# lightstep-tracer-go

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[![GoDoc](https://godoc.org/github.com/lightstep/lightstep-tracer-go?status.svg)](https://godoc.org/github.com/lightstep/lightstep-tracer-go)

The LightStep distributed tracing library for Go.

## Installation

```
$ go get 'github.com/lightstep/lightstep-tracer-go'
```

## API Documentation

Godoc: https://godoc.org/github.com/lightstep/lightstep-tracer-go

## Initialization: Starting a new tracer
To initialize a tracer, configure it with a valid Access Token and optional tuning parameters. Register the tracer as the OpenTracing global tracer so that it will become available to your installed intstrumentations libraries.

```go
import (
  "github.com/opentracing/opentracing-go"
  "github.com/lightstep/lightstep-tracer-go"
)

func main() {
  lightstepTracer := lightstep.NewTracer(lightstep.Options{
    AccessToken: "YourAccessToken",
  })

  opentracing.SetGlobalTracer(lightstepTracer)
}
```

## Instrumenting Code: Using the OpenTracing API

All instrumentation should be done through the OpenTracing API, rather than using the lightstep tracer type directly. For API documentation and advice on instrumentation in general, see the opentracing godocs and the opentracing website.

- https://godoc.org/github.com/opentracing/opentracing-go
- http://opentracing.io

## Flushing and Closing: Managing the tracer lifecycle

As part of managaing your application lifecycle, the lightstep tracer extends the `opentracing.Tracer` interface with methods for manual flushing and closing. To access these methods, you can take the global tracer and typecast it to a `lightstep.Tracer`. As a convenience, the lightstep package provides static methods which perform the typecasting.

```go
import (
  "context"
  "github.com/opentracing/opentracing-go"
  "github.com/lightstep/lightstep-tracer-go"
)

func shutdown(ctx context.Context) {
  // access the running tracer
  tracer := opentracing.GlobalTracer()
    
  // typecast from opentracing.Tracer to lightstep.Tracer
  lsTracer, ok := tracer.(lightstep.Tracer)
  if (!ok) { 
    return 
  }
  lsTracer.Close(ctx)

  // or use static methods
  lightstep.Close(ctx, tracer)
}
```

## Event Handling: Observing the LightStep tracer
In order to connect diagnostic information from the lightstep tracer into an application's logging and metrics systems, inject an event handler using the `OnEvent` static method. Events may be typecast to check for errors or specific events such as status reports.

```go
import (
  "example/logger"
  "example/metrics"
  "github.com/lightstep/lightstep-tracer-go"
)

logAndMetricsHandler := func(event lightstep.Event){
  switch event := event.(type) {
  case EventStatusReport:
    metrics.Count("tracer.dropped_spans", event.DroppedSpans())
  case ErrorEvent:
    logger.Error("LS Tracer error: %s", event)
  default:
    logger.Info("LS Tracer info: %s", event)
  }
}

func main() {
  // setup event handler first to catch startup errors
  lightstep.SetGlobalEventHandler(logAndMetricsHandler)
  
  lightstepTracer := lightstep.NewTracer(lightstep.Options{
    AccessToken: "YourAccessToken",
  })

  opentracing.SetGlobalTracer(lightstepTracer)
}
```

Event handlers will receive events from any active tracers, as well as errors in static functions. It is suggested that you set up event handling before initializing your tracer to catch any errors on initialization.

## Advanced Configuration: Transport and Serialization Protocols

By default, the tracer will send information to LightStep using GRPC and Protocol Buffers which is the recommended configuration. If there are no specific transport protocol needs you have, there is no need to change this default.

There are three total options for transport protocols:

- [Protocol Buffers](https://developers.google.com/protocol-buffers/) over [GRPC](https://grpc.io/) - The recommended, default, and most performant solution.
- \[ EXPERIMENTAL \] [Protocol Buffers](https://developers.google.com/protocol-buffers/) over HTTP - New transport protocol supported for use cases where GRPC isn't an option. In order to enable HTTP you will need to configure the LightStep collectors receiving the data to accept HTTP traffic. Reach out to LightStep for support in this.

You can configure which transport protocol the tracer uses using the `UseGRPC`, and `UseHttp` flags in the options.