This module embeds Lua, via the standard Lua 5.1 interpreter or [LuaJIT 2.0](http://luajit.org/luajit.html), into Nginx and by leveraging Nginx's subrequests, allows the integration of the powerful Lua threads (Lua coroutines) into the Nginx event model.
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 executed using this module can be *100% non-blocking* on network traffic as long as the [Nginx API for Lua](#nginx-api-for-lua) provided by this module is used to handle
Almost all the Nginx modules can be used with this ngx_lua module by means of [ngx.location.capture](#ngxlocationcapture) or [ngx.location.capture_multi](#ngxlocationcapture_multi) but it is recommended to use those `lua-resty-*` libraries instead of creating subrequests to access the Nginx upstream modules because the former is usually much more flexible and memory-efficient.
The Lua interpreter or LuaJIT instance is shared across all the requests in a single nginx worker process but request contexts are segregated using lightweight Lua coroutines.
Loaded Lua modules persist in the nginx worker process level resulting in a small memory footprint in Lua even when under heavy loads.
The regular expressions used in [ngx.re.match](#ngxrematch), [ngx.re.gmatch](#ngxregmatch), [ngx.re.sub](#ngxresub), and [ngx.re.gsub](#ngxregsub) 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 regular expressions 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:
Do not activate the `o` option for regular expressions (and/or `replace` string arguments for [ngx.re.sub](#ngxresub) and [ngx.re.gsub](#ngxregsub)) that are generated *on the fly* and give rise to infinite variations to avoid hitting the specified limit.
Specifies the "match limit" used by the PCRE library when executing the [ngx.re API](#ngxrematch). To quote the PCRE manpage, "the limit ... has the effect of limiting the amount of backtracking that can take place."
As from the `v0.5.0rc29` release, the special notation `$prefix` or `${prefix}` can be used in the search path string to indicate the path of the `server prefix` usually determined by the `-p PATH` command-line option while starting the Nginx server.
As from the `v0.5.0rc29` release, the special notation `$prefix` or `${prefix}` can be used in the search path string to indicate the path of the `server prefix` usually determined by the `-p PATH` command-line option while starting the Nginx server.
Runs the Lua code specified by the argument `<lua-script-str>` on the global Lua VM level when the Nginx master process (if any) is loading the Nginx config file.
When Nginx receives the `HUP` signal and starts reloading the config file, the Lua VM will also be re-created and `init_by_lua` will run again on the new Lua VM.
Usually you can register (true) Lua global variables or pre-load Lua modules at server start-up by means of this hook. Here is an example for pre-loading Lua modules:
But note that, the [lua_shared_dict](#lua_shared_dict)'s shm storage will not be cleared through a config reload (via the `HUP` signal, for example). So if you do *not* want to re-initialize the shm storage in your `init_by_lua` code in this case, then you just need to set a custom flag in the shm storage and always check the flag in your `init_by_lua` code.
Because the Lua code in this context runs before Nginx forks its worker processes (if any), data or code loaded here will enjoy the [Copy-on-write (COW)](http://en.wikipedia.org/wiki/Copy-on-write) feature provided by many operating systems among all the worker processes, thus saving a lot of memory.
More Nginx APIs for Lua may be supported in this context upon future user requests.
Basically you can safely use Lua libraries that do blocking I/O in this very context because blocking the master process during server start-up is completely okay. Even the Nginx core does blocking I/O (at least on resolving upstream's host names) at the configure-loading phase.
You should be very careful about potential security vulnerabilities in your Lua code registered in this context because the Nginx master process is often run under the `root` account.
This directive was first introduced in the `v0.5.5` release.
Equivalent to [init_by_lua](#init_by_lua), except that the file specified by `<path-to-lua-script-file>` contains the Lua code or [Lua/LuaJIT bytecode](#lualuajit-bytecode-support) to be executed.
When a relative path like `foo/bar.lua` is given, they will be turned into the absolute path relative to the `server prefix` path determined by the `-p PATH` command-line option while starting the Nginx server.
This directive was first introduced in the `v0.5.5` release.
The code in `<lua-script-str>` can make [API calls](#nginx-api-for-lua) and can retrieve input arguments from the `ngx.arg` table (index starts from `1` and increases sequentially).
This directive is designed to execute short, fast running code blocks as the Nginx event loop is blocked during code execution. Time consuming code sequences should therefore be avoided.
This directive can be freely mixed with all directives of the [ngx_http_rewrite_module](http://nginx.org/en/docs/http/ngx_http_rewrite_module.html), [set-misc-nginx-module](http://github.com/agentzh/set-misc-nginx-module), and [array-var-nginx-module](http://github.com/agentzh/array-var-nginx-module) modules. All of these directives will run in the same order as they appear in the config file.
As from the `v0.5.0rc29` release, Nginx variable interpolation is disabled in the `<lua-script-str>` argument of this directive and therefore, the dollar sign character (`$`) can be used directly.
Equivalent to [set_by_lua](#set_by_lua), except that the file specified by `<path-to-lua-script-file>` contains the Lua code, or, as from the `v0.5.0rc32` release, the [Lua/LuaJIT bytecode](#lualuajit-bytecode-support) to be executed.
Nginx variable interpolation is supported in the `<path-to-lua-script-file>` argument string of this directive. But special care must be taken for injection attacks.
When a relative path like `foo/bar.lua` is given, they will be turned into the absolute path relative to the `server prefix` path determined by the `-p PATH` command-line option while starting the Nginx server.
The Lua code may make [API calls](#nginx-api-for-lua) and is executed as a new spawned coroutine in an independent global environment (i.e. a sandbox).
Do not use this directive and other content handler directives in the same location. For example, this directive and the [proxy_pass](http://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_pass) directive should not be used in the same location.
Equivalent to [content_by_lua](#content_by_lua), except that the file specified by `<path-to-lua-script-file>` contains the Lua code, or, as from the `v0.5.0rc32` release, the [Lua/LuaJIT bytecode](#lualuajit-bytecode-support) to be executed.
Nginx variables can be used in the `<path-to-lua-script-file>` string to provide flexibility. This however carries some risks and is not ordinarily recommended.
When a relative path like `foo/bar.lua` is given, they will be turned into the absolute path relative to the `server prefix` path determined by the `-p PATH` command-line option while starting the Nginx server.
The Lua code may make [API calls](#nginx-api-for-lua) and is executed as a new spawned coroutine in an independent global environment (i.e. a sandbox).
Note that this handler always runs *after* the standard [ngx_http_rewrite_module](http://nginx.org/en/docs/http/ngx_http_rewrite_module.html). So the following will work as expected:
Note that the [ngx_eval](http://www.grid.net.ru/nginx/eval.en.html) module can be approximated by using [rewrite_by_lua](#rewrite_by_lua). For example,
Note that when calling `ngx.exit(ngx.OK)` within a [rewrite_by_lua](#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](#rewrite_by_lua) handler, calling [ngx.exit](#ngxexit) with status >= 200 (`ngx.HTTP_OK`) and status <300(`ngx.HTTP_SPECIAL_RESPONSE`)forsuccessfulquitsand`ngx.exit(ngx.HTTP_INTERNAL_SERVER_ERROR)`(oritsfriends)forfailures.
If the [ngx_http_rewrite_module](http://nginx.org/en/docs/http/ngx_http_rewrite_module.html)'s [rewrite](http://nginx.org/en/docs/http/ngx_http_rewrite_module.html#rewrite) directive is used to change the URI and initiate location re-lookups (internal redirections), then any [rewrite_by_lua](#rewrite_by_lua) or [rewrite_by_lua_file](#rewrite_by_lua_file) code sequences within the current location will not be executed. For example,
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 redirection and the `rewrite_by_lua` code will be executed.
The `rewrite_by_lua` code will always run at the end of the `rewrite` request-processing phase unless [rewrite_by_lua_no_postpone](#rewrite_by_lua_no_postpone) is turned on.
Equivalent to [rewrite_by_lua](#rewrite_by_lua), except that the file specified by `<path-to-lua-script-file>` contains the Lua code, or, as from the `v0.5.0rc32` release, the [Lua/LuaJIT bytecode](#lualuajit-bytecode-support) to be executed.
Nginx variables can be used in the `<path-to-lua-script-file>` string to provide flexibility. This however carries some risks and is not ordinarily recommended.
When a relative path like `foo/bar.lua` is given, they will be turned into the absolute path relative to the `server prefix` path determined by the `-p PATH` command-line option while starting the Nginx server.
When the Lua code cache is turned on (by default), the user code is loaded once at the first request and cached and the Nginx config must be reloaded each time the Lua source file is modified. The Lua code cache can be temporarily disabled during development by switching [lua_code_cache](#lua_code_cache) `off` in `nginx.conf` to avoid reloading Nginx.
The `rewrite_by_lua_file` code will always run at the end of the `rewrite` request-processing phase unless [rewrite_by_lua_no_postpone](#rewrite_by_lua_no_postpone) is turned on.
The Lua code may make [API calls](#nginx-api-for-lua) and is executed as a new spawned coroutine in an independent global environment (i.e. a sandbox).
