Question

当我开始从HTTP服务器下载文件时，我想知道某种文件校验和（如SHA-256哈希或其他任何东西）。它可以作为HTTP响应标头之一传输。

我知道http etag是类似的东西，我想，但这是Golang，我是新手学习的，虽然我查看过一些文档，但我仍然无能为力。任何帮助，将不胜感激。这就是我到目前为止所做的：

package main

import (
    "flag"
    "fmt"
    "log"
    "net/http"
    "strconv"
)

const (
    crlf       = "\r\n"
    colonspace = ": "
)

func Checksum(h http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {


        func HandleFunc(pattern string, handler func(ResponseWriter, *Request))
    })
}

// Do not change this function.
func main() {
    var listenAddr = flag.String("http", ":8080", "address to listen on for HTTP")
    flag.Parse()

    http.Handle("/", Checksum(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        w.Header().Set("X-Foo", "bar")
        w.Header().Set("Content-Type", "text/plain")
        w.Header().Set("Date", "Sun, 08 May 2016 14:04:53 GMT")
        msg := "Curiosity is insubordination in its purest form.\n"
        w.Header().Set("Content-Length", strconv.Itoa(len(msg)))
        fmt.Fprintf(w, msg)
    })))

    log.Fatal(http.ListenAndServe(*listenAddr, nil))
}

Answer 1

围绕http.ResponseWriter编写一个包装器以捕获响应主体和状态：

type rwWrapper struct {
   http.ResponseWriter
   buf bytes.Buffer
   status int
}

func (w *rwWrapper) Write(p []byte) (int, error) {
   return rw.buf.Write(p)
}
func (w *rwWrapper) WriteHeader(status int) {
   rw.status = status
}

处理程序返回后，校验主体，设置标题，然后将主体写入底层响应编写器：

func Checksum(h http.Handler) http.Handler {
  return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
    ww := &rwWrapper{ResponseWriter: w, status:200}
    h.ServeHttp(ww, r)
    // compute checksum of ww.buf.Bytes() here
    w.Header().Set("nameOfHeader", checksum)
    w.WriteHeader(ww.status)
    w.Write(ww.buf.Bytes())
  })
}

如何正确添加校验和标题？

1 个答案: