// 使用 OpenCensus 设置分布式跟踪
import (
    "context"
    "io"
    "time"

    "go.opencensus.io/plugin/ochttp"
    "go.opencensus.io/trace"
    "go.opencensus.io/trace/propagation"
)

func setupTracing(w io.Writer) {
    // 初始化 tracer
    trace.ApplyConfig(trace.Config{DefaultSampler: trace.AlwaysSample()})

    // 使用 OpenCensus HTTP 中间件启用 HTTP 请求追踪
    mux := http.NewServeMux()
    mux.Handle("/", ochttp.Handler(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        // 从传入请求中提取并跟踪上下文
        ctx := r.Context()
        span := trace.FromContext(ctx)
        defer span.End()

        // 创建子 span 并关联到 HTTP 请求
        childSpan := span.SpanContext().SpanID.NewSpanID(time.Now())
        ctx, childSpan = trace.StartSpan(ctx, "Child Span",
            trace.WithSpanID(childSpan), trace.WithParent(span.SpanContext()),
            trace.WithSampler(trace.AlwaysSample()))
        defer childSpan.End()

        // 记录请求处理时间
        childSpan.Annotate([]trace.Annotation{
            {Description: "Request received", Time: time.Now()},
        })
        // ... 请求处理逻辑

        childSpan.Annotate([]trace.Annotation{
            {Description: "Request processed", Time: time.Now()},
        })
    })))
    http.ListenAndServe(":8080", mux)
}

// 自定义固定速率采样器
import (
    "math/rand"

    "cloud.google.com/go/trace"

    "google.golang.org/protobuf/proto"
)

func newRateSampler(sampleRate float64) trace.Sampler {
    return &rateSampler{rate: sampleRate}
}

type rateSampler struct {
    rate float64
}

func (r *rateSampler) Sample(p proto.Message, _ trace.TraceOptions) trace.SamplingDecision {
    return trace.SamplingDecision(rand.Float64() <= r.rate)
}

// 验证服务之间是否正确传播，跟踪上下文
import (
    "net/http"

    "go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
    "go.opentelemetry.io/otel"
    "go.opentelemetry.io/otel/propagation"
)

func checkContextPropagation(w io.Writer) {
    // 初始化 OpenTelemetry tracer
    otel.SetTracerProvider(otel.NewNopTracerProvider())

    // 设置 HTTP 客户端和服务器端的中间部件
    httpClient := &http.Client{Transport: otelhttp.NewTransport(http.DefaultTransport)}
    mux := http.NewServeMux()
    mux.Handle("/", otelhttp.NewHandler(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        // 从传入请求中提取并跟踪上下文
        ctx := r.Context()
        carrier := propagation.HTTP{}
        if err := carrier.Extract(ctx); err != nil {
            log.Fprintf(w, "Error extracting tracking context: %v", err)
            return
        }
    })))
    http.ListenAndServe(":8080", mux)

    // 发送到服务器 HTTP 对上下文进行检查和跟踪
    req, err := http.NewRequest(http.MethodGet, "http://localhost:8080/", nil)
    if err != nil {
        log.Fatalf("Error creating request: %v", err)
    }
    if carrier := propagation.HTTP{}; err := carrier.Inject(ctx, req); err != nil {
        log.Fatalf("Error injecting tracing context: %v", err)
    }
    if resp, err := httpClient.Do(req); err != nil {
        log.Fatalf("Error sending request: %v", err)
    } else {
        log.Println("Request sent successfully")
        carrier := propagation.HTTP{}
        if err := carrier.Extract(resp.Header); err != nil {
            log.Fatalf("Error extracting tracing context from response: %v", err)
        }
        log.Println("Tracing context correctly forwarded")
    }
}