Note that this handler always runs *after* the standard [ngx_http_access_module](http://nginx.org/en/docs/http/ngx_http_access_module.html). So the following will work as expected:
That is, if a client IP address is in the blacklist, it will be denied before the MySQL query for more complex authentication is executed by [access_by_lua](#access_by_lua).
Note that the [ngx_auth_request](http://mdounin.ru/hg/ngx_http_auth_request_module/) module can be approximated by using [access_by_lua](#access_by_lua):
Note that when calling `ngx.exit(ngx.OK)` within a [access_by_lua](#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](#access_by_lua) handler, calling [ngx.exit](#ngxexit) with status >= 200 (`ngx.HTTP_OK`) and status <300(`ngx.HTTP_SPECIAL_RESPONSE`)forsuccessfulquitsand`ngx.exit(ngx.HTTP_INTERNAL_SERVER_ERROR)`(oritsfriends)forfailures.
Equivalent to [access_by_lua](#access_by_lua), except that the file specified by `<path-to-lua-script-file>` contains the Lua code, or, as from the `v0.5.0rc32` release, the [Lua/LuaJIT bytecode](#lualuajit-bytecode-support) to be executed.
Nginx variables can be used in the `<path-to-lua-script-file>` string to provide flexibility. This however carries some risks and is not ordinarily recommended.
When a relative path like `foo/bar.lua` is given, they will be turned into the absolute path relative to the `server prefix` path determined by the `-p PATH` command-line option while starting the Nginx server.
The Lua code cache can be temporarily disabled during development by switching [lua_code_cache](#lua_code_cache) `off` in `nginx.conf` to avoid repeatedly reloading Nginx.
Equivalent to [header_filter_by_lua](#header_filter_by_lua), except that the file specified by `<path-to-lua-script-file>` contains the Lua code, or as from the `v0.5.0rc32` release, the [Lua/LuaJIT bytecode](#lualuajit-bytecode-support) to be executed.
When a relative path like `foo/bar.lua` is given, they will be turned into the absolute path relative to the `server prefix` path determined by the `-p PATH` command-line option while starting the Nginx server.
The input data chunk is passed via [ngx.arg](#ngxarg)[1] (as a Lua string value) and the "eof" flag indicating the end of the response body data stream is passed via [ngx.arg](#ngxarg)[2] (as a Lua boolean value).
Behind the scene, the "eof" flag is just the `last_buf` (for main requests) or `last_in_chain` (for subrequests) flag of the Nginx chain link buffers. (Before the `v0.7.14` release, the "eof" flag does not work at all in subrequests.)
The Lua code can pass its own modified version of the input data chunk to the downstream Nginx output body filters by overriding [ngx.arg](#ngxarg)[1] with a Lua string or a Lua table of strings. For example, to transform all the lowercase letters in the response body, we can just write:
That is, when the body filter sees a chunk containing the word "hello", then it will set the "eof" flag to true immediately, resulting in truncated but still valid responses.
When the Lua code may change the length of the response body, then it is required to always clear out the `Content-Length` response header (if any) in a header filter to enforce streaming output, as in
Nginx output filters may be called multiple times for a single request because response body may be delivered in chunks. Thus, the Lua code specified by in this directive may also run multiple times in the lifetime of a single HTTP request.
Equivalent to [body_filter_by_lua](#body_filter_by_lua), except that the file specified by `<path-to-lua-script-file>` contains the Lua code, or, as from the `v0.5.0rc32` release, the [Lua/LuaJIT bytecode](#lualuajit-bytecode-support) to be executed.
When a relative path like `foo/bar.lua` is given, they will be turned into the absolute path relative to the `server prefix` path determined by the `-p PATH` command-line option while starting the Nginx server.
This directive was first introduced in the `v0.5.0rc32` release.
Run the Lua source code inlined as the `<lua-script-str>` at the `log` request processing phase. This does not replace the current access logs, but runs after.
Note that the following API functions are currently disabled within this context:
Here is an example of gathering average data for [$upstream_response_time](http://nginx.org/en/docs/http/ngx_http_upstream_module.html#var_upstream_response_time):
Equivalent to [log_by_lua](#log_by_lua), except that the file specified by `<path-to-lua-script-file>` contains the Lua code, or, as from the `v0.5.0rc32` release, the [Lua/LuaJIT bytecode](#lualuajit-bytecode-support) to be executed.
When a relative path like `foo/bar.lua` is given, they will be turned into the absolute path relative to the `server prefix` path determined by the `-p PATH` command-line option while starting the Nginx server.
This directive was first introduced in the `v0.5.0rc31` release.
Determines whether to force the request body data to be read before running rewrite/access/access_by_lua* or not. The Nginx core does not read the client request body by default and if request body data is required, then this directive should be turned `on` or the [ngx.req.read_body](#ngxreqread_body) function should be called within the Lua code.
To read the request body data within the [$request_body](http://nginx.org/en/docs/http/ngx_http_core_module.html#var_request_body) variable,
[client_body_buffer_size](http://nginx.org/en/docs/http/ngx_http_core_module.html#client_body_buffer_size) must have the same value as [client_max_body_size](http://nginx.org/en/docs/http/ngx_http_core_module.html#client_max_body_size). Because when the content length exceeds [client_body_buffer_size](http://nginx.org/en/docs/http/ngx_http_core_module.html#client_body_buffer_size) but less than [client_max_body_size](http://nginx.org/en/docs/http/ngx_http_core_module.html#client_max_body_size), Nginx will buffer the data into a temporary file on the disk, which will lead to empty value in the [$request_body](http://nginx.org/en/docs/http/ngx_http_core_module.html#var_request_body) variable.
If the current location includes [rewrite_by_lua](#rewrite_by_lua) or [rewrite_by_lua_file](#rewrite_by_lua_file) directives,
then the request body will be read just before the [rewrite_by_lua](#rewrite_by_lua) or [rewrite_by_lua_file](#rewrite_by_lua_file) code is run (and also at the
`rewrite` phase). Similarly, if only [content_by_lua](#content_by_lua) is specified,
It is recommended however, to use the [ngx.req.read_body](#ngxreqread_body) and [ngx.req.discard_body](#ngxreqdiscard_body) functions for finer control over the request body reading process instead.
This directive controls the default timeout value used in TCP/unix-domain socket object's [connect](#tcpsockconnect) method and can be overridden by the [settimeout](#tcpsocksettimeout) method.
The `<time>` argument can be an integer, with an optional time unit, like `s` (second), `ms` (millisecond), `m` (minute). The default time unit is `s`, i.e., "second". The default setting is `60s`.
This directive was first introduced in the `v0.5.0rc1` release.
Controls the default timeout value used in TCP/unix-domain socket object's [send](#tcpsocksend) method and can be overridden by the [settimeout](#tcpsocksettimeout) method.
The `<time>` argument can be an integer, with an optional time unit, like `s` (second), `ms` (millisecond), `m` (minute). The default time unit is `s`, i.e., "second". The default setting is `60s`.
This directive was first introduced in the `v0.5.0rc1` release.
lua_socket_send_lowat
---------------------
**syntax:** *lua_socket_send_lowat <size>*
**default:** *lua_socket_send_lowat 0*
**context:** *http, server, location*
Controls the `lowat` (low water) value for the cosocket send buffer.
This directive controls the default timeout value used in TCP/unix-domain socket object's [receive](#tcpsockreceive) method and iterator functions returned by the [receiveuntil](#tcpsockreceiveuntil) method. This setting can be overridden by the [settimeout](#tcpsocksettimeout) method.
The `<time>` argument can be an integer, with an optional time unit, like `s` (second), `ms` (millisecond), `m` (minute). The default time unit is `s`, i.e., "second". The default setting is `60s`.
This directive was first introduced in the `v0.5.0rc1` release.
lua_socket_buffer_size
----------------------
**syntax:** *lua_socket_buffer_size <size>*
**default:** *lua_socket_buffer_size 4k/8k*
**context:** *http, server, location*
Specifies the buffer size used by cosocket reading operations.
This buffer does not have to be that big to hold everything at the same time because cosocket supports 100% non-buffered reading and parsing. So even `1` byte buffer size should still work everywhere but the performance could be terrible.
This directive was first introduced in the `v0.5.0rc1` release.
lua_socket_pool_size
--------------------
**syntax:** *lua_socket_pool_size <size>*
**default:** *lua_socket_pool_size 30*
**context:** *http, server, location*
Specifies the size limit (in terms of connection count) for every cosocket connection pool associated with every remote server (i.e., identified by either the host-port pair or the unix domain socket file path).
When the connection pool exceeds the available size limit, the least recently used (idle) connection already in the pool will be closed to make room for the current connection.
Note that the cosocket connection pool is per nginx worker process rather than per nginx server instance, so size limit specified here also applies to every single nginx worker process.
This directive controls the default maximal idle time of the connections in the cosocket built-in connection pool. When this timeout reaches, idle connections will be closed and removed from the pool. This setting can be overridden by cosocket objects' [setkeepalive](#tcpsocksetkeepalive) method.
The `<time>` argument can be an integer, with an optional time unit, like `s` (second), `ms` (millisecond), `m` (minute). The default time unit is `s`, i.e., "second". The default setting is `60s`.
