[edit] Name

ngx_echo - Brings "echo", "sleep", "time", "exec" and more shell-style goodies to Nginx config file.

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

[edit] Status

This module is production ready.

[edit] Version

This document describes echo-nginx-module v0.40 released on 25 June 2012.

[edit] Synopsis

  location /hello {
    echo "hello, world!";
  }

  location /hello {
    echo -n "hello, "
    echo "world!";
  }

  location /timed_hello {
    echo_reset_timer;
    echo hello world;
    echo "'hello world' takes about $echo_timer_elapsed sec.";
    echo hiya igor;
    echo "'hiya igor' takes about $echo_timer_elapsed sec.";
  }

  location /echo_with_sleep {
    echo hello;
    echo_flush;  # ensure the client can see previous output immediately
    echo_sleep   2.5;  # in sec
    echo world;
  }

  # in the following example, accessing /echo yields
  #   hello
  #   world
  #   blah
  #   hiya
  #   igor
  location /echo {
      echo_before_body hello;
      echo_before_body world;
      proxy_pass $scheme://127.0.0.1:$server_port$request_uri/more;
      echo_after_body hiya;
      echo_after_body igor;
  }
  location /echo/more {
      echo blah;
  }

  # the output of /main might be
  #   hello
  #   world
  #   took 0.000 sec for total.
  # and the whole request would take about 2 sec to complete.
  location /main {
      echo_reset_timer;
 
      # subrequests in parallel
      echo_location_async /sub1;
      echo_location_async /sub2;
 
      echo "took $echo_timer_elapsed sec for total.";
  }
  location /sub1 {
      echo_sleep 2;
      echo hello;
  }
  location /sub2 {
      echo_sleep 1;
      echo world;
  }

  # the output of /main might be
  #   hello
  #   world
  #   took 3.003 sec for total.
  # and the whole request would take about 3 sec to complete.
  location /main {
      echo_reset_timer;
 
      # subrequests in series (chained by CPS)
      echo_location /sub1;
      echo_location /sub2;
 
      echo "took $echo_timer_elapsed sec for total.";
  }
  location /sub1 {
      echo_sleep 2;
      echo hello;
  }
  location /sub2 {
      echo_sleep 1;
      echo world;
  }

  # Accessing /dup gives
  #   ------ END ------
  location /dup {
    echo_duplicate 3 "--";
    echo_duplicate 1 " END ";
    echo_duplicate 3 "--";
    echo;
  }

  # /bighello will generate 1000,000,000 hello's.
  location /bighello {
    echo_duplicate 1000_000_000 'hello';
  }

  # echo back the client request
  location /echoback {
    echo_duplicate 1 $echo_client_request_headers;
    echo "\r";
 
    echo_read_request_body;
 
    echo_request_body;
  }

  # GET /multi will yields
  #   querystring: foo=Foo
  #   method: POST
  #   body: hi
  #   content length: 2
  #   ///
  #   querystring: bar=Bar
  #   method: PUT
  #   body: hello
  #   content length: 5
  #   ///
  location /multi {
      echo_subrequest_async POST '/sub' -q 'foo=Foo' -b 'hi';
      echo_subrequest_async PUT '/sub' -q 'bar=Bar' -b 'hello';
  }
  location /sub {
      echo "querystring: $query_string";
      echo "method: $echo_request_method";
      echo "body: $echo_request_body";
      echo "content length: $http_content_length";
      echo '///';
  }

  # GET /merge?/foo.js&/bar/blah.js&/yui/baz.js will merge the .js resources together
  location /merge {
      default_type 'text/javascript';
      echo_foreach_split '&' $query_string;
          echo "/* JS File $echo_it */";
          echo_location_async $echo_it;
          echo;
      echo_end;
  }

  # accessing /if?val=abc yields the "hit" output
  # while /if?val=bcd yields "miss":
  location ^~ /if {
      set $res miss;
      if ($arg_val ~* '^a') {
          set $res hit;
          echo $res;
      }
      echo $res;
  }

[edit] Description

This module wraps lots of Nginx internal APIs for streaming input and output, parallel/sequential subrequests, timers and sleeping, as well as various meta data accessing.

Basically it provides various utilities that help testing and debugging of other modules by trivially emulating different kinds of faked subrequest locations.

People will also find it useful in real-world applications that need to

1. serve static contents directly from memory (loading from the Nginx config file).
2. wrap the upstream response with custom header and footer (kinda like the addition module but with contents read directly from the config file and Nginx variables).
3. merge contents of various "Nginx locations" (i.e., subrequests) together in a single main request (using echo_location and its friends).

This is a special dual-role module that can lazily serve as a content handler or register itself as an output filter only upon demand. By default, this module does not do anything at all.

Technially, this module has also demonstrated the following techniques that might be helpful for module writers:

1. Issue parallel subreqeusts directly from content handler.
2. Issue chained subrequests directly from content handler, by passing continuation along the subrequest chain.
3. Issue subrequests with all HTTP 1.1 methods and even an optional faked HTTP request body.
4. Interact with the Nginx event model directly from content handler using custom events and timers, and resume the content handler back if necessary.
5. Dual-role module that can (lazily) serve as a content handler or an output filter or both.
6. Nginx config file variable creation and interpolation.
7. Streaming output control using output_chain, flush and its friends.
8. Read client request body from the content handler, and returns back (asynchronously) to the content handler after completion.
9. Use Perl-based declarative test suite to drive the development of Nginx C modules.

[edit] Content Handler Directives

Use of the following directives register this module to the current Nginx location as a content handler. If you want to use another module, like the standard proxy module, as the content handler, use the filter directives provided by this module.

All the content handler directives can be mixed together in a single Nginx location and they're supposed to run sequentially just as in the Bash scripting language.

Every content handler directive supports variable interpolation in its arguments (if any).

