Automatic repository detection

- Add wsgi_autodetect(ing).py with usage like the existing
  wsgi_autoreload(ing).py scripts.

- Can handle directories with and without .git suffix.

- Factor out the repository container functionality from the Klaus
  object into its own class hierarchy (RepoContainer).

- Certain aspects of the automatic detection are configurable
  (specifically, the path that determines whether a subdirectory is a
  valid repo, whether it should detect removed repos and what are
  acceptable suffixes).

klaus/__init__.py

@@ -12,7 +12,7 @@
 from dulwich.errors import NotGitRepository
 
 from klaus import utils, views
-from klaus.repo import FancyRepo, InvalidRepo
+from klaus.repo import DefaultRepoContainer
 
 KLAUS_VERSION = utils.guess_git_revision() or "3.0.1"
 
@@ -23,20 +23,40 @@ class Klaus(flask.Flask):
         "undefined": jinja2.StrictUndefined,
     }
 
-    def __init__(self, repo_paths, site_name, use_smarthttp, ctags_policy="none"):
+    def __init__(
+        self,
+        repo_paths,
+        site_name,
+        use_smarthttp,
+        ctags_policy="none",
+        repo_container_factory=None,
+    ):
         """(See `make_app` for parameter descriptions.)"""
         self.site_name = site_name
         self.use_smarthttp = use_smarthttp
         self.ctags_policy = ctags_policy
 
-        valid_repos, invalid_repos = self.load_repos(repo_paths)
-        self.valid_repos = {repo.namespaced_name: repo for repo in valid_repos}
-        self.invalid_repos = {repo.namespaced_name: repo for repo in invalid_repos}
+        if repo_container_factory is None:
+            repo_container_factory = DefaultRepoContainer
+
+        self.repo_container = repo_container_factory(repo_paths)
 
         flask.Flask.__init__(self, __name__)
 
         self.setup_routes()
 
+    @property
+    def valid_repos(self):
+        """Repositories that are considered valid by the repository manager"""
+
+        return self.repo_container.valid
+
+    @property
+    def invalid_repos(self):
+        """Repositories that were declined by the repository manager"""
+
+        return self.repo_container.invalid
+
     def create_jinja_environment(self):
         """Called by Flask.__init__"""
         env = super().create_jinja_environment()
@@ -95,17 +115,6 @@ def should_use_ctags(self, git_repo, git_commit):
         else:
             raise ValueError("Unknown ctags policy %r" % self.ctags_policy)
 
-    def load_repos(self, repo_paths):
-        valid_repos = []
-        invalid_repos = []
-        for namespace, paths in repo_paths.items():
-            for path in paths:
-                try:
-                    valid_repos.append(FancyRepo(path, namespace))
-                except NotGitRepository:
-                    invalid_repos.append(InvalidRepo(path, namespace))
-        return valid_repos, invalid_repos
-
 
 def make_app(
     repo_paths,
@@ -116,6 +125,7 @@ def make_app(
     disable_push=False,
     unauthenticated_push=False,
     ctags_policy="none",
+    repo_container_factory=None,
 ):
     """
     Returns a WSGI app with all the features (smarthttp, authentication)
@@ -145,6 +155,8 @@ def make_app(
         - 'tags-and-branches': use ctags for revisions that are the HEAD of
           a tag or branc
         - 'ALL': use ctags for all revisions, may result in high server load!
+    :param repo_container_factory: An instance of klaus.repo.BaseRepoContainer or None,
+         in which klaus.repo.DefaultRepoContainer will be used.
     """
     if unauthenticated_push:
         if not use_smarthttp:
@@ -159,25 +171,20 @@ def make_app(
         raise ValueError(
             "'htdigest_file' set without 'use_smarthttp' or 'require_browser_auth'"
         )
-    if not isinstance(repo_paths, dict):
-        # If repos is given as a flat list, put all repos under the "no namespace" namespace
-        repo_paths = {None: repo_paths}
 
     app = Klaus(
         repo_paths,
         site_name,
         use_smarthttp,
         ctags_policy,
+        repo_container_factory,
     )
     app.wsgi_app = utils.ProxyFix(app.wsgi_app)
 
     if use_smarthttp:
         # `path -> Repo` mapping for Dulwich's web support
         dulwich_backend = dulwich.server.DictBackend(
-            {
-                "/" + namespaced_name: repo
-                for namespaced_name, repo in app.valid_repos.items()
-            }
+            utils.SlashDictProxy(app.valid_repos)
         )
         # Dulwich takes care of all Git related requests/URLs
         # and passes through everything else to klaus

