2015-12-03 10:19
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I have a function which returns the Reader end of an io.Pipe and kicks off a go-routine which writes data to the Writer end of it, and then closes the pipe.

func GetPipeReader() io.ReadCloser {
    r, w := io.Pipe()
    go func() {
        _, err := io.CopyN(w, SomeReaderOfSize(N), N)
    return r

func main() {
    var buf bytes.Buffer
    io.Copy(&buf, GetPipeReader())
    println("got", buf.Len(), "bytes")


This seems to always work in my testing, in that I get all the data I wrote. But the API docs are a bit worrying to me:

func Pipe() (*PipeReader, *PipeWriter)

Pipe creates a synchronous in-memory pipe. [...] Reads on one end are matched with writes on the other, [...] there is no internal buffering.

func (w *PipeWriter) CloseWithError(err error) error

CloseWithError closes the writer; subsequent reads from the read half of the pipe will return no bytes and the error err, or EOF if err is nil.

What I want to know is, what are the possible race conditions here? Is is plausible that my go-routine will write a bunch of data and then close the pipe before I can read it all?

Do I need to use a channel for some signalling on when to close? What can go wrong, basically.

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