Read not buffered Server-Sent Event on client

Question

I need to read sse in my golang app, but instead of real-time, events return buffered. As I can see, this is because of standard golang transport. How can I fix this, without implementing my own transport? This code is inspired by cryptix solution:

resp, _ := http.Get(sseURL)
events := make(chan Event)
wg:= sync.WaitGroup{}
wg.Add(1)
go func() {
    event:= Event{}
    reader := bufio.NewReader(resp.Body)

    for {
        line, err := reader.ReadBytes('\n')

        if err != nil {
            log.Println(os.Stderr, "error during resp.Body read:%s\n", err)
            close(events)
        }

        json.Unmarshal(line,&event)

        events<-event
    }
    wg.Done()
}()

go func(){
    for ev:= range events {
        log.Println(ev)
    }
}()
wg.Wait()

There shouldn't be a delay because of the client's transport. Have you verified the timing by watching the data on the wire? (also, if you have newline delimited json, you can use json.Decoder directly) — JimB
Thx, @JimB. Yes, I verified that data is sent real time with curl. — hjortron
This method works correctly, provided the server flushed a complete json object and newline. (I'm seeing less then 1µs delay). You do need to fix problems like sending on a closed channel, and Println where you wanted Fprintf, but that shouldn't add any delay. Make sure the server is sending exactly the data you expect, when you expect it to. — JimB

hjortron hjortron · Accepted Answer · 2015-09-30T11:03:13

I figured out, data was buffered by nginx, because of transparent compression. So, to get data without delay we must disable compression like this:

client := &http.Client{}
transport := &http.Transport{}
transport.DisableCompression = true
client.Transport = transport
req, err := http.NewRequest("GET", essURL, nil)
if err != nil {
    log.Fatal(err);
}
resp, _ := client.Do(req)

reader := bufio.NewReader(resp.Body)
for {
    line,_:=reader.ReadSlice('\n')
    log.Println(string(line))       
}

Read not buffered Server-Sent Event on client

1 Answers