Detect non-upgraded Attic repositories

When opening a repository, always try to read the magic number of the
latest segment and compare it to the Attic segment magic (unless the
repository is opened for upgrading). If an Attic segment is detected,
raise a dedicated exception, telling the user to upgrade the repository
first.

Fixes #1933.

docs/internals/frontends.rst

@@ -499,6 +499,8 @@ Errors
         Insufficient free space to complete transaction (required: {}, available: {}).
     Repository.InvalidRepository
         {} is not a valid repository. Check repo config.
+    Repository.AtticRepository
+        Attic repository detected. Please run "borg upgrade {}".
     Repository.ObjectNotFound
         Object with key {} not found in repository {}.
 

src/borg/remote.py

@@ -726,6 +726,11 @@ def handle_error(unpacked):
                     raise IntegrityError('(not available)')
                 else:
                     raise IntegrityError(args[0].decode())
+            elif error == 'AtticRepository':
+                if old_server:
+                    raise Repository.AtticRepository('(not available)')
+                else:
+                    raise Repository.AtticRepository(args[0].decode())
             elif error == 'PathNotAllowed':
                 if old_server:
                     raise PathNotAllowed('(unknown)')

src/borg/repository.py

@@ -30,6 +30,8 @@
 
 MAGIC = b'BORG_SEG'
 MAGIC_LEN = len(MAGIC)
+ATTIC_MAGIC = b'ATTICSEG'
+assert len(ATTIC_MAGIC) == MAGIC_LEN
 TAG_PUT = 0
 TAG_DELETE = 1
 TAG_COMMIT = 2
@@ -116,6 +118,9 @@ class AlreadyExists(Error):
     class InvalidRepository(Error):
         """{} is not a valid repository. Check repo config."""
 
+    class AtticRepository(Error):
+        """Attic repository detected. Please run "borg upgrade {}"."""
+
     class CheckNeeded(ErrorWithTraceback):
         """Inconsistency detected. Please run "borg check {}"."""
 
@@ -134,7 +139,7 @@ class StorageQuotaExceeded(Error):
         """The storage quota ({}) has been exceeded ({}). Try deleting some archives."""
 
     def __init__(self, path, create=False, exclusive=False, lock_wait=None, lock=True,
-                 append_only=False, storage_quota=None):
+                 append_only=False, storage_quota=None, check_segment_magic=True):
         self.path = os.path.abspath(path)
         self._location = Location('file://%s' % self.path)
         self.io = None  # type: LoggedIO
@@ -154,6 +159,7 @@ def __init__(self, path, create=False, exclusive=False, lock_wait=None, lock=Tru
         self.storage_quota = storage_quota
         self.storage_quota_use = 0
         self.transaction_doomed = None
+        self.check_segment_magic = check_segment_magic
 
     def __del__(self):
         if self.lock:
@@ -370,6 +376,12 @@ def open(self, path, exclusive, lock_wait=None, lock=True):
             self.storage_quota = self.config.getint('repository', 'storage_quota', fallback=0)
         self.id = unhexlify(self.config.get('repository', 'id').strip())
         self.io = LoggedIO(self.path, self.max_segment_size, self.segments_per_dir)
+        if self.check_segment_magic:
+            # read a segment and check whether we are dealing with a non-upgraded Attic repository
+            segment = self.io.get_latest_segment()
+            if segment is not None and self.io.get_segment_magic(segment) == ATTIC_MAGIC:
+                self.close()
+                raise self.AtticRepository(path)
 
     def close(self):
         if self.lock:
@@ -1245,6 +1257,11 @@ def segment_exists(self, segment):
     def segment_size(self, segment):
         return os.path.getsize(self.segment_filename(segment))
 
+    def get_segment_magic(self, segment):
+        fd = self.get_fd(segment)
+        fd.seek(0)
+        return fd.read(MAGIC_LEN)
+
     def iter_objects(self, segment, offset=0, include_data=False, read_data=True):
         """
         Return object iterator for *segment*.

src/borg/testsuite/archiver.py

@@ -55,6 +55,7 @@
 from . import BaseTestCase, changedir, environment_variable, no_selinux
 from . import are_symlinks_supported, are_hardlinks_supported, are_fifos_supported, is_utime_fully_supported
 from .platform import fakeroot_detected
+from .upgrader import attic_repo
 from . import key
 
 
@@ -2725,6 +2726,27 @@ def test_extract_hardlinks(self):
             assert os.stat('input/dir1/aaaa').st_nlink == 2
             assert os.stat('input/dir1/source2').st_nlink == 2
 
+    def test_detect_attic_repo(self):
+        path = attic_repo(self.repository_path)
+        cmds = [
+            ['create', path + '::test', self.tmpdir],
+            ['extract', path + '::test'],
+            ['check', path],
+            ['rename', path + '::test', 'newname'],
+            ['list', path],
+            ['delete', path],
+            ['prune', path],
+            ['info', path + '::test'],
+            ['mount', path, self.tmpdir],
+            ['key', 'export', path, 'exported'],
+            ['key', 'import', path, 'import'],
+            ['change-passphrase', path],
+            ['break-lock', path],
+        ]
+        for args in cmds:
+            output = self.cmd(*args, fork=True, exit_code=2)
+            assert 'Attic repository detected.' in output
+
 
 @unittest.skipUnless('binary' in BORG_EXES, 'no borg.exe available')
 class ArchiverTestCaseBinary(ArchiverTestCase):

src/borg/testsuite/upgrader.py

@@ -85,8 +85,8 @@ def test_convert_segments(attic_repo, inplace):
     :param attic_repo: a populated attic repository (fixture)
     """
     repo_path = attic_repo
-    # check should fail because of magic number
+    with pytest.raises(Repository.AtticRepository):
-    assert not repo_valid(repo_path)
+        repo_valid(repo_path)
     repository = AtticRepositoryUpgrader(repo_path, create=False)
     with repository:
         segments = [filename for i, filename in repository.io.segment_iterator()]
@@ -149,8 +149,8 @@ def test_convert_all(attic_repo, attic_key_file, inplace):
     """
     repo_path = attic_repo
 
-    # check should fail because of magic number
+    with pytest.raises(Repository.AtticRepository):
-    assert not repo_valid(repo_path)
+        repo_valid(repo_path)
 
     def stat_segment(path):
         return os.stat(os.path.join(path, 'data', '0', '0'))

src/borg/upgrader.py

@@ -19,6 +19,7 @@
 class AtticRepositoryUpgrader(Repository):
     def __init__(self, *args, **kw):
         kw['lock'] = False  # do not create borg lock files (now) in attic repo
+        kw['check_segment_magic'] = False  # skip the Attic check when upgrading
         super().__init__(*args, **kw)
 
     def upgrade(self, dryrun=True, inplace=False, progress=False):