[models/utils] Track file offset for chunk parts

Preparation for smarter patching with downloader rewrite.

legendary/models/json_manifest.py

@@ -157,15 +157,18 @@ class JSONFML(FML):
             _fm.chunk_parts = []
             _fm.install_tags = _fmj.pop('InstallTags', list())
 
+            _offset = 0
             for _cpj in _fmj.pop('FileChunkParts'):
                 _cp = ChunkPart()
                 _cp.guid = guid_from_json(_cpj.pop('Guid'))
                 _cp.offset = blob_to_num(_cpj.pop('Offset'))
                 _cp.size = blob_to_num(_cpj.pop('Size'))
+                _cp.file_offset = _offset
                 _fm.file_size += _cp.size
                 if _cpj:
                     print(f'Non-read ChunkPart keys: {_cpj.keys()}')
                 _fm.chunk_parts.append(_cp)
+                _offset += _cp.size
 
             if _fmj:
                 print(f'Non-read FileManifest keys: {_fmj.keys()}')

legendary/models/manifest.py

@@ -507,13 +507,20 @@ class FML:
         # Each file is made up of "Chunk Parts" that can be spread across the "chunk stream"
         for fm in _fml.elements:
             _elem = struct.unpack('<I', bio.read(4))[0]
+            _offset = 0
             for i in range(_elem):
                 chunkp = ChunkPart()
+                _start = bio.tell()
                 _size = struct.unpack('<I', bio.read(4))[0]
                 chunkp.guid = struct.unpack('<IIII', bio.read(16))
                 chunkp.offset = struct.unpack('<I', bio.read(4))[0]
                 chunkp.size = struct.unpack('<I', bio.read(4))[0]
+                chunkp.file_offset = _offset
                 fm.chunk_parts.append(chunkp)
+                _offset += chunkp.size
+                if (diff := (bio.tell() - _start - _size)) > 0:
+                    logger.warning(f'Did not read {diff} bytes from chunk part!')
+                    bio.seek(diff)
 
         # we have to calculate the actual file size ourselves
         for fm in _fml.elements:
@@ -601,10 +608,11 @@ class FileManifest:
 
 
 class ChunkPart:
-    def __init__(self, guid=None, offset=0, size=0):
+    def __init__(self, guid=None, offset=0, size=0, file_offset=0):
         self.guid = guid
         self.offset = offset
         self.size = size
+        self.file_offset = file_offset
         # caches for things that are "expensive" to compute
         self._guid_str = None
         self._guid_num = None
@@ -623,8 +631,8 @@ class ChunkPart:
 
     def __repr__(self):
         guid_readable = '-'.join('{:08x}'.format(g) for g in self.guid)
-        return '<ChunkPart (guid={}, offset={}, size={})>'.format(
+        return '<ChunkPart (guid={}, offset={}, size={}, file_offset={})>'.format(
-            guid_readable, self.offset, self.size)
+            guid_readable, self.offset, self.size, self.file_offset)
 
 
 class CustomFields:

legendary/utils/savegame_helper.py

@@ -123,7 +123,8 @@ class SaveGameHelper:
 
                     # create chunk part and write it to chunk buffer
                     cp = ChunkPart(guid=cur_chunk.guid, offset=cur_buffer.tell(),
-                                   size=min(remaining, 1024 * 1024 - cur_buffer.tell()))
+                                   size=min(remaining, 1024 * 1024 - cur_buffer.tell()),
+                                   file_offset=cf.tell())
                     _tmp = cf.read(cp.size)
                     if not _tmp:
                         self.log.warning(f'Got EOF for "{f.filename}" with {remaining} bytes remaining! '