git_refs.py

# Copyright (C) 2009 The Android Open Source Project
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import os

import platform_utils
from repo_trace import Trace


HEAD = "HEAD"
R_CHANGES = "refs/changes/"
R_HEADS = "refs/heads/"
R_TAGS = "refs/tags/"
R_PUB = "refs/published/"
R_WORKTREE = "refs/worktree/"
R_WORKTREE_M = R_WORKTREE + "m/"
R_M = "refs/remotes/m/"


class GitRefs:
    def __init__(self, gitdir):
        self._gitdir = gitdir
        self._phyref = None
        self._symref = None
        self._mtime = {}

    @property
    def all(self):
        self._EnsureLoaded()
        return self._phyref

    def get(self, name):
        try:
            return self.all[name]
        except KeyError:
            return ""

    def deleted(self, name):
        if self._phyref is not None:
            if name in self._phyref:
                del self._phyref[name]

            if name in self._symref:
                del self._symref[name]

            if name in self._mtime:
                del self._mtime[name]

    def symref(self, name):
        try:
            self._EnsureLoaded()
            return self._symref[name]
        except KeyError:
            return ""

    def _EnsureLoaded(self):
        if self._phyref is None or self._NeedUpdate():
            self._LoadAll()

    def _NeedUpdate(self):
        with Trace(": scan refs %s", self._gitdir):
            for name, mtime in self._mtime.items():
                try:
                    if mtime != os.path.getmtime(
                        os.path.join(self._gitdir, name)
                    ):
                        return True
                except OSError:
                    return True
            return False

    def _LoadAll(self):
        with Trace(": load refs %s", self._gitdir):
            self._phyref = {}
            self._symref = {}
            self._mtime = {}

            self._ReadPackedRefs()
            self._ReadLoose("refs/")
            self._ReadLoose1(os.path.join(self._gitdir, HEAD), HEAD)

            scan = self._symref
            attempts = 0
            while scan and attempts < 5:
                scan_next = {}
                for name, dest in scan.items():
                    if dest in self._phyref:
                        self._phyref[name] = self._phyref[dest]
                    else:
                        scan_next[name] = dest
                scan = scan_next
                attempts += 1

    def _ReadPackedRefs(self):
        path = os.path.join(self._gitdir, "packed-refs")
        try:
            fd = open(path)
            mtime = os.path.getmtime(path)
        except OSError:
            return
        try:
            for line in fd:
                line = str(line)
                if line[0] == "#":
                    continue
                if line[0] == "^":
                    continue

                line = line[:-1]
                p = line.split(" ")
                ref_id = p[0]
                name = p[1]

                self._phyref[name] = ref_id
        finally:
            fd.close()
        self._mtime["packed-refs"] = mtime

    def _ReadLoose(self, prefix):
        base = os.path.join(self._gitdir, prefix)
        for name in platform_utils.listdir(base):
            p = os.path.join(base, name)
            # We don't implement the full ref validation algorithm, just the
            # simple rules that would show up in local filesystems.
            # https://git-scm.com/docs/git-check-ref-format
            if name.startswith(".") or name.endswith(".lock"):
                pass
            elif platform_utils.isdir(p):
                self._mtime[prefix] = os.path.getmtime(base)
                self._ReadLoose(prefix + name + "/")
            else:
                self._ReadLoose1(p, prefix + name)

    def _ReadLoose1(self, path, name):
        try:
            with open(path) as fd:
                mtime = os.path.getmtime(path)
                ref_id = fd.readline()
        except (OSError, UnicodeError):
            return

        try:
            ref_id = ref_id.decode()
        except AttributeError:
            pass
        if not ref_id:
            return
        ref_id = ref_id[:-1]

        if ref_id.startswith("ref: "):
            self._symref[name] = ref_id[5:]
        else:
            self._phyref[name] = ref_id
        self._mtime[name] = mtime