by Xiaozhe Wang (chaoslawful)
    <chaoslawful@gmail.com>.

    Copyright (C) 2009-2011, by Zhang "agentzh" Yichun (章亦春)
    <agentzh@gmail.com>.

    All rights reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are
    met:

    *   Redistributions of source code must retain the above copyright
        notice, this list of conditions and the following disclaimer.

    *   Redistributions in binary form must reproduce the above copyright
        notice, this list of conditions and the following disclaimer in the
        documentation and/or other materials provided with the distribution.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
    IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
    TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
    PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
    HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
    SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
    TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
    PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
    LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
    NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
    SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

See Also
    *   Routing requests to different MySQL queries based on URI arguments
        (<http://openresty.org/#RoutingMySQLQueriesBasedOnURIArgs>)

    *   Dynamic Routing Based on Redis and Lua
        (<http://openresty.org/#DynamicRoutingBasedOnRedis>)

    *   Using LuaRocks with ngx_lua (<http://openresty.org/#UsingLuaRocks>)

    *   Introduction to ngx_lua
        (<https://github.com/chaoslawful/lua-nginx-module/wiki/Introduction>
        )

    *   ngx_devel_kit (<http://github.com/simpl/ngx_devel_kit>)

    *   [[HttpEchoModule]]

    *   [[HttpDrizzleModule]]

    *   postgres-nginx-module (<http://github.com/FRiCKLE/ngx_postgres>)

    *   [[HttpMemcModule]]

    *   The ngx_openresty bundle (<http://openresty.org>)