如何使用中间件更改http请求的响应代码？

问题内容

我正在尝试使用 go-chi 开发一个 api 网关。我希望如果请求在查询中包含“_always200=true”，我会将状态代码设置为 200。 这是我尝试过的： 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)
}

中间件：

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)
        }
    })
}

总是返回404。有什么办法可以解决这个问题吗？

正确答案

代码中至少存在两个问题。

1. always200, _ := r.Context().Value(always200QueryKey).(bool) 不是获取查询参数的正确方法。我认为您应该使用 r.URL.Query().Get("_always200") 来读取它，并将该值与字符串 "true" 进行比较。

2. 在 next.ServeHTTP(crw, r) 之后调用 crw.WriteHeader(http.StatusOK) 已经太晚了。当我测试代码时，它打印了此警告消息：

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

以下是更改响应状态代码的修改示例：

<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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