The MIME type set by the standard default_type directive is respected by this module, as in:

  location /hello {
    default_type text/plain;
    echo hello;
  }

Then on the client side:

  $ curl -I 'http://localhost/echo'
  HTTP/1.1 200 OK
  Server: nginx/0.8.20
  Date: Sat, 17 Oct 2009 03:40:19 GMT
  Content-Type: text/plain
  Connection: keep-alive

Since the v0.22 release, all of the directives are allowed in the rewrite module's if directive block, for instance:

    location ^~ /if {
        set $res miss;
        if ($arg_val ~* '^a') {
            set $res hit;
            echo $res;
        }
        echo $res;
    }

[edit] echo

syntax: echo [options] <string>...

default: no

context: location, location if

phase: content

Sends arguments joined by spaces, along with a trailing newline, out to the client.

Note that the data might be buffered by Nginx's underlying buffer. To force the output data flushed immediately, use the echo_flush command just after echo, as in

   echo hello world;
   echo_flush;

When no argument is specified, echo emits the trailing newline alone, just like the echo command in shell.

Variables may appear in the arguments. An example is

   echo The current request uri is $request_uri;

where $request_uri is a variable exposed by the HttpCoreModule.

This command can be used multiple times in a single location configuration, as in

    location /echo {
        echo hello;
        echo world;
    }

The output on the client side looks like this

    $ curl 'http://localhost/echo'
    hello
    world

Special characters like newlines (\n) and tabs (\t) can be escaped using C-style escaping sequences. But a notable exception is the dollar sign ($). As of Nginx 0.8.20, there's still no clean way to esacpe this characters. (A work-around might be to use a $echo_dollor variable that is always evaluated to the constant $ character. This feature will possibly be introduced in a future version of this module.)

As of the echo v0.28 release, one can suppress the trailing newline character in the output by using the -n option, as in

    location /echo {
        echo -n "hello, ";
        echo "world";
    }

Accessing /echo gives

    $ curl 'http://localhost/echo'
    hello, world

Leading -n in variable values won't take effect and will be emitted literally, as in

    location /echo {
        set $opt -n;
        echo $opt "hello,";
        echo "world";
    }

This gives the following output

    $ curl 'http://localhost/echo'
    -n hello,
    world

One can output leading -n literals and other options using the special -- option like this

    location /echo {
        echo -- -n is an option;
    }

which yields

    $ curl 'http://localhost/echo'
    -n is an option

[edit] echo_duplicate

syntax: echo_duplicate <count> <string>

default: no

context: location, location if

phase: content

Outputs duplication of a string indicated by the second argument, using the times specified in the first argument.

For instance,

  location /dup {
      echo_duplicate 3 "abc";
  }

will lead to an output of "abcabcabc".

Underscores are allowed in the count number, just like in Perl. For example, to emit 1000,000,000 instances of "hello, world":

  location /many_hellos {
      echo_duplicate 1000_000_000 "hello, world";
  }

The count argument could be zero, but not negative. The second string argument could be an empty string ("") likewise.

Unlike the echo directive, no trailing newline is appended to the result. So it's possible to "abuse" this directive as a no-trailing-newline version of echo by using "count" 1, as in

  location /echo_art {
      echo_duplicate 2 '---';
      echo_duplicate 1 ' END ';  # we don't want a trailing newline here
      echo_duplicate 2 '---';
      echo;  # we want a trailing newline here...
  }

You get

  ------ END ------

This directive was first introduced in version 0.11.

[edit] echo_flush

syntax: echo_flush

default: no

context: location, location if

phase: content

Forces the data potentially buffered by underlying Nginx output filters to send immediately to the client side via socket.

Note that techically the command just emits a ngx_buf_t object with flush slot set to 1, so certain weird third-party output filter module could still block it before it reaches Nginx's (last) write filter.

This directive does not take any argument.

Consider the following example:

  location /flush {
     echo hello;
 
     echo_flush;
 
     echo_sleep 1;
     echo world;
  }

Then on the client side, using curl to access /flush, you'll see the "hello" line immediately, but only after 1 second, the last "world" line. Without calling echo_flush in the example above, you'll most likely see no output until 1 second is elapsed due to the internal buffering of Nginx.

This directive will fail to flush the output buffer in case of subrequests get involved. Consider the following example:

  location /main {
      echo_location_async /sub;
      echo hello;
      echo_flush;
  }
  location /sub {
      echo_sleep 1;
  }

Then the client won't see "hello" appear even if echo_flush has been executed before the subrequest to /sub has actually started executing. The outputs of /main that are sent after echo_location_async will be postponed and buffered firmly.

This does not apply to outputs sent before the subrequest initiated. For a modified version of the example given above:

  location /main {
      echo hello;
      echo_flush;
      echo_location_async /sub;
  }
  location /sub {
      echo_sleep 1;
  }

The client will immediately see "hello" before /sub enters sleeping.

See also echo, echo_sleep, and echo_location_async.

[edit] echo_sleep

syntax: echo_sleep <seconds>

default: no

context: location, location if

phase: content

Sleeps for the time period specified by the argument, which is in seconds.

This operation is non-blocking on server side, so unlike the echo_blocking_sleep directive, it won't block the whole Nginx worker process.

The period might takes three digits after the decimal point and must be greater than 0.001.

An example is

   location /echo_after_sleep {
       echo_sleep 1.234;
       echo resumed!;
   }

Behind the scene, it sets up a per-request "sleep" ngx_event_t object, and adds a timer using that custom event to the Nginx event model and just waits for a timeout on that event. Because the "sleep" event is per-request, this directive can work in parallel subrequests.

[edit] echo_blocking_sleep

syntax: echo_blocking_sleep <seconds>

default: no

context: location, location if

phase: content

This is a blocking version of the echo_sleep directive.

See the documentation of echo_sleep for more detail.

Behind the curtain, it calls the ngx_msleep macro provided by the Nginx core which maps to usleep on POSIX-compliant systems.

Note that this directive will block the current Nginx worker process completely while being executed, so never use it in production environment.

