为什么HTTP客户端强制使用Accept-Encoding标头 [英] Why does the HTTP Client Force an Accept-Encoding header

问题描述

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

仅使用 req.Header.Set("Accept-Encoding"，"*" 不加注释:

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

仅使用 req.Header.Del("Accept-Encoding")取消注释:

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

两行都未注释:

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

DisableCompression 确实对HTTP请求本身有任何作用吗?根据godocs:

Does DisableCompression actually do anything to the HTTP Request itself? According to the 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.

推荐答案

根据文档:

DumpRequestOut与DumpRequest类似，但用于传出客户端请求.它包括标准http.Transport添加的所有标头，例如User-Agent.

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

这意味着它将添加"Accept-Encoding:gzip"到印刷的电汇格式.

That means it adds "Accept-Encoding: gzip" to the printed wire format.

要测试实际写入连接的内容，您需要包装 Transport.Dial 或 Transport.DialContext 以提供记录已写入数据的连接.

To test what is actually written to the connection, you need to wrap Transport.Dial or Transport.DialContext to provide connection that logs written data.

如果您使用支持 httptrace 的传输器(所有内置和"x/http/..."传输实现均支持)，则可以设置WroteHeaderField 回调以检查已编写的标头字段.

If you are using a transport that supports httptrace (which all built-in and "x/http/..." transport implementation supports), you may set up a WroteHeaderField callback to inspect written header fields.

但是，如果您只需要检查标题，则可以生成 httptest.Server .

If you just need to inspect the headers, however, you can spawn up a httptest.Server.

@EmilePels提供的游乐场链接: https://play.golang.org/p/ZPi-_mfDxI8

Playground link provided by @EmilePels: https://play.golang.org/p/ZPi-_mfDxI8

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