# README

go-log

The logging library used by go-ipfs

It currently uses a modified version of go-logging to implement the standard printf-style log output.

Install

go get github.com/ipfs/go-log

Usage

Once the pacakge is imported under the name logging, an instance of EventLogger can be created like so:

var log = logging.Logger("subsystem name")

It can then be used to emit log messages, either plain printf-style messages at six standard levels or structured messages using Start, StartFromParentState, Finish and FinishWithErr methods.

Example

func (s *Session) GetBlock(ctx context.Context, c *cid.Cid) (blk blocks.Block, err error) {

    // Starts Span called "Session.GetBlock", associates with `ctx`
    ctx = log.Start(ctx, "Session.GetBlock")

    // defer so `blk` and `err` can be evaluated after call
    defer func() {
        // tag span associated with `ctx`
        log.SetTags(ctx, map[string]interface{}{
            "cid": c,
            "block", blk,
        })
        // if err is non-nil tag the span with an error
        log.FinishWithErr(ctx, err)
    }()

    if shouldStartSomething() {
        // log message on span associated with `ctx`
        log.LogKV(ctx, "startSomething", true)
    }
  ...
}

Tracing

go-log wraps the opentracing-go methods - StartSpan, Finish, LogKV, and SetTag.

go-log implements its own tracer - loggabletracer - based on the basictracer-go implementation. If there is an active WriterGroup the loggabletracer will record span data to the WriterGroup. An example of this can be seen in the log tail command of go-ipfs.

Third party tracers may be used by calling opentracing.SetGlobalTracer() with your desired tracing implementation. An example of this can be seen using the go-jaeger-plugin and the go-ipfs tracer plugin