http - 为什么 HTTP 客户端强制使用 Accept-Encoding header

Question

示例代码:

package main

import (
    "fmt"
    "net/http"
    "net/http/httputil"
)

func main() {
    client := &http.Client{
        Transport: &http.Transport{
            DisableCompression: true,
        },
    }
    url := "https://google.com"
    req, err := http.NewRequest(http.MethodGet, url, nil)
    if err != nil {
        return
    }
    //req.Header.Set("Accept-Encoding", "*")
    //req.Header.Del("Accept-Encoding")
    requestDump, err := httputil.DumpRequestOut(req, false)
    if err != nil {
        fmt.Println(err)
    }

    fmt.Println(string(requestDump))
    client.Do(req)
}

输出:

GET / HTTP/1.1
Host: google.com
User-Agent: Go-http-client/1.1
Accept-Encoding: gzip

只有 req.Header.Set("Accept-Encoding", "*"未注释:

GET / HTTP/1.1
Host: google.com
User-Agent: Go-http-client/1.1
Accept-Encoding: *

只有 req.Header.Del("Accept-Encoding")未注释:

GET / HTTP/1.1
Host: google.com
User-Agent: Go-http-client/1.1
Accept-Encoding: gzip

两行都没有注释:

GET / HTTP/1.1
Host: google.com
User-Agent: Go-http-client/1.1
Accept-Encoding: gzip

是否 DisableCompression实际上对 HTTP 请求本身做了什么？
根据godocs:

    // DisableCompression, if true, prevents the Transport from
    // requesting compression with an "Accept-Encoding: gzip"
    // request header when the Request contains no existing
    // Accept-Encoding value. If the Transport requests gzip on
    // its own and gets a gzipped response, it's transparently
    // decoded in the Response.Body. However, if the user
    // explicitly requested gzip it is not automatically
    // uncompressed.

Answer 1

根据文件:

DumpRequestOut is like DumpRequest but for outgoing client requests.It includes any headers that the standard http.Transport adds, such as User-Agent.

这意味着它将“接受编码:gzip”添加到打印线格式。
要测试实际写入连接的内容，您需要包装 Transport.Dial或 Transport.DialContext提供记录写入数据的连接。
如果您使用的传输支持 httptrace (所有内置和“x/http/...”传输实现都支持)，您可以设置一个 WroteHeaderField回调以检查写入的 header 字段。
但是，如果您只需要检查标题，则可以生成 httptest.Server .
@EmilePels 提供的游乐场链接:
https://play.golang.org/p/ZPi-_mfDxI8