revision_gitfast.py
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	# Copyright (C) 2017-2019 The Software Heritage developers
	# See the AUTHORS file at the top-level directory of this distribution
	# License: GNU General Public License version 3, or any later version
	# See top-level LICENSE file for more information

	import functools
	import os
	import time
	import zlib

	from fastimport.commands import (
	BlobCommand,
	CommitCommand,
	FileDeleteCommand,
	FileModifyCommand,
	ResetCommand,
	)

	from swh.model import hashutil
	from swh.model.from_disk import DentryPerms, mode_to_perms
	from swh.model.toposort import toposort
	from swh.vault.cookers.base import BaseVaultCooker
	from swh.vault.cookers.utils import revision_log
	from swh.vault.to_disk import get_filtered_files_content


	class RevisionGitfastCooker(BaseVaultCooker):
	"""Cooker to create a git fast-import bundle """

	CACHE_TYPE_KEY = "revision_gitfast"

	def check_exists(self):
	return not list(self.storage.revision_missing([self.obj_id]))

	def prepare_bundle(self):
	self.log = list(toposort(revision_log(self.storage, self.obj_id)))
	self.gzobj = zlib.compressobj(9, zlib.DEFLATED, zlib.MAX_WBITS \| 16)
	self.fastexport()
	self.write(self.gzobj.flush())

	def write_cmd(self, cmd):
	chunk = bytes(cmd) + b"\n"
	super().write(self.gzobj.compress(chunk))

	def fastexport(self):
	"""Generate all the git fast-import commands from a given log.
	"""
	self.rev_by_id = {r["id"]: r for r in self.log}
	self.obj_done = set()
	self.obj_to_mark = {}
	self.next_available_mark = 1

	last_progress_report = None

	for i, rev in enumerate(self.log, 1):
	# Update progress if needed
	ct = time.time()
	if last_progress_report is None or last_progress_report + 2 <= ct:
	last_progress_report = ct
	pg = "Computing revision {}/{}".format(i, len(self.log))
	self.backend.set_progress(self.obj_type, self.obj_id, pg)

	# Compute the current commit
	self._compute_commit_command(rev)

	def mark(self, obj_id):
	"""Get the mark ID as bytes of a git object.

	If the object has not yet been marked, assign a new ID and add it to
	the mark dictionary.
	"""
	if obj_id not in self.obj_to_mark:
	self.obj_to_mark[obj_id] = self.next_available_mark
	self.next_available_mark += 1
	return str(self.obj_to_mark[obj_id]).encode()

	def _compute_blob_command_content(self, file_data):
	"""Compute the blob command of a file entry if it has not been
	computed yet.
	"""
	obj_id = file_data["sha1"]
	if obj_id in self.obj_done:
	return
	contents = list(get_filtered_files_content(self.storage, [file_data]))
	content = contents[0]["content"]
	self.write_cmd(BlobCommand(mark=self.mark(obj_id), data=content))
	self.obj_done.add(obj_id)

	def _author_tuple_format(self, author, date):
	# We never want to have None values here so we replace null entries
	# by ''.
	if author is not None:
	author_tuple = (author.get("name") or b"", author.get("email") or b"")
	else:
	author_tuple = (b"", b"")
	if date is not None:
	date_tuple = (
	date.get("timestamp", {}).get("seconds") or 0,
	(date.get("offset") or 0) * 60,
	)
	else:
	date_tuple = (0, 0)
	return author_tuple + date_tuple

	def _compute_commit_command(self, rev):
	"""Compute a commit command from a specific revision.
	"""
	if "parents" in rev and rev["parents"]:
	from_ = b":" + self.mark(rev["parents"][0])
	merges = [b":" + self.mark(r) for r in rev["parents"][1:]]
	parent = self.rev_by_id[rev["parents"][0]]
	else:
	# We issue a reset command before all the new roots so that they
	# are not automatically added as children of the current branch.
	self.write_cmd(ResetCommand(b"refs/heads/master", None))
	from_ = None
	merges = None
	parent = None

