Specifically check for timeout error

Question

I use the following to check for timeouts when calling a webservice, but I would like to check specifically if there is a timeout error returned. How do I do that :S

Answer 1

As of go1.6, all errors from timeouts should conform to net.Error with Timeout() set properly. All you need to check for is:

if err, ok := err.(net.Error); ok && err.Timeout() {

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In older versions, checking for timeout through the http package was more difficult.

• You can get a *net.OpError with Timeout() if you hit a Deadline set on the underlying connection.
• You can get a tlsHandshakeTimeoutError (which is obviously not exported) that implements the net.Error interface.
• You can get a url.Error, if there was a problem within the url package (timeout during initial connection)
• You can get an error with "use of closed network connection" if you hit a timeout set with http.Client.Timeout[go1.3+] (which calls Transport.CancelRequest). As of go1.5, this will have the Timeout property set correctly.

You could check for a net.Error with a type switch:

switch err := err.(type) {
case net.Error:
    if err.Timeout() {
        fmt.Println("This was a net.Error with a Timeout")
    }
case *url.Error:
    fmt.Println("This is a *url.Error")
    if err, ok := err.Err.(net.Error); ok && err.Timeout() {
        fmt.Println("and it was because of a timeout")
    }
}

With go < 1.5 you will need to check the error string for an http.Client timeout:

if err != nil && strings.Contains(err.Error(), "use of closed network connection") {
    fmt.Println("Could be from a Transport.CancelRequest")
}