wireproto: function for testing if wire protocol command is available Currently, we perform simple membership testing for whether a wire command is available. In the future, not all wire protocol commands will be available on all transports. For example, a legacy transport may not support newer commands. In preparation of this, teach the protocol handlers to call into a function to determine if a wire protocol command is available. That function currently does membership testing like before, so behavior should be identical. In the case of the HTTP server, behavior is a bit wonkier. "cmd" is used by both the wire protocol and hgweb. We do want the protocol handler to handle requests for all commands that look like wire protocol commands, even if they aren't available. Otherwise, the fallback to hgweb would only confuse automated clients and make it easier for hgweb to accidentally implement a "cmd" that is identical to wire protocol commands (since they aren't centrally registered). Differential Revision: https://phab.mercurial-scm.org/D1999

wireproto: define and use types for wire protocol commands Wire protocol commands have historically been declared as 2-tuples in wireproto.commands. There are some additional features I'd like to implement that require going beyond 2-tuples. But because the 2-tuple API (both destructuring assignment and direct assignment into the dict) is used throughout the code base and in 3rd party extensions, we can't do a trivial type change. This commit creates a new "commandentry" type to represent declared wire protocol commands. It implements __getitem__ and __iter__ so it can quack like a 2-tuple. The @wireprotocommand decorator now creates "commandentry" instances. We also create a "commanddict" type to represent the dictionary of declared wire protocol commands. It inherits from "dict" but provides a custom __setitem__ to coerce passed 2-tuples to "commandentry" instances. wireproto.commands is now an instance of this type. Various callers in core rely on the new functionality. And tests pass. So I'm reasonably confident things will "just work" in 3rd party extensions as well. Differential Revision: https://phab.mercurial-scm.org/D1998

wireproto: improve docstring for @wireprotocommand I'm about to add more arguments and want them to be documented. Plus, good documentation is nice to have. Differential Revision: https://phab.mercurial-scm.org/D1997

wireproto: remove unnecessary exception trapping The `try..except error.Abort` was added in 8474be4412ca back in 2012. The intent was to ensure a failing pushkey hook didn't crash the server. Since that changeset, repo.pushkey() and the hooks mechanism is now much more robust about trapping errors itself. As such, we no longer need this try..except block. So it has been removed. Differential Revision: https://phab.mercurial-scm.org/D1996

sshpeer: implement peer for version 2 of wire protocol Since the protocol is now negotiated before we construct a peer instance, we can return the negotiated protocol from the handshake function and instantiate an appropriate peer class for the protocol. Version 2 of the SSH protocol is currently identical to version 1 post handshake. So our sshv2peer class just inherits from sshv1peer for the time being. This will obviously change over time. Differential Revision: https://phab.mercurial-scm.org/D2063

sshpeer: rename sshpeer class to sshv1peer (API) With the introduction of version 2 of the SSH wire protocol, we will need a new peer class to speak that protocol because it will be too difficult to shoehorn a single class to speak two protocols. We rename sshpeer.sshpeer to sshpeer.sshv1peer to reflect the fact that there will be multiple versions of the peer depending on the negotiated protocol. .. api:: sshpeer.sshpeer renamed to sshpeer.sshv1peer. Differential Revision: https://phab.mercurial-scm.org/D2062

sshpeer: initial definition and implementation of new SSH protocol The existing SSH protocol has several design flaws. Future commits will elaborate on these flaws as new features are introduced to combat these flaws. For now, hopefully you can take me for my word that a ground up rewrite of the SSH protocol is needed. This commit lays the foundation for a new SSH protocol by defining a mechanism to upgrade the SSH transport channel away from the default (version 1) protocol to something modern (which we'll call "version 2" for now). This upgrade process is detailed in the internals documentation for the wire protocol. The gist of it is the client sends a request line preceding the "hello" command/line which basically says "I'm requesting an upgrade: here's what I support." If the server recognizes that line, it processes the upgrade request and the transport channel is switched to use the new version of the protocol. If not, it sends an empty response, which is how all Mercurial SSH servers from the beginning of time reacted to unknown commands. The upgrade request is effectively ignored and the client continues to use the existing version of the protocol as if nothing happened. The new version of the SSH protocol is completely identical to version 1 aside from the upgrade dance and the bytes that follow. The immediate bytes that follow the protocol switch are defined to be a length framed "capabilities: " line containing the remote's advertised capabilities. In reality, this looks very similar to what the "hello" response would look like. But it will evolve quickly. The methodology by which the protocol will evolve is important. I'm not going to introduce the new protocol all at once. That would likely lead to endless bike shedding and forward progress would stall. Instead, I intend to tricle out new features and diversions from the existing protocol in small, incremental changes. To support the gradual evolution of the protocol, the on-the-wire advertised protocol name contains an "exp" to denote "experimental" and a 4 digit field to capture the sub-version of the protocol. Whenever we make a BC change to the wire protocol, we can increment this version and lock out all older clients because it will appear as a completely different protocol version. This means we can incur as many breaking changes as we want. We don't have to commit to supporting any one feature or idea for a long period of time. We can even evolve the handshake mechanism, because that is defined as being an implementation detail of the negotiated protocol version! Hopefully this lowers the barrier to accepting changes to the protocol and for experimenting with "radical" ideas during its development. In core, sshpeer received most of the attention. We haven't even implemented the server bits for the new protocol in core yet. Instead, we add very primitive support to our test server, mainly just to exercise the added code paths in sshpeer. Differential Revision: https://phab.mercurial-scm.org/D2061 # no-check-commit because of required foo_bar naming

internals: refactor wire protocol documentation Upcoming work will introduce a new version of the HTTP and SSH transports. The differences will be significant enough to consider them new transports. So, we now attach a version number to each transport. In addition, having the handshake documented after the transport and in a single shared section made it harder to follow the flow of the connection. The handshake documentation is now moved to the protocol section it describes. We now have a generic section about the purpose of the handshake, which was rewritten significantly. Differential Revision: https://phab.mercurial-scm.org/D2060

revlog: rename 'self.checkinlinesize' into '_enforceinlinesize' The name change has two motivations: 1) The function has no external caller, so we move it to protected space. 2) the function does more than checking it also split the data if we have more data than 'inline' supports.

revlog: add a _datareadfp context manager for data access needs The helper handles: 1) is there a file handle already open that we shall just reuse, 2) is the revlog inlined or not. Using a context manager for all read access will help setting up file pointer caching in later changesets.