用golang写个链路追踪的demo

好的，这是一个简单的 Go 语言链路追踪的示例代码：

package main

import (
	"fmt"
	"math/rand"
	"net/http"
	"time"

	"github.com/opentracing/opentracing-go"
	"github.com/opentracing/opentracing-go/ext"
	"github.com/uber/jaeger-client-go"
	"github.com/uber/jaeger-client-go/config"
)

func main() {
	rand.Seed(time.Now().UnixNano())

	cfg := config.Configuration{
		ServiceName: "my-service",
		Sampler: &config.SamplerConfig{
			Type:  "const",
			Param: 1,
		},
		Reporter: &config.ReporterConfig{
			LogSpans: true,
		},
	}

	tracer, closer, err := cfg.NewTracer()
	if err != nil {
		fmt.Printf("Error while initializing tracer: %s\n", err.Error())
		return
	}
	defer closer.Close()

	opentracing.SetGlobalTracer(tracer)

	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		span := opentracing.StartSpan("root")
		defer span.Finish()

		if rand.Intn(10) == 0 {
			childSpan := opentracing.StartSpan("child", opentracing.ChildOf(span.Context()))
			defer childSpan.Finish()
			childSpan.SetTag("random", "child")
		} else {
			span.SetTag("random", "root")
		}
		w.Write([]byte("Hello World!"))
	})

	err = http.ListenAndServe(":8080", nil)
	if err != nil {
		fmt.Printf("Error while starting HTTP server: %s\n", err.Error())
	}
}

这段代码使用了 `jaeger-client-go` 库实现了链路追踪。首先，它配置了一个名为 "my-service" 的服务，并使用了固定采样器，每次都会对请求进行采样。然后，它在 HTTP 服务器的处理函数中创建了一个根 Span，并在该 Span 中随机创建一