http_log.pl -- HTTP Logging module

Simple module for logging HTTP requests to a file. Logging is enabled by loading this file and ensure the setting http:logfile is not the empty atom. The default file for writing the log is httpd.log. See library(settings) for details.

The level of logging can modified using the multifile predicate http_log:nolog/1 to hide HTTP request fields from the logfile and http_log:password_field/1 to hide passwords from HTTP search specifications (e.g. /topsecret?password=secret).

http_log_stream(-Stream) is semidet

True when Stream is a stream to the opened HTTP log file. Opens the log file in append mode if the file is not yet open. The log file is determined from the setting http:logfile. If this setting is set to the empty atom (''), this predicate fails.

If a file error is encountered, this is reported using print_message/2, after which this predicate silently fails.

http_log_close(+Reason) is det

If there is a currently open HTTP logfile, close it after adding a term server(Reason, Time). to the logfile. This call is intended for cooperation with the Unix logrotate facility using the following schema:

Move logfile (the HTTP server keeps writing to the moved file)
Inform the server using an HTTP request that calls http_log_close/1
Compress the moved logfile

author: - Suggested by Jacco van Ossenbruggen

http_log(+Format, +Args) is det

Write message from Format and Args to log-stream. See format/2 for details. Succeed without side effects if logging is not enabled.

password_field(+Field) is semidet[multifile]

Multifile predicate that can be defined to hide passwords from the logfile.

nolog(+HTTPField)[multifile]

Multifile predicate that can be defined to hide request parameters from the request logfile.

nolog_post_content_type(+Type) is semidet[multifile]

Multifile hook called with the Content-type header. If the hook succeeds, the POST data is not logged. For example, to stop logging anything but application/json messages:

:- multifile http_log:nolog_post_content_type/1.

http_log:nolog_post_content_type(Type) :-
   Type \= (application/json).

Arguments:

Type

- is a term MainType/SubType

post_data_encoded(?Bytes:string, ?Encoded:string) is det

Encode the POST body for inclusion into the HTTP log file. The POST data is (in/de)flated using zopen/3 and base64 encoded using base64//1. The encoding makes long text messages shorter and keeps readable logfiles if binary data is posted.

http_logrotate(+Options) is det

Rotate the available log files. Note that there are two ways to deal with the rotation of log files:

Use the OS log rotation facility. In that case the OS must (1) move the logfile and (2) have something calling http_log_close/1 to close the (moved) file and make this server create a new one on the next log message. If library(http/http_unix_daemon) is used, closing is achieved by sending SIGHUP or SIGUSR1 to the process.
Call this predicate at scheduled intervals. This can be achieved by calling http_schedule_logrotate/2 in the context of library(http/http_unix_daemon) which schedules the maintenance actions.

Options:

min_size(+Bytes): Do not rotate if the log file is smaller than Bytes. The default is 1Mbytes.
keep_logs(+Count): Number of rotated log files to keep (default 10)
compress_logs(+Format): Compress the log files to the given format.
background(+Boolean): If true, rotate the log files in the background.

http_schedule_logrotate(When, Options)

Schedule log rotation based on maintenance broadcasts. When is one of:

daily(Hour:Min): Run each day at Hour:Min. Min is rounded to a multitude of 5.
weekly(Day, Hour:Min): Run at the given Day and Time each week. Day is either a number 1..7 (1 is Monday) or a weekday name or abbreviation.
monthly(DayOfTheMonth, Hour:Min): Run each month at the given Day (1..31). Note that not all months have all days.

This must be used with a timer that broadcasts a maintenance(_,_) message (see broadcast/1). Such a timer is part of library(http/http_unix_daemon).