# Module BatLogger

    module BatLogger: sig .. end

# Logging Library

This module defines functions which implement a flexible error logging system for applications.
Author(s): Warren Harris, Metaweb Technologies

###### log modules

    type log

    type level =

`|` | `NONE`
`|` | `FATAL`
`|` | `ERROR`
`|` | `WARN`
`|` | `NOTICE`
`|` | `INFO`
`|` | `DEBUG`

    val make_log : string -> log

`make_log name` returns a new logger.

    val log_name : log -> string

`log_name logger` returns the name of the logger.

    val log_enable : log -> level -> unit

`log_enable logger level` enables a log level for a logger.

    val log_level : log -> level

`log_level logger` returns the currently enabled level for a logger.

    val log_enabled : log -> level -> bool

`log_enabled logger level` returns true if the specified level is currently enabled for the logger.

###### log events

    type event = string * (string * string) list

A log `event` consists of an event name and a list of key-value parameters (an association list). Events are constructed by `log` when a log level is enabled and passed to log formatters to render them to any logging output stream.

    val log : log -> level -> (unit -> event) -> unit

`log logger level event_fun` raises a log event if if the specified level is currently enabled for the logger. The function `event_fun ()` is called to return the event record, and is a function in order to delay construction or formatting of any event parameters in the case where the specified log level is not enabled. For example:

    log io_log INFO (fun () -> "connect", ["ADDR", addr])

would only log the `"connect"` event (with the `"ADDR"` string parameter) when the `INFO` log level was enabled for the `io_log` logger.

    val with_log : log ->
           level ->
           (unit -> event) -> ?result:('a -> string) -> (unit -> 'a) -> 'a

`with_log logger level event_fun ?result body` logs an event before and after calling `body ()`. The function `event_fun ()` is called to return the event record to be logged. After the body is evaluated, the `result` function is used to convert the body's result value into a string, which is added to the event record as a `"RESULT"` parameter (if no `result` function is supplied then a `"-"` is used). In the case where the body raises an exception, an `"EXN"` parameter is instead added to the event containing the name of the exception. In addition, an indentation level is maintained throughout the duration of the body such that any other log statements occurring inside the body will see an incremented indentation level. This is added to the event key-value arguments as an additional `"I"` parameter.

###### log formatters

    type formatter = log -> level -> event -> float -> unit

the type of a log formatter is a function that takes the logger, the level of the log statement (which will be the currently enabled level or one of its successors), the event record, and a unix timestamp indicating the time the event was created.

    val register_formatter : string -> formatter -> unit

`register_formatter name formatter` registers a named log formatter. The name is only used for subsequent calls to identify the formatter via `unregister_formatter`.

    val unregister_formatter : string -> unit

`unregister_formatter name` unregisters a named log formatter.

    val make_std_formatter : 'a BatIO.output -> formatter

`make_std_formatter oc` constructs a formatter from an output channel. This formatter will format log events as tab-separated `<keyword>:<value>` pairs. The resulting formatter must be registered via `register_formatter` to be used when events are raised. This formatter also always outputs special parameters that describe the event timestamp (an ISO-8610 timestamp prefixed by `"D"`), the event name (the log module name followed by a dot, followed by the event name, prefixed by `"E"`), the log level (prefixed by `"L"`), the indentation level ( prefixed by `"I"`), followed by any other event parameters. For example, the log statement:

    log io_log INFO (fun () -> "connect", ["ADDR", addr])

would produce formatted output like the following when the `io_log` `INFO` level was enabled:

    D:2009-01-26T00:47:45.033329Z   E:io.connect   L:INFO   I:1   ADDR:localhost:8080

    val stderr_formatter : formatter

`stderr_formatter` is a standard formatter that outputs log events to stderr using the same format as `make_std_formatter`. The resulting formatter must be registered via `register_formatter` or supplied to `init` or `init_from_string` to be used when events are raised.

    val null_formatter : formatter

`null_formatter` is a formatter that does not output any events, but simply discards them.

    val make_dbg_formatter : 'a BatIO.output -> formatter

`make_dbg_formatter oc` constructs a debug formatter from an output channel. The debug formatter outputs simplified format that is easier to read for debugging purposes and displays indentation level. E.g.:

          with_log io_log DEBUG (fun () -> "listener" ["ADDR", addr])

            accept_connections (* calls other log statements *)

would produce formatted output like the following when the `io_log` `DEBUG` level was enabled:

          ### io.listener ADDR:localhost:8080 [DEBUG]

              ### | io.connected CLIENT_ADDR:192.168.0.23:28303 [DEBUG]

              ### | io.disconnected CLIENT_ADDR:192.168.0.23:28303 [DEBUG]

                                                                   ...

                ### io.listener ADDR:localhost:8080 RESULT:- [DEBUG]

    val dbg_formatter : formatter

`dbg_formatter` is a debug formatter that outputs log events to stderr using the same format as `make_dbg_formatter`. The resulting formatter must be registered via `register_formatter` or supplied to `init` or `init_from_string` to be used when events are raised.

###### logger initialization

    val init : (string * level) list -> formatter -> unit

`init name_level_list formatter` initializes the logging system enabling the specified levels for each named logger. The formatter is the initial formatter for any log events that are output and is registered with the name "default" (other formatters may be registered by `register_formatter`).

    val init_from_string : string -> formatter -> unit

`init_from_string name_level_string formatter` initializes the logging system enabling the specified levels for each named logger. The string must be a comma separated list of `<logger name>:<level name>` pairs, e.g. `"FOO:ERROR,BAR:WARN"`. If a un-prefixed level name is specified, then that becomes the default log level for all newly created logs, and all currently created logs are enabled to that level. If the logger does not yet exist, it is created. The formatter is the initial formatter for any log events that are output and is registered with the name "default" (other formatters may be registered by `register_formatter`).

###### log utilities

    val level_of_name : string -> level

`level_of_name str` returns the `level` associated with `str`.

    val name_of_level : level -> string

`name_of_level level` returns the name of the specified `level`.

    val format_timestamp : 'a BatIO.output -> float -> unit

`format_timestamp oc timestamp` prints an ISO-8601 formatted timestamp (extended to specify higher-resolution seconds) to the output channel, `oc`.