1logger_formatter(3) Erlang Module Definition logger_formatter(3)
2
6 logger_formatter - Default formatter for Logger.
7
9 Each Logger handler has a configured formatter specified as a module
10 and a configuration term. The purpose of the formatter is to translate
11 the log events to a final printable string (unicode:chardata()) which
12 can be written to the output device of the handler. See sections Han‐
13 dlers and Formatters in the Kernel User's Guide for more information.
14 logger_formatter is the default formatter used by Logger.
16
18 config() =
19 #{chars_limit => integer() >= 1 | unlimited,
20 depth => integer() >= 1 | unlimited,
21 legacy_header => boolean(),
22 max_size => integer() >= 1 | unlimited,
23 report_cb => logger:report_cb(),
24 single_line => boolean(),
25 template => template(),
26 time_designator => byte(),
27 time_offset => integer() | [byte()]}
28 The configuration term for logger_formatter is a map, and the
30 following keys can be set as configuration parameters:
31 chars_limit = integer() > 0 | unlimited:
33 A positive integer representing the value of the option with
34 the same name to be used when calling io_lib:format/3. This
35 value limits the total number of characters printed for each
36 log event. Notice that this is a soft limit. For a hard
37 truncation limit, see option max_size.
38 Defaults to unlimited.
40 depth = integer() > 0 | unlimited:
42 A positive integer representing the maximum depth to which
43 terms shall be printed by this formatter. Format strings
44 passed to this formatter are rewritten. The format controls
45 ~p and ~w are replaced with ~P and ~W, respectively, and the
46 value is used as the depth parameter. For details, see
47 io:format/2,3 in STDLIB.
48 Defaults to unlimited.
50 legacy_header = boolean():
52 If set to true a header field is added to logger_formatter's
53 part of Metadata. The value of this field is a string simi‐
54 lar to the header created by the old error_logger event han‐
55 dlers. It can be included in the log event by adding the
56 list [logger_formatter,header] to the template. See the
57 description of the template() type for more information.
58 Defaults to false.
60 max_size = integer() > 0 | unlimited:
62 A positive integer representing the absolute maximum size a
63 string returned from this formatter can have. If the format‐
64 ted string is longer, after possibly being limited by
65 chars_limit or depth, it is truncated.
66 Defaults to unlimited.
68 report_cb = logger:report_cb():
70 A report callback is used by the formatter to transform log
71 messages on report form to a format string and arguments.
72 The report callback can be specified in the metadata for the
73 log event. If no report callback exists in metadata, log‐
74 ger_formatter will use logger:format_report/1 as default
75 callback.
76 If this configuration parameter is set, it replaces both the
78 default report callback, and any report callback found in
79 metadata. That is, all reports are converted by this config‐
80 ured function.
81 single_line = boolean():
83 If set to true, each log event is printed as a single line.
84 To achieve this, logger_formatter sets the field width to 0
85 for all ~p and ~P control sequences in the format a string
86 (see io:format/2), and replaces all newlines in the message
87 with ", ". White spaces following directly after newlines
88 are removed. Notice that newlines added by the template
89 parameter are not replaced.
90 Defaults to true.
92 template = template():
94 The template describes how the formatted string is composed
95 by combining different data values from the log event. See
96 the description of the template() type for more information
97 about this.
98 time_designator = byte():
100 Timestamps are formatted according to RFC3339, and the time
101 designator is the character used as date and time separator.
102 Defaults to $T.
104 The value of this parameter is used as the time_designator
106 option to calendar:system_time_to_rcf3339/2.
107 time_offset = integer() | [byte()]:
109 The time offset, either a string or an integer, to be used
110 when formatting the timestamp.
111 An empty string is interpreted as local time. The values
113 "Z", "z" or 0 are interpreted as Universal Coordinated Time
114 (UTC).
115 Strings, other than "Z", "z", or "", must be on the form
117 ±[hh]:[mm], for example "-02:00" or "+00:00".
118 Integers must be in microseconds, meaning that the offset
120 7200000000 is equivalent to "+02:00".
121 Defaults to an empty string, meaning that timestamps are
123 displayed in local time. However, for backwards compatibil‐
124 ity, if the SASL configuration parameter utc_log=true, the
125 default is changed to "Z", meaning that timestamps are dis‐
126 played in UTC.