klaus/contrib/wsgi_autodetect.py

@@ -0,0 +1,43 @@
+import os
+import warnings
+import contextlib
+
+from .app_args import get_args_from_env, strtobool
+from .wsgi_autodetecting import make_autodetecting_app
+
+try:
+    repos_root = os.environ['KLAUS_REPOS_ROOT']
+except KeyError:
+    repos_root = os.environ['KLAUS_REPOS']
+    warnings.warn(
+        "use KLAUS_REPOS_ROOT instead of KLAUS_REPOS for the autodecting apps",
+        DeprecationWarning,
+    )
+
+args, kwargs = get_args_from_env()
+args = (repos_root,) + args[1:]
+
+with contextlib.suppress(KeyError):
+    kwargs['detect_removals'] = bool(strtobool(os.environ['KLAUS_DETECT_REMOVALS']))
+
+with contextlib.suppress(KeyError):
+    kwargs['export_ok_path'] = os.environ['KLAUS_EXPORT_OK_PATH']
+
+with contextlib.suppress(KeyError):
+    # How to deal with repository directories named "foo" and/or "foo.git".
+    # This is a list of potential suffixes, with your operating system's
+    # directory separator as a separator. Examples:
+    #
+    # KLAUS_EXPORT_OK_PATH="/.git"
+    #   Directories with and without .git are accepted
+    #   (the first entry is the empty string). Default.
+    #
+    # KLAUS_EXPORT_OK_PATH=".git"
+    #   Only .git directories are accepted.
+    #
+    # KLAUS_EXPORT_OK_PATH=""
+    #   The .git suffix is not considered.
+
+    kwargs['directory_suffixes'] = os.environ['KLAUS_EXPORT_OK_PATH'].split(os.sep)
+
+application = make_autodetecting_app(*args, **kwargs)

