HGitaly is Gitaly server for Mercurial.
It implements the subset of the Gitaly gRPC protocol that is relevant for Mercurial repositories, as well as its own HGitaly protocol, with methods that are specific to Mercurial.
It comes in two overlapping variants:
HGitaly proper is written in Python, using the grpcio official library.
RHGitaly is a high-performance partial implementation written in Rust, and
based on the tonic gRPC framework.
As of this writing, RHGitaly implements a strict subset of the methods implemented in HGitaly, but it is possible that some methods would be implemented in RHGitaly only in the future.
In what follows, $PYTHON is often the Python interpreter in a virtualenv,
but it can be a system-wide one (typical case in containers, strongly
discouraged on user systemes).
Install Mercurial with Rust parts (for the exact version, refer to the requirements file in the Heptapod main repository sources)
$PYTHON -m pip install --no-use-pep517 --global-option --rust Mercurial==6.6.2
Install HGitaly itself (check that it does not reinstall Mercurial)
$PYTHON -m pip install hgitaly
We distribute a self-contained source tarball. It includes the appropriate
hg-core Rust sources.
Fetch the tarball
wget https://download.heptapod.net/rhgitaly/rhgitaly-x.y.z.tgz
Fetch and verify the GPG signature
wget https://download.heptapod.net/rhgitaly/rhgitaly-x.y.z.tgz.asc
gpg --verify rhgitaly-x.y.z.tgz.asc
Build
tar xzf rhgitaly-x.y.z.tgz
cd rhgitaly-x.y.z/rust
cargo build --locked --release
Install wherever you want. Example given for a system-wide installation
sudo install -o root -g root target/release/rhgitaly /usr/local/bin
Define a service. Example given for systemd, to be adjusted for your needs. Make sure in particular that user and all directories exist, with appropriate permissions.
[Unit]
Description=Heptapod RHGitaly Server
[Service]
User=hgitaly
# HGRCPATH not needed yet but probably will be at some point
Environment=HGRCPATH=/etc/heptapod/heptapod.hgrc
Environment=RHGITALY_LISTEN_URL=unix:/run/heptapod/rhgitaly.socket
Environment=RHGITALY_REPOSITORIES_ROOT=/home/hg/repositories
ExecStartPre=rm -f /run/heptapod/rhgitaly.socket
ExecStart=/user/local/bin/rhgitaly
Restart=on-failure
[Install]
WantedBy=default.target
HGitaly needs several other programs to be installed and will run them as separate processes.
By default, it expects to find them on $PATH, but the actual path to
each executable can be configured.
Tokei is a programming languages analysis tool written in Rust. It is used by the CommitLanguages method.
Tokei is available in several Linux distributions.
As of this writing, HGitaly supports versions 12.0 and 12.1
Usually installed as license-detector, this standalone executable is
part of the go-enry suite. Its library version is also used by Gitaly.
It is used in the FindLicense method.
HGitaly can make use of some Git commands that do not involve repositories!
This is for example the case of GetPatchID: the
git patch-id command does not access any repository. Instead it computes any
patch into an identifier.
In forthcoming versions, it is probable that HGitaly and/or RHGitaly will invoke Mercurial subprocesses.
This is not yet the case as of this writing (HGitaly 1.1 / Heptapod 1.1).
HGitaly's configuration is done the standard way in the Mercurial world: through HGRC files.
In a typical Heptapod installation, these are split into a managed file, for
consistency with other components and another one for edit by the systems
administrator (/etc/gitlab/heptapod.hgrc in Omnibus/Docker instances).
Many Mercurial tweaks are interpreted simply because HGitaly internally calls into Mercurial, but HGitaly also gets its own section. Here are the settings available as of HGitaly 1.1
[hgitaly]
# paths to external executables
tokei-executable = tokei
license-detector-executable = license-detector
git-executable = git
# The number of workers process default value is one plus half the CPU count.
# It can be explicitly set this way:
#workers = 4
# Time to let a worker finish treating its current request, if any, when
# gracefully restarted. Default is high because of backup requests.
worker.graceful-shutdown-timeout-seconds = 300
# Maximum allowed resident size for worker processes (MiB).
# They get gracefully restarted if they cross that threshold
worker.max_rss_mib = 1024
# Interval between memory monitoring of workers (results dumped in logs)
worker.monitoring-interval-seconds = 60
Also heptapod.repositories-root is used if --repositories-root is
not passed on the command line.
HGitaly is using the standard logging Python module, and the
loggingmod Mercurial extension to emit logs from the Mercurial core
and other extensions. Therefore, the logging configuration is done
from the Mercurial configuration, typically from one of the Heptapod
HGRC files.
The general convention is that all logs emitted by hgitaly.service
provide GitLab's correlation_id in the extra dict, making it
available in the format string. Here is a minimal example:
[correlation_id=%(correlation_id)s] [%(levelname)s] [%(name)s] %(message)s"
Conversely, the format strings for logs emitted outside of
hgitaly.service must not use correlation_id, as subpackages such as
hgitaly.branch, hgitaly.message, etc. cannnot provide a
value: it is a hard error to use a format that relies on some
extra if the emitter does not provide it.
To summarize the resulting policy:
hgitaly.service, all logging must be done through
hgitaly.logging.LoggerAdapter. Using correlation_id in the
format is strongly encouraged.hgitaly.service, logging should be self-contained
useful without an obvious link to the calling gRPC method. For
instance a repository inconsistency should be logged at WARNING
level, with a message including the path.Usually, that would be in a virtualenv, but it's not necessary.
python3 -m pip install -r test-requirements.txt
./run-all-tests
Hint: Check the contents of run-all-tests, it's just pytest with
a standard set of options (mostly for coverage, see below).
These are the main tests. They lie inside the hgitaly
and hgext3rd.hgitaly Python packages. The layout follows the style where
each subpackage has its own tests package, to facilitate future refactorings.
The Mercurial integration tests are written with the mercurial-testhelpers library. Their duty is to assert that HGitaly works as expected and maintains compatibility with several versions of Mercurial and possibly other dependencies, such as grpcio.
The implicit assumption with these tests is that the test authors actually knew what was expected. HGitaly being meant to be a direct replacement, or rather a translation of Gitaly in Mercurial terms, those expectation are actually a mix of:
If an appropriate Gitaly installation is found, run-all-tests will also
run the tests from the tests_with_gitaly package. This happens automatically
from within a HDK workspace.
These are precisely meant for what the Mercurial integration tests can't do: check that HGitaly responses take the form expected by the various Gitaly clients, by comparing directly with the reference Gitaly implementation.
The comparisons work by using the conversions to Git provided by
py-heptapod, which are precisely what HGitaly aims to replace as a mean
to expose Mercurial content to GitLab.
Once there is no ambiguity with what Gitaly clients expect, the correctness of the implementation, with its various corner cases, should be left to the Mercurial integration tests.
This project is being developed with a strong test coverage policy, enforced by CI: without the Gitaly comparison tests, the coverage has to stay at 100%.
This does not mean that a contribution has to meet this goal to be worthwile, or even considered. Contributors can expect Maintainers to help them achieving the required 100% coverage mark, especially if they are newcomers. Of course, Contributors cannot expect Maintainers to go as far as write missing tests for them, even if that can still happen for critical urgent issues.
Selected statements can of course be excluded for good reasons, using
# pragma no cover.
Coverage exclusions depending on the Mercurial version are provided by the coverage plugin of mercurial-testhelpers.
Unexpected drop of coverage in different Mercurial versions is a powerful warning system that something not obvious is getting wrong, but the Gitaly comparison tests are run in CI against a fixed set of dependencies, hence 100% coverage must be achieved without the Gitaly comparison tests.
On the other hand, Gitaly comparison tests will warn us when we bump upstream GitLab if some critical behaviour has changed.
In some cases, yes, but it's limited.
For example, the comparison tests
can tell us that the FindAllBranchNames is actually expected to return
GitLab refs (refs/heads/some-branch), not GitLab branch names. That can
be settled with a few, very basic, test cases. There is no need to test all
the mapping rules for topics, and even less the various related corner cases
in the comparison tests. These, on the other hand depend strongly on Mercurial
internals, and absolutely have to be fully tested continuously against various
Mercurial versions.
Also, it is possible to deduplicate scenarios that are almost identical in Mercurial integration tests and Gitaly comparison tests: factorize out the common code in a helper function made available for both. The question is if it is worth the effort.
Finally, comparison tests should focus on the fact that Gitaly and HGitaly
results agree, not on what they contain. In the above example,
a comparison for FindAllBranchNames could simply assert equality of the
returned sets of branch names. This is a bit less cumbersome, and easier
to maintain.
compat CI stage?These are often due to statements being covered by the Gitaly comparison
tests only, leading to 100% coverage in the main stage, but not in the
compat stage.
The first thing to do is to run without the Gitaly comparison tests:
SKIP_GITALY_COMPARISON_TESTS=yes ./run-all-tests
(any non empty value in that environment variable, even no or false will
trigger the skipping)
In some rare cases, the drop in coverage could be due to an actual change between Mercurial versions. If that happens, there are good chances that an actual bug is lurking around.
./run-all-tests --cov tests_with_gitaly --cov-report html
The HTML report will be nice if you don't have 100% coverage. To display it, just do
firefox htmlcov/index.html
By default, the Gitaly comparison tests themselves are not covered, indeed.
This is because run-all-tests does not know whether they will be skipped for
lack of a Gitaly installation – which would be legitimate.
But they are covered in the CI jobs that launch them, because Gitaly is assumed to be available. For these, the coverage would tell us that something was broken, preventing the tests to run.
The Gitaly comparison tests provide exactly a harness for that: take a test,
modify it as needed, insert a pdb breakpoint, and get going.
The big advantage here is that startup of the Gitaly comparison tests is almost instantaneous, especially compared with RSpec, wich takes about a minute to start even a completely trivial test.
Of course that will raise the question whether it'll be useful to make true tests of these experiments.
Each time there's a need to be sure of what's expected and it can help answer that question. It doesn't have to do more than that.
If you need to make sure that Heptapod Rails, as a Gitaly client, sends the proper requests, because that can depend on specific dispatch code.
For instance, we are currently still converting to Git on the Rails side. A source of bugs would be to send Git commit ids to HGitaly.
Apart from that, it is expected to be vastly more efficient to use Gitaly comparison tests.
The more Heptapod progresses, the less complicated all of this should be.
The virtualenv has to be activated
pip install -r dev-requirements.txt
Copy the new proto files from a Gitaly checkout with
version matching the wanted GitLab upstream version.
Example in a HDK context:
cp ../gitaly/proto/*.proto protos/ # we dont want the `go` subdir
run ./generate-stubs
run the tests: ./run-all-tests
perform necessary hg add after close inspection of hg status
This package defines and implements an additional gRPC protocol, with gRPC services and methods that are specific to Mercurial, or more generally Heptapod.
The sources are proto files in the protos/ directory, same as for the
Gitaly protocol.
They distinguish themselves by this declaration:
package hgitaly;
Each time a change is made to the protocol, the libraries for all provided programming languages have to be regenerated and committed, ideally together with the protocol change.
It has a special status, being versioned together with the protocol and the server implementation. It is provided as the hgitaly.stub package.
The Python stubs are produced by the same script that takes care of Gitaly
proto files:
./generate-stubs
See the separate documentation
A Go library will probably be necessary quite soon for Workhorse or perhaps Heptapod Shell.
A Rust library would be nice to have
FAQs
Server-side implementation of Gitaly protocol for Mercurial
We found that hgitaly demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 3 open source maintainers collaborating on the project.
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