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()

debugcommands: introduce debugpeer command `hg debugpeer <path>` will establish a connection to a peer repository and print information about it. If you add --debug, it will log low-level protocol request info. This will be useful for upcoming tests around protocol handshaking. Differential Revision: https://phab.mercurial-scm.org/D2025

sshpeer: make "instance" a function The API is that peer modules must provide an "instance" symbol that is callable to return a peer. Making "instance" a function instead of an alias to "sshpeer" makes it easier to monkeypatch the "sshpeer" type. It will also make it possible to turn instance() into a factory function of sorts that returns different types based on connection properties. Differential Revision: https://phab.mercurial-scm.org/D2024

lfs: deduplicate oids in the transfer Apparently, we can't rely on the server to deduplicate for us. Sadly, the pointer object isn't hashable, so it can't be reduced by converting it to a set. In order to be hashable, it needs to be immutable. I had a bunch of code to change it to composition and forward the readonly dict methods to a member dict. But the pointer is updated via __setitem__() when creating the pointer file. So it didn't see worth adding all of that code to the class.

cat: call the storage prefetch hook It's not important to call in the case of a single file, but maybe it's better to do so for consistency.

archive: call the storage prefetch hook

lfs: prefetch lfs blobs during revert The revert command oddly prints out what it will do before requesting the files to be prefetched. But the 'need to transfer' line indicates the blobs are being grouped.

cmdutil: convert _revertprefetch() to a generic stored file hook (API) This will be used by LFS to fetch required files in a group for multiple commands, prior to being accessed. That avoids the one-at-a-time fetch when the filelog wrapper goes to access it, and it is missing locally (which costs two round trips to the server.) The core command list that needs this is probably at least: - annotate - archive (which is also used by extdiff) - cat - diff - export - grep - verify (sadly) - anything that has the '{data}' template There are no core users of the revert prefetch hook, and never have been since it was introduced in 45e02cfad4bd for remotefilelog. Thanks to Yuya for figuring out a way to reliably trigger the deprecated warning. Unfortunately, it wanted to blame the caller of revert. Passing along an adjusted stack level seemed the least bad choice (although it still blames a core function). One thing to note is that the store lock isn't being held when this is called. I'm not at all familiar with remotefilelog or its locking requirements, so this may not be a big deal. Currently, LFS doesn't hold a lock when downloading files. Even though largefiles doesn't either, I'm starting to think it should, and maybe the .hg/store/lock isn't good enough to cover the globally shared cache. .. api:: The cmdutil._revertprefetch() hook point for prefetching stored files has been replaced by the command agnostic cmdutil._prefetchfiles(). The new function takes a list of files, instead of a list of lists of files.

lfs: prefetch lfs blobs when applying merge updates In addition to merge, this method ultimately gets called by many commands: - backout - bisect - clone - fetch - graft - import (without --bypass) - pull -u - rebase - strip - share - transplant - unbundle - update Additionally, it's also called by histedit, shelve, unshelve, and split, but it seems that the related blobs should always be available locally for these. For `hg update`, it happens after the normal argument checking and pre-update hook processing, and remote corruption is detected prior to manipulating the working directory. Other commands could use this treatment (archive, cat, revert, etc), but this covers so many of the frequently used bulk commands, it seems like a good starting point. Losing the verbose message that prints the file name before a corrupt blob aborts the command is a little sad, because there's no easy way to go from oid to file name. I'd like to change that message to list the file name so it looks cleaner and less cryptic, but the pointer object is nowhere near where it needs to be to do this. So punt on that for now.

lfs: factor out a method for extracting the pointer of a single file This will be useful for filesets, among other things, instead of traversing the whole context.