Fixes file/directory collisions

A carefully crafted file could collide with a directory; this is no
longer possible.

file_archive/__init__.py

@@ -11,9 +11,10 @@
 
 
 def hash_file(f):
-    """Hashes a file to its 40 hex character SHA1.
+    """Hashes a file to a 40 hex character SHA1.
     """
     h = hashlib.sha1()
+    h.update('file\n')
     chunk = f.read(CHUNKSIZE)
     while chunk:
         h.update(chunk)
@@ -45,6 +46,7 @@ def hash_directory(path, visited=None):
         raise ValueError("Can't hash directory structure: loop detected at "
                          "%s" % path)
     visited.add(os.path.realpath(path))
+    h.update('dir\n')
     for f in sorted(os.listdir(path)):
         pf = os.path.join(path, f)
         if os.path.isdir(pf):

tests/test_api.py

@@ -84,12 +84,12 @@ def test_req_empty(self):
 
     def test_putfile(self):
         h1 = self.store.add_file(self.t('file1.bin'), {'a': 'b'})
-        self.assertEqual(h1, '6edc650f52e26ce867b3765e0563dc3e445cdaa9')
+        self.assertEqual(h1, 'fce92fa2647153f7d696a3c1884d732290273102')
         self.assertTrue(os.path.isfile(os.path.join(
                 self.path,
                 'objects',
-                '6e',
-                'dc650f52e26ce867b3765e0563dc3e445cdaa9')))
+                'fc',
+                'e92fa2647153f7d696a3c1884d732290273102')))
         self.assertEqual(
                 self.store.get(h1).metadata,
                 {'hash': h1, 'a': 'b'})