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Write man page for Log
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2
TODO.txt
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TODO.txt
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@ -36,7 +36,7 @@ Due: January 1, 2023
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[ ] Http
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[ ] HttpServer
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[ ] Json
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[ ] Log
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[x] Log
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[ ] Matrix
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[x] Queue
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[ ] Routes
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156
man/man3/Log.3
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156
man/man3/Log.3
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.Dd $Mdocdate: November 25 2022 $
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.Dt LOG 3
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.Os Telodendria Project
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.Sh NAME
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.Nm Log
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.Nd A simple logging framework for logging to files, standard output,
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or the system log.
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.Sh SYNOPSIS
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.In Log.h
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.Ft LogConfig *
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.Fn LogConfigCreate "void"
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.Ft void
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.Fn LogConfigFree "LogConfig *"
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.Ft void
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.Fn LogConfigLevelSet "LogConfig *" "int"
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.Ft void
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.Fn LogConfigIndent "LogConfig *"
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.Ft void
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.Fn LogConfigUnindent "LogConfig *"
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.Ft void
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.Fn LogConfigIndentSet "LogConfig *" "size_t"
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.Ft void
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.Fn LogConfigOutputSet "LogConfig *" "FILE *"
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.Ft void
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.Fn LogConfigFlagSet "LogConfig *" "int"
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.Ft void
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.Fn LogConfigFlagClear "LogConfig *" "int"
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.Ft void
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.Fn LogConfigTimeStampFormatSet "LogConfig *" "char *"
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.Ft void
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.Fn Log "LogConfig *" "int" "const char *" "..."
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.Sh DESCRIPTION
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.Pp
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A heavily-modifed version of Shlog, a simple C logging library facility
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that allows for colorful outputs, timestamps, and custom log levels.
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This library differs from Shlog in that the naming conventions have
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been updated to be consistent with Telodendria, and system log support
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has been added.
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.Pp
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Shlog was originally a learning project. It worked well and produced
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elegant logging output, so it was chosen to be the main logging
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mechanism of Telodendria. The original Shlog project is now dead; Shlog
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lives on now only as Telodendria's logging mechanism.
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.Pp
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One of the design choices made in this library, which unfortunately
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makes code using it a little more verbose, is that multiple logging
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configurations can exist in a program. No global variables are used,
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and all functions are thread-safe.
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.Pp
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.Fn LogConfigCreate
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creates a new log configuration with sane defaults that can be used
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immediately. Note that every call to
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.Fn Log
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requires a valid configuration pointer.
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.Fn LogConfigFree
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frees all memory associated with that configuration, invalidating
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it. Passing an invalid configuration pointer into any of the
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functions defined here result in undefined behavior. The
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.Fn LogConfig*Set
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functions manipulate the data pointed to by the pointer returned
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by
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.Fn LogConfigCreate .
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.Pp
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.Fn LogConfigLevelSet
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sets the current log level on the specified log configuration. This
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indicates that only messages at or above this level should be
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logged; all other messages are silently discarded by the
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.Fn Log
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function. The passed log level should be one of the log levels
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defined by
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.Xr syslog 3 .
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Refer to that page for a complete list of acceptable log levels,
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and note that passing in an invalid or unknown log level will
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result in undefined behavior.
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.Pp
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.Fn LogConfigIndent
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causes the output of
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.Fn Log
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to be indented two more spaces than it was previously. This can be
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helpful when generating stack traces, or otherwise producing
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hierarchical output. After calling this function, all future
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messages using the given config will be indented two more spaces
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than they were before. This is just a wrapper function around
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.Fn LogConfigIndentSet ,
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which allows the caller to specify an arbitrary indentation in
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spaces.
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.Fn LogConfigUnindent
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does the exact opposite of
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.Fn LogConfigIndent ;
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it subtracts two spaces from the indentation level, unless there
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is no indent, then it does nothing.
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.Pp
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.Fn LogConfigOutputSet
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sets the file stream that logging output should be written to. This
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defaults to standard output, but it can be standard error, or some
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other file stream. Passing a NULL value for the file pointer sets
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the log output to standard output. Note that the output file stream
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is only used if FLAG_OUTPUT_SYSLOG is not set.
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.Pp
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.Fn LogConfigFlagSet
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and
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.Fn LogConfigFlagClear
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are used for setting a number of boolean options on a log
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configuration. They utilize bitwise operators, so multiple options
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can be set or cleared with a single function call using bitwise OR
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operators. The flags defined as preprocessor macros, and are as
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follows:
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.Bl -tag -width Ds
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.It LOG_FLAG_COLOR
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When set, enable color-coded output on TTYs. Note that colors are
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implemented as ANSI escape sequences, and are not written to file
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streams that are not actually connected to a TTY, to prevent those
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sequences from being written to a file.
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.Xr isatty 3
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is checked before writing ANSI sequences.
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.It LOG_FLAG_SYSLOG
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When enabled, log output to the syslog using
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.Xr syslog 3 ,
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instead of logging to the file set by
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.Fn LogConfigOutputSet .
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This flag always overrides the file stream set by that function,
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regardless of when it was set.
