step5.go

func homeHandler(w http.ResponseWriter, r *http.Request) {
    w.Write([]byte("Request started"))
    span := opentracing.StartSpan("/home")
    defer span.Finish()
    
    // Since we have to inject our span into the HTTP headers, we create a request
    asyncReq, _ := http.NewRequest("GET", "http://localhost:8080/async", nil)
    // Inject the span context into the header
    err := span.Tracer().Inject(span.Context(), 
        opentracing.TextMap, 
        opentracing.HTTPHeaderTextMapCarrier(asyncReq.Header))
    if err != nil {
        log.Fatalf("Could not inject span context into header: %v", err)
    }
    go func() {
        if _, err := http.DefaultClient.Do(asyncReq); err != nil {
            span.SetTag("error", true)
            span.LogEvent(fmt.Sprintf("GET /async error: %v", err))
        }
    }()
    // Repeat for the /service call.
    // ....
}