Send a chunked HTTP response from a Go server

Question

I am creating a test Go HTTP server, and I am sending a response header of Transfer-Encoding: chunked so I can continually send new data as I retrieve it. This server should write a chunk to this server every one second. The client should be able to receive them on demand.

Unfortunately, the client(curl in this case), receives all of the chunks at the end of the duration, 5 seconds, rather than receiving one chunk every one second. Also, Go seems to send the Content-Length for me. I want to send the Content-Length at the end, and I want the the header's value to be 0.

Here is the server code:

package main  import (     "fmt"     "io"     "log"     "net/http"     "time" )  func main() {     http.HandleFunc("/test", HandlePost);     log.Fatal(http.ListenAndServe(":8080", nil)) }  func HandlePost(w http.ResponseWriter, r *http.Request) {     w.Header().Set("Connection", "Keep-Alive")     w.Header().Set("Transfer-Encoding", "chunked")     w.Header().Set("X-Content-Type-Options", "nosniff")      ticker := time.NewTicker(time.Second)     go func() {         for t := range ticker.C {             io.WriteString(w, "Chunk")             fmt.Println("Tick at", t)         }     }()     time.Sleep(time.Second * 5)     ticker.Stop()     fmt.Println("Finished: should return Content-Length: 0 here")     w.Header().Set("Content-Length", "0") } 

Answer 1

The trick appears to be that you simply need to call Flusher.Flush() after each chunk is written. Note also that the "Transfer-Encoding" header will be handled by the writer implicitly, so no need to set it.

func main() {   http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {     flusher, ok := w.(http.Flusher)     if !ok {       panic("expected http.ResponseWriter to be an http.Flusher")     }     w.Header().Set("X-Content-Type-Options", "nosniff")     for i := 1; i <= 10; i++ {       fmt.Fprintf(w, "Chunk #%d\n", i)       flusher.Flush() // Trigger "chunked" encoding and send a chunk...       time.Sleep(500 * time.Millisecond)     }   })    log.Print("Listening on localhost:8080")   log.Fatal(http.ListenAndServe(":8080", nil)) } 

You can verify by using telnet:

$ telnet localhost 8080 Trying ::1... Connected to localhost. Escape character is '^]'. GET / HTTP/1.1  HTTP/1.1 200 OK Date: Tue, 02 Jun 2015 18:16:38 GMT Content-Type: text/plain; charset=utf-8 Transfer-Encoding: chunked  9 Chunk #1  9 Chunk #2  ... 

You might need to do some research to verify that http.ResponseWriters support concurrent access for use by multiple goroutines.

Also, see this question for more information about the "X-Content-Type-Options" header.