[edit] echo_reset_timer

syntax: echo_reset_timer

default: no

context: location, location if

phase: content

Reset the timer begin time to now, i.e., the time when this command is executed during request.

The timer begin time is default to the starting time of the current request and can be overridden by this directive, potentially multiple times in a single location. For example:

  location /timed_sleep {
      echo_sleep 0.03;
      echo "$echo_timer_elapsed sec elapsed.";
 
      echo_reset_timer;
 
      echo_sleep 0.02;
      echo "$echo_timer_elapsed sec elapsed.";
  }

The output on the client side might be

    $ curl 'http://localhost/timed_sleep'
    0.032 sec elapsed.
    0.020 sec elapsed.

The actual figures you get on your side may vary a bit due to your system's current activities.

Invocation of this directive will force the underlying Nginx timer to get updated to the current system time (regardless the timer resolution specified elsewhere in the config file). Furthermore, references of the $echo_timer_elapsed variable will also trigger timer update forcibly.

See also echo_sleep and $echo_timer_elapsed.

[edit] echo_read_request_body

syntax: echo_read_request_body

default: no

context: location, location if

phase: content

Explicitly reads request body so that the $request_body variable will always have non-empty values (unless the body is so big that it has been saved by Nginx to a local temporary file).

Note that this might not be the original client request body because the current request might be a subrequest with a "artificial" body specified by its parent.

This directive does not generate any output itself, just like echo_sleep.

Here's an example for echo'ing back the original HTTP client request (both headers and body are included):

  location /echoback {
    echo_duplicate 1 $echo_client_request_headers;
    echo "\r";
    echo_read_request_body;
    echo $request_body;
  }

The content of /echoback looks like this on my side (I was using Perl's LWP utility to access this location on the server):

  $ (echo hello; echo world) | lwp-request -m POST 'http://localhost/echoback'
  POST /echoback HTTP/1.1
  TE: deflate,gzip;q=0.3
  Connection: TE, close
  Host: localhost
  User-Agent: lwp-request/5.818 libwww-perl/5.820
  Content-Length: 12
  Content-Type: application/x-www-form-urlencoded
 
  hello
  world

Because /echoback is the main request, $request_body holds the original client request body.

Before Nginx 0.7.56, it makes no sense to use this directive because $request_body was first introduced in Nginx 0.7.58.

This directive itself was first introduced in the echo module's v0.14 release.

[edit] echo_location_async

syntax: echo_location_async <location> [<url_args>]

default: no

context: location, location if

phase: content

Issue GET subrequest to the location specified (first argument) with optional url arguments specified in the second argument.

As of Nginx 0.8.20, the location argument does not support named location, due to a limitation in the ngx_http_subrequest function. The same is true for its brother, the echo_location directive.

A very simple example is

    location /main {
        echo_location_async /sub;
        echo world;
    }
    location /sub {
        echo hello;
    }

Accessing /main gets

  hello
  world

Calling multiple locations in parallel is also possible:

    location /main {
        echo_reset_timer;
        echo_location_async /sub1;
        echo_location_async /sub2;
        echo "took $echo_timer_elapsed sec for total.";
    }
    location /sub1 {
        echo_sleep 2; # sleeps 2 sec
        echo hello;
    }
    location /sub2 {
        echo_sleep 1; # sleeps 1 sec
        echo world;
    }

Accessing /main yields

  $ time curl 'http://localhost/main'
  hello
  world
  took 0.000 sec for total.
 
  real  0m2.006s
  user  0m0.000s
  sys   0m0.004s

You can see that the main handler /main does not wait the subrequests /sub1 and /sub2 to complete and quickly goes on, hence the "0.000 sec" timing result. The whole request, however takes approximately 2 sec in total to complete because /sub1 and /sub2 run in parallel (or "concurrently" to be more accurate).

If you use echo_blocking_sleep in the previous example instead, then you'll get the same output, but with 3 sec total response time, because "blocking sleep" blocks the whole Nginx worker process.

Locations can also take an optional querystring argument, for instance

    location /main {
        echo_location_async /sub 'foo=Foo&bar=Bar';
    }
    location /sub {
        echo $arg_foo $arg_bar;
    }

Accessing /main yields

  $ curl 'http://localhost/main'
  Foo Bar

Querystrings is not allowed to be concatenated onto the location argument with "?" directly, for example, /sub?foo=Foo&bar=Bar is an invalid location, and shouldn't be fed as the first argument to this directive.

Due to an unknown bug in Nginx (it still exists in Nginx 0.8.20), the standard SSI module is required to ensure that the contents of the subrequests issued by this directive are correctly merged into the output chains of the main one. Fortunately, the SSI module is enabled by default during Nginx's configure process.

If calling this directive without SSI module enabled, you'll get truncated response without contents of any subrequests and get an alert message in your Nginx's error.log, like this:

  [alert] 24212#0: *1 the http output chain is empty, client: 127.0.0.1, ...

Technically speaking, this directive is an example that Nginx content handler issues one or more subrequests directly. AFAIK, the fancyindex module also does such kind of things ;)

Nginx named locations like @foo is not supported here.

This directive is logically equivalent to the GET version of echo_subrequest_async. For example,

  echo_location_async /foo 'bar=Bar';

is logically equivalent to

  echo_subrequest_async GET /foo -q 'bar=Bar';

But calling this directive is slightly faster than calling echo_subrequest_async using GET because we don't have to parse the HTTP method names like GET and options like -q.

This directive is first introduced in version 0.09 of this module and requires at least Nginx 0.7.46.

[edit] echo_location

syntax: echo_location <location> [<url_args>]

default: no

context: location, location if

phase: content

Just like the echo_location_async directive, but echo_location issues subrequests in series rather than in parallel. That is, the content handler directives following this directive won't be executed until the subrequest issued by this directive completes.

The final response body is almost always equivalent to the case when echo_location_async is used instead, only if timing variables is used in the outputs.

