logger_formatter(3erl) Erlang Module Definition logger_formatter(3erl)
NAME
logger_formatter - Default formatter for Logger.
DESCRIPTION
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 (unicode:chardata()) which
can be written to the output device of the handler. See sections Han-
dlers and Formatters in the Kernel User's Guide for more information.
logger_formatter is the default formatter used by Logger.
DATA TYPES
config() =
#{chars_limit => integer() >= 1 | unlimited,
depth => integer() >= 1 | unlimited,
legacy_header => boolean(),
max_size => integer() >= 1 | unlimited,
report_cb => logger:report_cb(),
single_line => boolean(),
template => template(),
time_designator => byte(),
time_offset => integer() | [byte()]}
The configuration term for logger_formatter is a map, and the
following keys can be set as configuration parameters:
chars_limit = integer() > 0 | unlimited:
A positive integer representing the value of the option with
the same name to be used when calling io_lib:format/3. 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 max_size.
Defaults to unlimited.
depth = integer() > 0 | unlimited:
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
io:format/2,3 in STDLIB.
Defaults to unlimited.
legacy_header = boolean():
If set to true a header field is added to logger_formatter's
part of Metadata. The value of this field is a string simi-
lar to the header created by the old error_logger event han-
dlers. It can be included in the log event by adding the
list [logger_formatter,header] to the template. See the de-
scription of the template() type for more information.
Defaults to false.
max_size = integer() > 0 | unlimited:
A positive integer representing the absolute maximum size a
string returned from this formatter can have. If the format-
ted string is longer, after possibly being limited by
chars_limit or depth, it is truncated.
Defaults to unlimited.
report_cb = logger:report_cb():
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, log-
ger_formatter will use logger:format_report/1 as default
callback.
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 config-
ured function.
single_line = boolean():
If set to true, each log event is printed as a single line.
To achieve this, logger_formatter sets the field width to 0
for all ~p and ~P control sequences in the format a string
(see io:format/2), and replaces all newlines in the message
with ", ". White spaces following directly after newlines
are removed. Notice that newlines added by the template pa-
rameter are not replaced.
Defaults to true.
template = template():
The template describes how the formatted string is composed
by combining different data values from the log event. See
the description of the template() type for more information
about this.
time_designator = byte():
Timestamps are formatted according to RFC3339, and the time
designator is the character used as date and time separator.
Defaults to $T.
The value of this parameter is used as the time_designator
option to calendar:system_time_to_rcf3339/2.
time_offset = integer() | [byte()]:
The time offset, either a string or an integer, to be used
when formatting the timestamp.
An empty string is interpreted as local time. The values
"Z", "z" or 0 are interpreted as Universal Coordinated Time
(UTC).
Strings, other than "Z", "z", or "", must be on the form
+-[hh]:[mm], for example "-02:00" or "+00:00".
Integers must be in microseconds, meaning that the offset
7200000000 is equivalent to "+02:00".
Defaults to an empty string, meaning that timestamps are
displayed in local time. However, for backwards compatibil-
ity, if the SASL configuration parameter utc_log=true, the
default is changed to "Z", meaning that timestamps are dis-
played in UTC.
The value of this parameter is used as the offset option to
calendar:system_time_to_rcf3339/2.
metakey() = atom() | [atom()]
template() =
[metakey() | {metakey(), template(), template()} | string()]
The template is a list of atoms, atom lists, tuples and strings.
The atoms level or msg, 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 rep-
resent paths to sub keys when the metadata is a nested map. For
example the list [key1,key2] is replaced by the value of the
key2 field in the nested map below. The atom key1 on its own is
replaced by the complete value of the key1 field. The values are
converted to strings.
#{key1 => #{key2 => my_value,
...}
...}
Tuples in the template express if-exist tests for metadata keys.
For example, the following tuple says that if key1 exists in the
metadata map, print "key1=Value", where Value is the value that
key1 is associated with in the metadata map. If key1 does not
exist, print nothing.
{key1, ["key1=",key1], []}
Strings in the template are printed literally.
The default value for the template configuration parameter de-
pends on the value of the single_line and legacy_header configu-
ration parameters as follows.
The log event used in the examples is:
?LOG_ERROR("name: ~p~nexit_reason: ~p", [my_name, "It crashed"])
legacy_header = true, single_line = false:
Default template: [[logger_formatter,header],"\n",msg,"\n"]
Example log entry:
=ERROR REPORT==== 17-May-2018::18:30:19.453447 ===
name: my_name
exit_reason: "It crashed"
Notice that all eight levels can occur in the heading, not
only ERROR, WARNING or INFO as error_logger produces. And
microseconds are added at the end of the timestamp.
legacy_header = true, single_line = true:
Default template: [[logger_formatter,header],"\n",msg,"\n"]
Notice that the template is here the same as for sin-
gle_line=false, but the resulting log entry differs in that
there is only one line after the heading:
=ERROR REPORT==== 17-May-2018::18:31:06.952665 ===
name: my_name, exit_reason: "It crashed"
legacy_header = false, single_line = true:
Default template: [time," ",level,": ",msg,"\n"]
Example log entry:
2018-05-17T18:31:31.152864+02:00 error: name: my_name, exit_reason: "It crashed"
legacy_header = false, single_line = false:
Default template: [time," ",level,":\n",msg,"\n"]
Example log entry:
2018-05-17T18:32:20.105422+02:00 error:
name: my_name
exit_reason: "It crashed"
EXPORTS
check_config(Config) -> ok | {error, term()}
Types:
Config = config()
The function is called by Logger when the formatter configura-
tion for a handler is set or modified. It returns ok if the con-
figuration is valid, and {error,term()} if it is faulty.
The following Logger API functions can trigger this callback:
* logger:add_handler/3
* logger:set_handler_config/2,3
* logger:update_handler_config/2
* logger:update_formatter_config/2
format(LogEvent, Config) -> unicode:chardata()
Types:
LogEvent = logger:log_event()
Config = config()
This the formatter callback function to be called from handlers.
The log event is processed as follows:
* If the message is on report form, it is converted to {For-
mat,Args} by calling the report callback. See section Log
Message in the Kernel User's Guide for more information
about report callbacks and valid forms of log messages.
* The message size is limited according to the values of con-
figuration parameters chars_limit and depth.
* The full log entry is composed according to the template.
* If the final string is too long, it is truncated according
to the value of configuration parameter max_size.
SEE ALSO
calendar(3erl), error_logger(3erl), io(3erl), io_lib(3erl), log-
ger(3erl), maps(3erl), sasl(7), unicode(3erl)
Ericsson AB kernel 7.0 logger_formatter(3erl)