Add an option disable_keepalive

By default HTTP server sets a keep-alive option in connections to make
it persistent. However sometimes keeping connections alive is not
required and user may want to disable it for a certain connections.

Patch adds a new option 'disable_keepalive' that accepts a table with
user agent names. HTTP server will disable keep-alive for connections
established by user agents listed in a table.

Note: nginx web-server has a similar option, see [1].

Unfortunately HTTP client [1] builtin into Tarantool supports only HTTP
protocol version 1.1, so version 1.0 is not covered in regression tests.

Example:

local httpd = http_server.new('127.0.0.1', 8080, {
    disable_keepalive = { 'curl/7.68.0' },
})

1. https://nginx.org/en/docs/http/ngx_http_core_module.html#keepalive_disable
2. https://www.tarantool.io/en/doc/latest/reference/reference_lua/http/

Part of #137

Reviewed-by: Alexander Turenko <alexander.turenko@tarantool.org>

CHANGELOG.md

@@ -9,6 +9,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 - Allow to use a non-standard socket (for example, `sslsocket` with TLS
   support).
 
+### Added
+
+- Add option to control keepalive connection state (#137).
+
 ## [1.2.0] - 2021-11-10
 
 ### Changed

README.md

@@ -132,6 +132,20 @@ httpd = require('http.server').new(host, port[, { options } ])
 
   By default uses `log.info` function for requests logging.
 * `log_errors` - same as the `log_requests` option but is used for error messages logging. By default uses `log.error()` function.
+* `disable_keepalive` - disables keep-alive connections with misbehaving
+  clients. Parameter accept a table that contains a user agents names.
+  By default table is empty.
+
+  Example:
+
+  ```lua
+  local httpd = http_server.new('127.0.0.1', 8080, {
+      log_requests = true,
+      log_errors = true,
+      disable_keepalive = { 'curl/7.68.0' }
+  })
+  ```
+
 
 ## Using routes
 

http/server.lua

@@ -23,6 +23,16 @@ local function sprintf(fmt, ...)
     return string.format(fmt, ...)
 end
 
+-- Converts a table to a map, values becomes keys with value 'true'.
+-- { 'a', 'b', 'c' } -> { 'a' = true, 'b' == 'true', 'c' = true }
+local function tomap(tbl)
+    local map = {}
+    for _, v in pairs(tbl) do
+        map[v] = true
+    end
+    return map
+end
+
 local function valid_cookie_value_byte(byte)
     -- https://tools.ietf.org/html/rfc6265#section-4.1.1
     -- US-ASCII characters excluding CTLs, whitespace DQUOTE, comma, semicolon,
@@ -891,6 +901,11 @@ local function process_client(self, s, peer)
             end
         end
 
+        local useragent = p.headers['user-agent']
+        if self.disable_keepalive[useragent] == true then
+            hdrs.connection = 'close'
+        end
+
         local response = {
             "HTTP/1.1 ";
             status;
@@ -1259,7 +1274,9 @@ local function httpd_start(self)
     local server = self.tcp_server_f(self.host, self.port, {
         name = 'http',
         handler = function(...)
+            self.internal.preprocess_client_handler()
             process_client(self, ...)
+            self.internal.postprocess_client_handler()
         end,
         http_server = self,
     })
@@ -1285,6 +1302,11 @@ local exports = {
         if type(options) ~= 'table' then
             errorf("options must be table not '%s'", type(options))
         end
+        local disable_keepalive = options.disable_keepalive or {}
+        if type(disable_keepalive) ~= 'table' then
+            error('Option disable_keepalive must be a table.')
+        end
+
         local default = {
             max_header_size     = 4096,
             header_timeout      = 100,
@@ -1297,6 +1319,7 @@ local exports = {
             log_requests        = true,
             log_errors          = true,
             display_errors      = false,
+            disable_keepalive   = {},
         }
 
         local self = {
@@ -1330,6 +1353,13 @@ local exports = {
                 ctx         = {},
                 static      = {},
             },
+
+            disable_keepalive   = tomap(disable_keepalive),
+
+            internal = {
+                preprocess_client_handler = function() end,
+                postprocess_client_handler = function() end,
+            }
         }
 
         return self

test/integration/http_server_options_test.lua

@@ -0,0 +1,89 @@
+local t = require('luatest')
+local http_client = require('http.client')
+
+local helpers = require('test.helpers')
+
+local g = t.group()
+
+g.after_each(function()
+    helpers.teardown(g.httpd)
+end)
+
+g.before_test('test_keepalive_is_allowed', function()
+    g.httpd = helpers.cfgserv()
+    g.httpd:start()
+end)
+
+g.test_keepalive_is_allowed = function()
+    local conn_is_opened = false
+    local conn_is_closed = false
+    g.httpd.internal.preprocess_client_handler = function() conn_is_opened = true end
+    g.httpd.internal.postprocess_client_handler = function() conn_is_closed = true end
+
+    -- Set HTTP keepalive headers: Connection:Keep-Alive and
+    -- Keep-Alive:timeout=<keepalive_idle>. Otherwise HTTP client will send
+    -- "Connection:close".
+    local opts = {
+        keepalive_idle = 3600,
+        keepalive_interval = 3600,
+    }
+    local r = http_client.new():request('GET', helpers.base_uri .. '/test', nil, opts)
+    t.assert_equals(r.status, 200)
+    t.assert_equals(r.headers.connection, 'keep-alive')
+    t.assert_equals(conn_is_opened, true)
+    t.assert_equals(conn_is_closed, false) -- Connection is alive.
+end
+
+g.before_test('test_keepalive_is_disallowed', function()
+    g.useragent = 'Mozilla/4.0'
+    g.httpd = helpers.cfgserv({
+        disable_keepalive = { g.useragent },
+    })
+    g.httpd:start()
+end)
+
+g.test_keepalive_is_disallowed = function()
+    local conn_is_opened = false
+    local conn_is_closed = false
+    g.httpd.internal.preprocess_client_handler = function() conn_is_opened = true end
+    g.httpd.internal.postprocess_client_handler = function() conn_is_closed = true end
+
+    -- Set HTTP keepalive headers: Connection:Keep-Alive and
+    -- Keep-Alive:timeout=<keepalive_idle>. Otherwise HTTP client will send
+    -- "Connection:close".
+    local opts = {
+        headers = {
+            ['user-agent'] = g.useragent,
+        },
+        keepalive_idle = 3600,
+        keepalive_interval = 3600,
+    }
+    local r = http_client.new():request('GET', helpers.base_uri .. '/test', nil, opts)
+    t.assert_equals(r.status, 200)
+    t.assert_equals(r.headers.connection, 'close')
+    t.assert_equals(conn_is_opened, true)
+    t.assert_equals(conn_is_closed, true) -- Connection is closed.
+end
+
+g.before_test('test_disable_keepalive_is_set', function()
+    g.useragent = 'Mozilla/5.0'
+    g.httpd = helpers.cfgserv({
+        disable_keepalive = { g.useragent },
+    })
+    g.httpd:start()
+end)
+
+g.test_disable_keepalive_is_set = function(g)
+    local httpd = g.httpd
+    t.assert_equals(httpd.disable_keepalive[g.useragent], true)
+end
+
+g.before_test('test_disable_keepalive_default', function()
+    g.httpd = helpers.cfgserv()
+    g.httpd:start()
+end)
+
+g.test_disable_keepalive_default = function(g)
+    local httpd = g.httpd
+    t.assert_equals(table.getn(httpd.options.disable_keepalive), 0)
+end