View Source logger_formatter behaviour (kernel v10.1.2)
Default formatter for Logger.
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
Handlers and
Formatters in the Kernel User's Guide for more
information.
logger_formatter
is the default formatter used by Logger.
See Also
calendar
, error_logger
, io
, io_lib
, logger
, maps
,
sasl(6)
, unicode
Summary
Types
The configuration term for logger_formatter
is a map, and the
following keys can be set as configuration parameters
The template to be used by a logger formatter.
Callbacks: Formatter Callback Functions
The function is called by a Logger when formatter configuration is set or
modified. The formatter must validate the given configuration and return ok
if
it is correct, and {error,Reason}
if it is faulty.
The function can be called by a log handler to convert a log event term to a
printable string. The returned value can, for example, be printed as a log entry
to the console or a file using io:put_chars/1,2
.
Functions
The function is called by Logger when the formatter configuration for a handler
is set or modified. It returns ok
if the configuration is valid, and
{error,term()}
if it is faulty.
This the formatter callback function to be called from handlers.
Types
-type config() :: #{chars_limit => pos_integer() | unlimited, depth => pos_integer() | unlimited, legacy_header => boolean(), max_size => pos_integer() | 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 callingio_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 optionmax_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, seeio:format/2,3
in STDLIB.Defaults to
unlimited
.legacy_header = boolean()
- If set totrue
a header field is added to logger_formatter's part ofMetadata
. The value of this field is a string similar to the header created by the olderror_logger
event handlers. It can be included in the log event by adding the list[logger_formatter,header]
to the template. See the description of thetemplate/0
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 formatted string is longer, after possibly being limited bychars_limit
ordepth
, it is truncated.Defaults to
unlimited
.report_cb = ``t:logger:report_cb/0
- 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,logger_formatter
will uselogger: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 configured function.
single_line = boolean()
- If set totrue
, each log event is printed as a single line. To achieve this,logger_formatter
sets the field width to0
for all~p
and~P
control sequences in the format a string (seeio:format/2
), and replaces all newlines in the message with", "
. White spaces following directly after newlines are removed. Notice that newlines added by thetemplate
parameter are not replaced.Defaults to
true
.template =
template/0
- The template describes how the formatted string is composed by combining different data values from the log event. See the description of thetemplate/0
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 tocalendar:system_time_to_rfc3339/2
.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"
or0
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 compatibility, if the SASL configuration parameter
utc_log
=true
, the default is changed to"Z"
, meaning that timestamps are displayed in UTC.The value of this parameter is used as the
offset
option tocalendar:system_time_to_rfc3339/2
.
-type template() :: [metakey() | {metakey(), template(), template()} | unicode:chardata()].
The template to be used by a logger formatter.
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
represent 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 depends on the
value of the single_line
and legacy_header
configuration 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
orINFO
aserror_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
single_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"
Callbacks: Formatter Callback Functions
-callback check_config(FConfig) -> ok | {error, Reason} when FConfig :: logger:formatter_config(), Reason :: term().
The function is called by a Logger when formatter configuration is set or
modified. The formatter must validate the given configuration and return ok
if
it is correct, and {error,Reason}
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/2,3
logger:update_formatter_config/2
See logger_formatter
for an example implementation. logger_formatter
is
the default formatter used by Logger.
-callback format(LogEvent, FConfig) -> FormattedLogEntry when LogEvent :: logger:log_event(), FConfig :: logger:formatter_config(), FormattedLogEntry :: unicode:chardata().
The function can be called by a log handler to convert a log event term to a
printable string. The returned value can, for example, be printed as a log entry
to the console or a file using io:put_chars/1,2
.
See logger_formatter
for an example implementation. logger_formatter
is
the default formatter used by Logger.
Functions
The function is called by Logger when the formatter configuration for a handler
is set or modified. It returns ok
if the configuration is valid, and
{error,term()}
if it is faulty.
The following Logger API functions can trigger this callback:
-spec format(LogEvent, Config) -> unicode:chardata() when 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
{Format,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 configuration
parameters
chars_limit
anddepth
. - 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
.