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
```go
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](https://github.com/opentracing/opentracing-go) methods - `StartSpan`, `Finish`, `LogKV`, and `SetTag`.
`go-log` implements its own tracer - `loggabletracer` - based on the [basictracer-go](https://github.com/opentracing/basictracer-go) implementation. If there is an active [`WriterGroup`](https://github.com/ipfs/go-log/blob/master/writer/option.go) the `loggabletracer` will [record](https://github.com/ipfs/go-log/blob/master/tracer/recorder.go) span data to the `WriterGroup`. An example of this can be seen in the [`log tail`](https://github.com/ipfs/go-ipfs/blob/master/core/commands/log.go) 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`](https://github.com/ipfs/go-jaeger-plugin) and the `go-ipfs` [tracer plugin](https://github.com/ipfs/go-ipfs/blob/master/plugin/tracer.go)
## Contribute
Feel free to join in. All welcome. Open an [issue](https://github.com/ipfs/go-log/issues)!
This repository falls under the IPFS [Code of Conduct](https://github.com/ipfs/community/blob/master/code-of-conduct.md).