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.El
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.Pp
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.Fn LogConfigTimeStampFormatSet
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allows a custom timestamp to be prepended to each message
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if the output is not going to the system log. Consult your
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system's documentation for
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.Xr strftime 3 .
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A value of NULL disables outputting a timestamp before messages.
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.Pp
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The
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.Fn Log
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function actually writes a log message to a console, file, system
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log, or other supported output device using the given configuration.
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This function is thread-safe; it locks a mutex before writing a
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message, and then unlocks it after the message was written. Each
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log configuration has its own mutex, so this function can be used
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with mutiple active log configurations.
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.Pp
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This function only logs messages if their level is above or equal to
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the currently configured log level, making it easy to turn some
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messages on or off. The function has the same usage as
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.Xr printf 3 .
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.Sh RETURN VALUES
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.Pp
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.Fn LogConfigCreate
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returns a pointer to a configuration structure on the heap, or NULL
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if there was an error allocating memory for it. The returned
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structure is opaque to the caller; the
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.Fn LogConfig*
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functions should be used to manipulate it.
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.Pp
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All other functions do not return anything. They are simply
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assumed to always succeed. If any arguments are NULL, then the
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functions do nothing, unless otherwise specifically noted.
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@ -29,101 +29,26 @@
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#include <stddef.h>
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#include <syslog.h>
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/*
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* The possible flags that can be applied to alter the behavior of
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* the logger.
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*/
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typedef enum LogFlag
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{
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LOG_FLAG_COLOR = (1 << 0), /* Enable color output on TTYs */
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LOG_FLAG_SYSLOG = (1 << 1) /* Log to the syslog instead of a
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* file */
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} LogFlag;
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#define LOG_FLAG_COLOR (1 << 0)
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#define LOG_FLAG_SYSLOG (1 << 1)
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/*
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* The log configurations structure in which all settings exist.
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* It's not super elegant to pass around a pointer to the logging
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* configuration, but this really is the best way without having a
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* global variable. It allows multiple loggers to exist if necessary,
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* and makes things more thread safe.
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*/
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typedef struct LogConfig LogConfig;
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/*
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* Create a new log configuration on the heap. This will be passed to
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* every Log() call after it is configured.
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*
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* Return: A pointer to a new LogConfig that can be configured and used
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* for logging. It should have sane defaults; in other words, you should
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* be able to immediately start logging with it.
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*/
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extern LogConfig *
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LogConfigCreate(void);
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/*
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* Free a log configuration. Future attempts to log with the passed
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* configuration will fail in an undefined way, such as by hanging the
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* process or segfaulting.
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*
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* Params:
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*
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* (LogConfig *) The configuration to free. All memory associated with
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* configuring the logging mechanism will be
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* invalidated.
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*/
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extern void
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LogConfigFree(LogConfig *);
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/*
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* Set the current log level on the specified log configuration. This
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* indicates that only messages at or above this level should be
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* logged; all other messages are ignored by the Log() function.
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*
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* Params:
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*
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* (LogConfig *) The log configuration to set the log level on.
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* (int) The log level to set.
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*/
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extern void
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LogConfigLevelSet(LogConfig *, int);
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/*
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* Indent the log output by two spaces. This can be helpful in
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* generating stack traces, or otherwise producing hierarchical output.
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* After calling this function, all future log messages using this
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* configuration will be indented.
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*
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* Params:
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*
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* (LogConfig *) The log configuration to indent.
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*/
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extern void
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LogConfigIndent(LogConfig *);
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/*
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* Decrease the log output indent by two spaces. This can be helpful in
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* generating stack traces, or otherwise producing hierarchical output.
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* After calling this function, all future log messages using this
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* configuration will be unindented, unless there was no indentation
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* to begin with; in that case, this function will do nothing.
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*
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* Params:
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*
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* (LogConfig *) The log configuration to unindent.
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*/
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extern void
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LogConfigUnindent(LogConfig *);
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/*
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* Set the log output indent to an arbitrary amount. This can be helpful
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* in generating stack traces, or otherwise producing hierarchical
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* output. After calling this function, all future log messages using
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* this configuration will be indented by the given amount.
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*
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* Params:
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*
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* (LogConfig *) The log configuration to apply the indent to.
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*/
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extern void
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LogConfigIndentSet(LogConfig *, size_t);
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@ -139,29 +64,6 @@ extern void
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extern void
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LogConfigTimeStampFormatSet(LogConfig *, char *);
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/*
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* Actually log a message to a console, file, or other output device,
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* using the given log configuration. This function is thread-safe; it
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* locks a mutex before writing a message, and then unlocks it after
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* the message was written. It should therefore work well in
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* multithreaded environments, and with multiple different log
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* configurations, as each one has its own mutex.
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*
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* This function only logs messages if they are above the currently
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* configured log level. In this way, it is easy to turn some messages
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* on and off.
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*
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* This function is a printf() style function; it takes a format
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* string and any number of parameters to format.
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*
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* Params:
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*
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* (LogConfig *) The logging configuration.
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* (int) The level of the message to log.
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* (const char *) The format string, or a plain message string.
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* (...) Any items to map into the format string, printf()
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* style.
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*/
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extern void
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Log(LogConfig *, int, const char *,...);
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