Add file format detection to format_inspector

Change-Id: If0a4251465507be035ffaf9d855299611637cfa9
(cherry picked from commit 79271eaa5c742a1741321198c43807857fb6ed94)

glance/common/format_inspector.py

@@ -883,13 +883,7 @@ class InfoWrapper(object):
             self._source.close()
 
 
-def get_inspector(format_name):
-    """Returns a FormatInspector class based on the given name.
-
-    :param format_name: The name of the disk_format (raw, qcow2, etc).
-    :returns: A FormatInspector or None if unsupported.
-    """
-    formats = {
+ALL_FORMATS = {
     'raw': FileInspector,
     'qcow2': QcowInspector,
     'vhd': VHDInspector,
@@ -897,6 +891,44 @@ def get_inspector(format_name):
     'vmdk': VMDKInspector,
     'vdi': VDIInspector,
     'qed': QEDInspector,
-    }
+}
 
-    return formats.get(format_name)
+
+def get_inspector(format_name):
+    """Returns a FormatInspector class based on the given name.
+
+    :param format_name: The name of the disk_format (raw, qcow2, etc).
+    :returns: A FormatInspector or None if unsupported.
+    """
+
+    return ALL_FORMATS.get(format_name)
+
+
+def detect_file_format(filename):
+    """Attempts to detect the format of a file.
+
+    This runs through a file one time, running all the known inspectors in
+    parallel. It stops reading the file once one of them matches or all of
+    them are sure they don't match.
+
+    Returns the FileInspector that matched, if any. None if 'raw'.
+    """
+    inspectors = {k: v() for k, v in ALL_FORMATS.items()}
+    with open(filename, 'rb') as f:
+        for chunk in chunked_reader(f):
+            for format, inspector in list(inspectors.items()):
+                try:
+                    inspector.eat_chunk(chunk)
+                except ImageFormatError:
+                    # No match, so stop considering this format
+                    inspectors.pop(format)
+                    continue
+                if (inspector.format_match and inspector.complete and
+                        format != 'raw'):
+                    # First complete match (other than raw) wins
+                    return inspector
+            if all(i.complete for i in inspectors.values()):
+                # If all the inspectors are sure they are not a match, avoid
+                # reading to the end of the file to settle on 'raw'.
+                break
+    return inspectors['raw']

glance/tests/unit/common/test_format_inspector.py

@@ -313,62 +313,6 @@ class TestFormatInspectors(test_utils.BaseTestCase):
         data[0x4F] = 0x80
         self.assertTrue(inspector.has_unknown_features)
 
-    def test_vmdk_safety_checks(self):
-        region = format_inspector.CaptureRegion(0, 0)
-        inspector = format_inspector.VMDKInspector()
-        inspector.new_region('descriptor', region)
-
-        # This should be a legit VMDK descriptor which comments, blank lines,
-        # an extent, some ddb content, and some header values.
-        legit_desc = ['# This is a comment',
-                      '',
-                      ' ',
-                      'createType=monolithicSparse',
-                      'RW 1234 SPARSE "foo.vmdk"',
-                      'ddb.adapterType = "MFM',
-                      '# EOF']
-        region.data = ('\n'.join(legit_desc)).encode('ascii')
-        region.length = len(region.data)
-        self.assertTrue(inspector.safety_check())
-
-        # Any of these lines should trigger an error indicating that there is
-        # something in the descriptor we don't understand
-        bad_lines = [
-            '#\U0001F4A9',
-            'header Name=foo',
-            'foo bar',
-            'WR 123 SPARSE "foo.vmdk"',
-        ]
-
-        for bad_line in bad_lines:
-            # Encode as UTF-8 purely so we can test that anything non-ASCII
-            # will trigger the decode check
-            region.data = bad_line.encode('utf-8')
-            region.length = len(region.data)
-            self.assertRaisesRegex(format_inspector.ImageFormatError,
-                                   'Invalid VMDK descriptor',
-                                   inspector.safety_check)
-
-        # Extents with slashes in the name fail the safety check
-        region.data = b'RW 123 SPARSE "/etc/shadow"'
-        region.length = len(region.data)
-        self.assertFalse(inspector.safety_check())
-
-        # A descriptor that specifies no extents fails the safety check
-        region.data = b'# Nothing'
-        region.length = len(region.data)
-        self.assertFalse(inspector.safety_check())
-
-    def test_vmdk_reject_footer(self):
-        data = struct.pack('<4sIIQQQQIQQ', b'KDMV', 3, 0, 0, 0, 0, 1, 0, 0,
-                           format_inspector.VMDKInspector.GD_AT_END)
-        inspector = format_inspector.VMDKInspector()
-        inspector.region('header').data = data
-        inspector.region('header').length = len(data)
-        self.assertRaisesRegex(format_inspector.ImageFormatError,
-                               'footer',
-                               inspector.post_process)
-
     def test_vdi(self):
         self._test_format('vdi')