This directive can be used to toggle error logging when a failure occurs for the TCP or UDP cosockets. If you are already doing proper error handling and logging in your Lua code, then it is recommended to turn this directive off to prevent data flushing in your nginx error log files (which is usually rather expensive).
Enables or disables automatic response buffering for HTTP 1.0 (or older) requests. This buffering mechanism is mainly used for HTTP 1.0 keep-alive which replies on a proper `Content-Length` response header.
If the Lua code explicitly sets a `Content-Length` response header before sending the headers (either explicitly via [ngx.send_headers](#ngxsend_headers) or implicitly via the first [ngx.say](#ngxsay) or [ngx.print](#ngxprint) call), then the HTTP 1.0 response buffering will be disabled even when this directive is turned on.
To output very large response data in a streaming fashion (via the [ngx.flush](#ngxflush) call, for example), this directive MUST be turned off to minimize memory usage.
Controls whether or not to disable postponing [rewrite_by_lua](#rewrite_by_lua) and [rewrite_by_lua_file](#rewrite_by_lua_file) directives to run at the end of the `rewrite` request-processing phase. By default, this directive is turned off and the Lua code is postponed to run at the end of the `rewrite` phase.
Controls whether to transform underscores (`_`) in the response header names specified in the [ngx.header.HEADER](#ngxheaderheader) API to hypens (`-`).
When this directive is turned on, the ngx_lua module will monitor the premature connection close event on the downstream connections. And when there is such an event, it will call the user Lua function callback (registered by [ngx.on_abort](#ngxon_abort)) or just stop and clean up all the Lua "light threads" running in the current request's request handler when there is no user callback function registered.
According to the current implementation, however, if the client closes the connection before the Lua code finishes reading the request body data via [ngx.req.socket](#ngxreqsocket), then ngx_lua will neither stop all the running "light threads" nor call the user callback (if [ngx.on_abort](#ngxon_abort) has been called). Instead, the reading operation on [ngx.req.socket](#ngxreqsocket) will just return the error message "client aborted" as the second return value (the first return value is surely `nil`).
When TCP keepalive is disabled, it is relying on the client side to close the socket gracefully (by sending a `FIN` packet or something like that). For (soft) real-time web applications, it is highly recommended to configure the [TCP keepalive](http://tldp.org/HOWTO/TCP-Keepalive-HOWTO/overview.html) support in your system's TCP stack implementation in order to detect "half-open" TCP connections in time.
For example, on Linux, you can configure the standard [listen](http://nginx.org/en/docs/http/ngx_http_core_module.html#listen) directive in your `nginx.conf` file like this:
Controls the maximum number of "running timers" allowed.
Running timers are those timers whose user callback functions are still running.
When exceeding this limit, Nginx will stop running the callbacks of newly expired timers and log an error message "N lua_max_running_timers are not enough" where "N" is the current value of this directive.
This directive was first introduced in the `v0.8.0` release.
The various `*_by_lua` and `*_by_lua_file` configuration directives serve as gateways to the Lua API within the `nginx.conf` file. The Nginx Lua API described below can only be called within the user Lua code run in the context of these configuration directives.
The API is exposed to Lua in the form of two standard packages `ngx` and `ndk`. These packages are in the default global scope within ngx_lua and are always available within ngx_lua directives.
Use of the [package.seeall](http://www.lua.org/manual/5.1/manual.html#pdf-package.seeall) flag is strongly discouraged due to its various bad side-effects.
Network I/O operations in user code should only be done through the Nginx Lua API calls as the Nginx event loop may be blocked and performance drop off dramatically otherwise. Disk operations with relatively small amount of data can be done using the standard Lua `io` library but huge file reading and writing should be avoided wherever possible as they may block the Nginx process significantly. Delegating all network and disk I/O operations to Nginx's subrequests (via the [ngx.location.capture](#ngxlocationcapture) method and similar) is strongly recommended for maximum performance.
When this is used in the context of the [set_by_lua](#set_by_lua) or [set_by_lua_file](#set_by_lua_file) directives, this table is read-only and holds the input arguments to the config directives:
When this table is used in the context of [body_filter_by_lua](#body_filter_by_lua) or [body_filter_by_lua_file](#body_filter_by_lua_file), the first element holds the input data chunk to the output filter code and the second element holds the boolean flag for the "eof" flag indicating the end of the whole output data stream.
The data chunk and "eof" flag passed to the downstream Nginx output filters can also be overridden by assigning values directly to the corresponding table elements. When setting `nil` or an empty Lua string value to `ngx.arg[1]`, no data chunk will be passed to the downstream Nginx output filters at all.
**WARNING** When reading from an Nginx variable, Nginx will allocate memory in the per-request memory pool which is freed only at request termination. So when you need to read from an Nginx variable repeatedly in your Lua code, cache the Nginx variable value to your own Lua variable, for example,
local val = ngx.var.some_var
--- use the val repeatedly later
to prevent (temporary) memory leaking within the current request's lifetime.
Note that only three of these constants are utilized by the [Nginx API for Lua](#nginx-api-for-lua) (i.e., [ngx.exit](#ngxexit) accepts `NGX_OK`, `NGX_ERROR`, and `NGX_DECLINED` as input).
The `ngx.null` constant is a `NULL` light userdata usually used to represent nil values in Lua tables etc and is similar to the [lua-cjson](http://www.kyne.com.au/~mark/software/lua-cjson.php) library's `cjson.null` constant. This constant was first introduced in the `v0.5.0rc5` release.
These constants are usually used in [ngx.location.capture](#ngxlocationcapture) and [ngx.location.capture_multi](#ngxlocationcapture_multi) method calls.
Lua `nil` arguments are accepted and result in literal `"nil"` strings while Lua booleans result in literal `"true"` or `"false"` strings. And the `ngx.null` constant will yield the `"null"` string output.
There is a hard coded `2048` byte limitation on error message lengths in the Nginx core. This limit includes trailing newlines and leading time stamps. If the message size exceeds this limit, Nginx will truncate the message text accordingly. This limit can be manually modified by editing the `NGX_MAX_ERROR_STR` macro definition in the `src/core/ngx_log.h` file in the Nginx source tree.
Here, modification of the `ngx.ctx.blah` entry in the subrequest does not affect the one in the parent request. This is because they have two separate versions of `ngx.ctx.blah`.
Arbitrary data values, including Lua closures and nested tables, can be inserted into this "magic" table. It also allows the registration of custom meta methods.
Nginx's 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`,
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](#ngxredirect)) and internal redirection (via [ngx.exec](#ngxexec)).
You should always read the request body (by either calling [ngx.req.read_body](#ngxreqread_body) or configuring [lua_need_request_body](#lua_need_request_body) on) before initiating a subrequest.
`res.body` holds the subrequest's response body data, which might be truncated. You always need to check the `res.truncated` boolean flag to see if `res.body` contains truncated data.
specify a Lua table to be the [ngx.ctx](#ngxctx) table for the subrequest. It can be the current request's [ngx.ctx](#ngxctx) table, which effectively makes the parent and its subrequest to share exactly the same context table. This option was first introduced in the `v0.3.1rc25` release.
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.
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.
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.
when set to true, the current (parent) request's request body will always be forwarded to the subrequest being created if the `body` option is not specified. The request body read by either [ngx.req.read_body()](#ngxreqread_body) or [lua_need_request_body on](#lua_need_request_body) will be directly forwarded to the subrequest without copying the whole request body data when creating the subrequest (no matter the request body data is buffered in memory buffers or temporary files). By default, this option is `false` and when the `body` option is not specified, the request body of the current (parent) request is only forwarded when the subrequest takes the `PUT` or `POST` request method.
concatenate 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](#ngxencode_args) method.
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.
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.
When the `body` option is not specified and the `always_forward_body` option is false (the default value), the `POST` and `PUT` subrequests will inherit the request bodies of the parent request (if any).
There is a hard-coded upper limit on the number of concurrent subrequests possible for every main request. In older versions of Nginx, the limit was `50` concurrent subrequests and in more recent versions, Nginx `1.1.x` onwards, this was increased to `200` concurrent subrequests. When this limit is exceeded, the following error message is added to the `error.log` file:
The limit can be manually modified if required by editing the definition of the `NGX_HTTP_MAX_SUBREQUESTS` macro in the `nginx/src/http/ngx_http_request.h` file in the Nginx source tree.
Please also refer to restrictions on capturing locations configured by [subrequest directives of other modules](#locations_configured_by_subrequest_directives_of_other_modules).
Please also refer to restrictions on capturing locations configured by [subrequest directives of other modules](#locations_configured_by_subrequest_directives_of_other_modules).
Underscores (`_`) in the header names will be replaced by hyphens (`-`) by default. This transformation can be turned off via the [lua_transform_underscores_in_response_headers](#lua_transform_underscores_in_response_headers) directive.
Only Lua tables are accepted (Only the last element in the table will take effect for standard headers such as `Content-Type` that only accept a single value).
Setting `ngx.header.HEADER` after sending out response headers (either explicitly with [ngx.send_headers](#ngxsend_headers) or implicitly with [ngx.print](#ngxprint) and similar) will throw out a Lua exception.
