设置响应头的Content-Type以及设置自定义内容

package main

import (
   "encoding/json"
   "net/http"
)

func main() {
   // 演示地址：http://localhost:8080/demo.html
   http.HandleFunc("/demo.html", func(writer http.ResponseWriter, request *http.Request) {
      // 数据
      data := map[string]any{}
      data["errcode"] = 40029
      data["errmsg"] = "invalid code"

      // 设置响应头的Content-Type为application/json，否则默认为text/plain
      writer.Header().Set("Content-Type", "application/json; charset=utf-8")

      // 设置自定义内容
      writer.Header().Set("X-AspNetMvc-Version", "4.0")
      writer.Header().Set("X-AspNet-Version", "4.0.30319")
      writer.Header().Set("X-Powered-By", "ASP.NET")

      // map转为json
      jsonByte, _ := json.Marshal(data)

      // 在页面输出json字符串
      _, _ = writer.Write(jsonByte)
   })

   // 启动HTTP服务器
   err := http.ListenAndServe(":8080", nil)
   if err != nil {
      panic("启动HTTP服务器失败")
   }
}