# This file is part of GAnarchy - decentralized project hub
# Copyright (C) 2020 Soni L.
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU Affero General Public License for more details.
#
# You should have received a copy of the GNU Affero General Public License
# along with this program. If not, see <https://www.gnu.org/licenses/>.
"""Git abstraction.
"""
# Errors are raised when we can't provide an otherwise valid result.
# For example, we return 0 for counts instead of raising, but raise
# instead of returning empty strings for commit hashes and messages.
import shutil
import subprocess
class GitError(Exception):
"""Raised when a git operation fails, generally due to a
missing commit or branch, or network connection issues.
"""
pass
class Git:
"""A git repo.
Takes a ``pathlib.Path`` as argument.
"""
def __init__(self, path):
self.path = path
#########################################
# Operations supported on any git repo. #
#########################################
def check_branchname(self, branchname):
"""Checks if the given branchname is a valid branch name.
Raises if it isn't.
Args:
branchname (str): Name of branch.
Raises:
GitError: If an error occurs.
"""
try:
if branchname.startswith("-"):
raise GitError("check branchname", branchname)
out = self._cmd(
"check-ref-format", "--branch", branchname
).stdout.decode("utf-8")
# protect against @{-1}/@{-n} ("previous checkout operation")
# is also fairly future-proofed, I hope?
if (not out.startswith(branchname)) or (
out.removeprefix(branchname) not in ('\r\n', '\n', '')
):
raise GitError("check branchname", out, branchname)
except subprocess.CalledProcessError as e:
raise GitError("check branchname") from e
def get_hash(self, target):
"""Returns the commit hash for a given target.
Args:
target (str): a refspec.
Raises:
GitError: If an error occurs.
"""
try:
return self._cmd(
"show", target, "-s", "--format=format:%H", "--"
).stdout.decode("utf-8")
except subprocess.CalledProcessError as e:
raise GitError("get hash") from e
def get_commit_message(self, target):
"""Returns the commit message for a given target.
Args:
target (str): a refspec.
Raises:
GitError: If an error occurs.
"""
try:
return self._cmd(
"show", target, "-s", "--format=format:%B", "--"
).stdout.decode("utf-8", "replace")
except subprocess.CalledProcessError as e:
raise GitError("get commit message") from e
def check_history(self, local_head, commit):
"""Checks if the local head contains commit in its history.
Raises if it doesn't.
Args:
local_head (str): Name of local head.
commit (str): Commit hash.
Raises:
GitError: If an error occurs.
"""
try:
self._cmd("merge-base", "--is-ancestor", commit, local_head)
except subprocess.CalledProcessError as e:
raise GitError("check history") from e
########################
# Low-level operations #
########################
def _cmd_init(self, *args):
"""Runs a command for initializing this git repo.
Always uses ``--bare``.
Returns:
subprocess.CompletedProcess: The results of running the command.
Raises:
subprocess.CalledProcessError: If the command exited with a non-zero
status.
"""
return self._cmd_common('init', '--bare', *args, self.path)
def _cmd_clone_from(self, from_, *args):
"""Runs a command for cloning into this git repo.
Always uses ``--bare``.
Returns:
subprocess.CompletedProcess: The results of running the command.
Raises:
subprocess.CalledProcessError: If the command exited with a non-zero
status.
"""
return self._cmd_common('clone', '--bare', *args, from_, self.path)
def _cmd(self, *args):
"""Runs a command for operating on this git repo.
Note: Doesn't work for git init and git clone operations. Use
``_cmd_init`` and ``_cmd_clone_from`` instead.
Always uses ``--bare``.
Returns:
subprocess.CompletedProcess: The results of running the command.
Raises:
subprocess.CalledProcessError: If the command exited with a non-zero
status.
"""
return self._cmd_common('-C', self.path, '--bare', *args)
def _cmd_common(self, *args):
"""Runs a git command with the given args.
This is a simple wrapper around ``subprocess.run``.
Returns:
subprocess.CompletedProcess: The results of running the command.
Raises:
subprocess.CalledProcessError: If the command exited with a non-zero
status.
"""
return subprocess.run(
('git',) + args,
check=True,
stdout=subprocess.PIPE,
stderr=subprocess.PIPE
)
class GitCache(Git):
"""A permanent repository used to cache remote objects.
"""
#####################
# Public operations #
#####################
def create(self):
"""Creates the local repo.
Can safely be called on an existing repo.
"""
try:
return self._cmd_init()
except subprocess.CalledProcessError as e:
raise GitError("create") from e
def with_work_repos(self, count):
"""Creates a context manager for managing work repos.
Args:
count (int): The number of work repos.
"""
"""From Rust:
/// Creates the given number of work repos, and calls the closure to run
/// operations on them.
///
/// The operations can be done on the individual repos, and they'll be
/// merged into the main repo as this function returns.
///
/// If the callback fails, the work repos will be deleted. If the function
/// succeeds, the work repos will be merged back into the main repo.
///
/// # Panics
///
/// Panics if a merge conflict is detected. Specifically, if two work repos
/// modify the same work branch.
///
/// # "Poisoning"
///
/// If this method unwinds, the underlying git repos, if any, will not be
/// deleted. Instead, future calls to this method will return a GitError.
"""
work_repos = []
for i in range(0, count):
new_path = self.path.with_name('ganarchy-fetch-{}.git'.format(i))
work_repos.append(GitFetch(new_path))
physical_work_repos = []
for repo in work_repos:
self._fork(repo)
physical_work_repos.append(repo)
return _WithWorkRepos(self, physical_work_repos)
#######################
# Internal operations #
#######################
def _fetch_work(self, from_, branch, from_branch):
try:
self._cmd(
"fetch", from_.path, "+{}:{}".format(from_branch, branch)
)
except subprocess.CalledProcessError as e:
raise GitError("fetch work") from e
def _replace(self, old_name, new_name):
try:
self._cmd(
"branch", "-M", old_name, new_name
)
except subprocess.CalledProcessError as e:
raise GitError("replace") from e
def _fork(self, into):
"""Makes a shared clone of this local repo into the given work repo.
Equivalent to ``git clone --bare --shared``, which is very dangerous!
"""
try:
return into._cmd_clone_from(self.path, '--shared')
except subprocess.CalledProcessError as e:
raise GitError("fork") from e
class GitFetch(Git):
"""A temporary repository used to fetch remote objects.
"""
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
self.pending_branches = set()
#####################
# Public operations #
#####################
def force_fetch(self, url, remote_head, local_head):
"""Fetches a remote head into a local head.
If the local head already exists, it is replaced.
Args:
url (str): Remote url.
remote_head (str): Name of remote head.
local_head (str): Name of local head.
Raises:
GitError: If an error occurs.
"""
try:
self._cmd(
"fetch", url, "+" + remote_head + ":" + local_head
)
self.pending_branches.add(local_head)
except subprocess.CalledProcessError as e:
raise GitError("fetch source") from e
def get_count(self, first_hash, last_hash):
"""Returns a count of the commits added since ``first_hash``
up to ``last_hash``.
Args:
first_hash (str): A commit.
last_hash (str): Another commit.
Returns:
int: A count of commits added between the hashes, or 0
if an error occurs.
"""
try:
res = self._cmd(
"rev-list", "--count", first_hash + ".." + last_hash, "--"
).stdout.decode("utf-8").strip()
return int(res)
except subprocess.CalledProcessError as e:
return 0
#######################
# Internal operations #
#######################
def _rm_branch(self, branch):
try:
self._cmd("branch", "-D", branch)
except subprocess.CalledProcessError as e:
raise GitError("rm branch") from e
def _delete(self):
try:
shutil.rmtree(self.path)
except IOError as e:
raise GitError("delete", self.path) from e
class _WithWorkRepos:
"""Context manager for merging forked repos in ``with_work_repos``.
"""
def __init__(self, cache_repo, work_repos):
self.cache_repo = cache_repo
self.work_repos = work_repos
def __enter__(self):
return self.work_repos
def __exit__(self, exc_type, exc_val, exc_tb):
if exc_type is None:
branches = set()
for work in self.work_repos:
for branch in work.pending_branches:
if branch in branches:
raise GitError("Branch {} is in conflict!".format(branch))
branches.add(branch)
del branches
del work
del branch
for i, repo in enumerate(self.work_repos):
for branch in repo.pending_branches:
fetch_head = "{}-{}".format(branch, i)
# First collect the work branch into a fetch head
self.cache_repo._fetch_work(repo, fetch_head, branch)
# If that succeeds, delete the work branch to free up disk
repo._rm_branch(branch)
# We have all the objects in the main repo and we probably
# have enough disk, so just replace the fetch head into
# the main branch and hope nothing errors.
self.cache_repo._replace(fetch_head, branch)
repo._delete()
