Add an option to control keep-alive connections

By default http module set keep-alive option in connections to make it
persistent. However sometimes we need persistent connection and close it
instead. It is possible with option keepalive_disable. Option accepts a
map where key is a user agent name with assigned non-nil value.
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 untested.

Example:

local httpd = http_server.new('127.0.0.1', 8080, {
    log_requests = true,
    log_errors = true,
    keepalive_disable = {
        ['curl/7.68.0'] = true
    },
})

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

CHANGELOG.md

@@ -6,6 +6,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+### Added
+
+- Add option to control keepalive connection state (#137).
+
 ## [1.2.0] - 2021-11-10
 
 ### Changed

README.md

@@ -131,6 +131,22 @@ 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.
+* `keepalive_disable` - disables keep-alive connections with misbehaving
+  clients. Parameter accept a map that contains a user agents with non-nil
+  value. By default map is empty.
+
+  Example:
+
+  ```lua
+  local httpd = http_server.new('127.0.0.1', 8080, {
+      log_requests = true,
+      log_errors = true,
+      keepalive_disable = {
+          ['curl/7.68.0'] = true
+      },
+  })
+  ```
+
 
 ## Using routes
 

http/server.lua

@@ -23,6 +23,17 @@ local function sprintf(fmt, ...)
     return string.format(fmt, ...)
 end
 
+local function is_no_keepalive(disallowed_map, useragent)
+    if useragent == nil then
+        return false
+    end
+    if disallowed_map[useragent] == true then
+        return true
+    end
+
+    return false
+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 +902,12 @@ local function process_client(self, s, peer)
             end
         end
 
+        local no_keepalive = is_no_keepalive(self.options.keepalive_disable,
+                                             p.headers['user-agent'])
+        if no_keepalive == true then
+            hdrs.connection = 'close'
+        end
+
         local response = {
             "HTTP/1.1 ";
             status;
@@ -1282,6 +1299,11 @@ local exports = {
         if type(options) ~= 'table' then
             errorf("options must be table not '%s'", type(options))
         end
+        options.keepalive_disable = options.keepalive_disable or {}
+        if type(options.keepalive_disable) ~= 'table' then
+            error('Option keepalive_disable must be a table.')
+        end
+
         local default = {
             max_header_size     = 4096,
             header_timeout      = 100,
@@ -1294,6 +1316,7 @@ local exports = {
             log_requests        = true,
             log_errors          = true,
             display_errors      = false,
+            keepalive_disable   = {},
         }
 
         local self = {

test/integration/http_server_options_test.lua

@@ -0,0 +1,75 @@
+local t = require('luatest')
+local http_client = require('http.client')
+
+local helpers = require('test.helpers')
+
+local g = t.group()
+
+g.before_test('test_keepalive_default', function()
+    g.httpd = helpers.cfgserv()
+    g.httpd:start()
+end)
+
+g.before_test('test_keepalive_change_in_runtime', function()
+    g.httpd = helpers.cfgserv()
+    g.httpd:start()
+end)
+
+g.before_test('test_keepalive_allowed', function()
+    g.httpd = helpers.cfgserv()
+    g.httpd:start()
+end)
+
+g.before_test('test_keepalive_disallowed', function()
+    local useragent = 'Mozilla/4.0'
+    g.httpd = helpers.cfgserv({
+        keepalive_disable = {
+            [useragent] = true,
+        }
+    })
+    g.httpd:start()
+end)
+
+g.after_each(function()
+    helpers.teardown(g.httpd)
+end)
+
+g.test_keepalive_default = function(g)
+    local httpd = g.httpd
+    t.assert_equals(httpd.options.keepalive_disable, {})
+end
+
+g.test_keepalive_allowed = function()
+    local useragent = 'Mozilla/4.0'
+    local r = http_client.request('GET', helpers.base_uri .. '/test', nil, {
+        headers = {
+            ['user-agent'] = useragent,
+            connection = 'keep-alive'
+        },
+    })
+    t.assert_equals(r.status, 200)
+    t.assert_equals(r.headers.connection, 'keep-alive')
+end
+
+g.test_keepalive_disallowed = function()
+    local useragent = 'Mozilla/4.0'
+    local r = http_client.request('GET', helpers.base_uri .. '/test', nil, {
+        headers = {
+            ['user-agent'] = useragent,
+            connection = 'keep-alive'
+        },
+    })
+    t.assert_equals(r.status, 200)
+    t.assert_equals(r.headers.connection, 'close')
+end
+
+g.test_keepalive_change_in_runtime = function(g)
+    local httpd = g.httpd
+    t.assert_equals(httpd.options.keepalive_disable, {})
+    httpd.options.keepalive_disable = {
+        ['Mozilla/4.0'] = true
+    }
+    t.assert_equals(httpd.options.keepalive_disable, {
+        ["Mozilla/4.0"] = true
+    })
+end