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 [header_filter_by_lua](#header_filter_by_lua) and [header_filter_by_lua_file](#header_filter_by_lua_file), for example,
The following example emulates the `$request_time` variable value (provided by [ngx_http_log_module](http://nginx.org/en/docs/http/ngx_http_log_module.html)) in pure Lua:
Retrieves the current request's request method name. Strings like `"GET"` and `"POST"` are returned instead of numerical [method constants](#http-method-constants).
Overrides the current request's request method with the `request_id` argument. Currently only numerical [method constants](#http-method-constants) are supported, like `ngx.HTTP_POST` and `ngx.HTTP_GET`.
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 [ngx_http_rewrite_module](http://nginx.org/en/docs/http/ngx_http_rewrite_module.html)'s [rewrite](http://nginx.org/en/docs/http/ngx_http_rewrite_module.html#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.
The `jump` can only be set to `true` in [rewrite_by_lua](#rewrite_by_lua) and [rewrite_by_lua_file](#rewrite_by_lua_file). Use of jump in other contexts is prohibited and will throw out a Lua exception.
Note that it is not possible to use this interface to rewrite URI arguments and that [ngx.req.set_uri_args](#ngxreqset_uri_args) should be used for this instead. For instance, Nginx config
That is, they will take Lua boolean values `true`. However, they are different from arguments taking empty string values. `GET /test?foo=&bar=` will give something like
Note that a maximum of 100 request arguments are parsed by default (including those with the same name) and that additional request arguments are silently discarded to guard against potential denial of service attacks.
Returns a Lua table holding all the current request POST query arguments (of the MIME type `application/x-www-form-urlencoded`). Call [ngx.req.read_body](#ngxreqread_body) to read the request body first or turn on the [lua_need_request_body](#lua_need_request_body) directive to avoid errors.
That is, they will take Lua boolean values `true`. However, they are different from arguments taking empty string values. `POST /test` with request body `foo=&bar=` will return something like
Note that a maximum of 100 request arguments are parsed by default (including those with the same name) and that additional request arguments are silently discarded to guard against potential denial of service attacks.
Note that the [ngx.var.HEADER](#ngxvarvariable) API call, which uses core [$http_HEADER](http://nginx.org/en/docs/http/ngx_http_core_module.html#var_http_) variables, may be more preferable for reading individual request headers.
Note that a maximum of 100 request headers are parsed by default (including those with the same name) and that additional request headers are silently discarded to guard against potential denial of service attacks.
Since the `0.6.9` release, all the header names in the Lua table returned are converted to the pure lower-case form by default, unless the `raw` argument is set to `true` (default to `false`).
Also, by default, an `__index` metamethod is added to the resulting Lua table and will normalize the keys to a pure lowercase form with all underscores converted to dashes in case of a lookup miss. For example, if a request header `My-Foo-Header` is present, then the following invocations will all pick up the value of this header correctly:
By default, all the subrequests subsequently initiated by [ngx.location.capture](#ngxlocationcapture) and [ngx.location.capture_multi](#ngxlocationcapture_multi) will inherit the new header.
If the request body is already read previously by turning on [lua_need_request_body](#lua_need_request_body) or by using other modules, then this function does not run and returns immediately.
If the request body has already been explicitly discarded, either by the [ngx.req.discard_body](#ngxreqdiscard_body) function or other modules, this function does not run and returns immediately.
In case of errors, such as connection errors while reading the data, this method will throw out a Lua exception *or* terminate the current request with a 500 status code immediately.
The request body data read using this function can be retrieved later via [ngx.req.get_body_data](#ngxreqget_body_data) or, alternatively, the temporary file name for the body data cached to disk using [ngx.req.get_body_file](#ngxreqget_body_file). This depends on
1. whether the current request body is already larger than the [client_body_buffer_size](http://nginx.org/en/docs/http/ngx_http_core_module.html#client_body_buffer_size),
1. and whether [client_body_in_file_only](http://nginx.org/en/docs/http/ngx_http_core_module.html#client_body_in_file_only) has been switched on.
In cases where current request may have a request body and the request body data is not required, The [ngx.req.discard_body](#ngxreqdiscard_body) function must be used to explicitly discard the request body to avoid breaking things under HTTP 1.1 keepalive or HTTP 1.1 pipelining.
Explicitly discard the request body, i.e., read the data on the connection and throw it away immediately. Please note that ignoring request body is not the right way to discard it, and that this function must be called to avoid breaking things under HTTP 1.1 keepalive or HTTP 1.1 pipelining.
Retrieves in-memory request body data. It returns a Lua string rather than a Lua table holding all the parsed query arguments. Use the [ngx.req.get_post_args](#ngxreqget_post_args) function instead if a Lua table is required.
If the request body has not been read yet, call [ngx.req.read_body](#ngxreqread_body) first (or turned on [lua_need_request_body](#lua_need_request_body) to force this module to read the request body. This is not recommended however).
To force in-memory request bodies, try setting [client_body_buffer_size](http://nginx.org/en/docs/http/ngx_http_core_module.html#client_body_buffer_size) to the same size value in [client_max_body_size](http://nginx.org/en/docs/http/ngx_http_core_module.html#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.
If the request body has not been read yet, call [ngx.req.read_body](#ngxreqread_body) first (or turned on [lua_need_request_body](#lua_need_request_body) to force this module to read the request body. This is not recommended however).
To force in-file request bodies, try turning on [client_body_in_file_only](http://nginx.org/en/docs/http/ngx_http_core_module.html#client_body_in_file_only).
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 was first introduced in the `v0.3.1rc18` release.
If the optional `auto_clean` argument is given a `true` value, then this file will be removed at request completion or the next time this function or [ngx.req.set_body_data](#ngxreqset_body_data) are called in the same request. The `auto_clean` is default to `false`.
Please ensure that the file specified by the `file_name` argument exists and is readable by an Nginx worker process by setting its permission properly to avoid Lua exception errors.
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 was first introduced in the `v0.3.1rc18` release.
Creates a new blank request body for the current request and inializes the buffer for later request body data writing via the [ngx.req.append_body](#ngxreqappend_body) and [ngx.req.finish_body](#ngxreqfinish_body) APIs.
If the `buffer_size` argument is specified, then its value will be used for the size of the memory buffer for body writing with [ngx.req.append_body](#ngxreqappend_body). If the argument is omitted, then the value specified by the standard [client_body_buffer_size](http://nginx.org/en/docs/http/ngx_http_core_module.html#client_body_buffer_size) directive will be used instead.
When the data can no longer be hold in the memory buffer for the request body, then the data will be flushed onto a temporary file just like the standard request body reader in the Nginx core.
It is important to always call the [ngx.req.finish_body](#ngxreqfinish_body) after all the data has been appended onto the current request body. Also, when this function is used together with [ngx.req.socket](#ngxreqsocket), it is required to call [ngx.req.socket](#ngxreqsocket) *before* this function, or you will get the "request body already exists" error message.
This function can be used with [ngx.req.append_body](#ngxreqappend_body), [ngx.req.finish_body](#ngxreqfinish_body), and [ngx.req.socket](#ngxreqsocket) to implement efficient input filters in pure Lua (in the context of [rewrite_by_lua](#rewrite_by_lua)* or [access_by_lua](#access_by_lua)*), which can be used with other Nginx content handler or upstream modules like [ngx_http_proxy_module](http://nginx.org/en/docs/http/ngx_http_proxy_module.html) and [ngx_http_fastcgi_module](http://nginx.org/en/docs/http/ngx_http_fastcgi_module.html).
When the data can no longer be hold in the memory buffer for the request body, then the data will be flushed onto a temporary file just like the standard request body reader in the Nginx core.
This function can be used with [ngx.req.init_body](#ngxreqinit_body), [ngx.req.finish_body](#ngxreqfinish_body), and [ngx.req.socket](#ngxreqsocket) to implement efficient input filters in pure Lua (in the context of [rewrite_by_lua](#rewrite_by_lua)* or [access_by_lua](#access_by_lua)*), which can be used with other Nginx content handler or upstream modules like [ngx_http_proxy_module](http://nginx.org/en/docs/http/ngx_http_proxy_module.html) and [ngx_http_fastcgi_module](http://nginx.org/en/docs/http/ngx_http_fastcgi_module.html).
Completes the construction process of the new request body created by the [ngx.req.init_body](#ngxreqinit_body) and [ngx.req.append_body](#ngxreqappend_body) calls.
This function can be used with [ngx.req.init_body](#ngxreqinit_body), [ngx.req.append_body](#ngxreqappend_body), and [ngx.req.socket](#ngxreqsocket) to implement efficient input filters in pure Lua (in the context of [rewrite_by_lua](#rewrite_by_lua)* or [access_by_lua](#access_by_lua)*), which can be used with other Nginx content handler or upstream modules like [ngx_http_proxy_module](http://nginx.org/en/docs/http/ngx_http_proxy_module.html) and [ngx_http_fastcgi_module](http://nginx.org/en/docs/http/ngx_http_fastcgi_module.html).
Returns a read-only cosocket object that wraps the downstream connection. Only [receive](#tcpsockreceive) and [receiveuntil](#tcpsockreceiveuntil) methods are supported on this object.
