As per this original mailing list thread: Xpra Client in Listen Mode Enquiry
I think it would be better, safer and more useful to simply reverse the connection so that the server connects to the client: no need for passing the user+host to connect to using a new magic message to trigger yet another connection. (with the inherent security risks every time - and new connections cannot traverse NAT back to the server).
The "listen" mode should probably be a new subcommand, rather than overloading "attach", ie:
xpra listen tcp:host:port
I really don't see much point at all in the listen via SSH option: if you can SSH to the client, you might as well start the client command via SSH, which is also much safer.
Pointers:
- the Protocol is quite well abstracted and is used by both client and server, it does not care about which end initiates the connection
- the client (and its subclasses / superclasses) will need a bit of work to be able to start:
- without timing out
- create a tray icon (or not?) and handle menus that are not meant to be used yet
- create the socket in listen mode (same code as the server) - when the connection is received, it just goes through the normal startup sequence: send hello and everything else should fall into place
- the Server Base Class (and sub/super classes) will just need a new bit of code to create a new TCP connection and add it to its "sources" list. This should be available via "xpra control" and the dbus server so we can initiate new ones after the server is started if necessary. Think about timeouts, and retries..
- authentication / encryption: the client should authenticate the server if the password option is used - and maybe we should be doing this anyway in all cases? (which we sort of do when you have encryption)
@adarrab: if you can take a look at the comments above and maybe even play with the code a little bit, I should be able to take a look at this for the next release
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