Abstract recvtty to a single function

[deitch]

Right now, to use a console socket to retrieve the file descriptor for the container's console when terminal: true, you need to figure out how to do it from reverse-engineering recvtty.go.

This PR creates a func in utils.go so a go client easily can do:

import 	"github.com/opencontainers/runc/libcontainer/utils"

	// Open a socket.
	c, err := utils.ConsoleSocket(path)

       // c is a Console. so it implements Reader, Writer, Closer
      c.Read() 
      c.Write() 
      c.Close()

It also changes recvtty.go to leverage it.

Open to suggestion of course.

[deitch]

Also discussed with @cyphar earlier.

[deitch]

@cyphar this also is ~2 months old, per our discussion back then. Please review?

[dqminh]

Not sure if its necessary to extract this out because this may encourage people to pull in the utils lib instead of other more friendly way such as using a runc-bindings.

For example, there is https://godoc.org/github.com/containerd/go-runc#Socket to interact with the socket.

[deitch]

@dqminh it has been 4+ months since I opened it, so I cannot recall all the details about what I was after at the time, except that I had come across several apps that had to do a chunk of work to interact with it, essentially replicating what was in recvtty.go.

For example, there is https://godoc.org/github.com/containerd/go-runc#Socket to interact with the socket.

What would the moral equivalent of the above be using go-runc? How would I connect/read/write/close using that?

[dqminh]

@deitch To use go-runc's Socket interface, it should roughly be:

socket, _ = runc.NewConsoleSocket(path)
console, _ = socket.ReceiveMaster()

console is https://godoc.org/github.com/containerd/console#Console which you can read/write/close/resize etc.

You can see some example of the usages in containerd https://github.com/containerd/containerd/blob/356b0d59646253bc040e8d6365418f20badd59eb/runtime/linux/proc/init.go#L213-L220

[deitch]

Oh that is nice. It essentially provides what I was trying to do here, then? If so, I think we can close this out.

[dqminh]

@deitch indeed, its quite similar to the proposed api here. I'm going to close this. Thanks for the help !