wireprotoframing: buffer emitted data to reduce frame count An upcoming commit introduces a wire protocol command that can emit hundreds of thousands of small objects. Without a buffering layer, we would emit a single, small frame for every object. Performance profiling revealed this to be a source of significant overhead for both client and server. This commit introduces a very crude buffering layer so that we emit fewer, bigger frames in such a scenario. This code will likely get rewritten in the future to be part of the streams API, as we'll need a similar strategy for compressing data. I don't want to think about it too much at the moment though. server before: user 32.500+0.000 sys 1.160+0.000 after: user 20.230+0.010 sys 0.180+0.000 client before: user 133.400+0.000 sys 93.120+0.000 after: user 68.370+0.000 sys 32.950+0.000 This appears to indicate we have significant overhead in the frame processing code on both client and server. It might be worth profiling that at some point... Differential Revision: https://phab.mercurial-scm.org/D4473

wireprotov2: implement commands as a generator of objects Previously, wire protocol version 2 inherited version 1's model of having separate types to represent the results of different wire protocol commands. As I implemented more powerful commands in future commits, I found I was using a common pattern of returning a special type to hold a generator. This meant the command function required a closure to do most of the work. That made logic flow more difficult to follow. I also noticed that many commands were effectively a sequence of objects to be CBOR encoded. I think it makes sense to define version 2 commands as generators. This way, commands can simply emit the data structures they wish to send to the client. This eliminates the need for a closure in command functions and removes encoding from the bodies of commands. As part of this commit, the handling of response objects has been moved into the serverreactor class. This puts the reactor in the driver's seat with regards to CBOR encoding and error handling. Having error handling in the function that emits frames is particularly important because exceptions in that function can lead to things getting in a bad state: I'm fairly certain that uncaught exceptions in the frame generator were causing deadlocks. I also introduced a dedicated error type for explicit error reporting in command handlers. This will be used in subsequent commits. There's still a bit of work to be done here, especially around formalizing the error handling "protocol." I've added yet another TODO to track this so we don't forget. Test output changed because we're using generators and no longer know we are at the end of the data until we hit the end of the generator. This means we can't emit the end-of-stream flag until we've exhausted the generator. Hence the introduction of 0-sized end-of-stream frames. Differential Revision: https://phab.mercurial-scm.org/D4472

internals: extract frame-based protocol docs to own document wireprotocol.txt is quite long and difficult to digest. The frame-based protocol is effectively a standalone concept (and could even be used outside of Mercurial). So this commit extracts its docs to a standalone file. The first few paragraphs were rewritten as part of the extraction. Sections headers were adjusted accordingly. Existing referalls in wireprotocol.txt were updated to refer to the new doc / concept, which I've started referring to as `hgrpc`. I'm on the fence as to whether to move the HTTP and SSH transport details to the new doc as well. For now, I'm leaving them in wireprotocol.txt. Differential Revision: https://phab.mercurial-scm.org/D4443

narrow: remove hack to write narrowspec to shared .hg directory AFAIK, we no longer need it since the narrowspec file was move to the store directory in 576eef1ab43d, "narrow: move .hg/narrowspec to .hg/store/narrowspec."

narrowspec: remove parseserverpatterns() which isn't used anymore Follows up 10a8472f6662, "narrow: drop support for remote expansion."

hg: write narrow patterns after repo creation Now that hg.clone() knows when a narrow clone is requested, it makes sense to have it update the narrow patterns for the repo soon after the repo is created, before any exchange occurs. Previously, the narrow extension was monkeypatching an exchange function to do this. The old code is redundant and has been removed. Differential Revision: https://phab.mercurial-scm.org/D4541

narrow: don't wrap exchange.pull() during clone The wrapped version was setting up the narrow repo requirement when a narrow clone was requested. Previous commits taught hg.clone() and repo creation to add the narrow requirement when a narrow clone was requested. So this requirement should already be set up for us and this code is no longer necessary. Differential Revision: https://phab.mercurial-scm.org/D4540