The socket object returned by this method is usually used to read the current request's body in a streaming fashion. Do not turn on the [lua_need_request_body](#lua_need_request_body) directive, and do not mix this call with [ngx.req.read_body](#ngxreqread_body) and [ngx.req.discard_body](#ngxreqdiscard_body).
If any request body data has been pre-read into the Nginx core request header buffer, the resulting cosocket object will take care of this to avoid potential data loss resulting from such pre-reading.
Since the `v0.9.0` release, this function accepts an optional boolean `raw` argument. When this argument is `true`, this function returns a full duplex cosocket object wrapping around the raw downstream connection socket, upon which you can call the [receive](#tcpsockreceive), [receiveuntil](#tcpsockreceiveuntil), and [send](#tcpsocksend) methods.
When the `raw` argument is `true`, it is required that no pending data from any previous [ngx.say](#ngxsay), [ngx.print](#ngxprint), or [ngx.send_headers](#ngxsend_headers) calls exists. So if you have these downstream output calls previously, you should call [ngx.flush(true)](#ngxflush) before calling `ngx.req.socket(true)` to ensure that there is no pending output data. Another requirement for this case is that the request body must have already been read completely.
You can use the "raw request socket" returned by `ngx.req.socket(true)` to implement fancy protocols like [WebSocket](http://en.wikipedia.org/wiki/WebSocket), or just emit your own raw HTTP response header or body data. You can refer to the [lua-resty-websocket library](https://github.com/agentzh/lua-resty-websocket) for a real world example.
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](#ngxencode_args) method.
This method is similar to the [echo_exec](http://github.com/agentzh/echo-nginx-module#echo_exec) directive of the [echo-nginx-module](http://github.com/agentzh/echo-nginx-module).
This method *must* be called before [ngx.send_headers](#ngxsend_headers) or explicit response body outputs by either [ngx.print](#ngxprint) or [ngx.say](#ngxsay).
This method is very much like the [rewrite](http://nginx.org/en/docs/http/ngx_http_rewrite_module.html#rewrite) directive with the `redirect` modifier in the standard
[[HttpRewriteModule]], for example, this `nginx.conf` snippet
This method call terminates the current request's processing and never returns. It is recommended to combine the `return` statement with this call, i.e., `return ngx.redirect(...)`, so as to be more explicit.
Emits arguments concatenated to the HTTP client (as response body). If response headers have not been sent, this function will send headers out first and then output body data.
This is an asynchronous call and will return immediately without waiting for all the data to be written into the system send buffer. To run in synchronous mode, call `ngx.flush(true)` after calling `ngx.print`. This can be particularly useful for streaming output. See [ngx.flush](#ngxflush) for more details.
Please note that both `ngx.print` and [ngx.say](#ngxsay) will always invoke the whole Nginx output body filter chain, which is an expensive operation. So be careful when calling either of these two in a tight loop; buffer the data yourself in Lua and save the calls.
Lua `nil` arguments are accepted and result in literal `"nil"` string while Lua booleans result in literal `"true"` or `"false"` string outputs. And the `ngx.null` constant will yield the `"null"` string output.
The `log_level` argument can take constants like `ngx.ERR` and `ngx.WARN`. Check out [Nginx log level constants](#nginx-log-level-constants) for details.
There is a hard coded `2048` byte limitation on error message lengths in the Nginx core. This limit includes trailing newlines and leading time stamps. If the message size exceeds this limit, Nginx will truncate the message text accordingly. This limit can be manually modified by editing the `NGX_MAX_ERROR_STR` macro definition in the `src/core/ngx_log.h` file in the Nginx source tree.
`ngx.flush` accepts an optional boolean `wait` argument (Default: `false`) first introduced in the `v0.3.1rc34` release. When called with the default argument, it issues an asynchronous call (Returns immediately without waiting for output data to be written into the system send buffer). Calling the function with the `wait` argument set to `true` switches to synchronous mode.
In synchronous mode, the function will not return until all output data has been written into the system send buffer or until the [send_timeout](http://nginx.org/en/docs/http/ngx_http_core_module.html#send_timeout) setting has expired. Note that using the Lua coroutine mechanism means that this function does not block the Nginx event loop even in the synchronous mode.
When `ngx.flush(true)` is called immediately after [ngx.print](#ngxprint) or [ngx.say](#ngxsay), it causes the latter functions to run in synchronous mode. This can be particularly useful for streaming output.
When `status == 0` (i.e., `ngx.OK`), it will only quit the current phase handler (or the content handler if the [content_by_lua](#content_by_lua) directive is used) and continue to run later phases (if any) for the current request.
Note that while this method accepts all [HTTP status constants](#http-status-constants) as input, it only accepts `NGX_OK` and `NGX_ERROR` of the [core constants](#core-constants).
It is recommended, though not necessary, to combine the `return` statement with this call, i.e., `return ngx.exit(...)`, to give a visual hint to others reading the code.
Explicitly specify the end of the response output stream. In the case of HTTP 1.1 chunked encoded output, it will just trigger the Nginx core to send out the "last chunk".
When you disable the HTTP 1.1 keep-alive feature for your downstream connections, you can rely on descent HTTP clients to close the connection actively for you when you call this method. This trick can be used do back-ground jobs without letting the HTTP clients to wait on the connection, as in the following example:
location = /async {
keepalive_timeout 0;
content_by_lua '
ngx.say("got the task!")
ngx.eof() -- descent HTTP client will close the connection at this point
-- access MySQL, PostgreSQL, Redis, Memcached, and etc here...
But if you create subrequests to access other locations configured by Nginx upstream modules, then you should configure those upstream modules to ignore client connection abortions if they are not by default. For example, by default the standard [ngx_http_proxy_module](http://nginx.org/en/docs/http/ngx_http_proxy_module.html) will terminate both the subrequest and the main request as soon as the client closes the connection, so it is important to turn on the [proxy_ignore_client_abort](http://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_ignore_client_abort) directive in your location block configured by [ngx_http_proxy_module](http://nginx.org/en/docs/http/ngx_http_proxy_module.html):
The optional `max_args` argument can be used to specify the maximum number of arguments parsed from the `str` argument. By default, a maximum of 100 request arguments are parsed (including those with the same name) and that additional URI arguments are silently discarded to guard against potential denial of service attacks.
This method performs better on relatively short `str` inputs (i.e., less than 30 ~ 60 bytes), as compared to [ngx.crc32_long](#ngxcrc32_long). The result is exactly the same as [ngx.crc32_long](#ngxcrc32_long).
This method performs better on relatively long `str` inputs (i.e., longer than 30 ~ 60 bytes), as compared to [ngx.crc32_short](#ngxcrc32_short). The result is exactly the same as [ngx.crc32_short](#ngxcrc32_short).
The raw binary form of the `HMAC-SHA1` digest will be generated, use [ngx.encode_base64](#ngxencode_base64), for example, to encode the result to a textual representation if desired.
Returns a floating-point number for the elapsed time in seconds (including milliseconds as the decimal part) from the epoch for the current time stamp from the nginx cached time (no syscall involved unlike Lua's date library).
Returns the current time stamp (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).
Returns the current time stamp (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).
Returns a formated string can be used as the cookie expiration time. The parameter `sec` is the time stamp in seconds (like those returned from [ngx.time](#ngxtime)).
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 time stamp in seconds (like those returned from [ngx.time](#ngxtime)).
Parse the http time string (as returned by [ngx.http_time](#ngxhttp_time)) into seconds. Returns the seconds or `nil` if the input string is in bad forms.
Only the first occurrence of the match is returned, or `nil` if no match is found. In case of errors, like seeing a bad regular expression or exceeding the PCRE stack limit, `nil` and a string describing the error will be returned.
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 sub-pattern's capturing, `captures[2]` the second, and so on.
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. The upper limit of the regex cache can be tuned via the [lua_regex_cache_max_entries](#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.
Note that, the `options` argument is not optional when the `ctx` argument is specified and that the empty Lua string (`""`) must be used as placeholder for `options` if no meaningful regex options are required.
To confirm that PCRE JIT is enabled, activate the Nginx debug log by adding the `--with-debug` option to Nginx or ngx_openresty's `./configure` script. Then, enable the "debug" error log level in `error_log` directive. The following message will be generated if PCRE JIT is enabled:
Similar to [ngx.re.match](#ngxrematch), 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`.
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.
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](#ngxrematch).
This method returns the resulting new string as well as the number of successful substitutions. In case of failures, like syntax errors in the regular expressions or the `<replace>` string argument, it will return `nil` and a string describing the error.
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](#ngxrematch). Here is an example:
The number `8` will be consistently output when accessing `/get` regardless of 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).
Retrieving the value in the dictionary [ngx.shared.DICT](#ngxshareddict) for the key `key`. If the key does not exist or has been expired, then `nil` will be returned.
The `value` argument inserted can be Lua booleans, numbers, strings, or `nil`. Their value type will also be stored into the dictionary and the same data type can be retrieved later via the [get](#ngxshareddictget) 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.
The optional `flags` argument specifies a user flags value associated with the entry to be stored. It can also be retrieved later with the value. The user flags is stored as an unsigned 32-bit integer internally. Defaults to `0`. The user flags argument was first introduced in the `v0.5.0rc2` release.
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](#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`.
