fix: Create media files atomically #1658
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It’s unlikely, but very bad, for a partially-written media file to be served by nginx (which doesn’t consult the `media` table) with `Cache-Control: immutable`. It would be nice if we could use the standard library’s `tempfile.NamedTemporaryFile` for this, but its deletion options are too limited to be much cleaner, and it sets different file permissions.
…dia` table row Might as well? `os.open` applies `O_CLOEXEC` by default.
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+53
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+69
| with _os_closing(os.open(dir_path, os.O_RDONLY | os.O_DIRECTORY)) as dir_fd: | ||
| temp_name = f"tmp-{os.urandom(8).hex()}" | ||
| outfile = open(temp_name, "xb", opener=partial(os.open, dir_fd=dir_fd)) | ||
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| try: | ||
| with outfile: | ||
| outfile.write(data) | ||
| outfile.flush() | ||
| os.fsync(outfile) | ||
| except: | ||
| os.unlink(temp_name, dir_fd=dir_fd) | ||
| raise | ||
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| os.replace(temp_name, hash_filename, src_dir_fd=dir_fd, dst_dir_fd=dir_fd) | ||
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| # Try to make sure the hash-named file is persisted before inserting it into the database | ||
| os.fsync(dir_fd) |
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The new atomic file creation logic (lines 53-69) lacks test coverage. Consider adding tests to verify: 1) temporary files are cleaned up on write failures, 2) the atomic rename succeeds, and 3) the fsync operations complete without errors. The existing tests in libweasyl/test/test_media.py only verify successful file creation paths.
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and do a best-effort directory
fsyncafter the rename before inserting them into the database.It’s unlikely, but very bad, for a partially-written media file to be served by nginx (which doesn’t consult the
mediatable) withCache-Control: immutable.It would be nice if we could use the standard library’s
tempfile.NamedTemporaryFilefor this, but its deletion options are too limited to be much cleaner, and it sets different file permissions.