download_metadata(): fix off-by-one error

If the block starts after the end of the file, we don't need to download it.

src/s3ql/database.py

@@ -505,7 +505,7 @@ def download_metadata(
     with open(db_file, 'w+b', buffering=0) as fh:
         for (blockno, candidates) in block_list.items():
             off = blockno * blocksize
-            if off > file_size and not failsafe:
+            if off >= file_size and not failsafe:
                 log.debug('download_metadata: skipping obsolete block %d', blockno)
                 continue
             try:
@@ -551,6 +551,8 @@ def first_le_than(l: List[int], threshold: int):
         if e <= threshold:
             return e
 
+    raise ValueError('No element below %d in list of length %d' % (threshold, len(l)))
+
 
 def get_available_seq_nos(backend: AbstractBackend) -> List[int]:
     nos = []

tests/t1_database.py

@@ -343,3 +343,34 @@ def test_expiration_downup(backend):
         [None, 40, None],  # block 3
     ]
     _test_expiration(backend, contents_pre, contents_post, db_sizes=db_sizes, versions_to_keep=3)
+
+
+@pytest.mark.parametrize("incremental", (True, False))
+def test_download_shorter(backend, incremental):
+    # Test downloading older snapshot when the filesize has grown
+    sqlite3ext.reset()
+    params = FsAttributes(
+        metadata_block_size=BLOCKSIZE,
+        data_block_size=BLOCKSIZE,
+        seq_no=1,
+    )
+    with tempfile.NamedTemporaryFile() as tmpfh:
+        db = Connection(tmpfh.name, BLOCKSIZE)
+        db.execute("CREATE TABLE foo (id INT, data BLOB);")
+        for i in range(2):
+            db.execute("INSERT INTO foo VALUES(?, ?)", (i, DUMMY_DATA))
+
+        db.checkpoint()
+        upload_metadata(backend, db, params, incremental=incremental)
+        old_params = params.copy()
+        params.seq_no += 1
+
+        # Grow database
+        for i in range(2, 6):
+            db.execute("INSERT INTO foo VALUES(?, ?)", (i, DUMMY_DATA))
+        db.checkpoint()
+        upload_metadata(backend, db, params)
+        db.close()
+
+    with tempfile.NamedTemporaryFile() as tmpfh:
+        download_metadata(backend, tmpfh.name, old_params)