klaus/contrib/wsgi_autodetecting.py

@@ -0,0 +1,178 @@
+"""
+Alternative take on the "automatically discovered repositories" concept
+that requires no threads, polling or inotify. Instead the filesystem is
+consulted whenever a repository name is looked up.
+
+Since Path.exists() and Path.iterdir() are fairly quick filesystem
+operations, performance should be good for small to medium sites.
+FancyRepo() objects are cached.
+
+Repositories are identified by the existence of a
+
+    <reponame>/git-daemon-export-ok
+
+file (for compatibility with gitweb). You can customize this path using
+the export_ok_path parameter. Setting it to '.' will cause every
+subdirectory to be considered a git repository.
+
+For large sites this approach may be hard on the filesystem when listing
+repositories, because the process of enumerating the git repositories
+causes the git-daemon-export-ok file to be checked in every repository.
+This can be mitigated by setting detect_removals to False.
+"""
+
+import collections.abc
+import functools
+import os
+import pathlib
+
+import klaus
+import klaus.repo
+
+_bad_names = frozenset([os.curdir, os.pardir])
+_bad_chars = frozenset(['\0', os.sep, os.altsep])
+_default_directory_suffixes = ['', '.git']
+
+
+def coalesce(*args):
+    """Return the first argument that is not None"""
+
+    return next(arg for arg in args if arg is not None)
+
+
+class AutodetectingRepoDict(collections.abc.Mapping):
+    """
+    Maintain a virtual read-only dictionary whose contents represent
+    the presence of git repositories in the given root directory.
+
+    :param root: The path to a directory containing repositories, each
+        a direct subdirectory of the root.
+    :param namespace: A namespace that will be applied to all detected
+        repositories.
+    :param detect_removals: Detect if repositories have been removed.
+        Defaults to True. Setting it to False can improve performance
+        for repository listings in very large sites.
+    :param export_ok_path: The filesystem path to check (relative to
+        the candidate repository root) to see if it is a valid servable
+        git repository. Defaults to 'git-daemon-export-ok'. Set to '.'
+        if every directory is known to be a valid repository root.
+    :param directory_suffixes: A list of suffixes that your git directories
+        may have. The default is ['', '.git'].
+    """
+
+    def __init__(
+        self,
+        root,
+        namespace=None,
+        detect_removals=None,
+        export_ok_path=None,
+        directory_suffixes=None,
+    ):
+        self._root = pathlib.Path(root)
+        self._cache = {}
+        self._namespace = namespace
+        self._detect_removals = coalesce(detect_removals, True)
+        self._export_ok_path = coalesce(export_ok_path, 'git-daemon-export-ok')
+        # Use the keys of a dict in reverse order so that we can create a sort
+        # of "poor man's splay tree": the suffixes are always tried in reverse
+        # order. If a suffix was matched succesfully it is moved to the end by
+        # removing and readding it so that it is tried as the first option for
+        # the next repository.
+        self._suffixes = dict.fromkeys(
+            reversed(list(coalesce(directory_suffixes, _default_directory_suffixes)))
+        )
+
+    def __getitem__(self, name):
+        if (
+            not name
+            or name.startswith('.')
+            or name in _bad_names
+            or not _bad_chars.isdisjoint(name)
+        ):
+            raise KeyError(name)
+
+        if not self._detect_removals:
+            # Try returning a cached version first, to avoid filesystem access
+            try:
+                return self._cache[name]
+            except KeyError:
+                pass
+
+        for suffix in reversed(self._suffixes):
+            # Bare git repositories may have a .git suffix on the directory name:
+            path = self._root / (name + suffix)
+            if (path / self._export_ok_path).exists():
+                # Reorder suffix test order on the assumption that most repos will
+                # have the same suffix:
+                del self._suffixes[suffix]
+                self._suffixes[suffix] = None
+                break
+        else:
+            self._cache.pop(name, None)
+            raise KeyError(name)
+
+        if self._detect_removals:
+            try:
+                return self._cache[name]
+            except KeyError:
+                pass
+
+        repo = klaus.repo.FancyRepo(str(path), self._namespace)
+        self._cache[name] = repo
+        return repo
+
+    def __iter__(self):
+        def is_valid_repo(path):
+            if not self._detect_removals and path.name in self._cache:
+                return True
+            return (path / self._export_ok_path).exists()
+
+        suffixes = sorted(self._suffixes, key=len, reverse=True)
+
+        def removesuffixes(string):
+            for suffix in suffixes:
+                attempt = string.removesuffix(suffix)
+                if attempt != string:
+                    return attempt
+            return string
+
+        return (
+            removesuffixes(path.name)
+            for path in self._root.iterdir()
+            if is_valid_repo(path)
+        )
+
+    def __len__(self):
+        return sum(1 for _ in self)
+
+
+class AutodetectingRepoContainer(klaus.repo.BaseRepoContainer):
+    """
+    RepoContainer based on AutodetectingRepoDict.
+    See AutodetectingRepoDict for parameter descriptions.
+    """
+
+    def __init__(self, repos_root, *args, **kwargs):
+        super().__init__(repos_root)
+        self.valid = AutodetectingRepoDict(repos_root, *args, **kwargs)
+
+
+def make_autodetecting_app(
+    repos_root,
+    *args,
+    detect_removals=None,
+    export_ok_path=None,
+    directory_suffixes=None,
+    **kwargs,
+):
+    return klaus.make_app(
+        repos_root,
+        *args,
+        repo_container_factory=functools.partial(
+            AutodetectingRepoContainer,
+            detect_removals=detect_removals,
+            export_ok_path=export_ok_path,
+            directory_suffixes=directory_suffixes,
+        ),
+        **kwargs,
+    )

klaus/repo.py

@@ -7,7 +7,7 @@
 
 import dulwich
 import dulwich.patch
-from dulwich.errors import NotTreeError
+from dulwich.errors import NotGitRepository, NotTreeError
 from dulwich.object_store import tree_lookup_path
 from dulwich.objects import S_ISGITLINK, Blob
 
@@ -435,3 +435,32 @@ def namespaced_name(self):
             return f"~{self.namespace}/{self.name}"
         else:
             return self.name
+
+
+class BaseRepoContainer:
+    """Abstract base class for repository containers."""
+
+    def __init__(self, repo_paths):
+        self._repo_paths = repo_paths
+        self.valid = {}
+        self.invalid = {}
+
+
+class DefaultRepoContainer(BaseRepoContainer):
+    """Default repository container that holds a preset list of repositories"""
+
+    def __init__(self, repo_paths):
+        if not isinstance(repo_paths, dict):
+            # If repos is given as a flat list, put all repos under the "no namespace" namespace
+            repo_paths = {None: repo_paths}
+
+        super().__init__(repo_paths)
+
+        for namespace, paths in repo_paths.items():
+            for path in paths:
+                try:
+                    repo = FancyRepo(path, namespace)
+                    self.valid[repo.namespaced_name] = repo
+                except NotGitRepository:
+                    repo = InvalidRepo(path, namespace)
+                    self.invalid[repo.namespaced_name] = repo