x/crypto/ssh: provide Client.DialContext method

[ydnar]

Similar to #17759, it would be useful for ssh.Client to provide a DialContext method next to its Dial method. We use SSH tunnels for connecting to domain registries that use IP allowlists.

Note: per some confusion in the comments below, this does not refer to the top-level Dial func that opens an SSH connection. This proposal specifically refers to adding a (*ssh.Client).DialContext method that opens a TCP/IP tunnel, (returning a net.Conn), useful for proxying connections across an SSH connection.

An implementation can be found here: CL 504735

Original context from 2017:

We’ve been progressively consolidating our timeout and deadline code to use context.Context throughout, implementing workarounds for dialers in APIs that lack Context support.

[hanwen]

what exactly do you want controlled with deadline? The underlying TCP deadline? Or were you thinking of a SSH-level support for deadlines?

[glycerine]

My use case is not leaking goroutines. When my goroutine does a blocking read on an ssh.Channel it is always blocked, I can't signal that goroutine to shutdown. The usual way with a net.Conn is to set read and write deadlines, then poll for errors. So I was thinking of SSH channel level support for (both read and write) deadlines.

[glycerine]

My experimental fork https://github.com/glycerine/xcryptossh provides Dial with context and idle timers for Read/Write unblocking.

[denisvmedia]

Actually it's doable with user code without forking/modifying the lib.

func Dial(ctx context.Context, network, addr string, config *ssh.ClientConfig) (*ssh.Client, error) {
	d := net.Dialer{Timeout: config.Timeout}
	conn, err := d.DialContext(ctx, network, addr)
	if err != nil {
		return nil, err
	}
	c, chans, reqs, err := ssh.NewClientConn(conn, addr, config)
	if err != nil {
		return nil, err
	}
	return ssh.NewClient(c, chans, reqs), nil
}

[prochac]

Actually it's doable with user code without forking/modifying the lib.

func Dial(ctx context.Context, network, addr string, config *ssh.ClientConfig) (*ssh.Client, error) {
	d := net.Dialer{Timeout: config.Timeout}
	conn, err := d.DialContext(ctx, network, addr)
	if err != nil {
		return nil, err
	}
	c, chans, reqs, err := ssh.NewClientConn(conn, addr, config)
	if err != nil {
		return nil, err
	}
	return ssh.NewClient(c, chans, reqs), nil
}

This should be part of library as ssh.DialWithContext or similar.

[gopherbot]

Change https://go.dev/cl/504735 mentions this issue: ssh: add (*Client).DialContext method