Similar to the [set](#ngxshareddictset) method, but never overrides the (least recently used) unexpired items in the store when running out of storage in the shared memory zone. In this case, it will immediately return `nil` and the string "no memory".
Just like the [set](#ngxshareddictset) method, but only stores the key-value pair into the dictionary [ngx.shared.DICT](#ngxshareddict) 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.
Similar to the [add](#ngxshareddictadd) method, but never overrides the (least recently used) unexpired items in the store when running out of storage in the shared memory zone. In this case, it will immediately return `nil` and the string "no memory".
Just like the [set](#ngxshareddictset) method, but only stores the key-value pair into the dictionary [ngx.shared.DICT](#ngxshareddict) 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.
Increments the (numerical) value for `key` in the shm-based dictionary [ngx.shared.DICT](#ngxshareddict) by the step value `value`. Returns the new resulting number if the operation is successfully completed or `nil` and an error message otherwise.
Flushes out all the items in the dictionary. This method does not actuall free up all the memory blocks in the dictionary but just marks all the existing items as expired.
Flushes out the expired items in the dictionary, up to the maximal number specified by the optional `max_count` argument. When the `max_count` argument is given `0` or not given at all, then it means unlimited. Returns the number of items that have actually been flushed.
Fetch a list of the keys from the dictionary, up to `<max_count>`.
By default, only the first 1024 keys (if any) are returned. When the `<max_count>` argument is given the value `0`, then all the keys will be returned even there is more than 1024 keys in the dictionary.
**WARNING** Be careful when calling this method on dictionaries with a really huge number of keys. This method may lock the dictionary for quite a while and block all the nginx worker processes that are trying to access the dictionary.
This feature was first introduced in the `v0.7.3` release.
Creates and returns a UDP or datagram-oriented unix domain socket object (also known as one type of the "cosocket" objects). The following methods are supported on this object:
It is intended to be compatible with the UDP API of the [LuaSocket](http://w3.impa.br/~diego/software/luasocket/udp.html) library but is 100% nonblocking out of the box.
This feature was first introduced in the `v0.5.7` release.
Attempts to connect a UDP socket object to a remote server or to a datagram unix domain socket file. Because the datagram protocol is actually connection-less, this method does not really establish a "connection", but only just set the name of the remote peer for subsequent read/write operations.
Both IP addresses and domain names can be specified as the `host` argument. In case of domain names, this method will use Nginx core's dynamic resolver to parse the domain name without blocking and it is required to configure the [resolver](http://nginx.org/en/docs/http/ngx_http_core_module.html#resolver) directive in the `nginx.conf` file like this:
assuming the datagram service is listening on the unix domain socket file `/tmp/some-datagram-service.sock` and the client socket will use the "autobind" feature on Linux.
The input argument `data` can either be a Lua string or a (nested) Lua table holding string fragments. In case of table arguments, this method will copy all the string elements piece by piece to the underlying Nginx socket send buffers, which is usually optimal than doing string concatenation operations on the Lua land.
Receives data from the UDP or datagram unix domain socket object with an optional receive buffer size argument, `size`.
This method is a synchronous operation and is 100% nonblocking.
In case of success, it returns the data received; in case of error, it returns `nil` with a string describing the error.
If the `size` argument is specified, then this method will use this size as the receive buffer size. But when this size is greater than `8192`, then `8192` will be used instead.
If no argument is specified, then the maximal buffer size, `8192` is assumed.
Timeout for the reading operation is controlled by the [lua_socket_read_timeout](#lua_socket_read_timeout) config directive and the [settimeout](#udpsocksettimeout) method. And the latter takes priority. For example:
Closes the current UDP or datagram unix domain socket. It returns the `1` in case of success and returns `nil` with a string describing the error otherwise.
Socket objects that have not invoked this method (and associated connections) will be closed when the socket object is released by the Lua GC (Garbage Collector) or the current client HTTP request finishes processing.
Creates and returns a TCP or stream-oriented unix domain socket object (also known as one type of the "cosocket" objects). The following methods are supported on this object:
It is intended to be compatible with the TCP API of the [LuaSocket](http://w3.impa.br/~diego/software/luasocket/tcp.html) library but is 100% nonblocking out of the box. Also, we introduce some new APIs to provide more functionalities.
This feature was first introduced in the `v0.5.0rc1` release.
Before actually resolving the host name and connecting to the remote backend, this method will always look up the connection pool for matched idle connections created by previous calls of this method (or the [ngx.socket.connect](#ngxsocketconnect) function).
Both IP addresses and domain names can be specified as the `host` argument. In case of domain names, this method will use Nginx core's dynamic resolver to parse the domain name without blocking and it is required to configure the [resolver](http://nginx.org/en/docs/http/ngx_http_core_module.html#resolver) directive in the `nginx.conf` file like this:
Timeout for the connecting operation is controlled by the [lua_socket_connect_timeout](#lua_socket_connect_timeout) config directive and the [settimeout](#tcpsocksettimeout) method. And the latter takes priority. For example:
specify a custom name for the connection pool being used. If omitted, then the connection pool name will be generated from the string template `"<host>:<port>"` or `"<unix-socket-path>"`.
This method is a synchronous operation that will not return until *all* the data has been flushed into the system socket send buffer or an error occurs.
In case of success, it returns the total number of bytes that have been sent. Otherwise, it returns `nil` and a string describing the error.
The input argument `data` can either be a Lua string or a (nested) Lua table holding string fragments. In case of table arguments, this method will copy all the string elements piece by piece to the underlying Nginx socket send buffers, which is usually optimal than doing string concatenation operations on the Lua land.
Timeout for the sending operation is controlled by the [lua_socket_send_timeout](#lua_socket_send_timeout) config directive and the [settimeout](#tcpsocksettimeout) method. And the latter takes priority. For example:
In case of success, it returns the data received; in case of error, it returns `nil` with a string describing the error and the partial data received so far.
If a number-like argument is specified (including strings that look like numbers), then it is interpreted as a size. This method will not return until it reads exactly this size of data or an error occurs.
If a non-number-like string argument is specified, then it is interpreted as a "pattern". The following patterns are supported:
*`'*a'`: reads from the socket until the connection is closed. No end-of-line translation is performed;
*`'*l'`: reads a line of text from the socket. The line is terminated by a `Line Feed` (LF) character (ASCII 10), optionally preceded by a `Carriage Return` (CR) character (ASCII 13). The CR and LF characters are not included in the returned line. In fact, all CR characters are ignored by the pattern.
If no argument is specified, then it is assumed to be the pattern `'*l'`, that is, the line reading pattern.
Timeout for the reading operation is controlled by the [lua_socket_read_timeout](#lua_socket_read_timeout) config directive and the [settimeout](#tcpsocksettimeout) method. And the latter takes priority. For example:
Since the `v0.8.8` release, this method no longer automatically closes the current connection when the read timeout error happens. For other connection errors, this method always automatically closes the connection.
This method returns an iterator Lua function that can be called to read the data stream until it sees the specified pattern or an error occurs.
Here is an example for using this method to read a data stream with the boundary sequence `--abcedhb`:
local reader = sock:receiveuntil("\r\n--abcedhb")
local data, err, partial = reader()
if not data then
ngx.say("failed to read the data stream: ", err)
end
ngx.say("read the data stream: ", data)
When called without any argument, the iterator function returns the received data right *before* the specified pattern string in the incoming data stream. So for the example above, if the incoming data stream is `'hello, world! -agentzh\r\n--abcedhb blah blah'`, then the string `'hello, world! -agentzh'` will be returned.
In case of error, the iterator function will return `nil` along with a string describing the error and the partial data bytes that have been read so far.
The iterator function can be called multiple times and can be mixed safely with other cosocket method calls or other iterator function calls.
The iterator function behaves differently (i.e., like a real iterator) when it is called with a `size` argument. That is, it will read that `size` of data on each invocation and will return `nil` at the last invocation (either sees the boundary pattern or meets an error). For the last successful invocation of the iterator function, the `err` return value will be `nil` too. The iterator function will be reset after the last successful invocation that returns `nil` data and `nil` error. Consider the following example:
Note that, the actual data returned *might* be a little longer than the size limit specified by the `size` argument when the boundary pattern has ambiguity for streaming parsing. Near the boundary of the data stream, the data string actually returned could also be shorter than the size limit.
Timeout for the iterator function's reading operation is controlled by the [lua_socket_read_timeout](#lua_socket_read_timeout) config directive and the [settimeout](#tcpsocksettimeout) method. And the latter takes priority. For example:
It is important here to call the [settimeout](#tcpsocksettimeout) method *before* calling the iterator function (note that the `receiveuntil` call is irrelevant here).
As from the `v0.5.1` release, this method also takes an optional `options` table argument to control the behavior. The following options are supported:
The `inclusive` takes a boolean value to control whether to include the pattern string in the returned data string. Default to `false`. For example,
local reader = tcpsock:receiveuntil("_END_", { inclusive = true })
local data = reader()
ngx.say(data)
Then for the input data stream `"hello world _END_ blah blah blah"`, then the example above will output `hello world _END_`, including the pattern string `_END_` itself.
Since the `v0.8.8` release, this method no longer automatically closes the current connection when the read timeout error happens. For other connection errors, this method always automatically closes the connection.
