如何使用Golang服務器檢查隱式設置的HTTP標頭？

Question

我創建了一個簡單的http2服務器，如果我用curl向它發送請求，它會響應一些標頭，盡管我沒有明確設置它們。 如何在requesthandling函數（sayhello）中訪問它們？ 我的代碼（我以前從未使用過golang）

server.go

package main

import (
  "net/http"
  "strings"
  "fmt"
  "github.com/gorilla/mux"
  "golang.org/x/net/http2"
)

func sayHello(w http.ResponseWriter, r *http.Request) {
  message := r.URL.Path
  message = strings.TrimPrefix(message, "/")
  message = "Hello " + message

  w.Header().Set("myFirst", "golangQuestion")
  w.Write([]byte(message))
  for k, v := range w.Header() {
    fmt.Println("[RESPONSE][Header]", k,":", v)
    }
}

func main() {
    router := mux.NewRouter()
    router.PathPrefix("/").HandlerFunc(sayHello) // catch everything else rule
    var srv = &http.Server{
        Addr: "127.0.0.1:8081",
    }
    http2.ConfigureServer(srv, nil)
    srv.Handler = router
    sslCert := "./ssl.cert"
    sslKey := "./ssl.key"
    if err := srv.ListenAndServeTLS(sslCert, sslKey); err != nil {
        panic(err)
    }
}

發送請求：

curl --head-不安全https://127.0.0.1:8081

HTTP/1.1 200 OK
Myfirst: golangQuestion
Date: Tue, 18 Jun 2019 09:18:29 GMT
Content-Length: 6
Content-Type: text/plain; charset=utf-8

我可以看到一些標頭被發回，我明確設置的標頭也收到了，但是輸出

去運行server.go

[RESPONSE][Header] Myfirst : [golangQuestion]

我如何才能訪問未明確設置但也通過curl接收的其他標頭？ 我遍歷了w.Headers ，但是它不包含隱式設置的頭

  for k, v := range w.Header() {
    fmt.Println("[RESPONSE][Header]", k,":", v)
    }

我期望go run server.go的輸出應如下所示：

[RESPONSE][Header] Myfirst : [golangQuestion]
[RESPONSE][Header] Date: [2019.02.12 ]
[RESPONSE][Header] Content-Length: [6]

Answer 1

當您調用ResponseWriter.Write()時，將自動發送這些標頭。 引用其文檔：

// Write writes the data to the connection as part of an HTTP reply.
//
// If WriteHeader has not yet been called, Write calls
// WriteHeader(http.StatusOK) before writing the data. If the Header
// does not contain a Content-Type line, Write adds a Content-Type set
// to the result of passing the initial 512 bytes of written data to
// DetectContentType. Additionally, if the total size of all written
// data is under a few KB and there are no Flush calls, the
// Content-Length header is added automatically.
//
// Depending on the HTTP protocol version and the client, calling
// Write or WriteHeader may prevent future reads on the
// Request.Body. For HTTP/1.x requests, handlers should read any
// needed request body data before writing the response. Once the
// headers have been flushed (due to either an explicit Flusher.Flush
// call or writing enough data to trigger a flush), the request body
// may be unavailable. For HTTP/2 requests, the Go HTTP server permits
// handlers to continue to read the request body while concurrently
// writing the response. However, such behavior may not be supported
// by all HTTP/2 clients. Handlers should read before writing if
// possible to maximize compatibility.
Write([]byte) (int, error)

ResponseWriter.Header()僅包含顯式設置的標頭。 Content-Type和Content-Length由w.Write()發送。

注意：如果要禁止顯示此類自動標頭，則必須將其值設置為nil ，例如：

w.Header()["Date"] = nil

另請注意，如果您手動設置此類標頭的值，這些值將被發送而不會更改。