Adding a tunnel class to connect to a remote host via HTTP Connect

[NalinG]

Usually, you cannot initiate an SSH connection via a non-standard transport( here: HTTP Connect). This change adds a Protocol class which allows you to ssl to a proxy host and then send an HTTP Connect request to the target host. After that, you can setup an SSH connection over the tunnel.

I haven't added any tests yet as I wanted to check in with the maintainer about the method and plausibility of adding this to the asyncssh lib.

[ronf]

Thank you for the submission, but I'm not sure this code really belongs in AsyncSSH itself. There are MANY different ways to tunnel traffic -- SOCKS, Proxy Protocol, and HTTP CONNECT all come to mind, and that's far from a complete list. Rather than growing the AsyncSSH code to include all of these and more, I tried to provide a general mechanism that would allow a caller to implement tunneling code (much like you did here) in their own application, with AsyncSSH then using that object in place of a standard TCP socket object. I also recently provided a way to allow the tunneling code to run in a separate process, for cases where someone wanted to tunnel using code not written in Python.

You can find an example of creating a SOCKS tunnel and some other related discussion of the more generic ProxyCommand support in #376.

[NalinG]

Makes sense, thank you for the reply. We can probably close the PR.