Go语言Web开发：深入理解HTTP HEAD方法与模板渲染的兼容性问题

// GET works fine, HEAD results in an error:
// template: main.html:1:0: executing "main.html" at <"homeHandler">:
//   http: request method or response status code does not allow body
func homeHandler(w http.ResponseWriter, req *http.Request) {
    err := templates.ExecuteTemplate(w, "main.html", nil)
    if err != nil {
        log.Fatal(err)
    }
}

// OK, HEAD + GET work fine
func fooHandler(w http.ResponseWriter, req *http.Request) {
    w.Write([]byte("fooHandler"))
}

package main

import (
    "html/template"
    "log"
    "net/http"
)

var (
    templates *template.Template
)

// 正确处理HEAD和GET请求的homeHandler
func homeHandler(w http.ResponseWriter, req *http.Request) {
    // 对于HEAD请求，仅设置头部，不写入响应体
    if req.Method == http.MethodHead {
        // 可以根据需要设置其他响应头，例如Content-Type, Content-Length等
        // 但不要尝试写入任何body内容
        w.Header().Set("Content-Type", "text/html; charset=utf-8")
        w.WriteHeader(http.StatusOK) // 显式设置状态码，尽管默认200
        return // 提前返回，不执行模板渲染
    }

    // 对于GET请求，正常渲染模板并写入响应体
    if req.Method == http.MethodGet {
        err := templates.ExecuteTemplate(w, "main.html", nil)
        if err != nil {
            // 记录错误，但不使用log.Fatal，避免程序退出
            log.Printf("Error executing template for GET request: %v", err)
            http.Error(w, "Internal Server Error", http.StatusInternalServerError)
        }
        return
    }

    // 对于其他不支持的方法，返回405 Method Not Allowed
    http.Error(w, "Method Not Allowed", http.StatusMethodNotAllowed)
}

// fooHandler 同样需要修正以正确处理HEAD请求的错误
func fooHandler(w http.ResponseWriter, req *http.Request) {
    if req.Method == http.MethodHead {
        w.Header().Set("Content-Type", "text/plain; charset=utf-8")
        w.WriteHeader(http.StatusOK)
        return
    }

    if req.Method == http.MethodGet {
        _, err := w.Write([]byte("fooHandler"))
        if err != nil {
            log.Printf("Error writing response for GET request: %v", err)
            http.Error(w, "Internal Server Error", http.StatusInternalServerError)
        }
        return
    }

    http.Error(w, "Method Not Allowed", http.StatusMethodNotAllowed)
}


func main() {
    var err error
    templates, err = template.ParseGlob("templates/*.html")
    if err != nil {
        log.Fatalf("Loading template: %v", err) // 使用Fatalf而非Fatal，可以打印错误信息
    }
    http.HandleFunc("/", homeHandler)
    http.HandleFunc("/foo", fooHandler)
    log.Println("Server listening on :8080")
    log.Fatal(http.ListenAndServe(":8080", nil))
}

homeHandler