在Go服务器中优雅处理CORS预检请求的最佳实践

package main

import (
    "fmt"
    "net/http"
)

func AddResourceHandler(rw http.ResponseWriter, r *http.Request) {
    switch r.Method {
    case http.MethodOptions:
        // 处理预检请求
        rw.Header().Set("Access-Control-Allow-Origin", "http://localhost:3000")
        rw.Header().Set("Access-Control-Allow-Methods", "PUT, OPTIONS")
        rw.Header().Set("Access-Control-Allow-Headers", "Content-Type")
        rw.WriteHeader(http.StatusOK)
        return
    case http.MethodPut:
        // 处理实际的PUT请求
        fmt.Fprintf(rw, "Received PUT request for resource.")
    default:
        http.Error(rw, "Method not allowed", http.StatusMethodNotAllowed)
    }
}

func main() {
    http.HandleFunc("/someresource/item", AddResourceHandler)
    fmt.Println("Server listening on :8080")
    http.ListenAndServe(":8080", nil)
}

package main

import (
    "fmt"
    "net/http"

    "github.com/gorilla/mux"
)

func PreflightAddResourceHandler(rw http.ResponseWriter, r *http.Request) {
    rw.Header().Set("Access-Control-Allow-Origin", "http://localhost:3000")
    rw.Header().Set("Access-Control-Allow-Methods", "PUT, OPTIONS")
    rw.Header().Set("Access-Control-Allow-Headers", "Content-Type")
    rw.WriteHeader(http.StatusOK)
}

func AddResourceHandler(rw http.ResponseWriter, r *http.Request) {
    fmt.Fprintf(rw, "Received PUT request for resource.")
}

func main() {
    r := mux.NewRouter()
    r.HandleFunc("/someresource/item", AddResourceHandler).Methods(http.MethodPut)
    r.HandleFunc("/someresource/item", PreflightAddResourceHandler).Methods(http.MethodOptions)

    fmt.Println("Server listening on :8080")
    http.ListenAndServe(":8080", r)
}

package main

import (
    "fmt"
    "net/http"
    "time" // 用于设置Access-Control-Max-Age

    "github.com/gorilla/mux" // 也可以与标准库的http.ServeMux结合使用
)

// corsMiddleware 是一个HTTP处理程序包装器，用于处理CORS预检请求。
// 它接收一个http.Handler并返回一个新的http.HandlerFunc。
func corsMiddleware(next http.Handler) http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {
        // 设置通用的CORS响应头
        // 生产环境应将 "*" 替换为具体的允许来源，例如 "http://yourfrontend.com"
        w.Header().Set("Access-Control-Allow-Origin", "*")
        // 允许的HTTP方法，根据你的API实际支持的方法进行设置
        w.Header().Set("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS")
        // 允许的请求头，包括Content-Type和自定义头
        w.Header().Set("Access-Control-Allow-Headers", "Content-Type, Authorization, X-Custom-Header")
        // 预检结果的缓存时间，单位秒。浏览器在此时间内不再发送重复预检请求。
        w.Header().Set("Access-Control-Max-Age", "86400") // 24小时

        // 如果是预检请求 (OPTIONS方法)，则直接返回200 OK
        if r.Method == http.MethodOptions {
            w.WriteHeader(http.StatusOK)
            return // 预检请求处理完毕，不再执行后续的处理程序
        }

        // 如果不是预检请求，则将请求传递给链中的下一个处理程序（即原始业务逻辑处理程序）
        next.ServeHTTP(w, r)
    }
}

// resourceHandler 模拟一个实际的RESTful业务逻辑处理函数
func resourceHandler(w http.ResponseWriter, r *http.Request) {
    if r.Method == http.MethodPut {
        w.WriteHeader(http.StatusOK)
        fmt.Fprintf(w, "Received PUT request for resource: %s", r.URL.Path)
        return
    }
    if r.Method == http.MethodGet {
        w.WriteHeader(http.StatusOK)
        fmt.Fprintf(w, "Received GET request for resource: %s", r.URL.Path)
        return
    }
    http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
}

func main() {
    // 实例化一个普通的HTTP处理程序
    myResourceHandler := http.HandlerFunc(resourceHandler)

    // 使用corsMiddleware包装器来处理CORS，将其应用于业务处理程序
    // 这里使用Gorilla Mux作为路由示例，但同样适用于标准库的http.ServeMux
    r := mux.NewRouter()
    r.Handle("/api/item", corsMiddleware(myResourceHandler)).Methods(http.MethodGet, http.MethodPut, http.MethodOptions)

    // 启动服务器
    fmt.Println("Server listening on :8080")
    http.ListenAndServe(":8080", r)
}