127 The value of this parameter is used as the offset option to
129 calendar:system_time_to_rcf3339/2.
130 metakey() = atom() | [atom()]
132 template() =
134 [metakey() | {metakey(), template(), template()} | string()]
135 The template is a list of atoms, atom lists, tuples and strings.
137 The atoms level or msg, are treated as placeholders for the
138 severity level and the log message, respectively. Other atoms or
139 atom lists are interpreted as placeholders for metadata, where
140 atoms are expected to match top level keys, and atom lists rep‐
141 resent paths to sub keys when the metadata is a nested map. For
142 example the list [key1,key2] is replaced by the value of the
143 key2 field in the nested map below. The atom key1 on its own is
144 replaced by the complete value of the key1 field. The values are
145 converted to strings.
146 #{key1 => #{key2 => my_value,
148 ...}
149 ...}
150 Tuples in the template express if-exist tests for metadata keys.
152 For example, the following tuple says that if key1 exists in the
153 metadata map, print "key1=Value", where Value is the value that
154 key1 is associated with in the metadata map. If key1 does not
155 exist, print nothing.
156 {key1, ["key1=",key1], []}
158 Strings in the template are printed literally.
160 The default value for the template configuration parameter
162 depends on the value of the single_line and legacy_header con‐
163 figuration parameters as follows.
164 The log event used in the examples is:
166 ?LOG_ERROR("name: ~p~nexit_reason: ~p", [my_name, "It crashed"])
168 legacy_header = true, single_line = false:
170 Default template: [[logger_formatter,header],"\n",msg,"\n"]
171 Example log entry:
173 =ERROR REPORT==== 17-May-2018::18:30:19.453447 ===
175 name: my_name
176 exit_reason: "It crashed"
177 Notice that all eight levels can occur in the heading, not
179 only ERROR, WARNING or INFO as error_logger produces. And
180 microseconds are added at the end of the timestamp.
181 legacy_header = true, single_line = true:
183 Default template: [[logger_formatter,header],"\n",msg,"\n"]
184 Notice that the template is here the same as for sin‐
186 gle_line=false, but the resulting log entry differs in that
187 there is only one line after the heading:
188 =ERROR REPORT==== 17-May-2018::18:31:06.952665 ===
190 name: my_name, exit_reason: "It crashed"
191 legacy_header = false, single_line = true:
193 Default template: [time," ",level,": ",msg,"\n"]
194 Example log entry:
196 2018-05-17T18:31:31.152864+02:00 error: name: my_name, exit_reason: "It crashed"
198 legacy_header = false, single_line = false:
200 Default template: [time," ",level,":\n",msg,"\n"]
201 Example log entry:
203 2018-05-17T18:32:20.105422+02:00 error:
205 name: my_name
206 exit_reason: "It crashed"
207
209 check_config(Config) -> ok | {error, term()}
210 Types:
212 Config = config()
214 The function is called by Logger when the formatter configura‐
216 tion for a handler is set or modified. It returns ok if the con‐
217 figuration is valid, and {error,term()} if it is faulty.
218 The following Logger API functions can trigger this callback:
220 * logger:add_handler/3
222 * logger:set_handler_config/2,3
224 * logger:update_handler_config/2
226 * logger:update_formatter_config/2
228 format(LogEvent, Config) -> unicode:chardata()
230 Types:
232 LogEvent = logger:log_event()
234 Config = config()
235 This the formatter callback function to be called from handlers.
237 The log event is processed as follows:
238 * If the message is on report form, it is converted to {For‐
240 mat,Args} by calling the report callback. See section Log
241 Message in the Kernel User's Guide for more information
242 about report callbacks and valid forms of log messages.
243 * The message size is limited according to the values of con‐
245 figuration parameters chars_limit and depth.
246 * The full log entry is composed according to the template.
248 * If the final string is too long, it is truncated according
250 to the value of configuration parameter max_size.
251
253 calendar(3), error_logger(3), io(3), io_lib(3), logger(3), maps(3),
254 sasl(6), unicode(3)
255Ericsson AB kernel 6.5 logger_formatter(3)