Open tracing in HTTP Request Latency

原文链接

在分布式中，最关键的是distributed context propagation

If we assign a unique ID to each inbound request and carry it as part of the distributed context, we can then stitch together various profiling data from multiple threads and multiple processes into a single “trace” that represents the execution of the request by our system

import (
   "net/http"
   "net/http/httptrace"

   "github.com/opentracing/opentracing-go"
   "github.com/opentracing/opentracing-go/log"
   "golang.org/x/net/context"
)

// We will talk about this later
var tracer opentracing.Tracer

func AskGoogle(ctx context.Context) error {
   // retrieve current Span from Context
   var parentCtx opentracing.SpanContext
   parentSpan := opentracing.SpanFromContext(ctx); 
   if parentSpan != nil {
      parentCtx = parentSpan.Context()
   }

   // start a new Span to wrap HTTP request
   span := tracer.StartSpan(
      "ask google",
      opentracing.ChildOf(parentCtx),
   )

   // make sure the Span is finished once we're done
   defer span.Finish()

   // make the Span current in the context
   ctx = opentracing.ContextWithSpan(ctx, span)

   // now prepare the request
   req, err := http.NewRequest("GET", "http://google.com", nil)
   if err != nil {
      return err
   }

   // attach ClientTrace to the Context, and Context to request 
   trace := NewClientTrace(span)
   ctx = httptrace.WithClientTrace(ctx, trace)
   req = req.WithContext(ctx)

   // execute the request
   res, err := http.DefaultClient.Do(req)
   if err != nil {
      return err
   }
   
   // Google home page is not too exciting, so ignore the result
   res.Body.Close()
   return nil
}

关于异步关闭span的问题？