json - 如何为所有 API 端点全局设置 http.ResponseWriter Content-Type header ？

Question

我是 Go 的新手，我现在正在用它构建一个简单的 API:

package main

import (
    "encoding/json"
    "fmt"
    "github.com/gorilla/mux"
    "github.com/gorilla/handlers"
    "log"
    "net/http"
)

func main() {
    port := ":3000"
    var router = mux.NewRouter()
    router.HandleFunc("/m/{msg}", handleMessage).Methods("GET")
    router.HandleFunc("/n/{num}", handleNumber).Methods("GET")

    headersOk := handlers.AllowedHeaders([]string{"Authorization"})
    originsOk := handlers.AllowedOrigins([]string{"*"})
    methodsOk := handlers.AllowedMethods([]string{"GET", "POST", "OPTIONS"})

    fmt.Printf("Server is running at http://localhost%s\n", port)
    log.Fatal(http.ListenAndServe(port, handlers.CORS(originsOk, headersOk, methodsOk)(router)))
}

func handleMessage(w http.ResponseWriter, r *http.Request) {
    vars := mux.Vars(r)
    message := vars["msg"]
    response := map[string]string{"message": message}
    w.Header().Set("Content-Type", "application/json") // this
    json.NewEncoder(w).Encode(response)
}

func handleNumber(w http.ResponseWriter, r *http.Request) {
    vars := mux.Vars(r)
    number := vars["num"]
    response := map[string]string{"number": number}
    w.Header().Set("Content-Type", "application/json") // and this
    json.NewEncoder(w).Encode(response)
}

我觉得在我拥有的每个 API 函数中不断重复 w.Header().Set("Content-Type", "application/json") 行是不干净的。

所以我的问题是，是否可以为我拥有的所有 API 函数全局设置 http.ResponseWriter Content-Type header ？

Answer 1

你可以为mux router定义middleware，这里是一个例子:

func main() {
    port := ":3000"
    var router = mux.NewRouter()
    router.Use(commonMiddleware)

    router.HandleFunc("/m/{msg}", handleMessage).Methods("GET")
    router.HandleFunc("/n/{num}", handleNumber).Methods("GET")
    // rest of code goes here
}

func commonMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        w.Header().Add("Content-Type", "application/json")
        next.ServeHTTP(w, r)
    })
}

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