Filter out broken pipe errors

Question

I'm getting an error returned from an io.Copy call, to which I've passed a socket (TCPConn) as the destination. It's expected that the remote host will simply drop the connection when they've had enough, and I'm not receiving anything from them.

When the drop occurs, I get this error:

write tcp 192.168.26.5:21277: broken pipe

But all I have is an error interface. How can I differentiate broken pipe errors from other kinds of error?

if err.Errno == EPIPE...

Answer 1

The broken pipe error is defined in the syscall package. You can use the equality operator to compare the error to the one in syscall. Check http://golang.org/pkg/syscall/#constants for a complete list of syscall errors. Search "EPIPE" on the page and you will find all the defined errors grouped together.

if err == syscall.EPIPE {
    /* ignore */
}

If you wish to get the actual errno number (although it is pretty useless) you can use a type assertion:

if e, ok := err.(syscall.Errno); ok {
    errno = uintptr(e)
}

Answer 2

As of go 1.13, you can use errors.Is instead of type assertions.

if errors.Is(err, syscall.EPIPE) {
  // broken pipe
}

Answer 3

Having all but an error interface is enough to perform a type assertion or a type switch to reveal the concrete type held by the interface.