	# Retrieve the file commands while yielding new blob commands if
	# needed.
	files = list(self._compute_file_commands(rev, parent))

	# Construct and write the commit command
	author = self._author_tuple_format(rev["author"], rev["date"])
	committer = self._author_tuple_format(rev["committer"], rev["committer_date"])
	self.write_cmd(
	CommitCommand(
	ref=b"refs/heads/master",
	mark=self.mark(rev["id"]),
	author=author,
	committer=committer,
	message=rev["message"] or b"",
	from_=from_,
	merges=merges,
	file_iter=files,
	)
	)

	@functools.lru_cache(maxsize=4096)
	def _get_dir_ents(self, dir_id=None):
	"""Get the entities of a directory as a dictionary (name -> entity).

	This function has a cache to avoid doing multiple requests to retrieve
	the same entities, as doing a directory_ls() is expensive.
	"""
	data = self.storage.directory_ls(dir_id) if dir_id is not None else []
	return {f["name"]: f for f in data}

	def _compute_file_commands(self, rev, parent=None):
	"""Compute all the file commands of a revision.

	Generate a diff of the files between the revision and its main parent
	to find the necessary file commands to apply.
	"""
	# Initialize the stack with the root of the tree.
	cur_dir = rev["directory"]
	parent_dir = parent["directory"] if parent else None
	stack = [(b"", cur_dir, parent_dir)]

	while stack:
	# Retrieve the current directory and the directory of the parent
	# commit in order to compute the diff of the trees.
	root, cur_dir_id, prev_dir_id = stack.pop()
	cur_dir = self._get_dir_ents(cur_dir_id)
	prev_dir = self._get_dir_ents(prev_dir_id)

	# Find subtrees to delete:
	# - Subtrees that are not in the new tree (file or directory
	# deleted).
	# - Subtrees that do not have the same type in the new tree
	# (file -> directory or directory -> file)
	# After this step, every node remaining in the previous directory
	# has the same type than the one in the current directory.
	for fname, f in prev_dir.items():
	if fname not in cur_dir or f["type"] != cur_dir[fname]["type"]:
	yield FileDeleteCommand(path=os.path.join(root, fname))

	# Find subtrees to modify:
	# - Leaves (files) will be added or modified using `filemodify`
	# - Other subtrees (directories) will be added to the stack and
	# processed in the next iteration.
	for fname, f in cur_dir.items():
	# A file is added or modified if it was not in the tree, if its
	# permissions changed or if its content changed.
	if f["type"] == "file" and (
	fname not in prev_dir
	or f["sha1"] != prev_dir[fname]["sha1"]
	or f["perms"] != prev_dir[fname]["perms"]
	):
	# Issue a blob command for the new blobs if needed.
	self._compute_blob_command_content(f)
	yield FileModifyCommand(
	path=os.path.join(root, fname),
	mode=mode_to_perms(f["perms"]).value,
	dataref=(b":" + self.mark(f["sha1"])),
	data=None,
	)
	# A revision is added or modified if it was not in the tree or
	# if its target changed
	elif f["type"] == "rev" and (
	fname not in prev_dir or f["target"] != prev_dir[fname]["target"]
	):
	yield FileModifyCommand(
	path=os.path.join(root, fname),
	mode=DentryPerms.revision,
	dataref=hashutil.hash_to_hex(f["target"]).encode(),
	data=None,
	)
	# A directory is added or modified if it was not in the tree or
	# if its target changed.
	elif f["type"] == "dir":
	f_prev_target = None
	if fname in prev_dir and prev_dir[fname]["type"] == "dir":
	f_prev_target = prev_dir[fname]["target"]
	if f_prev_target is None or f["target"] != f_prev_target:
	stack.append(
	(os.path.join(root, fname), f["target"], f_prev_target)
	)

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