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<header>
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<year>2017</year><year>2018</year>
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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 since="OTP 21.0">logger_formatter</module>
<modulesummary>Default formatter for Logger.</modulesummary>
<description>
<p>Each Logger 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
(<seealso marker="stdlib:unicode#type-chardata"><c>unicode:chardata()</c>
</seealso>) which can be written to the output device of the
handler. See
sections <seealso marker="logger_chapter#handlers">Handlers</seealso>
and <seealso marker="logger_chapter#formatters">Formatters</seealso>
in the Kernel User's Guide for more information.</p>
<p><c>logger_formatter</c> is the default formatter used by
Logger.</p>
</description>
<datatypes>
<datatype>
<name name="config"/>
<desc>
<p>The configuration term for <c>logger_formatter</c> is a
<seealso marker="stdlib:maps">map</seealso>, and the
following keys can be set as configuration parameters:</p>
<taglist>
<tag><marker id="chars_limit"/>
<c>chars_limit = integer() > 0 | 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">
<c>io_lib:format/3</c></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>Defaults to <c>unlimited</c>.</p>
</item>
<tag><marker id="depth"/><c>depth = integer() > 0 | 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"><c>io:format/2,3</c></seealso>
in STDLIB.</p>
<p>Defaults to <c>unlimited</c>.</p>
</item>
<tag><c>legacy_header = boolean()</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 <seealso marker="error_logger"><c>error_logger</c></seealso>
event handlers. It can be included in the log event by
adding the list <c>[logger_formatter,header]</c> to the
template. See the description of
the <seealso marker="#type-template"><c>template()</c></seealso>
type for more information.</p>
<p>Defaults to <c>false</c>.</p>
</item>
<tag><marker id="max_size"/>
<c>max_size = integer() > 0 | 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>Defaults to <c>unlimited</c>.</p>
</item>
<tag><c>report_cb = </c><seealso marker="logger#type-report_cb">
<c>logger:report_cb()</c></seealso></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 exists
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>
</item>
<tag><c>single_line = boolean()</c></tag>
<item>
<p>If set to <c>true</c>, each log event is printed as a
single line. To achieve this, <c>logger_formatter</c>
sets the field width to <c>0</c> for all <c>~p</c>
and <c>~P</c> control sequences in the format a string
(see <seealso marker="stdlib:io#format-2">
<c>io:format/2</c></seealso>), and replaces all
newlines in the message with <c>", "</c>. White spaces
following directly after newlines are removed. Notice
that newlines added by the <c>template</c> parameter are
not replaced.</p>
<p>Defaults to <c>true</c>.</p>
</item>
<tag><marker id="template"/>
<c>template = </c><seealso marker="#type-template"><c>template()</c>
</seealso></tag>
<item>
<p>The template describes how the formatted string is
composed by combining different data values from the log
event. See the description of
the <seealso marker="#type-template"><c>template()</c></seealso>
type for more information about this.</p>
</item>
<tag><c>time_designator = byte()</c></tag>
<item>
<p>Timestamps are formatted according to RFC3339, and the
time designator is the character used as date and time
separator.</p>
<p>Defaults to <c>$T</c>.</p>
<p>The value of this parameter is used as
the <c>time_designator</c> option
to <seealso marker="stdlib:calendar#system_time_to_rfc3339-2">
<c>calendar:system_time_to_rcf3339/2</c></seealso>.</p>
</item>
<tag><c>time_offset = integer() | [byte()]</c></tag>
<item>
<p>The time offset, either a string or an integer, to be
used when formatting the timestamp.</p>
<p>An empty string is interpreted as local time. The
values <c>"Z"</c>, <c>"z"</c> or <c>0</c> are
interpreted as Universal Coordinated Time (UTC).</p>
<p>Strings, other than <c>"Z"</c>, <c>"z"</c>,
or <c>""</c>, must be on the form <c>±[hh]:[mm]</c>, for
example <c>"-02:00"</c> or <c>"+00:00"</c>.</p>
<p>Integers must be in microseconds, meaning that the
offset <c>7200000000</c> is equivalent
to <c>"+02:00"</c>.</p>
<p>Defaults to an empty string, meaning that timestamps
are displayed in local time. However, for backwards
compatibility, if the SASL configuration
parameter <seealso marker="sasl:sasl_app#utc_log">
<c>utc_log</c></seealso><c>=true</c>, the default is
changed to <c>"Z"</c>, meaning that timestamps are displayed
in UTC.</p>
<p>The value of this parameter is used as
the <c>offset</c> option
to <seealso marker="stdlib:calendar#system_time_to_rfc3339-2">
<c>calendar:system_time_to_rcf3339/2</c></seealso>.</p>
</item>
</taglist>
</desc>
</datatype>
<datatype>
<name name="metakey"/>
<desc>
