Gosteno is a golang implementation of the steno log tool. The feature set of Gosteno is very similar with that of ruby steno.

Core concepts behind Gosteno includes codec, sink, level, tag.

A codec encodes log entries to structural data, more specifically, JSON format data. Besides JSON codecs, Gosteno provides prettified codec which generates more human-readable data.

Roughly speaking, a sink is the destination where you store your log data. It's an abstraction of the underlying data storage systems. Currently Gosteno supports two kinds of sinks, namely IOSink and SyslogSink. IOSink includes files and standard output while SyslogSink streams your log data to syslog daemons such as rsyslogd. You can register as many sinks as you want. Everytime you log information, it will be written to all the sinks you have registered.

Gosteno supports 9 levels(from low to high): all, debug2, debug1, debug, info, warn, error, fatal, off. You can change the level on the fly without respawning the process.

In gosteno, tags are extended information that will be encoded together with other normal log information. You can add as many tags as you want. Tag makes the log information extensive.

go get -u github.com/cloudfoundry/gosteno

Here is a short but complete program showing how to registering sinks, chosing codec, tagging the information.

package main

import (
    "github.com/cloudfoundry/gosteno"
    "os"
)

func main() {
    c := &gosteno.Config{
        Sinks: []gosteno.Sink{
            gosteno.NewFileSink("./a.log"),
            gosteno.NewIOSink(os.Stdout),
            gosteno.NewSyslogSink("foobar"),
        },
        Level:     gosteno.LOG_INFO,
        Codec:     gosteno.NewJsonCodec(),
        EnableLOC: true,
    }
    gosteno.Init(c)
    logger := gosteno.NewLogger("test")
    t := gosteno.NewTaggedLogger(logger, map[string]string{"foo": "bar", "hello": "world"})
    t.Info("Hello")
}

Changing logger properties such as log level without restarting system is allowed in Gosteno. It is achieved through a http interface by some APIs and data is exchanged as JSON:

1. GET /regexp : get something like {"RexExp": "test$", "Level": "fatal"}
2. PUT /regexp : put with data like {"RegExp": "test$", "Level":"fatal"}
3. GET /loggers/{name} : get information about the logger by name
4. PUT /loggers/{name} : put with data like {"Level" : "fatal" }
5. GET /loggers : get information about all loggers

Currently targeting modern flavors of darwin and linux.

Apache 2.0