106 lines
4.0 KiB
Python
106 lines
4.0 KiB
Python
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"""Watch parts of the file system for changes."""
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from mypy.fscache import FileSystemCache
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from typing import AbstractSet, Dict, Iterable, List, NamedTuple, Optional, Set, Tuple
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FileData = NamedTuple('FileData', [('st_mtime', float),
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('st_size', int),
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('hash', str)])
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class FileSystemWatcher:
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"""Watcher for file system changes among specific paths.
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All file system access is performed using FileSystemCache. We
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detect changed files by stat()ing them all and comparing hashes
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of potentially changed files. If a file has both size and mtime
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unmodified, the file is assumed to be unchanged.
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An important goal of this class is to make it easier to eventually
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use file system events to detect file changes.
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Note: This class doesn't flush the file system cache. If you don't
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manually flush it, changes won't be seen.
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"""
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# TODO: Watching directories?
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# TODO: Handle non-files
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def __init__(self, fs: FileSystemCache) -> None:
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self.fs = fs
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self._paths: Set[str] = set()
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self._file_data: Dict[str, Optional[FileData]] = {}
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def dump_file_data(self) -> Dict[str, Tuple[float, int, str]]:
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return {k: v for k, v in self._file_data.items() if v is not None}
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def set_file_data(self, path: str, data: FileData) -> None:
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self._file_data[path] = data
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def add_watched_paths(self, paths: Iterable[str]) -> None:
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for path in paths:
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if path not in self._paths:
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# By storing None this path will get reported as changed by
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# find_changed if it exists.
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self._file_data[path] = None
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self._paths |= set(paths)
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def remove_watched_paths(self, paths: Iterable[str]) -> None:
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for path in paths:
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if path in self._file_data:
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del self._file_data[path]
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self._paths -= set(paths)
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def _update(self, path: str) -> None:
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st = self.fs.stat(path)
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hash_digest = self.fs.hash_digest(path)
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self._file_data[path] = FileData(st.st_mtime, st.st_size, hash_digest)
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def _find_changed(self, paths: Iterable[str]) -> AbstractSet[str]:
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changed = set()
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for path in paths:
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old = self._file_data[path]
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try:
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st = self.fs.stat(path)
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except FileNotFoundError:
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if old is not None:
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# File was deleted.
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changed.add(path)
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self._file_data[path] = None
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else:
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if old is None:
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# File is new.
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changed.add(path)
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self._update(path)
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# Round mtimes down, to match the mtimes we write to meta files
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elif st.st_size != old.st_size or int(st.st_mtime) != int(old.st_mtime):
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# Only look for changes if size or mtime has changed as an
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# optimization, since calculating hash is expensive.
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new_hash = self.fs.hash_digest(path)
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self._update(path)
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if st.st_size != old.st_size or new_hash != old.hash:
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# Changed file.
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changed.add(path)
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return changed
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def find_changed(self) -> AbstractSet[str]:
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"""Return paths that have changes since the last call, in the watched set."""
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return self._find_changed(self._paths)
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def update_changed(self,
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remove: List[str],
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update: List[str],
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) -> AbstractSet[str]:
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"""Alternative to find_changed() given explicit changes.
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This only calls self.fs.stat() on added or updated files, not
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on all files. It believes all other files are unchanged!
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Implies add_watched_paths() for add and update, and
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remove_watched_paths() for remove.
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"""
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self.remove_watched_paths(remove)
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self.add_watched_paths(update)
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return self._find_changed(update)
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