httptrace底层链路追踪

[dduo518]

httptrace

httptrace 包提供了对 HTTP 跟踪的支持。收集的信息可用于调试延迟问题、服务监控、编写自适应系统等。

http 事件

httptrace 包提供了许多挂钩，用于在 HTTP 往返期间收集有关各种事件的信息。这些事件包括:

• Connection creation
• Connection reuse
• DNS lookups
• Writing the request to the wire
• Reading the response

链路追踪事件

http.RoundTripper 实现通过查找放入请求的context.Context上下文的*httptrace.ClientTrace来启用 HTTP 跟踪, 并调用相关的钩子函数来报告内部事件。跟踪的范围是请求的上下文，应该在开始请求之前将 *httptrace.ClientTrace 放入请求上下文。

示例

package main

import (
	"fmt"
	"log"
	"net/http"
	"net/http/httptrace"
)

func main() {
	t := &transport{}
	req, _ := http.NewRequest("GET", "https://www.google.com.hk", nil)
	trace := &httptrace.ClientTrace{
		GotConn:      t.GotConn,
		GetConn:      t.GetConn,
		ConnectStart: t.ConnectStart,
		ConnectDone:  t.ConnectDone,
	}
	req = req.WithContext(httptrace.WithClientTrace(req.Context(), trace))
	client := &http.Client{Transport: t}
	if _, err := client.Do(req);err != nil {
		log.Fatal(err)
	}
}
type transport struct {
	current *http.Request
}
func (t *transport) RoundTrip(req *http.Request) (*http.Response, error) {
	t.current = req
	return http.DefaultTransport.RoundTrip(req)
}

func (t *transport) GotConn(info httptrace.GotConnInfo) {
	fmt.Printf("GotConn Connection reused for %v? %v\n", t.current.URL, info.Reused)
}

func (t *transport) GetConn(hostPort string) {
	fmt.Printf("GetConn connection hostPort: %v\n", hostPort)
}

func (t *transport) ConnectStart(network, addr string) {
	fmt.Printf("ConnectStart network %s | addr: %s \n", network, addr)
}
func (t *transport) ConnectDone(network, addr string, err error) {
	fmt.Printf("ConnectDone network %s | addr: %s\n", network, addr)
}

http实现

在http中的RoundTrip接口实现钩子函数的执行

func (t *Transport) getConn(treq *transportRequest, cm connectMethod) (pc *persistConn, err error) {
	req := treq.Request
	trace := treq.trace
	ctx := req.Context()
	if trace != nil && trace.GetConn != nil {
		trace.GetConn(cm.addr())
	}
    // ...
    if w.pc != nil && w.pc.alt == nil && trace != nil && trace.GotConn != nil {
		trace.GotConn(httptrace.GotConnInfo{Conn: w.pc.conn, Reused: w.pc.isReused()})
	}
}

// 创建 tcp 连接
func (sd *sysDialer) dialSingle(ctx context.Context, ra Addr) (c Conn, err error) {
	trace, _ := ctx.Value(nettrace.TraceKey{}).(*nettrace.Trace)
	if trace != nil {
		raStr := ra.String()
		if trace.ConnectStart != nil {
			trace.ConnectStart(sd.network, raStr)
		}
		if trace.ConnectDone != nil {
			defer func() { trace.ConnectDone(sd.network, raStr, err) }()
		}
	}
}

作用

对调试 HTTP请求延迟和编写出站流量网络调试工具来说，HTTP跟踪是 Go 的一个非常有用的包。