Closes the current TCP or stream unix domain socket. It returns the `1` in case of success and returns `nil` with a string describing the error otherwise.
Note that there is no need to call this method on socket objects that have invoked the [setkeepalive](#tcpsocksetkeepalive) method because the socket object is already closed (and the current connection is saved into the built-in connection pool).
Socket objects that have not invoked this method (and associated connections) will be closed when the socket object is released by the Lua GC (Garbage Collector) or the current client HTTP request finishes processing.
Set the timeout value in milliseconds for subsequent socket operations ([connect](#tcpsockconnect), [receive](#tcpsockreceive), and iterators returned from [receiveuntil](#tcpsockreceiveuntil)).
Settings done by this method takes priority over those config directives, i.e., [lua_socket_connect_timeout](#lua_socket_connect_timeout), [lua_socket_send_timeout](#lua_socket_send_timeout), and [lua_socket_read_timeout](#lua_socket_read_timeout).
Note that this method does *not* affect the [lua_socket_keepalive_timeout](#lua_socket_keepalive_timeout) setting; the `timeout` argument to the [setkeepalive](#tcpsocksetkeepalive) method should be used for this purpose instead.
This function is added for [LuaSocket](http://w3.impa.br/~diego/software/luasocket/tcp.html) API compatibility and does nothing for now. Its functionality will be implemented in future.
This feature was first introduced in the `v0.5.0rc1` release.
Puts the current socket's connection immediately into the cosocket built-in connection pool and keep it alive until other [connect](#tcpsockconnect) method calls request it or the associated maximal idle timeout is expired.
The first optional argument, `timeout`, can be used to specify the maximal idle timeout (in milliseconds) for the current connection. If omitted, the default setting in the [lua_socket_keepalive_timeout](#lua_socket_keepalive_timeout) config directive will be used. If the `0` value is given, then the timeout interval is unlimited.
The second optional argument, `size`, can be used to specify the maximal number of connections allowed in the connection pool for the current server (i.e., the current host-port pair or the unix domain socket file path). Note that the size of the connection pool cannot be changed once the pool is created. When this argument is omitted, the default setting in the [lua_socket_pool_size](#lua_socket_pool_size) config directive will be used.
When the connection pool exceeds the available size limit, the least recently used (idle) connection already in the pool will be closed to make room for the current connection.
Note that the cosocket connection pool is per Nginx worker process rather than per Nginx server instance, so the size limit specified here also applies to every single Nginx worker process.
Idle connections in the pool will be monitored for any exceptional events like connection abortion or unexpected incoming data on the line, in which cases the connection in question will be closed and removed from the pool.
This method also makes the current cosocket object enter the "closed" state, so there is no need to manually call the [close](#tcpsockclose) method on it afterwards.
This method returns the (successfully) reused times for the current connection. In case of error, it returns `nil` and a string describing the error.
If the current connection does not come from the built-in connection pool, then this method always returns `0`, that is, the connection has never been reused (yet). If the connection comes from the connection pool, then the return value is always non-zero. So this method can also be used to determine if the current connection comes from the pool.
This feature was first introduced in the `v0.5.0rc1` release.
This function is a shortcut for combining [ngx.socket.tcp()](#ngxsockettcp) and the [connect()](#tcpsockconnect) method call in a single operation. It is actually implemented like this:
There is no way to use the [settimeout](#tcpsocksettimeout) method to specify connecting timeout for this method and the [lua_socket_connect_timeout](#lua_socket_connect_timeout) directive must be set at configure time instead.
Spawns a new user "light thread" with the Lua function `func` as well as those optional arguments `arg1`, `arg2`, and etc. Returns a Lua thread (or Lua coroutine) object represents this "light thread".
Before `ngx.thread.spawn` returns, the `func` will be called with those optional arguments until it returns, aborts with an error, or gets yielded due to I/O operations via the [Nginx API for Lua](#nginx-api-for-lua) (like [tcpsock:receive](#tcpsockreceive)).
All the Lua code chunks running by [rewrite_by_lua](#rewrite_by_lua), [access_by_lua](#access_by_lua), and [content_by_lua](#content_by_lua) are in a boilerplate "light thread" created automatically by ngx_lua. Such boilerplate "light thread" are also called "entry threads".
1. a "light thread" (either the "entry thread" or a user "light thread" aborts by calling [ngx.exit](#ngxexit), [ngx.exec](#ngxexec), [ngx.redirect](#ngxredirect), or [ngx.req.set_uri(uri, true)](#ngxreqset_uri), or
Due to the limitation in the Nginx subrequest model, it is not allowed to abort a running Nginx subrequest in general. So it is also prohibited to abort a running "light thread" that is pending on one ore more Nginx subrequests. You must call [ngx.thread.wait](#ngxthreadwait) to wait for those "light thread" to terminate before quitting the "world". A notable exception here is that you can abort pending subrequests by calling [ngx.exit](#ngxexit) with and only with the status code `ngx.ERROR` (-1), `408`, `444`, or `499`.
The "light threads" are not scheduled in a pre-emptive way. In other words, no time-slicing is performed automatically. A "light thread" will keep running exclusively on the CPU until
1. it calls [coroutine.yield](#coroutineyield) to actively give up execution, or
1. it is aborted by a Lua error or an invocation of [ngx.exit](#ngxexit), [ngx.exec](#ngxexec), [ngx.redirect](#ngxredirect), or [ngx.req.set_uri(uri, true)](#ngxreqset_uri).
User "light threads" can create "light threads" themselves and normal user coroutiens created by [coroutine.create](#coroutinecreate) can also create "light threads". The coroutine (be it a normal Lua coroutine or a "light thread") that directly spawns the "light thread" is called the "parent coroutine" for the "light thread" newly spawned.
"Light threads" are mostly useful for doing concurrent upstream requests in a single Nginx request handler, kinda like a generalized version of [ngx.location.capture_multi](#ngxlocationcapture_multi) that can work with all the [Nginx API for Lua](#nginx-api-for-lua). The following example demonstrates parallel requests to MySQL, Memcached, and upstream HTTP services in a single Lua handler, and outputting the results in the order that they actually return (very much like the Facebook BigPipe model):
The return values have exactly the same meaning as [coroutine.resume](#coroutineresume), that is, the first value returned is a boolean value indicating whether the "light thread" terminates successfully or not, and subsequent values returned are the return values of the user Lua function that was used to spawn the "light thread" (in case of success) or the error object (in case of failure).
The following example demonstrates the use of `ngx.thread.wait` and [ngx.location.capture](#ngxlocationcapture) to emulate [ngx.location.capture_multi](#ngxlocationcapture_multi):
All the [Nginx API for Lua](#nginx-api-for-lua) can be used in the callback function because the function is run in a special "light thread", just as those "light threads" created by [ngx.thread.spawn](#ngxthreadspawn).
The callback function can decide what to do with the client abortion event all by itself. For example, it can simply ignore the event by doing nothing and the current Lua request handler will continue executing without interruptions. And the callback function can also decide to terminate everything by calling [ngx.exit](#ngxexit), for example,
When [lua_check_client_abort](#lua_check_client_abort) is set to `off` (which is the default), then this function call will always return the error message "lua_check_client_abort is off".
According to the current implementation, this function can only be called once in a single request handler; subsequent calls will return the error message "duplicate call".
This API was first introduced in the `v0.7.4` release.
original request and the timer user callback function.
Here is a simple example:
location / {
...
log_by_lua '
local function push_data(premature, uri, args, status)
-- push the data uri, args, and status to the remote
-- via ngx.socket.tcp or ngx.socket.udp
-- (one may want to buffer the data in Lua a bit to
-- save I/O operations)
end
local ok, err = ngx.timer.at(0, push_data,
ngx.var.uri, ngx.var.args, ngx.header.status)
if not ok then
ngx.log(ngx.ERR, "failed to create timer: ", err)
return
end
';
}
One can also create infinite re-occuring timers, for instance, a timer getting triggered every `5` seconds, by calling `ngx.timer.at` recursively in the timer callback function. Here is such an example,
local delay = 5
local handler
handler = function (premature)
-- do some routine job in Lua just like a cron job
if premature then
return
end
local ok, err = ngx.timer.at(delay, handler)
if not ok then
ngx.log(ngx.ERR, "failed to create the timer: ", err)
return
end
end
local ok, err = ngx.timer.at(delay, handler)
if not ok then
ngx.log(ngx.ERR, "failed to create the timer: ", err)
return
end
Because timer callbacks run in the background and their running time
will not add to any client request's response time, they can easily
accumulate in the server and exhaust system resources due to either
Lua programming mistakes or just too much client traffic. To prevent
extreme consequences like crashing the Nginx server, there are
built-in limitations on both the number of "pending timers" and the
number of "running timers" in an Nginx worker process. The "pending
timers" here mean timers that have not yet been expired and "running
timers" are those whose user callbacks are currently running.
The maximal number of pending timers allowed in an Nginx
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`.
Similarly, the following directives provided by [encrypted-session-nginx-module](http://github.com/agentzh/encrypted-session-nginx-module) can be invoked from within Lua too:
Creates a user Lua coroutines with a Lua function, and returns a coroutine object.
