Simple Leveled Logger

github.com/andrewslotin/llog is a library that provides leveled logs to the Go standard library's log.Logger.

Installation

go get github.com/andrewslotin/llog

Usage

The leveled logger is implemented as an io.Writer to be provided to the stdlib's log.SetOutput(). The writer determines log record level by looking at the message prefix. For example, a message that starts with warn will be considered as a llog.WarnLevel and sent to the underlying writer, if the writer has the minimal level set to llog.WarnLevel or lower.

// configure standard logger to write warning messages and above to STDERR
log.SetOutput(llog.NewWriter(os.Stderr, llog.WarnLevel))

log.Printf("warn: failed to close the output file: %s", err) // warn level, will be printed out
log.Println("something just happened") // info level, will be ignored

If a message does not contain any known prefixes, its level is considered to be llog.InfoLevel.

Please consult the package documentation for the list of available log levels as well as how they are mapped to the message prefixes.

Performance

There is nearly no overhead in using the llog.Writer to write log messages.

Below is the benchstat output comparing the benchmarks of log.Println() with io.Discard and llog.Writer set as outputs. The llog.Writer is configured to write to io.Discard as well with the minimal log level sufficient to print out all messages used in the benchmark.

name            old time/op    new time/op    delta
Writer_Write-4     306ns ± 0%     362ns ± 0%   ~     (p=1.000 n=1+1)

name            old alloc/op   new alloc/op   delta
Writer_Write-4     16.0B ± 0%     16.0B ± 0%   ~     (all equal)

name            old allocs/op  new allocs/op  delta
Writer_Write-4      1.00 ± 0%      1.00 ± 0%   ~     (all equal)