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[](https://gitter.im/opentracing/public) [](https://travis-ci.org/opentracing/opentracing-go) [](http://godoc.org/github.com/opentracing/opentracing-go)
[](https://sourcegraph.com/github.com/opentracing/opentracing-go?badge)
# OpenTracing API for Go
This package is a Go platform API for OpenTracing.
## Required Reading
In order to understand the Go platform API, one must first be familiar with the
[OpenTracing project](https://opentracing.io) and
[terminology](https://opentracing.io/specification/) more specifically.
## API overview for those adding instrumentation
Everyday consumers of this `opentracing` package really only need to worry
about a couple of key abstractions: the `StartSpan` function, the `Span`
interface, and binding a `Tracer` at `main()`-time. Here are code snippets
demonstrating some important use cases.
#### Singleton initialization
The simplest starting point is `./default_tracer.go`. As early as possible, call
```go
import "github.com/opentracing/opentracing-go"
import ".../some_tracing_impl"
func main() {
opentracing.SetGlobalTracer(
// tracing impl specific:
some_tracing_impl.New(...),
)
...
}
```
#### Non-Singleton initialization
If you prefer direct control to singletons, manage ownership of the
`opentracing.Tracer` implementation explicitly.
#### Creating a Span given an existing Go `context.Context`
If you use `context.Context` in your application, OpenTracing's Go library will
happily rely on it for `Span` propagation. To start a new (blocking child)
`Span`, you can use `StartSpanFromContext`.
```go
func xyz(ctx context.Context, ...) {
...
span, ctx := opentracing.StartSpanFromContext(ctx, "operation_name")
defer span.Finish()
span.LogFields(
log.String("event", "soft error"),
log.String("type", "cache timeout"),
log.Int("waited.millis", 1500))
...
}
```
#### Starting an empty trace by creating a "root span"
It's always possible to create a "root" `Span` with no parent or other causal
reference.
```go
func xyz() {
...
sp := opentracing.StartSpan("operation_name")
defer sp.Finish()
...
}
```
#### Creating a (child) Span given an existing (parent) Span
```go
func xyz(parentSpan opentracing.Span, ...) {
...
sp := opentracing.StartSpan(
"operation_name",
opentracing.ChildOf(parentSpan.Context()))
defer sp.Finish()
...
}
```
#### Serializing to the wire
```go
func makeSomeRequest(ctx context.Context) ... {
if span := opentracing.SpanFromContext(ctx); span != nil {
httpClient := &http.Client{}
httpReq, _ := http.NewRequest("GET", "http://myservice/", nil)
// Transmit the span's TraceContext as HTTP headers on our
// outbound request.
opentracing.GlobalTracer().Inject(
span.Context(),
opentracing.HTTPHeaders,
opentracing.HTTPHeadersCarrier(httpReq.Header))
resp, err := httpClient.Do(httpReq)
...
}
...
}
```
#### Deserializing from the wire
```go
http.HandleFunc("/", func(w http.ResponseWriter, req *http.Request) {
var serverSpan opentracing.Span
appSpecificOperationName := ...
wireContext, err := opentracing.GlobalTracer().Extract(
opentracing.HTTPHeaders,
opentracing.HTTPHeadersCarrier(req.Header))
if err != nil {
// Optionally record something about err here
}
// Create the span referring to the RPC client if available.
// If wireContext == nil, a root span will be created.
serverSpan = opentracing.StartSpan(
appSpecificOperationName,
ext.RPCServerOption(wireContext))
defer serverSpan.Finish()
ctx := opentracing.ContextWithSpan(context.Background(), serverSpan)
...
}
```
#### Conditionally capture a field using `log.Noop`
In some situations, you may want to dynamically decide whether or not
to log a field. For example, you may want to capture additional data,
such as a customer ID, in non-production environments:
```go
func Customer(order *Order) log.Field {
if os.Getenv("ENVIRONMENT") == "dev" {
return log.String("customer", order.Customer.ID)
}
return log.Noop()
}
```
#### Goroutine-safety
The entire public API is goroutine-safe and does not require external
synchronization.
## API pointers for those implementing a tracing system
Tracing system implementors may be able to reuse or copy-paste-modify the `basictracer` package, found [here](https://github.com/opentracing/basictracer-go). In particular, see `basictracer.New(...)`.
## API compatibility
For the time being, "mild" backwards-incompatible changes may be made without changing the major version number. As OpenTracing and `opentracing-go` mature, backwards compatibility will become more of a priority.
## Tracer test suite
A test suite is available in the [harness](https://godoc.org/github.com/opentracing/opentracing-go/harness) package that can assist Tracer implementors to assert that their Tracer is working correctly.
## Licensing
[Apache 2.0 License](./LICENSE).
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