Similar to the standard Lua [coroutine.create](http://www.lua.org/manual/5.1/manual.html#pdf-coroutine.create) API, but works in the context of the Lua coroutines created by ngx_lua.
This API was first introduced in the `v0.6.0` release.
Resumes the executation of a user Lua coroutine object previously yielded or just created.
Similar to the standard Lua [coroutine.resume](http://www.lua.org/manual/5.1/manual.html#pdf-coroutine.resume) API, but works in the context of the Lua coroutines created by ngx_lua.
This API was first introduced in the `v0.6.0` release.
Yields the executation of the current user Lua coroutine.
Similar to the standard Lua [coroutine.yield](http://www.lua.org/manual/5.1/manual.html#pdf-coroutine.yield) API, but works in the context of the Lua coroutines created by ngx_lua.
This API was first introduced in the `v0.6.0` release.
Similar to the standard Lua [coroutine.wrap](http://www.lua.org/manual/5.1/manual.html#pdf-coroutine.wrap) API, but works in the context of the Lua coroutines created by ngx_lua.
This API was first introduced in the `v0.6.0` release.
As from the `v0.5.0rc32` release, all `*_by_lua_file` configure directives (such as [content_by_lua_file](#content_by_lua_file)) support loading Lua 5.1 and LuaJIT 2.0 raw bytecode files directly.
Please note that the bytecode format used by LuaJIT 2.0 is not compatible with that used by the standard Lua 5.1 interpreter. So if using LuaJIT 2.0 with ngx_lua, LuaJIT compatible bytecode files must be generated as shown:
Similarly, if using the standard Lua 5.1 interpreter with ngx_lua, Lua compatible bytecode files must be generated using the `luac` commandline utility as shown:
Unlike as with LuaJIT, debug information is included in standard Lua 5.1 bytecode files by default. This can be striped out by specifying the `-s` option as shown:
Attempts to load standard Lua 5.1 bytecode files into ngx_lua instances linked to LuaJIT 2.0 or vice versa, will result in an error message, such as that below, being logged into the Nginx `error.log` file:
The HTTP 1.0 protocol does not support chunked output and requires an explicit `Content-Length` header when the response body is not empty in order to support the HTTP 1.0 keep-alive.
So when a HTTP 1.0 request is made and the [lua_http10_buffering](#lua_http10_buffering) directive is turned `on`, ngx_lua will buffer the
output of [ngx.say](#ngxsay) and [ngx.print](#ngxprint) calls and also postpone sending response headers until all the response body output is received.
If the `Content-Length` response header is set in the running Lua code, however, this buffering will be disabled even if the [lua_http10_buffering](#lua_http10_buffering) directive is turned `on`.
To globally share data among all the requests handled by the same nginx worker process, encapsulate the shared data into a Lua module, use the Lua `require` builtin to import the module, and then manipulate the shared data in Lua. This works because required Lua modules are loaded only once and all coroutines will share the same copy of the module (both its code and data). Note however that Lua global variables (note, not module-level variables) WILL NOT persist between requests because of the one-coroutine-per-request isolation design.
Note that this data sharing is on a *per-worker* basis and not on a *per-server* basis. That is, when there are multiple nginx worker processes under an Nginx master, data sharing cannot cross the process boundary between these workers.
1. Use only a single nginx worker and a single server (this is however not recommended when there is a multi core CPU or multiple CPUs in a single machine).
1. Use data storage mechanisms such as `memcached`, `redis`, `MySQL` or `PostgreSQL`. [The ngx_openresty bundle](http://openresty.org) associated with this module comes with a set of companion Nginx modules and Lua libraries that provide interfaces with these data storage mechanisms.
However, later attempts to manipulate the cosocket object will fail and return the actual error status message generated by the failed connect operation.
* Lua's `dofile` builtin is implemented as a C function in both Lua 5.1 and LuaJIT 2.0 and when [ngx.location.capture](#ngxlocationcapture) is called, [ngx.exec](#ngxexec), [ngx.exit](#ngxexit) or [ngx.req.read_body](#ngxreqread_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 normally 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 and use the Lua `require` builtin instead.
* As the standard Lua 5.1 interpreter's VM is not fully resumable, the methods [ngx.location.capture](#ngxlocationcapture), [ngx.location.capture_multi](#ngxlocationcapture_multi), [ngx.redirect](#ngxredirect), [ngx.exec](#ngxexec), and [ngx.exit](#ngxexit) 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) or even the first line of the `for ... in ...` statement when the standard Lua 5.1 interpreter is used and the `attempt to yield across metamethod/C-call boundary` error will be produced. Please use LuaJIT 2.0, which supports a fully resumable VM, to avoid this.
Here is the reason: by design, the global environment has exactly the same lifetime as the Nginx request handler associated with it. Each request handler has its own set of Lua global variables and that is the idea of request isolation. The Lua module is actually loaded by the first Nginx request handler and is cached by the `require()` built-in in the package.loaded table for later reference, and `require()` has the side effect of setting a global variable to the loaded module table. But this global variable will be cleared at the end of the request handler, and every subsequent request handler all has its own (clean) global environment. So one will get Lua exception for accessing the `nil` value.
To find out all the uses of Lua global variables in your Lua code, you can run the [lua-releng tool](https://github.com/agentzh/nginx-devel-utils/blob/master/lua-releng) across all your .lua source files:
$ lua-releng
Checking use of Lua global variables in file lib/foo/bar.lua ...
The output says that the line 1489 of file `lib/foo/bar.lua` writes to a global variable named `contains`, the line 1506 reads from the global variable `setvar`, and line 1545 reads the global `varexpand`.
This tool will guarantee that local variables in the Lua module functions are all declared with the `local` keyword, otherwise a runtime exception will be thrown. It prevents undesirable race conditions while accessing such variables. See [Data Sharing within an Nginx Worker](#data_sharing_within_an_nginx_worker) for the reasons behind this.
The [ngx.location.capture](#ngxlocationcapture) and [ngx.location.capture_multi](#ngxlocationcapture_multi) directives cannot capture locations that include the [echo_location](http://github.com/agentzh/echo-nginx-module#echo_location), [echo_location_async](http://github.com/agentzh/echo-nginx-module#echo_location_async), [echo_subrequest](http://github.com/agentzh/echo-nginx-module#echo_subrequest), or [echo_subrequest_async](http://github.com/agentzh/echo-nginx-module#echo_subrequest_async) directives.
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:
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, the regex pattern can be presented 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.
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.
Mixing SSI with ngx_lua in the same Nginx request is not supported at all. Just use ngx_lua exclusively. Everything you can do with SSI can be done atop ngx_lua anyway and it can be more efficient when using ngx_lua.
Certain Lua APIs provided by ngx_lua do not work in Nginx's SPDY mode yet: [ngx.location.capture](#ngxlocationcapture), [ngx.location.capture_multi](#ngxlocationcapture_multi), and [ngx.req.socket](#ngxreqsocket).
* 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,
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.
On a ThinkPad T400 2.80 GHz laptop, the Hello World example readily achieves 28k req/sec using `http_load -p 10`. By 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 Hello World equivalents.
The [ngx_openresty bundle](http://openresty.org) can be used to install Nginx, ngx_lua, either one of the standard Lua 5.1 interpreter or LuaJIT 2.0, as well as a package of powerful companion Nginx modules. The basic installation step is a simple `./configure --with-luajit && make && make install`.
1. Install LuaJIT 2.0 (recommended) or Lua 5.1 (Lua 5.2 is *not* supported yet). LuajIT can be downloaded from the [the LuaJIT project website](http://luajit.org/download.html) and Lua 5.1, from the [Lua project website](http://www.lua.org/). Some distribution package managers also distribute LuajIT and/or Lua.
Everything should be installed correctly, except for one small tweak.
Library name `liblua.so` has been changed in liblua5.1 package, it only comes with `liblua5.1.so`, which needs to be symlinked to `/usr/lib` so it could be found during the configuration process.
* review and apply vadim-pavlov's patch for [ngx.location.capture](#ngxlocationcapture)'s `extra_headers` option
* use `ngx_hash_t` to optimize the built-in header look-up process for [ngx.req.set_header](#ngxreqset_header), [ngx.header.HEADER](#ngxheaderheader), and etc.
* add `ignore_resp_headers`, `ignore_resp_body`, and `ignore_resp` options to [ngx.location.capture](#ngxlocationcapture) and [ngx.location.capture_multi](#ngxlocationcapture_multi) methods, to allow micro performance tuning on the user side.
* memcached: listening on the default port, 11211.
* redis: listening on the default port, 6379.
See also the [developer build script](https://github.com/chaoslawful/lua-nginx-module/blob/master/util/build2.sh) for more details on setting up the testing environment.
To run the whole test suite in the default testing mode:
To run a specific test block in a particular test file, add the line `--- ONLY` to the test block you want to run, and then use the `prove` utility to run that `.t` file.
There are also various testing modes based on mockeagain, valgrind, and etc. Refer to the [Test::Nginx documentation](http://search.cpan.org/perldoc?Test::Nginx) for more details for various advanced testing modes. See also the test reports for the Nginx test cluster running on Amazon EC2: <http://qa.openresty.org.>
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