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() {

---

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")
}

Answer 2

You want the net.Error interface. http://golang.org/pkg/net/#Error

if e,ok := err.(net.Error); ok && e.Timeout() {
    // This was a timeout
} else if err != nil {
    // This was an error, but not a timeout
}

Note that the type assertion err.(net.Error) will correctly handle the nil case and return false for the ok value if nil is returned as the error, short-circuiting the Timeout check.

Answer 3

You can simply pass an error to os.IsTimeout() and if it's a timeout returned by net/http then it will return true.

func IsTimeout(err error) bool

IsTimeout returns a boolean indicating whether the error is known to report that a timeout occurred.