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

sshpeer: establish SSH connection before class instantiation We want to move the handshake to before peers are created so we can instantiate a different peer class depending on the results of the handshake. This necessitates moving the SSH process invocation to outside the peer class. As part of the code move, some variables were renamed for clarity. util.popen4() returns stdin, stdout, and stderr in their typical file descriptor order. However, stdin and stdout were being mapped to "pipeo" and "pipei" respectively. "o" for "stdin" and "i" for "stdout" is a bit confusing. Although it does make sense for "output" and "input" from the perspective of the client. But in the context of the new function, it makes sense to refer to these as their file descriptor names. In addition, the last use of self._path disappeared, so we stop setting that attribute and we can delete the redundant URL parsing necessary to set it. Differential Revision: https://phab.mercurial-scm.org/D2031

sshpeer: remove frivolous call to _cleanup() _validaterepo() is called once during __init__. _cleanup() no-ops if the self._pipe* attributes aren't set. These attributes are set during _validaterepo(). So the call to _cleanup() isn't necessary. But just to be on the safe side, we add an assertion. Differential Revision: https://phab.mercurial-scm.org/D2030

sshpeer: extract pipe cleanup logic to own function So it can be used outside of instantiated classes. This is needed to support pipe creation before __init__ is called. Differential Revision: https://phab.mercurial-scm.org/D2029

sshpeer: move ssh command and repo creation logic out of __init__ It was easier to move both of these at once because repository creation requires various variables and I didn't want to add tons of arguments and code to __init__ that will soon be deleted anyway. We do add an extra argument so we can proxy values to the _validaterepo() call. But this is minimally invasive. Some callers of self._abort() were converted to just raise. Like before, the _abort() call wasn't necessary because self._pipe* aren't populated this early in the object's lifetime. As part of this, various private attributes derived from the parsed URL are no longer used. So we no longer set them. Differential Revision: https://phab.mercurial-scm.org/D2028

sshpeer: move URL validation out of sshpeer.__init__ We will soon have another SSH peer class to support the new version of the SSH protocol. However, we won't know which peer class to instantiate until we perform a handshake on an active connection. This means that we need to move connection establishment and handshake code out of sshpeer.__init__. This commit starts the process of migrating peer creation code out of sshpeer.__init__ into instance(), which is the API for creating peers. The moved code no longer calls _abort(). _abort() runs _cleanup() and raises. _cleanup() only performs actions on self._pipe*. These objects aren't instantiated until we actually connect to the peer. So _abort() was not necessary in the old code. To keep the API the same, __init__() now makes a redundant call to util.url(). This will be fixed in subsequent commits. Differential Revision: https://phab.mercurial-scm.org/D2027

tests: add low-level SSH protocol tests We don't really have good low-level tests for the behavior of the SSH wire protocol. This commit attempts to establish some. The added tests consist of a mixture of starting a server with `hg serve --stdio` and sending bytes to it and using `hg debugpeer` to go through the official client code. Having insight into what raw bytes are exchanged as well as what the peer does is useful. We also introduce a test extension for modifying the behavior of the SSH server and peer. For example, we change the server to not recognize the "hello" command, simulating behavior of <0.9.1 servers. These tests are generally useful to have. But the impetus for creating them now is they will be needed for verifying behavior of old clients and servers when a new SSH protocol is introduced. Differential Revision: https://phab.mercurial-scm.org/D2026 # no-check-commit because of serve_forever()