proposal: net: add context/timeout/deadline for Resolve*

[LionNatsu]

To resolve an address, it needs a communication between local host and name server. When the routes changed or something else makes the address being unreachable, or there is loss of UDP datagram, there will be a high delay (maybe the goroutine will never wake up again).

What I can do now is use net.DialContext() with a deadline or net.Dialer. But when I want to only resolve the host name/domain, net.Resolve*Addr() or net.Lookup*() never timeout.

I read source code of net and I found net.Resolve*Addr() does have some code about context:

/src/net/tcpsock.go:64

    56	func ResolveTCPAddr(net, addr string) (*TCPAddr, error) {
    57		switch net {
    58		case "tcp", "tcp4", "tcp6":
    59		case "": // a hint wildcard for Go 1.0 undocumented behavior
    60			net = "tcp"
    61		default:
    62			return nil, UnknownNetworkError(net)
    63		}
    64		addrs, err := internetAddrList(context.Background(), net, addr)
    65		if err != nil {
    66			return nil, err
    67		}
    68		return addrs.first(isIPv4).(*TCPAddr), nil
    69	}

Can we export the context argument?

Maybe add something like net.ResolveTCPAddrContext() ? or an interface called, maybe, Resolver?

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Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

1.7.4

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH=""
GORACE=""
GOROOT="/usr/lib/go"
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build628929889=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"

[LionNatsu]

Possibly dup of #6340 (6 Sep 2013). Should I leave this issue open?

[LionNatsu]

Okay... there is net.Resolver in 1.8 . Closing.