Source: dial.go in package golang.org/x/net/proxy


package proxy

import (
	"context"
	"net"
)

A ContextDialer dials using a context.

type ContextDialer interface {
	DialContext(ctx context.Context, network, address string) (net.Conn, error)
}

Dial works like DialContext on net.Dialer but using a dialer returned by FromEnvironment. The passed ctx is only used for returning the Conn, not the lifetime of the Conn. Custom dialers (registered via RegisterDialerType) that do not implement ContextDialer can leak a goroutine for as long as it takes the underlying Dialer implementation to timeout. A Conn returned from a successful Dial after the context has been cancelled will be immediately closed.

func Dial(ctx context.Context, network, address string) (net.Conn, error) {
	d := FromEnvironment()
	if xd, ok := d.(ContextDialer); ok {
		return xd.DialContext(ctx, network, address)
	}
	return dialContext(ctx, d, network, address)
}

WARNING: this can leak a goroutine for as long as the underlying Dialer implementation takes to timeout A Conn returned from a successful Dial after the context has been cancelled will be immediately closed.

func dialContext(ctx context.Context, d Dialer, network, address string) (net.Conn, error) {
	var (
		conn net.Conn
		done = make(chan struct{}, 1)
		err  error
	)
	go func() {
		conn, err = d.Dial(network, address)
		close(done)
		if conn != nil && ctx.Err() != nil {
			conn.Close()
		}
	}()
	select {
	case <-ctx.Done():
		err = ctx.Err()
	case <-done:
	}
	return conn, err