This module provides functions to deal with logging. It support:
- logging to multiple destination at the same time
- filtering logs per destination
type level =
Debugging message. They can be automatically removed by the syntax extension.*)
Informational message. Suitable to be displayed when the program is in verbose mode.*)
Something strange happend*)
An error message, which should not means the end of the program.*)
A fatal error happened, in most cases the program will end after a fatal error.*)
Type of log levels. A level determines the importance of a message
Type of a logger. A logger is responsible for dispatching messages and storing them somewhere.
Each logging message has a section. Sections can be used to structure your logs. For example you can choose different loggers according to the section.
Each section carries a level, and messages with a lower log level than than the section level will be dropped.
Section levels are initialised using the contents of the
LWT_LOG environment variable, which must contain one or more rules of the form
pattern -> level separated by ";". Where
pattern is a string that may contain
For example, if
access -> warning; foo[*] -> error
If the pattern is omited in a rule then the pattern
"*" is used instead, so
LWT_LOG may just contain
"debug" for instance.
By default, the following rule apply :
"* -> notice"
val string_of_level : level -> string
val level_of_string : string -> level option
Reset the rules set when parsing the
LWT_LOG environment variable using this string.
val add_rule : string -> level -> unit
add_rule pattern level adds a rule for sections logging levels. The rule is added before all other rules. It takes effect immediately and affects all sections for which the level has not been set explicitly with
pattern may contains
*. For example:
Lwt_log_core.add_rule "lwt*" Lwt_log_core.Info
val append_rule : string -> level -> unit
append_rule pattern level adds the given rule after all other rules. For example to set the default fallback rule:
Lwt_log_core.append_rule "*" Lwt_log_core.Info
val log : ?exn:exn -> ?section:section -> ?location:(string * int * int) -> ?logger:logger -> level:level -> string -> unit Lwt.t
log ?section ?logger ~level message logs a message.
exn is provided, then its string representation (=
Printexc.to_string exn) will be append to the message, and if possible the backtrace will also be logged.
location contains the location of the logging directive, it is of the form
(file_name, line, column).
val log_f : ?exn:exn -> ?section:section -> ?location:(string * int * int) -> ?logger:logger -> level:level -> ( 'a, unit, string, unit Lwt.t ) Pervasives.format4 -> 'a
log_f is the same as
log except that it takes a format string
val ign_log : ?exn:exn -> ?section:section -> ?location:(string * int * int) -> ?logger:logger -> level:level -> string -> unit
log but ignore the resulting thread.
val ign_log_f : ?exn:exn -> ?section:section -> ?location:(string * int * int) -> ?logger:logger -> level:level -> ( 'a, unit, string, unit ) Pervasives.format4 -> 'a
log_f but ignore the resulting thread.
The following functions are the same as
log except that their name determines which level is used.
module Section : sig ... end
A template is for generating log messages.
It is a string which may contains variables of the form
var is one of:
messagewhich will be replaced by the message emited
levelwhich will be replaced by a string representation of the level
sectionwhich will be replaced by the name of the message's section
loc-filewhich will be replaced by the file name of the calling logging function
loc-linewhich will be replaced by the line number of the calling logging function
loc-columnwhich will be replaced by the column number of the calling logging function
"$(name): $(loc-file): $(loc-line): $(loc-column): $(message)"
val render : buffer:Buffer.t -> template:template -> section:section -> level:level -> message:string -> unit
render ~buffer ~template ~section ~level ~message instantiate all variables of
template, and store the result in
buffer. The location is obtained from threads local storage.
val location_key : (string * int * int) Lwt.key
The key for storing current location.
val make : output:( section -> level -> string list -> unit Lwt.t ) -> close:( unit -> unit Lwt.t ) -> logger
make ~output ~close creates a new logger.
The default logger. It is used as default when no one is specified. If
Lwt_core is linked (in the package
lwt.unix) the default logger sends all messages to standard error. Otherwise the default logger is
broadcast loggers is a logger which send messages to all the given loggers.
Note: closing a broadcast logger does not close its components.
dispatch f is a logger which dispatch logging instructions to different logger according to their level and/or section.
Here is an example:
let access_logger = Lwt_log.file "access.log" and error_logger = Lwt_log.file "error.log" in Lwt_log_core.dispatch (fun section level -> match Lwt_log_core.Section.name section, level with | "access", _ -> access_logger | _, Lwt_log_core.Error -> error_logger)
val null : logger
Logger which drops everything