Consider the following example:

    location /main {
        echo_reset_timer;
        echo_location /sub1;
        echo_location /sub2;
        echo "took $echo_timer_elapsed sec for total.";
    }
    location /sub1 {
        echo_sleep 2;
        echo hello;
    }
    location /sub2 {
        echo_sleep 1;
        echo world;
    }

The location /main above will take for total 3 sec to complete (compared to 2 sec if echo_location_async is used instead here). Here's the result in action on my machine:

  $ curl 'http://localhost/main'
  hello
  world
  took 3.003 sec for total.
 
  real  0m3.027s
  user  0m0.020s
  sys   0m0.004s

This directive is logically equivalent to the GET version of echo_subrequest. For example,

  echo_location /foo 'bar=Bar';

is logically equivalent to

  echo_subrequest GET /foo -q 'bar=Bar';

But calling this directive is slightly faster than calling echo_subrequest using GET because we don't have to parse the HTTP method names like GET and options like -q.

Behind the scene, it creates an ngx_http_post_subrequest_t object as a continuation and passes it into the ngx_http_subrequest function call. Nginx will later reopen this "continuation" in the subrequest's ngx_http_finalize_request function call. We resumes the execution of the parent-request's content handler and starts to run the next directive (command) if any.

Nginx named locations like @foo is not supported here.

This directive was first introduced in the release v0.12.

See also echo_location_async for more details about the meaning of the arguments.

[edit] echo_subrequest_async

syntax: echo_subrequest_async <HTTP_method> <location> [-q <url_args>] [-b <request_body>] [-f <request_body_path>]

default: no

context: location, location if

phase: content

Initiate an asynchronous subrequest using HTTP method, an optional url arguments (or querystring) and an optional request body which can be defined as a string or as a path to a file which contains the body.

This directive is very much like a generalized version of the echo_location_async directive.

Here's a small example demonstrating its usage:

    location /multi {
        # body defined as string
        echo_subrequest_async POST '/sub' -q 'foo=Foo' -b 'hi';
        # body defined as path to a file, relative to nginx prefix path if not absolute
        echo_subrequest_async PUT '/sub' -q 'bar=Bar' -f '/tmp/hello.txt';
    }
    location /sub {
        echo "querystring: $query_string";
        echo "method: $echo_request_method";
        echo "body: $echo_request_body";
        echo "content length: $http_content_length";
        echo '///';
    }

Then on the client side:

  $ echo -n hello > /tmp/hello.txt
  $ curl 'http://localhost/multi'
  querystring: foo=Foo
  method: POST
  body: hi
  content length: 2
  ///
  querystring: bar=Bar
  method: PUT
  body: hello
  content length: 5
  ///

Here's more funny example using the standard proxy module to handle the subrequest:

    location /main {
        echo_subrequest_async POST /sub -b 'hello, world';
    }
    location /sub {
        proxy_pass $scheme://127.0.0.1:$server_port/proxied;
    }
    location /proxied {
        echo "method: $echo_request_method.";
 
        # we need to read body explicitly here...or $echo_request_body
        #   will evaluate to empty ("")
        echo_read_request_body;
 
        echo "body: $echo_request_body.";
    }

Then on the client side, we can see that

  $ curl 'http://localhost/main'
  method: POST.
  body: hello, world.

Nginx named locations like @foo is not supported here.

This directive was first introduced in the release v0.15.

The -f option to define a file path for the body was introduced in the release v0.35.

See also the echo_subrequest and echo_location_async directives.

[edit] echo_subrequest

syntax: echo_subrequest_async <HTTP_method> <location> [-q <url_args>] [-b <request_body>] [-f <request_body_path>]

default: no

context: location, location if

phase: content

This is the synchronous version of the echo_subrequest_async directive. And just like echo_location, it does not block the Nginx worker process (while echo_blocking_sleep does), rather, it uses continuation to pass control along the subrequest chain.

See echo_subrequest_async for more details.

Nginx named locations like @foo is not supported here.

This directive was first introduced in the release v0.15.

[edit] echo_foreach_split

syntax: echo_foreach_split <delimiter> <string>

default: no

context: location, location if

phase: content

Split the second argument string using the delimiter specified in the first argument, and then iterate through the resulting items. For instance:

  location /loop {
    echo_foreach_split ',' $arg_list;
      echo "item: $echo_it";
    echo_end;
  }

Accessing /main yields

  $ curl 'http://localhost/loop?list=cat,dog,mouse'
  item: cat
  item: dog
  item: mouse

As seen in the previous example, this directive should always be accompanied by an echo_end directive.

Parallel echo_foreach_split loops are allowed, but nested ones are currently forbidden.

The delimiter argument could contain multiple arbitrary characters, like

  echo_foreach_split '-a-' 'cat-a-dog-a-mouse';
    echo $echo_it;
  echo_end;

Logically speaking, this looping structure is just the foreach loop combined with a split function call in Perl (using the previous example):

   foreach (split ',', $arg_list) {
       print "item $_\n";
   }

People will also find it useful in merging multiple .js or .css resources into a whole. Here's an example:

  location /merge {
      default_type 'text/javascript';
 
      echo_foreach_split '&' $query_string;
          echo "/* JS File $echo_it */";
          echo_location_async $echo_it;
          echo;
      echo_end;
  }

Then accessing /merge to merge the .js resources specified in the query string:

  $ curl 'http://localhost/merge?/foo/bar.js&/yui/blah.js&/baz.js'

One can also use third-party Nginx cache module to cache the merged response generated by the /merge location in the previous example.

This directive was first introduced in the release v0.17.

[edit] echo_end

syntax: echo_end

default: no

context: location, location if

phase: content

This directive is used to terminate the body of looping and conditional control structures like echo_foreach_split.

This directive was first introduced in the release v0.17.

[edit] echo_request_body

syntax: echo_request_body

default: no

context: location, location if

phase: content

Outputs the contents of the request body previous read.

