sshpeer: document the handshake mechanism The mechanism by which SSH peers establish connections with remotes is wonky and requires a bit of code archeology to understand. While it is already documented in `hg help internals.wireproto`, it helps to have documentation in the code as well. Differential Revision: https://phab.mercurial-scm.org/D2035

sshpeer: move handshake outside of sshpeer With the handshake now performed before a peer class is instantiated, we can now instantiate a different peer class depending on the results of the handshake. Our test extension had to change to cope with the new API. Because we now issue the command via raw I/O calls and don't call _callstream(), we no longer have to register the fake command. (_callstream() uses the command registration to see what args to send). Differential Revision: https://phab.mercurial-scm.org/D2034

sshpeer: inline I/O into _validaterepo() We want to move the handshake code out of the peer class so the peer factory function can perform the handshake and instantiate a proper class depending on the results. To make that refactor easier to read, we first inline I/O functionality into _validaterepo(). Test output for low-level protocol tests didn't change, thus hopefully demonstrating that this refactor didn't change any material behavior. Because we no longer call _callstream(), our test extension for monkeypatching the peer had to change its hook point. Differential Revision: https://phab.mercurial-scm.org/D2033

sshpeer: clean up API for sshpeer.__init__ (API) Our refactoring left the state of sshpeer.__init__ in a poor state. "create" was no longer used. Process/pipe arguments were passed poorly. "name" was really a URL. This commit cleans all that up. .. api:: sshpeer.sshpeer.__init__ now receives arguments describing an existing connection instead of creating a connection itself. Differential Revision: https://phab.mercurial-scm.org/D2032