如何冲洗 Go 中的 tcp 插座？

Question

How do I flush a tcp socket in Go?

I'm sending messages one at a time down a socket, indicating progress to a client, but the messages get bunched up and all sent at the same time. I can't see a flush function anywhere.

The messages are sent a couple of seconds apart, they're <100bytes each, and I'm sending them to localhost. By flushing, I mean I want to clear any buffers stopping them from getting out on the wire; they're clearly being buffered somewhere in this case.

If Go doesn't expose this, can I reach down into the depths of hell to flush the underlying buffer/socket myself?

Answer 1

As @JimB mentioned you can't Flush() a net.Conn , so if your data-flow is stuttering, it is being buffered elsewhere.

If you - or an intermediate package in your data-flow - is using for example bufio :

w := bufio.NewWriter(conn)

if _, err := w.WriteString(msg); err != nil {
   return err
}

w.Flush()

while the conn cannot be flushed, the bufio.Writer can.

If, however, your connection is given to you as a pure io.Writer type (ie Write() method only - no Flush() ) you may try a runtime conversion/check to see if it is "flushable":

// var connWriter io.Writer

type Flusher interface {
    // Flush sends any buffered data to the client.
    Flush() error
}

flushable, ok := connWriter.(Flusher) // runtime interface/type check

if !ok {
    log.Println("flushing not supported")
    return
}

flushable.Flush()

Answer 2

Argh. It was being buffered client-side in a bash pipe. Removed the | ts -s '%.T' | ts -s '%.T' which I had to try to measure the time elapsed between responses, and now it works.

brew install expect and unbuffer my-command -a -b --foo | ts -s '%.T' unbuffer my-command -a -b --foo | ts -s '%.T' to work around this on mac, linux suggestions here https://unix.stackexchange.com/questions/25372/turn-off-buffering-in-pipe

Leaving the question open since I got a good answer on the question I posed, which might help others.