Behind the scene, it's implemented roughly like this:

  if (r->request_body && r->request_body->bufs) {
      return ngx_http_output_filter(r, r->request_body->bufs);
  }

Unlike the $echo_request_body and $request_body variables, this directive will show the whole request body even if some parts or all parts of it are saved in temporary files on the disk.

It is a "no-op" if no request body has been read yet.

This directive was first introduced in the release v0.18.

See also echo_read_request_body and the chunkin module.

[edit] echo_exec

syntax: echo_exec <location> [<query_string>]

syntax: echo_exec <named_location>

default: no

context: location, location if

phase: content

Does an internal redirect to the location specified. An optional query string can be specified for normal locations, as in

  location /foo {
      echo_exec /bar weight=5;
  }
  location /bar {
      echo $arg_weight;
  }

Or equivalently

  location /foo {
      echo_exec /bar?weight=5;
  }
  location /bar {
      echo $arg_weight;
  }

Named locations are also supported. Here's an example:

  location /foo {
      echo_exec @bar;
  }
  location @bar {
      # you'll get /foo rather than @bar
      #  due to a potential bug in nginx.
      echo $echo_request_uri;
  }

But query string (if any) will always be ignored for named location redirects due to a limitation in the ngx_http_named_location function.

Never try to echo things before the echo_exec directive or you won't see the proper response of the location you want to redirect to. Because any echoing will cause the original location handler to send HTTP headers before the redirection happens.

Technically speaking, this directive exposes the Nginx internal API functions ngx_http_internal_redirect and ngx_http_named_location.

This directive was first introduced in the v0.21 release.

[edit] echo_status

syntax: echo_status <status-num>

default: echo_status 200

context: location, location if

phase: content

Specify the default response status code. Default to 200. This directive is declarative and the relative order with other echo-like directives is not important.

Here is an example,

    location = /bad {
        echo_status 404;
        echo "Something is missing...";
    }

then we get a response like this:

    HTTP/1.1 404 Not Found
    Server: nginx/1.2.1
    Date: Sun, 24 Jun 2012 03:58:18 GMT
    Content-Type: text/plain
    Transfer-Encoding: chunked
    Connection: keep-alive
 
    Something is missing...

This directive was first introduced in the v0.40 release.

[edit] Filter Directives

Use of the following directives trigger the filter registration of this module. By default, no filter will be registered by this module.

Every filter directive supports variable interpolation in its arguments (if any).

[edit] echo_before_body

syntax: echo_before_body [options] [argument]...

default: no

context: location, location if

phase: output filter

It's the filter version of the echo directive, and prepends its output to the beginning of the original outputs generated by the underlying content handler.

An example is

    location /echo {
        echo_before_body hello;
        proxy_pass $scheme://127.0.0.1:$server_port$request_uri/more;
    }
    location /echo/more {
        echo world
    }

Accessing /echo from the client side yields

  hello
  world

In the previous sample, we borrow the standard proxy module to serve as the underlying content handler that generates the "main contents".

Multiple instances of this filter directive are also allowed, as in:

    location /echo {
        echo_before_body hello;
        echo_before_body world;
        echo !;
    }

On the client side, the output is like

  $ curl 'http://localhost/echo'
  hello
  world
  !

In this example, we also use the content handler directives provided by this module as the underlying content handler.

This directive also supports the -n and -- options like the echo directive.

This directive can be mixed with its brother directive echo_after_body.

[edit] echo_after_body

syntax: echo_after_body [argument]...

default: no

context: location, location if

phase: output filter

WARNING this directive does not work for nginx >= 0.7.65.

It's very much like the echo_before_body directive, but appends its output to the end of the original outputs generated by the underlying content handler.

Here's a simple example:

    location /echo {
        echo_after_body hello;
        proxy_pass http://127.0.0.1:$server_port$request_uri/more;
    }
    location /echo/more {
        echo world
    }

Accessing /echo from the client side yields

  world
  hello

Multiple instances are allowed, as in:

    location /echo {
        echo_after_body hello;
        echo_after_body world;
        echo i;
        echo say;
    }

The output on the client side while accessing the /echo location looks like

  i
  say
  hello
  world

This directive also supports the -n and -- options like the echo directive.

When this directive is used in a location accessed by a subrequest, it replies on the sync flag set in a chain buffer to indicate the end of the output for nginx >= 0.8.7. This is a hack because Nginx does not provide a reliable way to determine the end of the output chain in a subrequest's output filter. Use it in subrequests with care.

This directive can be mixed with its brother directive echo_before_body.

[edit] Variables

[edit] $echo_it

This is a "topic variable" used by echo_foreach_split, just like the $_ variable in Perl.

[edit] $echo_timer_elapsed

This variable holds the seconds elapsed since the start of the current request (might be a subrequest though) or the last invocation of the echo_reset_timer command.

The timing result takes three digits after the decimal point.

References of this variable will force the underlying Nginx timer to update to the current system time, regardless the timer resolution settings elsewhere in the config file, just like the echo_reset_timer directive.

[edit] $echo_request_body

Evaluates to the current (sub)request's request body previously read if no part of the body has been saved to a temporary file. To always show the request body even if it's very large, use the echo_request_body directive.

[edit] $echo_request_method

Evaluates to the HTTP request method of the current request (it can be a subrequest).

Behind the scene, it just takes the string data stored in r->method_name.

Compare it to the $echo_client_request_method variable.

At least for Nginx 0.8.20 and older, the $request_method variable provided by the http core module is actually doing what our $echo_client_request_method is doing.

This variable was first introduced in our v0.15 release.

[edit] $echo_client_request_method

Always evaluates to the main request's HTTP method even if the current request is a subrequest.

Behind the scene, it just takes the string data stored in r->main->method_name.

Compare it to the $echo_request_method variable.

This variable was first introduced in our v0.15 release.

[edit] $echo_client_request_headers

Evaluates to the original client request's headers.

Just as the name suggests, it will always take the main request (or the client request) even if it's currently executed in a subrequest.

A simple example is below:

  location /echoback {
     echo "headers are:"
     echo $echo_client_request_headers;
  }

Accessing /echoback yields

  $ curl 'http://localhost/echoback'
  headers are
  GET /echoback HTTP/1.1
  User-Agent: curl/7.18.2 (i486-pc-linux-gnu) libcurl/7.18.2 OpenSSL/0.9.8g
  Host: localhost:1984
  Accept: */*

Behind the scene, it recovers r->main->header_in on the C level and does not construct the headers itself by traversing parsed results in the request object, and strips the last (trailing) CRLF.

This variable was first introduced in version 0.15.

[edit] $echo_cacheable_request_uri

Evaluates to the parsed form of the URI (usually led by /) of the current (sub-)request. Unlike the $echo_request_uri variable, it is cacheable.

See $echo_request_uri for more details.

This variable was first introduced in version 0.17.

[edit] $echo_request_uri

Evaluates to the parsed form of the URI (usually led by /) of the current (sub-)request. Unlike the $echo_cacheable_request_uri variable, it is not cacheable.

This is quite different from the $request_uri variable exported by the HttpCoreModule, because $request_uri is the unparsed form of the current request's URI.

This variable was first introduced in version 0.17.

[edit] $echo_incr

It is a counter that always generate the current counting number, starting from 1. The counter is always associated with the main request even if it is accessed within a subrequest.

Consider the following example

    location /main {
        echo "main pre: $echo_incr";
        echo_location_async /sub;
        echo_location_async /sub;
        echo "main post: $echo_incr";
    }
    location /sub {
        echo "sub: $echo_incr";
    }

Accessing /main yields

   main pre: 1
   sub: 3
   sub: 4
   main post: 2

This directive was first introduced in the v0.18 release.

[edit] $echo_response_status

Evaluates to the status code of the current (sub)request, null if not any.

Behind the scene, it's just the textual representation of r->headers_out->status.

This directive was first introduced in the v0.23 release.

[edit] Installation

You're recommended to install this module (as well as the Nginx core and many other goodies) via the ngx_openresty bundle. See the detailed instructions for downloading and installing ngx_openresty into your system. This is the easiest and most safe way to set things up.

Alternatively, you can install this module manually with the Nginx source:

Grab the nginx source code from nginx.org, for example, the version 1.2.1 (see nginx compatibility), and then build the source with this module:

    $ wget 'http://sysoev.ru/nginx/nginx-1.2.1.tar.gz'
    $ tar -xzvf nginx-1.2.1.tar.gz
    $ cd nginx-1.2.1/
 
    # Here we assume you would install you nginx under /opt/nginx/.
    $ ./configure --prefix=/opt/nginx \
        --add-module=/path/to/echo-nginx-module
 
    $ make -j2
    $ make install

Download the latest version of the release tarball of this module from echo-nginx-module file list.

Also, this module is included and enabled by default in the ngx_openresty bundle.

[edit] Compatibility

The following versions of Nginx should work with this module:

• 1.2.x (last tested: 1.2.1)
• 1.1.x (last tested: 1.1.5)
• 1.0.x (last tested: 1.0.11)
• 0.9.x (last tested: 0.9.4)
• 0.8.x (last tested: 0.8.54)
• 0.7.x >= 0.7.21 (last tested: 0.7.68)

In particular,

• the directive echo_location_async and its brother echo_subrequest_async do not work with 0.7.x < 0.7.46.
• the echo_after_body directive does not work at all with nginx < 0.8.7.
• the echo_sleep directive cannot be used after echo_location or echo_subrequest for nginx < 0.8.11.

Earlier versions of Nginx like 0.6.x and 0.5.x will not work at all.

If you find that any particular version of Nginx above 0.7.21 does not work with this module, please consider reporting a bug.

[edit] Modules that use this module for testing

The following modules take advantage of this echo module in their test suite:

• The memc module that supports almost the whole memcached TCP protocol.
• The chunkin module that adds HTTP 1.1 chunked input support to Nginx.
• The headers_more module that allows you to add, set, and clear input and output headers under the conditions that you specify.
• The echo module itself.

Please mail me other modules that use echo in any form and I'll add them to the list above :)

[edit] Limitations

By design, all of this module's directives do not inherit between nested locations. So nginx's if may not be used this way:

    ? location /foo {
    ?    set $a 32;
    ?    if ($a = 32) {
    ?        set $a 56;
    ?    }
    ?
    ?    echo $a;
    ? }

[edit] Report Bugs

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

1. create a ticket on the issue tracking interface provided by GitHub,
2. or send a bug report, questions, or even patches to the nginx mailing list.

[edit] Source Repository

Available on github at agentzh/echo-nginx-module.

[edit] ChangeLog

[edit] v0.37

January 13, 2012

• bugfix: data truncation might occur with echo_after_body in not-so-good networks (we should be prepared for NGX_AGAIN returned by downstream output filters). thanks 林青 (Kindy Lin) for reporting it.
• bugfix: we no longer check sync buffers for subrequests because it is incorrect.
• bugfix: fixed a bug when sending out response headers: we did not take into account the NGX_ERROR error code returned by ngx_http_send_header.
• bugfix: we did not work with HEAD http requests before.
• bugfix: now we carefully eliminate empty flush buffers in echo_after_body to work around a long-standing bug in the standard HttpGzipModule.
• bugfix: we might send empty chain link in echo_after_body because it may trigger the infamous "the http output chain is empty" alert in error.log when the standard HttpSsiModule is disabled. thanks Sparsh Gupta.
• bugfix: we did not set subrequest's Content-Length request headers which could cause problems in the backends.
• bugfix: echo_exec + named locations might cause weird issues and now we explicitly clear all the modules' contexts before calling ngx_http_named_location.
• bugfix: echo_exec might hang when running after echo_sleep (or other I/O interruption calls): we should have called ngx_http_finalize_request on NGX_DONE to decrement r->main->count anyway.
• bugfix: there was a memory issue in both echo_sleep and echo_blocking_sleep: we should not pass ngx_str_t strings to atof() which expects C strings.
• bugfix: some users report that this module cannot be compiled with Nginx 1.0.x on their systems due to ngx_time_update (as in github issue #7). this is a blind attemp to fix it because we could not reproduce it on our side.
• bugfix: fixed places in the source code that we did not check null pointers returned by the memory allocator.

