Logs reporter using syslog
The logs library provides basic logging support, each log source has an independent logging level, and reporting is decoupled from logging.
This library implements log reporters via syslog, using syslog-message.
A variety of transport mechanisms are implemented:
The UDP transport sends each log message to the remote log host using sendto. If sendto raises an Unix.Unix_error, this error is printed together with the log message on standard error.
When using a stream transport, TCP or TLS, the creation of a reporter attempts to establish a connection to the log host, and only results in Ok Logs.reporter on success, otherwise the Error msg is returned. At runtime when the connection failed, the message is printed on standard error, and a re-establishment of the connection is attempted.
Syslog messages need to be framed when transported over TCP and TLS streams. In the historical RFC 6587 this is defined to be either non-transparent (which lets you stream the message), by terminating each syslog message with a line feed (0x0A), a null byte (0x00), a CR-LF sequence, or any custom byte sequence. The alternative is octet counting, also defined in RFC 5425, which prepends the message with the message length, ASCII-encoded as decimal number, followed by a whitespace (0x20). We support all three popular methods, and also a `Custom one appending any byte sequence at the end of each message. There are defaults (TCP: null byte, TLS: octet counting) passed to the individual reporter constructors (see the framing type below).
Every time a library logs a message which reaches the reporter (depending on log level), the function message is evaluated with the hostname provided while creating the reporter, the log level is mapped to a syslog level, and the current timestamp is added. The log message is prepended with the log source name.
This module contains the pure fragments shared between the effectful implementation for Unix, Lwt, and MirageOS. TLS support is available for Lwt and MirageOS.
Not implemented is the reliable transport for syslog (see RFC 3195) (using port 601), which is an alternative transport of syslog messages over TCP.
v0.4.1 - homepage
val message :
?facility:Syslog_message.facility ->
host:string ->
source:string ->
tags:Logs.Tag.set ->
?header:string ->
Logs.level ->
Ptime.t ->
string ->
Syslog_message.tmessage ~facility ~host ~source ~tags ~header level now msg is message, a syslog message with the given values. The default facility is Syslog_message.System_Daemons.
Different framing methods used in the wild, as described in RFC 6587
val frame_message : string -> framing -> stringframe_msg msg framing is framed_message, where the framing is applied.
val facility : Syslog_message.facility Logs.Tag.deffacility is a Logs.Tag.def tag to give a message a different syslog facility from the reporter's default.