net: add context-aware Dialer methods DialTCP, DialUDP, DialIP, DialUnix

[nkeonkeo]

The accepted proposal is to add new methods to new.Dialer: #49097 (comment)

--

Such like given below:

func DialTCP(network string, laddr, raddr *TCPAddr) (*TCPConn, error) {
	return DialTCPContext(context.Background(), network, laddr, raddr)
}
func DialTCPContext(ctx context.Context, network string, laddr, raddr *TCPAddr) (*TCPConn, error) {
	switch network {
	case "tcp", "tcp4", "tcp6":
	default:
		return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: UnknownNetworkError(network)}
	}
	if raddr == nil {
		return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: nil, Err: errMissingAddress}
	}
	sd := &sysDialer{network: network, address: raddr.String()}
	c, err := sd.dialTCP(ctx, laddr, raddr)
	if err != nil {
		return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: err}
	}
	return c, nil
}

func DialUDP(network string, laddr, raddr *UDPAddr) (*UDPConn, error) {
	return DialUDPContext(context.Background(), network, laddr, raddr)
}
func DialUDPContext(ctx context.Context, network string, laddr, raddr *UDPAddr) (*UDPConn, error) {
	switch network {
	case "udp", "udp4", "udp6":
	default:
		return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: UnknownNetworkError(network)}
	}
	if raddr == nil {
		return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: nil, Err: errMissingAddress}
	}
	sd := &sysDialer{network: network, address: raddr.String()}
	c, err := sd.dialUDP(ctx, laddr, raddr)
	if err != nil {
		return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: err}
	}
	return c, nil
}

func DialIP(network string, laddr, raddr *IPAddr) (*IPConn, error) {
	return DialIPContext(context.Background(), network, laddr, raddr)
}
func DialIPContext(ctx context.Context, network string, laddr, raddr *IPAddr) (*IPConn, error) {
	if raddr == nil {
		return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: nil, Err: errMissingAddress}
	}
	sd := &sysDialer{network: network, address: raddr.String()}
	c, err := sd.dialIP(ctx, laddr, raddr)
	if err != nil {
		return nil, &OpError{Op: "dial", Net: network, Source: laddr.opAddr(), Addr: raddr.opAddr(), Err: err}
	}
	return c, nil
}

[cherrymui]

Could you give more information about the reason you want to add them and how they will be used? Thanks.

[nkeonkeo]

such as:

ctx, cancel := context.WithTimeout(context.Background(), 30000*time.Millisecond)
defer cancel()
taddr := &net.TCPAddr{}
c, err := net.DialTCPContext(ctx, "tcp", nil, taddr)
...

It can realize the timeout processing of DialTCP.

DialUDP and DialIP are similary like this.

[nkeonkeo]

Hi @nkeonkeo - Isn't that what https://pkg.go.dev/net#Dialer.DialContext does? What would your proposal allow that isn't possible as of today? Thanks!

Dialer.DialContext will resolve the address each time, it may cause errors like:

lookup xxxx.com on 223.x.x.x:53: read udp 180.x.x.x:7792->223.x.x.x:53: i/o timeout

Use net.DialTCP to dial net.TCPAddr can avoid such problems.

And I hope I can use net.DialTCP with context to deal with timeout problems.

[rsc]

We could add these to net.Dialer, which is what we are using instead of adding new context-aware versions of all the top-level functions. The specific methods we'd need to add would be:

DialTCP(context.Context, string, *TCPAddr, *TCPAddr) (*TCPConn, error)
DialUDP
DialIP
DialUnix

Note that all take contexts but don't say "Context" in the name.

Thoughts?

[rsc]

This proposal has been added to the active column of the proposals project
and will now be reviewed at the weekly proposal review meetings.
— rsc for the proposal review group

[rsc]

Any objections to #49097 (comment) ?