英文:
Not buffered http.ResponseWritter in Golang
问题
我正在使用Go编写一个简单的Web应用程序，并希望将响应流式传输到客户端（即不缓冲并在请求完全处理后以块的形式发送）：
func handle(res http.ResponseWriter, req *http.Request) {fmt.Fprintf(res, "sending first line of data")sleep(10) //not real codefmt.Fprintf(res, "sending second line of data")}
从客户端的角度来看，这两行将同时发送。欢迎任何建议 
###在@dystroy回答后编辑
我可以在我个人编写的每个写入之后进行刷新，但在我的用例中这还不够：
cmd := exec.Command("a long command that outputs lots of lines")cmd.Stdout = res //where res is a http.ResponseWrittercmd.Stderr = reserr := cmd.Run()
我希望我的cmd的输出也能被刷新。有没有办法“自动刷新”ResponseWriter？
###解决方案
我在golang的邮件列表上找到了帮助。有两种方法可以实现这一点：使用hijacker来接管HTTP的底层TCP连接，或者将命令的stdout和stderr管道化到一个go例程中进行写入和刷新：
pipeReader, pipeWriter := io.Pipe()cmd.Stdout = pipeWritercmd.Stderr = pipeWritergo writeCmdOutput(res, pipeReader)err := cmd.Run()pipeWriter.Close()//---------------------func writeCmdOutput(res http.ResponseWriter, pipeReader *io.PipeReader) {buffer := make([]byte, BUF_LEN)for {n, err := pipeReader.Read(buffer)if err != nil {pipeReader.Close()break}data := buffer[0:n]res.Write(data)if f, ok := res.(http.Flusher); ok {f.Flush()}//reset bufferfor i := 0; i < n; i++ {buffer[i] = 0}}}
###最后更新
更好的方法：http://play.golang.org/p/PpbPyXbtEs
英文:
I'm writing a simple web app in Go and I want my responses to be streamed to the client (i.e. not buffered and sent in blocks once the request is fully processed) :
func handle(res http.ResponseWriter, req *http.Request) {fmt.Fprintf(res, "sending first line of data")sleep(10) //not real codefmt.Fprintf(res, "sending second line of data")}
From the client point of view, the two lines will be sent at the same time. Any suggestions are appreciated
###Edit after @dystroy answer
It's possible to flush after each write I personally make, but in my use case it's not enough:
cmd := exec.Command("a long command that outputs lots of lines")cmd.Stdout = res //where res is a http.ResponseWrittercmd.Stderr = reserr := cmd.Run()
I want the output of my cmd to be flushed as well. Anyway to "autoflush" the ResponseWritter ?
###Solution
I found help on golang's mailing list. There is 2 way to achieve this: using hijacker that allow to take over the underlying TCP connection of HTTP, or piping the stdout and stderr of the command in a go routine that will write and flush :
pipeReader, pipeWriter := io.Pipe()cmd.Stdout = pipeWritercmd.Stderr = pipeWritergo writeCmdOutput(res, pipeReader)err := cmd.Run()pipeWriter.Close()//---------------------func writeCmdOutput(res http.ResponseWriter, pipeReader *io.PipeReader) {buffer := make([]byte, BUF_LEN)for {n, err := pipeReader.Read(buffer)if err != nil {pipeReader.Close()break}data := buffer[0:n]res.Write(data)if f, ok := res.(http.Flusher); ok {f.Flush()}//reset bufferfor i := 0; i < n; i++ {buffer[i] = 0}}}
###Last update
Even nicer: http://play.golang.org/p/PpbPyXbtEs
答案1
得分: 38
根据文档的暗示，一些ResponseWriter可能实现了Flusher接口。
这意味着你可以这样做：
func handle(res http.ResponseWriter, req *http.Request) {fmt.Fprintf(res, "发送第一行数据")if f, ok := res.(http.Flusher); ok {f.Flush()} else {log.Println("糟糕，无法刷新");}sleep(10) //不是真实的代码fmt.Fprintf(res, "发送第二行数据")}
请注意，在网络或客户端端的许多其他位置可能会发生缓冲。
英文:
As implied in the documentation, some ResponseWriter may implement the Flusher interface.
This means you can do something like this :
func handle(res http.ResponseWriter, req *http.Request) {fmt.Fprintf(res, "sending first line of data")if f, ok := res.(http.Flusher); ok {f.Flush()} else {log.Println("Damn, no flush");}sleep(10) //not real codefmt.Fprintf(res, "sending second line of data")}
Be careful that buffering can occur in many other places in the network or client side.
答案2
得分: 1
抱歉，如果我误解了你的问题，但是下面的代码是否能满足你的需求？
package mainimport ("bytes""fmt""net/http")func handler(w http.ResponseWriter, r *http.Request) {body := make([]byte, int(r.ContentLength))b := bytes.NewBuffer(body)if _, err := b.ReadFrom(r.Body); err != nil {fmt.Fprintf(w, "%s", err)}if _, err := b.WriteTo(w); err != nil {fmt.Fprintf(w, "%s", err)}}func main() {http.HandleFunc("/", handler)if err := http.ListenAndServe(":8080", nil); err != nil {panic(err)}}
$ curl --data "param1=value1¶m2=value2" http://localhost:8080
返回：
param1=value1¶m2=value2
你可以在body中添加任何你想要的数据，或者从其他地方读取更多的字节到缓冲区中，然后再将其全部写出。
英文:
Sorry if I've misunderstood your question, but would something like the below do the trick?
package mainimport ("bytes""fmt""net/http")func handler(w http.ResponseWriter, r *http.Request) {body := make([]byte, int(r.ContentLength))b := bytes.NewBuffer(body)if _, err := b.ReadFrom(r.Body); err != nil {fmt.Fprintf(w, "%s", err)}if _, err := b.WriteTo(w); err != nil {fmt.Fprintf(w, "%s", err)}}func main() {http.HandleFunc("/", handler)if err := http.ListenAndServe(":8080", nil); err != nil {panic(err)}}
$ curl --data "param1=value1&param2=value2" http://localhost:8080
returns:
>>param1=value1¶m2=value2
You could always append whatever data you wanted to body, or read more bytes into the buffer from elsewhere before writing it all out again.
答案3
得分: 1
在Go 1.20或更高版本中，使用ResponseController.Flush来刷新响应。
func handle(res http.ResponseWriter, req *http.Request) {rc := http.NewResponseController(res)fmt.Fprintf(res, "发送第一行数据")if err := rc.Flush(); err != nil {// 以某种方式处理错误。log.Println("哎呀，没有刷新")}sleep(10) //不是真正的代码fmt.Fprintf(res, "发送第二行数据")}
英文:
In Go 1.20 or later, use ResponseController.Flush to flush the response.
func handle(res http.ResponseWriter, req *http.Request) {rc := http.NewResponseController(res)fmt.Fprintf(res, "sending first line of data")if err := rc.Flush(); err != nil {// Handle error in some way.log.Println("Oops, no flush")}sleep(10) //not real codefmt.Fprintf(res, "sending second line of data")}
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