<?xml version="1.0"?>

<!--
  Copyright (C) Nginx, Inc.
  -->

<!DOCTYPE module SYSTEM "../../../../dtd/module.dtd">

<module name="Module ngx_stream_log_module"
        link="/en/docs/stream/ngx_stream_log_module.html"
        lang="en"
        rev="7">

<section id="summary">

<para>
The <literal>ngx_stream_log_module</literal> module (1.11.4) writes session logs
in the specified format.
</para>

</section>


<section id="example" name="Example Configuration">

<para>
<example>
log_format basic '$remote_addr [$time_local] '
                 '$protocol $status $bytes_sent $bytes_received '
                 '$session_time';

access_log /spool/logs/nginx-access.log basic buffer=32k;
</example>
</para>

</section>


<section id="directives" name="Directives">

<directive name="access_log">
<syntax>
    <value>path</value>
    <value>format</value>
    [<literal>buffer</literal>=<value>size</value>]
    [<literal>gzip[=<value>level</value>]</literal>]
    [<literal>flush</literal>=<value>time</value>]
    [<literal>if</literal>=<value>condition</value>]</syntax>
<syntax><literal>off</literal></syntax>
<default>off</default>
<context>stream</context>
<context>server</context>

<para>
Sets the path, <link id="log_format">format</link>,
and configuration for a buffered log write.
Several logs can be specified on the same level.
Logging to <link doc="../syslog.xml">syslog</link>
can be configured by specifying
the “<literal>syslog:</literal>” prefix in the first parameter.
The special value <literal>off</literal> cancels all
<literal>access_log</literal> directives on the current level.
</para>

<para>
If either the <literal>buffer</literal> or <literal>gzip</literal>
parameter is used, writes to log will be buffered.
<note>
The buffer size must not exceed the size of an atomic write to a disk file.
For FreeBSD this size is unlimited.
</note>
</para>

<para>
When buffering is enabled, the data will be written to the file:
<list type="bullet">

<listitem>
if the next log line does not fit into the buffer;
</listitem>

<listitem>
if the buffered data is older than specified by the <literal>flush</literal>
parameter;
</listitem>

<listitem>
when a worker process is <link doc="../control.xml">re-opening</link> log
files or is shutting down.
</listitem>

</list>
</para>

<para>
If the <literal>gzip</literal> parameter is used, then the buffered data will
be compressed before writing to the file.
The compression level can be set between 1 (fastest, less compression)
and 9 (slowest, best compression).
By default, the buffer size is equal to 64K bytes, and the compression level
is set to 1.
Since the data is compressed in atomic blocks, the log file can be decompressed
or read by “<literal>zcat</literal>” at any time.
</para>

<para>
Example:
<example>
access_log /path/to/log.gz basic gzip flush=5m;
</example>
</para>

<para>
<note>
For gzip compression to work, nginx must be built with the zlib library.
</note>
</para>

<para>
The file path can contain variables,
but such logs have some constraints:
<list type="bullet">

<listitem>
the <link doc="../ngx_core_module.xml" id="user"/>
whose credentials are used by worker processes should
have permissions to create files in a directory with
such logs;
</listitem>

<listitem>
buffered writes do not work;
</listitem>

<listitem>
the file is opened and closed for each log write.
However, since the descriptors of frequently used files can be stored
in a <link id="open_log_file_cache">cache</link>, writing to the old file
can continue during the time specified by the <link id="open_log_file_cache"/>
directive’s <literal>valid</literal> parameter
</listitem>

</list>
</para>

<para>
The <literal>if</literal> parameter enables conditional logging.
A session will not be logged if the <value>condition</value> evaluates to “0”
or an empty string.
</para>

</directive>


<directive name="log_format">
<syntax>
    <value>name</value>
    [<literal>escape</literal>=<literal>default</literal>|<literal>json</literal>|<literal>none</literal>]
    <value>string</value> ...</syntax>
<default></default>
<context>stream</context>

<para>
Specifies the log format, for example:
<example>
log_format proxy '$remote_addr [$time_local] '
                 '$protocol $status $bytes_sent $bytes_received '
                 '$session_time "$upstream_addr" '
                 '"$upstream_bytes_sent" "$upstream_bytes_received" "$upstream_connect_time"';
</example>
</para>

<para id="log_format_escape">
The <literal>escape</literal> parameter (1.11.8) allows setting
<literal>json</literal> or <literal>default</literal> characters escaping
in variables, by default, <literal>default</literal> escaping is used.
The <literal>none</literal> parameter (1.13.10) disables escaping.
</para>

<para id="log_format_escape_default">
For <literal>default</literal> escaping,
characters “<literal>"</literal>”, “<literal>\</literal>”,
and other characters with values less than 32 or above 126
are escaped as “<literal>\xXX</literal>”.
If the variable value is not found,
a hyphen (“<literal>-</literal>”) will be logged.
</para>

<para id="log_format_escape_json">
For <literal>json</literal> escaping,
all characters not allowed
in JSON <link url="https://tools.ietf.org/html/rfc8259#section-7">strings</link>
will be escaped:
characters “<literal>"</literal>” and
“<literal>\</literal>” are escaped as
“<literal>\"</literal>” and “<literal>\\</literal>”,
characters with values less than 32 are escaped as
“<literal>\n</literal>”,
“<literal>\r</literal>”,
“<literal>\t</literal>”,
“<literal>\b</literal>”,
“<literal>\f</literal>”, or
“<literal>\u00XX</literal>”.
</para>

</directive>


<directive name="open_log_file_cache">

<syntax>
<literal>max</literal>=<value>N</value>
[<literal>inactive</literal>=<value>time</value>]
[<literal>min_uses</literal>=<value>N</value>]
[<literal>valid</literal>=<value>time</value>]</syntax>
<syntax><literal>off</literal></syntax>
<default>off</default>
<context>stream</context>
<context>server</context>

<para>
Defines a cache that stores the file descriptors of frequently used logs
whose names contain variables.
The directive has the following parameters:
<list type="tag">

<tag-name><literal>max</literal></tag-name>
<tag-desc>
sets the maximum number of descriptors in a cache;
if the cache becomes full the least recently used (LRU)
descriptors are closed
</tag-desc>

<tag-name><literal>inactive</literal></tag-name>
<tag-desc>
sets the time after which the cached descriptor is closed
if there were no access during this time;
by default, 10 seconds
</tag-desc>

<tag-name><literal>min_uses</literal></tag-name>
<tag-desc>
sets the minimum number of file uses during the time
defined by the <literal>inactive</literal> parameter
to let the descriptor stay open in a cache;
by default, 1
</tag-desc>

<tag-name><literal>valid</literal></tag-name>
<tag-desc>
sets the time after which it should be checked that the file
still exists with the same name; by default, 60 seconds
</tag-desc>

<tag-name><literal>off</literal></tag-name>
<tag-desc>
disables caching
</tag-desc>

</list>
</para>

<para>
Usage example:
<example>
open_log_file_cache max=1000 inactive=20s valid=1m min_uses=2;
</example>
</para>

</directive>

</section>

</module>