microlog

A simple customizable logging library. Features:

• Log topics
  • To filter log messages by subsystems, e.g. "network", "storage", etc.
• Callbacks for custom output
  • E.g. files, serial ports, etc.
• Thread-safety
  • Via external locking injection
• Customizable log format
  • Color, custom dynamic data, emojis, etc.
• Support for embedded systems
  • Optional static memory allocation, optional color, no special dependencies

In the default configuration it looks like this:

...but in can be very minimalistic

... or feature-rich:

The project is based on several core principles:

• Universal for embedded and desktop applications
• No feature - no code for compilation
• Shallow learning curve, works out of box
• No dependencies
• Two files

Table of Contents

• microlog
  • Table of Contents
  • Core Features
    • Logging Level
    • Quite Mode
    • Thread-safety
    • Library Configuration
  • Feature: Log Topics
  • Feature: Extra Outputs
    • File output
    • Custom output
  • Log Format Customization
    • Custom log prefix
    • Timestamp
    • Other Customization
  • License
  • Credits

Core Features

The library can be linked as a CMake project, Meson subproject or can be added manually: copy ulog.c and ulog.h into your project and compiled along with it.

The library provides 6 function-like macros for logging:

log_trace(const char *fmt, ...);
log_debug(const char *fmt, ...);
log_info(const char *fmt, ...);
log_warn(const char *fmt, ...);
log_error(const char *fmt, ...);
log_fatal(const char *fmt, ...);

Each function takes a printf format string followed by additional arguments:

log_trace("Hello %s", "world")

Resulting in a line with the given format printed to stderr:

TRACE src/main.c:11: Hello world

Logging Level

The current logging level can be set by using the ulog_set_level() function. All logs below the given level will not be written to stderr. By default the level is LOG_TRACE, such that nothing is ignored.

ulog_set_level(LOG_INFO);

To get the name of the log level use ulog_get_level_string:

const char *level = ulog_get_level_string(LOG_INFO);
ptrintf("Level: %s\n", level);

Quiet Mode

Quiet-mode can be enabled by passing true to the ulog_set_quiet() function. While this mode is enabled the library will not output anything to stderr, but will continue to write to files and callbacks if any are set.

ulog_set_quiet(true);

Thread-safety

If the log will be written to from multiple threads a lock function can be set. To do this use the ulog_set_lock() function. The function is passed the boolean true if the lock should be acquired or false if the lock should be released and the given udata value.

void lock_function(bool lock, void *lock_arg) {
    if (lock) {
        pthread_mutex_lock((pthread_mutex_t *) lock_arg);
    } else {
        pthread_mutex_unlock((pthread_mutex_t *) lock_arg);
    }
}

. . .

pthread_mutex_t mutex;
ulog_set_lock(lock_function, mutex);

Library Configuration

You can use the defines in the compiler options, e.g. -DULOG_NO_COLOR.

For CMake projects, you can use the add_definitions function.

add_definitions(-DULOG_NO_COLOR)

For Meson projects, you can use the meson command.

add_global_arguments('-DULOG_NO_COLOR', language: 'c')

Note: You might want to adjust the compiler argument -fmacro-prefix-map=OLD_PATH=NEW_PATH to to get the right file paths, e.g. for meson:

add_global_arguments('-fmacro-prefix-map=../=',language: 'c')

Feature: Log Topics

The feature is controlled by ULOG_TOPICS_NUM. It allows to filter log messages by subsystems, e.g. "network", "storage", etc.

There are two mechanism of working with the topics:

• dynamic - slower, but new topic will be added automatically
• static - faster, but you need to define all topic using ulog_add_topic

If you want to use dynamic topics, you need to define ULOG_TOPICS_NUM to be -1. Otherwise, you need to define the number of topics for static allocation.

