How to set timeout while doing a net.DialTCP in golang?

Question

As net.DialTCP seems like the only way to get net.TCPConn, I'm not sure how to set timeouts while doing the DialTCP. https://golang.org/pkg/net/#DialTCP

func connectAddress(addr *net.TCPAddr, wg *sync.WaitGroup) error {
    start := time.Now()
    conn, err := net.DialTCP("tcp", nil, addr)
    if err != nil {
        log.Printf("Dial failed for address: %s, err: %s", addr.String(), err.Error())
        return err
    }
    elasped := time.Since(start)
    log.Printf("Connected to address: %s in %dms", addr.String(), elasped.Nanoseconds()/1000000)
    conn.Close()
    wg.Done()
    return nil
}

score 31 · Accepted Answer · 2017-11-05 03:52:28Z

31

Use net.Dialer with either the Timeout or Deadline fields set.

d := net.Dialer{Timeout: timeout}
conn, err := d.Dial("tcp", addr)
if err != nil {
   // handle error
}

A variation is to call Dialer.DialContext with a deadline or timeout applied to the context.

Type assert to *net.TCPConn if you specifically need that type instead of a net.Conn:

tcpConn, ok := conn.(*net.TCPConn)

edited Nov 5, 2017 at 3:52

answered Nov 5, 2017 at 3:31

user5728991

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4 Comments

Berkant İpek Over a year ago

Is Timeout field counted as a counterpart for curl's --connect-timeout? Or is that like --max-time?

cpr4t3s Over a year ago

As a side note, net.Dial() will try to resolve the address while net.DialTCP() does not. This can be a performance concern or not, depending on you use case

Oleg Over a year ago

The problem is that net.DialTCP is not completly the same as net.Dialer{}.Dial the first one has localAddr parameter but general dialer not.

user5728991 Over a year ago

@Oleg Use the dialer's LocalAddr field to specify the local address.

jeanluc · Accepted Answer · 2018-03-31 23:17:26Z

11

One can use net.DialTimeout:

func DialTimeout(network, address string, timeout time.Duration) (Conn, error)
    DialTimeout acts like Dial but takes a timeout.

    The timeout includes name resolution, if required. When using TCP, and the
    host in the address parameter resolves to multiple IP addresses, the timeout
    is spread over each consecutive dial, such that each is given an appropriate
    fraction of the time to connect.

    See func Dial for a description of the network and address parameters.

answered Mar 31, 2018 at 23:17

jeanluc

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