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PONot buffered http.ResponseWritter in Golang
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  1. PONot buffered http.ResponseWritter in Golang
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    copied!<p>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) :</p> <pre><code>func handle(res http.ResponseWriter, req *http.Request) { fmt.Fprintf(res, "sending first line of data") sleep(10) //not real code fmt.Fprintf(res, "sending second line of data") } </code></pre> <p>From the client point of view, the two lines will be sent at the same time. Any suggestions are appreciated :)</p> <h3>Edit after @dystroy answer</h3> <p>It's possible to flush after each write I personally make, but in my use case it's not enough:</p> <pre><code>cmd := exec.Command("a long command that outputs lots of lines") cmd.Stdout = res //where res is a http.ResponseWritter cmd.Stderr = res err := cmd.Run() </code></pre> <p>I want the output of my <code>cmd</code> to be flushed as well. Anyway to "autoflush" the ResponseWritter ?</p> <h3>Solution</h3> <p>I found help on golang's mailing list. There is 2 way to achieve this: using <a href="http://golang.org/pkg/net/http/#example_Hijacker" rel="noreferrer">hijacker</a> 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 :</p> <pre><code>pipeReader, pipeWriter := io.Pipe() cmd.Stdout = pipeWriter cmd.Stderr = pipeWriter go 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 buffer for i := 0; i &lt; n; i++ { buffer[i] = 0 } } } </code></pre> <h3>Last update</h3> <p>Even nicer: <a href="http://play.golang.org/p/PpbPyXbtEs" rel="noreferrer">http://play.golang.org/p/PpbPyXbtEs</a></p>
 

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