Pinelog - a lightweight logging API

Pinelog is a lightweight logging API for C programs that's designed to be included in your program source code. Parameters for Pinelog are configured at build time by means of preprocessor flags.

Usage

Logging macros

Pinelog uses printf style formatting, using the following list of macros. The macro indicates the level at which the message is logged. Note that Pinelog will automatically append a trailing newline to your log message, so you should not include one in your format string.

• PINELOG_FATAL
• PINELOG_ERROR
• PINELOG_WARN
• PINELOG_INFO
• PINELOG_DEBUG
• PINELOG_TRACE

Note: PINELOG_FATAL is used when the program encounters a fatal condition and needs to abort. This will log the fatal message and terminate the program with an exit code of 1.

Example

PINELOG_INFO("configuration file %s not found, using defaults", config_file);

Modules

Pinelog supports individual logging modules, which can be used by an application to individually control the log level for each module separately. This is managed at runtime, where the application must call pinelog_init to register a total count of modules, and then, for each module, it must call pinelog_setup_module to initialize the module name for that module. The module name is printed in the output.

Pinelog also allows the log level of the module to default to the global log level. By default, module log level is set to PINELOG_LVL_NOTSET, which will force Pinelog to use the global log level for that module.

In order to use the given module, the application must define PINELOG_MODULE before the line #include "pinelog.h". If it is not defined, Pinelog will default to using the root module.

Example

Initialization

pinelog_init(2); // Initialize 2 modules
pinelog_setup_module(0, "foo"); // Module 0 name is "foo"
pinelog_setup_module(1, "bar"); // Module 1 name is "bar"

Inside module

#define PINELOG_MODULE MODULE_FOO
#include "pinelog.h"

Logging levels

The default logging level is ERROR, and this can be controlled by the preprocessor flag PINELOG_DEFAULT_LEVEL.

The program can control the level at which messages can be logged at runtime, by using the pinelog_set_level function. This function takes in the level definition, which is one of the following, in increasing order of priority.

• PINELOG_LVL_TRACE
• PINELOG_LVL_DEBUG
• PINELOG_LVL_INFO
• PINELOG_LVL_WARNING
• PINELOG_LVL_ERROR
• PINELOG_LVL_FATAL
• PINELOG_LVL_NONE
• PINELOG_LVL_NOTSET - for modules only

Setting the level to a given priority suppresses all log messages of lower priority, i.e., if the level is set to PINELOG_LVL_ERROR, messages at WARNING level and below will be suppressed, but ERROR and FATAL messages will be logged.

Note: PINELOG_LVL_NONE suppresses all log messages, but PINELOG_FATAL will still terminate the program, even though nothing is logged.

Note: PINELOG_LVL_NOTSET is only applicable to module log level, it will be rejected if the application attempts to use it for the global log level.

Example

pinelog_set_level(PINELOG_LVL_WARNING);
pinelog_set_module_level(MODULE_ID, PINELOG_LVL_TRACE);

-DPINELOG_DEFAULT_LEVEL=PINELOG_LVL_WARNING

Output redirection

Pinelog defaults to writing the log messages to standard output, and this can be controlled by the preprocessor flag PINELOG_DEFAULT_STREAM.

However, the application can redirect log messages at runtime to a different FILE * stream, or to a file by using one of the following two methods:

FILE *out = fopen("/run/app.fifo", "w");
pinelog_set_output_stream(out);
pinelog_set_output_file("/var/log/app.log");

-DPINELOG_DEFAULT_STREAM=stderr

Logging format

Pinelog uses an opinionated logging format that is fixed as follows. Fields within [] are optional and controlled by build time flags.

[2021-07-14 11:08:04 ][ERROR: ][./test_pinelog.c:108 ][module-name: ]formatted message\n

The program can be controlled by the following preprocessor flags, all of which default to 0 (disabled). Set the flag to 1 to enable it.

• PINELOG_SHOW_DATE - Display the ISO 8601 date and time when the message is logged.
• PINELOG_SHOW_LEVEL - Display the level at which the message is logged.
• PINELOG_SHOW_BACKTRACE - Display the file and line where the message is logged.

Module name will always be displayed, if it is not the root module.

Set these flags by using the -D compiler argument, .e.g. -DPINELOG_SHOW_LEVEL=1 -DPINELOG_SHOW_DATE=1

Note that Pinelog will always add a newline after the message, so the format string does not need to and should not specify one.

Level strings

The application can control the level strings displayed by means of preprocessor flags, if the application wishes to display the log messages in a language other than English. This can be achieved by means of the following preprocessor definitions.

• PINELOG_FATAL_STR
• PINELOG_ERROR_STR
• PINELOG_WARNING_STR
• PINELOG_INFO_STR
• PINELOG_DEBUG_STR
• PINELOG_TRACE_STR

Note that these strings are not internationalized, and will be printed as configured, regardless of the chosen locale.

Example

-DPINELOG_ERROR_STR=\"E\" -DPINELOG_FATAL_STR=\"F\"

Temporary buffer

By default, Pinelog will write the individual components of the log output, i.e., date, log level, backtrace, module and log message individually to the output stream. The drawback of this is that if Pinelog is used in a multithreaded application, then the messages from multiple threads may be interleaved. In order to reduce the chances of this happening, you can define PINELOG_BUFFER_SZ to a positive value. This should be of sufficient size such that the largest log message can fit into this buffer, along with the individual components (timestamp, log level, etc.). A reasonable starting point for this is 256 bytes.

Note that this will result in a greater use of stack space, so applications with limited stack space should not use this, or they risk a stack overflow. Finally, note that the write system call is not guaranteed to be atomic, so you may still see interleaved data, especially if you have a large value configured for PINELOG_BUFFER_SZ.

Usage

Add the following definition to your CFLAGS when building Pinelog

-DPINELOG_BUFFER_SZ=256

Integrating Pinelog

Pinelog is intended to be integrated into your application source tree, either by means of including the sources directly, or by including the repository as a Git submodule or subtree.

Pinelog uses the autotools framework and includes preset configure.ac and Makefile.am files. These include unit tests to ensure that Pinelog is behaving as expected. However, you are free to use any build framework, since the entirety of Pinelog is contained within a single source file with an associated header.