如何使用中介軟體更改http請求的回應代碼？

問題內容

我正在嘗試使用 go-chi 開發一個 api 網關。我希望如果請求在查詢中包含“_always200=true”，我會將狀態代碼設為 200。 這是我嘗試過的： custom_response_writer.go：

type CustomResponseWriter struct {
    http.ResponseWriter
    Buf         *bytes.Buffer
    StatusCode  int
    WroteHeader bool
}

func NewCustomResponseWriter(w http.ResponseWriter) *CustomResponseWriter {
    return &CustomResponseWriter{ResponseWriter: w, Buf: new(bytes.Buffer)}
}

func (c *CustomResponseWriter) WriteHeader(code int) {
    c.StatusCode = code
    c.ResponseWriter.WriteHeader(code)
}

func (c *CustomResponseWriter) Write(b []byte) (int, error) {
    return c.Buf.Write(b)
}

中介軟體:

func HeaderFilterMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        always200, _ := r.Context().Value(always200QueryKey).(bool)
        crw := NewCustomResponseWriter(w)
        next.ServeHTTP(crw, r)

        if always200 {
            crw.WriteHeader(http.StatusOK)
        }
    })
}

總是回傳404。有什麼辦法可以解決這個問題嗎？

正確答案

程式碼中至少存在兩個問題。

1. always200, _ := r.Context().Value(always200QueryKey).(bool) 不是取得查詢參數的正確方法。我認為您應該使用 r.URL.Query().Get("_always200") 來讀取它，並將該值與字串 "true" 進行比較。

2. 在 next.ServeHTTP(crw, r) 之後呼叫 crw.WriteHeader(http.StatusOK) 已經太晚了。當我測試程式碼時，它列印了此警告訊息：

   http: superfluous response.WriteHeader call from main.(*CustomResponseWriter).WriteHeader

以下是更改回應狀態程式碼的修改範例：

<code>package main

import (
    "bytes"
    "net/http"
    "strings"

    "github.com/go-chi/chi/v5"
)

type CustomResponseWriter struct {
    http.ResponseWriter
    Buf                *bytes.Buffer
    OriginalStatusCode int
    WroteHeader        bool
    always200          bool
}

func NewCustomResponseWriter(w http.ResponseWriter, always200 bool) *CustomResponseWriter {
    return &CustomResponseWriter{
        ResponseWriter: w,
        Buf:            new(bytes.Buffer),
        always200:      always200,
    }
}

func (c *CustomResponseWriter) WriteHeader(code int) {
    c.OriginalStatusCode = code

    if c.always200 {
        code = http.StatusOK
    }
    c.ResponseWriter.WriteHeader(code)
}

func (c *CustomResponseWriter) Write(b []byte) (int, error) {
    return c.Buf.Write(b)
}

func HeaderFilterMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        always200 := r.URL.Query().Get("_always200")
        crw := NewCustomResponseWriter(w, strings.EqualFold(always200, "true"))
        next.ServeHTTP(crw, r)
    })
}

func main() {
    r := chi.NewRouter()

    r.Use(HeaderFilterMiddleware)

    r.Get("/", func(w http.ResponseWriter, r *http.Request) {
        w.Write([]byte("welcome"))
    })
    http.ListenAndServe(":3000", r)
}
</code>

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