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<header>
<copyright>
<year>2017</year>
<holder>Ericsson AB. All Rights Reserved.</holder>
</copyright>
<legalnotice>
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
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<title>logger_formatter</title>
<prepared></prepared>
<responsible></responsible>
<docno></docno>
<approved></approved>
<checked></checked>
<date></date>
<rev>A</rev>
<file>logger_formatter.xml</file>
</header>
<module>logger_formatter</module>
<modulesummary>Default formatter for Logger.</modulesummary>
<description>
<p>Each log handler has a configured formatter specified as a
module and a configuration term. The purpose of the formatter is
to translate the log events to a final printable string
(<c>unicode:chardata()</c>) which can be written to the output
device of the handler.</p>
<p><c>logger_formatter</c> is the default formatter used by
Logger.</p>
</description>
<section>
<title>Configuration</title>
<p>The configuration term for <c>logger_formatter</c> is a map,
and the following keys can be set as configuration
parameters:</p>
<taglist>
<tag><c>chars_limit = pos_integer() | unlimited</c></tag>
<item>
<p>A positive integer representing the value of the option
with the same name to be used when calling
<seealso marker="stdlib:io_lib#format-3">io_lib:format/3</seealso>.
This value limits the total number of characters printed
for each log event. Notice that this is a soft limit. For a
hard truncation limit, see option <c>max_size</c>.</p>
<p>Default is <c>unlimited</c>.</p>
<note>
<p><c>chars_limit</c> has no effect on log messages on
string form. These are expected to be short, but can still
be truncated by the <c>max_size</c> parameter.</p>
</note>
</item>
<tag><c>depth = pos_integer() | unlimited</c></tag>
<item>
<p>A positive integer representing the maximum depth to
which terms shall be printed by this formatter. Format
strings passed to this formatter are rewritten. The format
controls ~p and ~w are replaced with ~P and ~W,
respectively, and the value is used as the depth
parameter. For details, see
<seealso marker="stdlib:io#format-2">io:format/2,3</seealso>
in STDLIB.</p>
<p>Default is <c>unlimited</c>.</p>
<note>
<p><c>depth</c> has no effect on log messages on string
form. These are expected to be short, but can still be
truncated by the <c>max_size</c> parameter.</p>
</note>
</item>
<tag><c>max_size = pos_integer() | unlimited</c></tag>
<item>
<p>A positive integer representing the absolute maximum size a
string returned from this formatter can have. If the
formatted string is longer, after possibly being limited
by <c>chars_limit</c> or <c>depth</c>, it is truncated.</p>
<p>Default is <c>unlimited</c>.</p>
</item>
<tag><c>single_line = boolean()</c></tag>
<item>
<p>If set to <c>true</c>, all newlines in the message are
replaced with <c>", "</c>, and whitespaces following
directly after newlines are removed. Note that newlines
added by the <c>template</c> parameter are not replaced.</p>
<p>Default is <c>true</c>.</p>
</item>
<tag><c>legacy_header = boolen()</c></tag>
<item>
<p>If set to <c>true</c> a header field is added to
logger_formatter's part of <c>Metadata</c>. The value of
this field is a string similar to the header created by the
old <c>error_logger</c> event handlers. It can be included
in the log event by adding the
tuple <c>{logger_formatter,header}</c> to the template. See
section <seealso marker="#default_templates">Default
Templates</seealso> for more information.</p>
<p>Default is <c>false</c>.</p>
</item>
<tag><c>report_cb = fun((</c><seealso marker="logger#type-report"><c>logger:report()</c></seealso><c>) -> {</c><seealso marker="stdlib:io#type-format"><c>io:format()</c></seealso><c>,[term()]})</c></tag>
<item>
<p>A report callback is used by the formatter to transform log
messages on report form to a format string and
arguments. The report callback can be specified in the
metadata for the log event. If no report callback exist in
