cache: add seek()/tell()/read() to SyncFile, use SaveFile in _write_files_cache, fixes #9390

Author: mr-raj12

src/borg/cache.py

@@ -582,36 +582,39 @@ def _write_files_cache(self, files):
         discard_after = min(newest_cmtime, start_backup_time)
         ttl = int(os.environ.get("BORG_FILES_CACHE_TTL", 2))
         files_cache_logger.debug("FILES-CACHE-SAVE: starting...")
-        # TODO: use something like SaveFile here, but that didn't work due to SyncFile missing .seek().
-        with IntegrityCheckedFile(path=str(self.path / self.files_cache_name()), write=True) as fd:
-            entries = 0
-            age_discarded = 0
-            race_discarded = 0
-            for path_hash, entry in files.items():
-                entry = self.decompress_entry(entry)
-                if entry.age == 0:  # current entries
-                    if max(timestamp_to_int(entry.ctime), timestamp_to_int(entry.mtime)) < discard_after:
-                        # Only keep files seen in this backup that old enough not to suffer race conditions relating
-                        # to filesystem snapshots and ctime/mtime granularity or being modified while we read them.
-                        keep = True
-                    else:
-                        keep = False
-                        race_discarded += 1
-                else:  # old entries
-                    if entry.age < ttl:
-                        # Also keep files from older backups that have not reached BORG_FILES_CACHE_TTL yet.
-                        keep = True
-                    else:
-                        keep = False
-                        age_discarded += 1
-                if keep:
-                    msgpack.pack((path_hash, entry), fd)
-                    entries += 1
+        cache_path = str(self.path / self.files_cache_name())
+        with SaveFile(cache_path, binary=True) as sync_file:
+            with IntegrityCheckedFile(path=cache_path, write=True, override_fd=sync_file) as fd:
+                entries = 0
+                age_discarded = 0
+                race_discarded = 0
+                for path_hash, entry in files.items():
+                    entry = self.decompress_entry(entry)
+                    if entry.age == 0:  # current entries
+                        if max(timestamp_to_int(entry.ctime), timestamp_to_int(entry.mtime)) < discard_after:
+                            # Only keep files seen in this backup that old enough not to suffer race conditions
+                            # relating to filesystem snapshots and ctime/mtime granularity or being modified
+                            # while we read them.
+                            keep = True
+                        else:
+                            keep = False
+                            race_discarded += 1
+                    else:  # old entries
+                        if entry.age < ttl:
+                            # Also keep files from older backups that have not reached BORG_FILES_CACHE_TTL yet.
+                            keep = True
+                        else:
+                            keep = False
+                            age_discarded += 1
+                    if keep:
+                        msgpack.pack((path_hash, entry), fd)
+                        entries += 1
+            integrity_data = fd.integrity_data
         files_cache_logger.debug(f"FILES-CACHE-KILL: removed {age_discarded} entries with age >= TTL [{ttl}]")
         t_str = datetime.fromtimestamp(discard_after / 1e9, timezone.utc).isoformat()
         files_cache_logger.debug(f"FILES-CACHE-KILL: removed {race_discarded} entries with ctime/mtime >= {t_str}")
         files_cache_logger.debug(f"FILES-CACHE-SAVE: finished, {entries} remaining entries saved.")
-        return fd.integrity_data
+        return integrity_data
 
     def file_known_and_unchanged(self, hashed_path, path_hash, st):
         """

src/borg/platform/base.py

@@ -1,4 +1,5 @@
 import errno
+import io
 import os
 import socket
 import unicodedata
@@ -163,7 +164,7 @@ def __init__(self, path, *, fd=None, binary=False):
                that corresponds to path (like from os.open(path, ...) or os.mkstemp(...))
         :param binary: whether to open in binary mode, default is False.
         """
-        mode = "xb" if binary else "x"  # x -> raise FileExists exception in open() if file exists already
+        mode = "x+b" if binary else "x+"  # x -> raise FileExists exception in open() if file exists already
         self.path = path
         if fd is None:
             self.f = open(str(path), mode=mode)  # Python file object
@@ -180,6 +181,15 @@ def __exit__(self, exc_type, exc_val, exc_tb):
     def write(self, data):
         self.f.write(data)
 
+    def read(self, *args, **kwargs):
+        return self.f.read(*args, **kwargs)
+
+    def seek(self, offset, whence=io.SEEK_SET):
+        return self.f.seek(offset, whence)
+
+    def tell(self):
+        return self.f.tell()
+
     def sync(self):
         """
         Synchronize file contents. Everything written prior to sync() must become durable before anything written
@@ -195,6 +205,8 @@ def sync(self):
 
     def close(self):
         """sync() and close."""
+        if self.f.closed:
+            return
         from .. import platform
 
         dirname = None

src/borg/testsuite/crypto/file_integrity_test.py

@@ -1,6 +1,7 @@
 import pytest
 
-from ...crypto.file_integrity import DetachedIntegrityCheckedFile, FileIntegrityError
+from ...crypto.file_integrity import DetachedIntegrityCheckedFile, FileIntegrityError, IntegrityCheckedFile
+from ...platform import SyncFile
 
 
 class TestReadIntegrityFile:
@@ -130,3 +131,19 @@ def test_part_independence(self, integrity_protected_file, partial_read):
                 if not partial_read:
                     fd.read()
                 # But overall it explodes with the final digest. Neat, eh?
+
+
+class TestIntegrityCheckedFileWithSyncFile:
+    def test_write_and_verify_with_syncfile(self, tmp_path):
+        """IntegrityCheckedFile works correctly with SyncFile as override_fd."""
+        path = str(tmp_path / "testfile")
+        with SyncFile(path, binary=True) as sf:
+            with IntegrityCheckedFile(path=path, write=True, override_fd=sf) as fd:
+                fd.write(b"test data for integrity check")
+            integrity_data = fd.integrity_data
+
+        assert integrity_data is not None
+
+        # verify the written data can be read back with integrity check
+        with IntegrityCheckedFile(path=path, write=False, integrity_data=integrity_data) as fd:
+            assert fd.read() == b"test data for integrity check"

src/borg/testsuite/platform/all_test.py

@@ -1,4 +1,6 @@
-from ...platform import swidth
+import io
+
+from ...platform import swidth, SyncFile
 
 
 def test_swidth_ascii():
@@ -11,3 +13,28 @@ def test_swidth_cjk():
 
 def test_swidth_mixed():
     assert swidth("borgバックアップ") == 4 + 6 * 2
+
+
+def test_syncfile_seek_tell(tmp_path):
+    """SyncFile exposes seek() and tell() from the underlying file object."""
+    path = tmp_path / "testfile"
+    with SyncFile(path, binary=True) as sf:
+        sf.write(b"hello world")
+        assert sf.tell() == 11
+        sf.seek(0, io.SEEK_SET)
+        assert sf.tell() == 0
+        sf.seek(0, io.SEEK_END)
+        assert sf.tell() == 11
+        sf.seek(5, io.SEEK_SET)
+        assert sf.tell() == 5
+        assert sf.read() == b" world"
+    assert path.read_bytes() == b"hello world"
+
+
+def test_syncfile_close_idempotent(tmp_path):
+    """Calling SyncFile.close() twice does not raise."""
+    path = tmp_path / "testfile"
+    sf = SyncFile(path, binary=True)
+    sf.write(b"data")
+    sf.close()
+    sf.close()  # must not raise