[edit] v0.36

July 08, 2011

• now we back-ported the subrequest mechanism of ngx_lua to ngx_echo. this also helps some crazy test cases of mixing echo_location and echo_location_async pass now.
• now echo_location and its friends can work with ngx_xss (as well as other output filter modules) completely. thanks wd for reporting this issue.
• done some minor optimization when modifying subrequest's content-length header.
• now we always pad a trailing \0 to filepath in "echo_subrequest(_async) METHOD /path -f filepath" because ngx_open_cached_file requires a C string file name. thanks dr-dr xp.
• made our filter optimization works with nginx HUP by clearing the ngx_http_echo_filter_used flag at nginx pre-config callback. thanks Marcus Clyne.

[edit] v0.35

February 07, 2011

• added the -f /path/to/file option to the echo_subrequest and echo_subrequest_async directives to allow POST/PUT a disk file in the subrequest. thanks Bernd Dorn.

[edit] v0.34

September 14, 2010

• we no longer use the problematic ngx_strXcmp macros in our source because it may cause invalid reads and thus segmentation faults. thanks Piotr Sikora.

[edit] v0.33

June 08, 2010

• fixed compatibility with nginx 0.7.66+ because the ngx_time_update macro's parameter list has changed. thanks Guang Feng (蔡镜明).

[edit] v0.32

June 04, 2010

• we should have used ngx_calloc_buf instead of ngx_alloc_buf for the last chunk generated for echo_after_body. thanks valgrind's memcheck tool.
• we should initialize flags before feeding it into ngx_http_parse_unsafe_uri. thanks valgrind's memcheck tool.
• fixed a minor issue in the echo_location/echo_subrequest implementation, which used to have race conditions.

[edit] v0.31

May 24, 2010

• the echo wev handler should not proceed if it is still waiting for some sequential subrequest or has just processed one to avoid bouncing issues.
• fixed a segfault for echo_exec for 0.7.x: we should check r->done before proceeding.
• no longer explicitly set r->write_event_handler to ngx_http_request_empty_handler because it's totally wrong for the state machine.
• fixed the sequential subrequest model bugs: we should ensure the pr->write_event_handler gets called immediately after the post_subrequest callback when the subrequest finalizes.

[edit] v0.30

May 06, 2010

• fixed the echo_exec directive for nginx >= 0.8.11. we didn't get the r->main->count right in the previous version.

[edit] v0.29

May 05, 2010

• refactored the core of this module. now the implementation of echo_location, echo_subrequest, echo_sleep, and echo_read_request_body finally fit well with the nginx event model and Igor Sysoev's way of thinking.

[edit] v0.28

May 03, 2010

• added support for the -n and -- options to the echo, echo_before_body, and echo_after_body directives.

[edit] v0.27

April 02, 2010

• applied the patch from Sergey A. Osokin to work with nginx 0.8.35.

[edit] v0.26

January 26, 2010

• bug fix: we should bypass upstream filters in our echo filters. an output filter should ever call ngx_http_output_filter nor ngx_http_send_special.

[edit] v0.25

January 15, 2010

• now we register a request cleanup handler to ensure our sleep event's timer will always get properly deleted even if the request is quit prematurely. this affects the echo_sleep directive.
• use ngx_null_string whenever possible in the source.
• sync'd the bundled test scaffold to Test::Nginx 0.07.

[edit] v0.24

December 28, 2009

• various source file name and coding style fixes. (the code now looks more like Igor Sysoev's.)

[edit] v0.23

December 04, 2009

• now the subrequest can read the client request body directly (for the main request) because we made subrequests inherit its parent's r->header_in as well. This affects the echo_read_request_body directive.
• fixed echo_after_body in subrequests by using a hack (checking cl->buf->sync for the last buf) for nginx 0.8.7+ only.
• added new varaible $echo_response_status to help testing the status code of a subrequest. (The memc module makes use of it.)
• use the ngx_calloc_buf macro to allocate new bufs in the code rather than explicit ngx_pcalloc calls for safety.

[edit] v0.22

November 25, 2009

• Now we allowed all the directives appear in the rewrite module's if block. But so far I've only tested the echo directive.

[edit] v0.21

November 23, 2009

• Added a new directive named echo_exec which does internal redirect to other (named) locations.

[edit] v0.20

November 20, 2009

• Fixed a bug in echo_sleep's r->main->count handling for nginx 0.8.x. This bug will cause the server to hang when proxing a location with echo_sleep.
• Applied the ngx_str3cmp, ngx_str4cmp, and ngx_str6cmp optimizing macros to the parse_method_name function, as suggested by Marcus Clyne.
• Added TODO items regarding $echo_random and echo_repeat suggested by Marcus Clyne.

[edit] v0.19

November 19, 2009

• Fixed the CPS-style chained subrequest model for the echo_location and echo_subrequest directives. they are now working perfectly and will not hang the server with the recent nginx 0.8.21 ~ 0.8.27 releases. To be specifically, the chained subrequest should call ngx_http_finalize_request on its parent request if the content handler of the parent request does not return NGX_DONE.
• Undeprecated the echo_location and echo_subrequest directives.

[edit] v0.18

November 15, 2009

• Fixed the "zero size buf in output" alerts in error.log.
• Added the new directive echo_request_body.
• Now we use the ngx_http_parse_unsafe_uri function to check the locations to echo_location_async and its friends. Thanks Arvind Jayaprakash for suggesting this fix.
• Deprecated the echo_location and echo_subrequest directives.
• For HTTP 1.0 clients, use the buf length of the first chain link as the output header Content-Length.
• Implemented new variable $echo_incr.