metadata, <c>logger_formatter</c> will
use <seealso marker="logger#format_report-1">
<c>logger:format_report/1</c></seealso> as default
callback.</p>
<p>If this configuration parameter is set, it replaces both
the default report callback, and any report callback found
in metadata. That is, all reports are converted by this
configured function.</p>
<p>The value must be a function with arity 1,
returning <c>{Format,Args}</c>, and it will be called with a
report as only argument.</p>
</item>
<tag><c>template = </c><seealso marker="#type-template"><c>template()</c></seealso></tag>
<item>
<p>The template is a list of atoms, tuples and strings. The
atoms <c>level</c> or <c>msg</c>, are treated as
placeholders for the severity level and the log message,
repectively. Other atoms or tuples are interpreted as
placeholders for metadata, where atoms are expected to match
top level keys, and tuples represent paths to sub keys when
the metadata is a nested map. For example the
tuple <c>{key1,key2}</c> is replaced by the value of
the <c>key2</c> field in the nested map below. The
atom <c>key1</c> on its own is replaced by the complete
value of the <c>key1</c> field. The values are converted to
strings.</p>
<code>
#{key1=>#{key2=>my_value,
...}
...}</code>
<p>Strings in the template are printed literally.</p>
<p>The default template differs depending on the values
of <c>legacy_header</c>
and <c>single_line</c>. See <seealso marker="#default_templates">Default
Templates</seealso> for more information</p>
</item>
<tag><c>utc = boolean()</c></tag>
<item>
<p>If set to <c>true</c>, all dates are displayed in Universal
Coordinated Time.</p>
<p>Default is <c>false</c>.</p>
</item>
</taglist>
</section>
<section>
<marker id="default_templates"/>
<title>Default templates</title>
<p>The default value for the <c>template</c> configuration
parameter depends on the value of <c>single_line</c>
and <c>legacy_header</c> as follows.</p>
<p>The log event used in the examples is:</p>
<code>
?LOG_ERROR("name: ~p~nexit_reason: ~p",[my_reg_name,"It crashed"])</code>
<taglist>
<tag><c>legacy_header=true</c></tag>
<item>
<p>Default template: <c>[{logger_formatter,header},"\n",msg,"\n"]</c></p>
<p>Example log entry:</p>
<code>
=ERROR REPORT==== 29-Dec-2017::13:30:51.245123 ===
name: my_reg_name
exit_reason: "It crashed"</code>
<p>Notice that all eight levels might occur in the heading,
not only <c>ERROR</c>, <c>WARNING</c> or <c>INFO</c> as the
old <c>error_logger</c> produced. And microseconds are
added at the end of the timestamp.</p>
</item>
<tag><c>single_line=true</c></tag>
<item>
<p>Default template: <c>[time," ",level,": ",msg,"\n"]</c></p>
<p>Example log entry:</p>
<code>2017-12-29 13:31:49.640317 error: name: my_reg_name, exit_reason: "It crashed"</code>
</item>
<tag><c>legacy_header=false, single_line=false</c></tag>
<item>
<p>Default template: <c>[time," ",level,":\n",msg,"\n"]</c></p>
<p>Example log entry:</p>
<code>
2017-12-29 13:32:25.191925 error:
name: my_reg_name
exit_reason: "It crashed"</code>
</item>
</taglist>
</section>
<datatypes>
<datatype>
<name name="template"/>
<desc>
</desc>
</datatype>
</datatypes>
<funcs>
<func>
<name name="format" arity="2"/>
<fsummary>Formats the given message.</fsummary>
<desc>
<p>This the formatter callback function to be called from
handlers. The log event is processed as follows:</p>
<list>
<item>If the message is on report form, it is converted to
<c>{Format,Args}</c> by calling the report
callback.</item>
<item>The size is limited according to the values of
configuration parameters <c>chars_limit</c>
and <c>depth</c>. Notice that this does not apply to
messages on string form.</item>
<item>The full log entry is composed according to
the <c>template</c>.</item>
<item>If the final string is too long, it is truncated
according to the value of configuration
parameter <c>max_size</c>.</item>
</list>
</desc>
</func>
</funcs>
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