cborutil: change buffering strategy Profiling revealed that we were spending a lot of time on the line that was concatenating the old buffer with the incoming data when attempting to decode long byte strings, such as manifest revisions. Essentially, we were feeding N chunks of size len(X) << len(Y) into decode() and continuously allocating a new, larger buffer to hold the undecoded input. This created substantial memory churn and slowed down execution. Changing the code to aggregate pending chunks in a list until we have enough data to fully decode the next atom makes things much more efficient. I don't have exact data, but I recall the old code spending >1s on manifest fulltexts from the mozilla-unified repo. The new code doesn't significantly appear in profile output. Differential Revision: https://phab.mercurial-scm.org/D4854

cleanup: some Yoda conditions, this patch removes It seems the factor 20 is less than the frequency of " < \d" compared to " \d > ". Differential Revision: https://phab.mercurial-scm.org/D4862

streamclone: don't support stream clone unless repo feature present This change means custom repository types must opt in to enabling stream clone. This seems reasonable, as stream clones are a very low-level feature that has historically assumed the use of revlogs and the layout of .hg/ that they entail. Differential Revision: https://phab.mercurial-scm.org/D4853

localrepo: add repository feature when repo can be stream cloned Right now, the wire protocol server assumes all repository objects can be stream cloned (unless the stream clone feature is disabled via config option). But not all storage backends or repository objects may support stream clone. This commit defines a repository feature denoting whether stream clone is supported. The feature is defined for revlog-based repositories, which should currently be "all repositories." Differential Revision: https://phab.mercurial-scm.org/D4852

wireprotov2: client support for following content redirects And with the server actually sending content redirects, it is finally time to implement client support for following them! When a redirect response is seen, we wait until all data for that request has been received (it should be nearly immediate since no data is expected to follow the redirect message). Then we use a URL opener to make a request. We stuff that response into the client handler and construct a new response object to track it. When readdata() is called for servicing requests, we attempt to read data from the first redirected response. During data reading, data is processed similarly to as if it came from a frame payload. The existing test for the functionality demonstrates the client transparently following the redirect and obtaining the command response data from an alternate URL! There is still plenty of work to do here, including shoring up testing. I'm not convinced things will work in the presence of multiple redirect responses. And we don't yet implement support for integrity verification or configuring server certificates to validate the connection. But it's a start. And it should enable us to start experimenting with "real" caches. Differential Revision: https://phab.mercurial-scm.org/D4778

wireprotov2: server support for sending content redirects A "content redirect" can be sent in place of inline response content. In terms of code, we model a content redirect as a special type of response object holding the attributes describing that redirect. Sending a content redirect thus becomes as simple as the object emission layer sending an instance of that type. A cacher using externally-addressable content storage could replace the outgoing object stream with an object advertising its location. The bulk of the code in this commit is teaching the output layer which handles the object stream to recognize alternate location objects. The rules are that if an alternate location object is present, it must be the first and only object in the object stream. Otherwise the server emits an error. Differential Revision: https://phab.mercurial-scm.org/D4777

wireprotov2: client support for advertising redirect targets With the server now able to emit a redirect target descriptor, we can start to teach the client to recognize it. This commit implements support for filtering the advertised redirect targets against supported features and for advertising compatible redirect targets as part of command requests. It also adds the minimal boilerplate required to fail when a content redirect is seen. The server doesn't yet do anything with the advertised redirect targets. And the client can't yet follow redirects if it did. But at least we're putting bytes on the wire. Differential Revision: https://phab.mercurial-scm.org/D4776