<p></p>
</desc>
</datatype>
<datatype>
<name name="template"/>
<desc>
<p>The template is a list of atoms, atom lists, tuples and strings. The
atoms <c>level</c> or <c>msg</c>, are treated as
placeholders for the severity level and the log message,
respectively. Other atoms or atom lists are interpreted as
placeholders for metadata, where atoms are expected to match
top level keys, and atom lists represent paths to sub keys when
the metadata is a nested map. For example the
list <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>Tuples in the template express if-exist tests for metadata
keys. For example, the following tuple says that
if <c>key1</c> exists in the metadata map,
print <c>"key1=Value"</c>, where <c>Value</c> is the value
that <c>key1</c> is associated with in the metadata map. If
<c>key1</c> does not exist, print nothing.</p>
<code>
{key1, ["key1=",key1], []}</code>
<p>Strings in the template are printed literally.</p>
<p>The default value for the <c>template</c> configuration
parameter depends on the value of the <c>single_line</c>
and <c>legacy_header</c> configuration parameters as
follows.</p>
<p>The log event used in the examples is:</p>
<code>
?LOG_ERROR("name: ~p~nexit_reason: ~p", [my_name, "It crashed"])</code>
<taglist>
<tag><c>legacy_header = true, single_line = false</c></tag>
<item>
<p>Default
template: <c>[[logger_formatter,header],"\n",msg,"\n"]</c></p>
<p>Example log entry:</p>
<code type="none">
=ERROR REPORT==== 17-May-2018::18:30:19.453447 ===
name: my_name
exit_reason: "It crashed"</code>
<p>Notice that all eight levels can occur in the heading,
not only <c>ERROR</c>, <c>WARNING</c> or <c>INFO</c> as
<seealso marker="error_logger"><c>error_logger</c></seealso>
produces. And microseconds are added at the end of the
timestamp.</p>
</item>
<tag><c>legacy_header = true, single_line = true</c></tag>
<item>
<p>Default
template: <c>[[logger_formatter,header],"\n",msg,"\n"]</c></p>
<p>Notice that the template is here the same as
for <c>single_line=false</c>, but the resulting log entry
differs in that there is only one line after the
heading:</p>
<code type="none">
=ERROR REPORT==== 17-May-2018::18:31:06.952665 ===
name: my_name, exit_reason: "It crashed"</code>
</item>
<tag><c>legacy_header = false, single_line = true</c></tag>
<item>
<p>Default template: <c>[time," ",level,": ",msg,"\n"]</c></p>
<p>Example log entry:</p>
<code type="none">
2018-05-17T18:31:31.152864+02:00 error: name: my_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 type="none">
2018-05-17T18:32:20.105422+02:00 error:
name: my_name
exit_reason: "It crashed"</code>
</item>
</taglist>
</desc>
</datatype>
</datatypes>
<funcs>
<func>
<name name="check_config" arity="1" since="OTP 21.0"/>
<fsummary>Validates the given formatter configuration.</fsummary>
<desc>
<p>The function is called by Logger when the formatter
configuration for a handler is set or modified. It
returns <c>ok</c> if the configuration is valid,
and <c>{error,term()}</c> if it is faulty.</p>
<p>The following Logger API functions can trigger this callback:</p>
<list>
<item><seealso marker="logger#add_handler-3">
<c>logger:add_handler/3</c></seealso></item>
<item><seealso marker="logger#set_handler_config-2">
<c>logger:set_handler_config/2,3</c></seealso></item>
<item><seealso marker="logger#update_handler_config-2">
<c>logger:update_handler_config/2</c></seealso></item>
<item><seealso marker="logger#update_formatter_config-2">
<c>logger:update_formatter_config/2</c></seealso></item>
</list>
</desc>
</func>
<func>
<name name="format" arity="2" since="OTP 21.0"/>
<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. See
section <seealso marker="logger_chapter#log_message">Log
Message</seealso> in the Kernel User's Guide for more
information about report callbacks and valid forms of log
messages.</item>
<item>The message size is limited according to the values of
configuration parameters <seealso marker="#chars_limit">
<c>chars_limit</c></seealso>
and <seealso marker="#depth"><c>depth</c></seealso>.</item>
<item>The full log entry is composed according to
the <seealso marker="#template"><c>template</c></seealso>.</item>
<item>If the final string is too long, it is truncated
according to the value of configuration
parameter <seealso marker="#max_size"><c>max_size</c></seealso>.</item>
</list>
</desc>
</func>
</funcs>
<section>
<title>See Also</title>
<p>
<seealso marker="stdlib:calendar"><c>calendar(3)</c></seealso>,
<seealso marker="error_logger"><c>error_logger(3)</c></seealso>,
<seealso marker="stdlib:io"><c>io(3)</c></seealso>,
<seealso marker="stdlib:io_lib"><c>io_lib(3)</c></seealso>,
<seealso marker="logger"><c>logger(3)</c></seealso>,
<seealso marker="stdlib:maps"><c>maps(3)</c></seealso>,
<seealso marker="sasl:sasl_app"><c>sasl(6)</c></seealso>,
<seealso marker="stdlib:unicode"><c>unicode(3)</c></seealso>
</p>
</section>
</erlref>