Printing the log message with the topic is done by the set of function-like macros similar to log_xxx, but with the topic as the first argument:

logt_trace(const char *topic_name, const char *fmt, ...)
logt_debug(const char *topic_name, const char *fmt, ...)
logt_info(const char *topic_name, const char *fmt, ...) 
logt_warn(const char *topic_name, const char *fmt, ...) 
logt_error(const char *topic_name, const char *fmt, ...)
logt_fatal(const char *topic_name, const char *fmt, ...)

In static mode you can decide whether enable or disable the topic during its definition. In dynamic mode all topics are disabled by default.

For example:

// Static topics

ulog_add_topic("network", true); // enabled by default
ulog_add_topic("storage", false); // disabled by default

logt_info("network", "Connected to server");

ulog_enable_topic("storage");
logt_warn("storage", "No free space");

. . .

// Dynamic topics

// by default all topics are disabled
ulog_enable_topic("storage");
logt_error("storage", "No free space");

ulog_enable_all_topics(); 
logt_trace("network", "Disconnected from server");
logt_fatal("video", "No signal");

Feature: Extra Outputs

The feature is controlled by the following defines:

• ULOG_EXTRA_OUTPUTS - The maximum number of extra logging outputs that can be added. Each extra output requires some memory. When it is 0, the entire extra output code is not compiled. Default is 0.

File output

One or more file pointers where the log will be written can be provided to the library by using the ulog_add_fp() function. The data written to the file output is of the following format (with the full time stamp):

2047-03-11 20:18:26 TRACE src/main.c:11: Hello world

Any messages below the given level are ignored. If the library failed to add a file pointer a value less-than-zero is returned.

FILE *fp = fopen("log.txt", "w");
if (fp) {
    ulog_add_fp(fp, LOG_INFO);
}

Custom Output

One or more callback functions which are called with the log data can be provided to the library by using the ulog_add_callback() function. Yo ucan use ulog_event_to_cstr to convert the ulog_Event structure to a string.

void arduino_callback(ulog_Event *ev, void *arg) {
    static char buffer[128];
    int result = ulog_event_to_cstr(ev, buffer, sizeof(buffer));
    if (result == 0) {
        Serial.println(buffer);
    }
}

. . .

ulog_add_callback(arduino_callback, NULL, LOG_INFO);

Log Format Customization

Custom log prefix

Sets a custom prefix function. The function is called with the log level and should return a string that will be printed right before the log level. It can be used to add custom data to the log messages, e.g. millisecond time.

Requires ULOG_CUSTOM_PREFIX_SIZE to be more than 0.

void update_prefix(ulog_Event *ev, char *prefix, size_t prefix_size) {
    snprintf(prefix, prefix_size, ", %d ms", millis());
}

. . .

ulog_set_prefix_fn(prefix_fn);

The output will be:

19:51:42, 105 ms ERROR src/main.c:38: Error message

Timestamp

The feature is controlled by ULOG_HAVE_TIME. You platform must support time.h.

The time to the file output will be written with the date, while time to the console will be written with the time only.

log.txt:

2021-03-11 20:18:26 TRACE src/main.c:11: Hello world

console:

20:18:26 TRACE src/main.c:11: Hello world

Other Customization

The following defines can be used to customize the library's output:

• ULOG_NO_COLOR - Do not use ANSI color escape codes when printing to stdout.
• ULOG_HIDE_FILE_STRING - Hide the file name and line number.
• ULOG_SHORT_LEVEL_STRINGS - Use short level strings, e.g. "T" for "TRACE", "I" for "INFO".
• ULOG_USE_EMOJI - Use emojis for log levels (⚪, 🟢, 🔵, 🟡, 🟠, 🔴, 💥). Overrides ULOG_SHORT_LEVEL_STRINGS. WARNING: not all compilers and terminals support emojis.

License

This library is free software; you can redistribute it and/or modify it under the terms of the MIT license. See LICENSE for details.

Credits

Based on https://github.com/rxi/log.c.git