github.com/etnz/logfmt

#logfmt

• Package "logfmt" implements a logger for objects in logfmt format: details
• Package "logfmt/logreader" implements a parser for logfmt streams: details
• Package "logfmt/ql" implements an interpreter of a query language for logfmt records. details
• Package "logfmt/cmd" is a collection of command line utilities for working with logfmt, it complements brandur's own collection. details

#logfmt

To use the package:

go get github.com/etnz/logfmt

logfmt is defined in Brandur's blog as a logging format optimal for easy development, consistency, and good legibility for humans and computers.

at=info method=GET path=/ host=mutelight.org status=200

The example above can be generated like:

logfmt.
  S("at", "info").
  S("method",r.Method).
  S("path", r.URL.Path).
  D("status", code ).
  Log()

Where 'S', 'Q', 'D' are method mapping the usual 'fmt' verbs.

Key/Value are stored in a map, so it's ok to call S("at", "info") several time, the last one is always right.

When writing the line in the output stream, keys are not printed in random order. Logs would be hard to read, and not reproducible. Instead key/value pairs are sorted in significance order: the shortest keys first, then alphabetically

at=info path=/ host=mutelight.org method=GET status=200

It enforce the tendency to keep generic keys short, and specific one longer, the first information you read is the most important.

Usually it is faster than the default "log" package

    r := Rec()
    r.D("timestamp", int(n))
    r.D("at", i)
    r.Q("username", "eric")
    r.K("debug")
    r.Log()

At 1389 ns/op : 720 logs per milliseconds

     log.Printf("at=%d", i)
     log.Printf("debug")
     log.Printf("username=%q\n", "eric")

At 2248 ns/op, that is 445 logs per milliseconds

Because using logfmt, you tend to group together information in less records, but richer, I compared a single logfmt record with 4 attributes with a 3 default logs.

'Record' object is idiomatic:

log:= logfmt.Rec()
defer log.Log()
//set an initial value
r.S("level", "debug")
...
if err != nil{
  r.S("level", "error") // escalate the record
  r.V("err", err)
}

See Examples or directly the godoc for more details.

Still on the workbench

• rewriter logs (sort keys, filter out some matches), highlight lowlight some lines or keys
• trim logs (before first match and after last match)