[edit] v0.17

October 26, 2009

• Added new directives echo_foreach_split and echo_end. Also introduced a "topic variable" named $echo_it.
• Added new variables $echo_request_uri and $echo_cacheable_request_uri.

[edit] v0.16

October 25, 2009

• Now the subrequests issued by the echo_location_async and echo_location directives no longer inherit cached variable values from its parent request. (The underlying ngx_http_subrequest function, however, does automatic cachable variable value inheritance.)
• Added an undocumented variable echo_cached_request_uri to help testing of this module.

[edit] v0.15

October 24, 2009

• Added new directives echo_subrequest and echo_subrequest_async for the full nginx subrequest API.
• Removed the echo_client_request_headers directive, and provided the $echo_client_request_headers variable instead.
• Added new variables $echo_request_method and $echo_client_request_method.

[edit] v0.14

October 22, 2009

• Added new directive echo_read_request_body to explicitly read client request body so that the HttpCoreModule#$request_body variable will always have non-empty values.
• Now we shuffer test cases automatically in .t files and fixed bugs in the tests themselves which are hidden by config reload fallback in failure.

[edit] v0.13

October 21, 2009

• Fixed the special cases when the outputs of a echo_duplicate directive is empty.
• Now we explicitly clear content length and accept ranges headers in the content handler.

[edit] v0.12

October 21, 2009

• Implemented the echo_location directive, which can issue chained GET subrequests in the Continuation Passing Style (CPS), rather than the parallel subrequest issued by the echo_location_async directive.

[edit] v0.11

October 20, 2009

• Implemented the echo_duplicate directive to help generating large chunk of data for testing.

[edit] v0.10

October 20, 2009

• Fixed compilation regression against Nginx 0.7.21. This bug appears in version 0.09.
• Refactored the codebase by splitting source into various small files.

[edit] v0.09

October 19, 2009

• Reimplement the echo_sleep directive using per-request event and timer; the old implementation uses the global connection's read/write event to register timer, so it will break horribly when multiple subrequests "sleep" at the same time.
• Added the echo_location_async directive which can issue a GET subrequest and insert its contents herein.

[edit] v0.08

October 18, 2009

• echo_sleep: now we delete our write event timer in the post_sleep handle.
• Added doc/manpage.wiki which tracks changes in the wiki page.
• Added the util/wiki2pod.pl script to convert doc/manpage.wiki to README.
• Disabled the DDEBUG macro in the C source by default.

[edit] Test Suite

This module comes with a Perl-driven test suite. The test cases are declarative too. Thanks to the Test::Nginx module in the Perl world.

To run it on your side:

    $ PATH=/path/to/your/nginx-with-echo-module:$PATH prove -r t

You need to terminate any Nginx processes before running the test suite if you have changed the Nginx server binary.

Because a single nginx server (by default, localhost:1984) is used across all the test scripts (.t files), it's meaningless to run the test suite in parallel by specifying -jN when invoking the prove utility.

Some parts of the test suite requires standard modules proxy, rewrite and SSI to be enabled as well when building Nginx.

[edit] TODO

• Fix the echo_after_body directive in subrequests.
• Add directives echo_read_client_request_body and echo_request_headers.
• Add new directive echo_log to use Nginx's logging facility directly from the config file and specific loglevel can be specified, as in

  echo_log debug "I am being called.";

• Add support for options -h and -t to echo_subrequest_async and echo_subrequest. For example

  echo_subrequest POST /sub -q 'foo=Foo&bar=Bar' -b 'hello' -t 'text/plan' -h 'X-My-Header: blah blah'

• Add options to control whether a subrequest should inherit cached variables from its parent request (i.e. the current request that is calling the subrequest in question). Currently none of the subrequests issued by this module inherit the cached variables from the parent request.
• Add new variable $echo_active_subrequests to show r->main->count - 1.
• Add the echo_file and echo_cached_file directives.
• Add new varaible $echo_request_headers to accompany the existing $echo_client_request_headers variable.
• Add new directive echo_foreach, as in

  echo_foreach 'cat' 'dog' 'mouse';
    echo_location_async "/animals/$echo_it";
  echo_end;

• Add new directive echo_foreach_range, as in

  echo_foreach_range '[1..100]' '[a-zA-z0-9]';
    echo_location_async "/item/$echo_it";
  echo_end;

• Add new directive echo_repeat, as in

  echo_repeat 10 $i {
      echo "Page $i";
      echo_location "/path/to/page/$i";
  }

This is just another way of saying

  echo_foreach_range $i [1..10];
      echo "Page $i";
      echo_location "/path/to/page/$i";
  echo_end;

Thanks Marcus Clyne for providing this idea.

• Add new variable $echo_random which always returns a random non-negative integer with the lower/upper limit specified by the new directives echo_random_min and echo_random_max. For example,

  echo_random_min  10
  echo_random_max  200
  echo "random number: $echo_random";

Thanks Marcus Clyne for providing this idea.

[edit] Getting involved

You'll be very welcomed to submit patches to the author or just ask for a commit bit to the source repository on GitHub.

[edit] Author

Zhang "agentzh" Yichun (章亦春) <agentzh@gmail.com>

This wiki page is also maintained by the author himself, and everybody is encouraged to improve this page as well.

[edit] Copyright & License

Copyright (c) 2009, 2010, 2011, Taobao Inc., Alibaba Group ( http://www.taobao.com ).

Copyright (c) 2009, 2010, 2011, Zhang "agentzh" Yichun (章亦春) <agentzh@gmail.com>.

This module is licensed under the terms of the BSD license.

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

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

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

[edit] See Also

• The original blog post about this module's initial development.
• The standard addition filter module.
• The standard proxy module.
• The ngx_openresty bundle.