Merge pull request #1 from JosiahWI/main

Offset caching for file blocks

blendparse.py

@@ -3,44 +3,55 @@
 import io
 
 # A class for opening and reading data from .blend files
-class Blendfile():
+class Blendfile(io.FileIO):
     def __init__(self, filename):
-        self.filename = filename
-        with open(filename, "rb") as f:
-            self.stream = io.BufferedReader(f)
-            self.stream.seek(0)
+        super().__init__(filename, "rb")
+        # Offset of first file block header.
+        self._block_start = 12
+        self.read_header()
+        # Offsets of each file block by code.
+        self._block_offsets = self._read_block_offsets()
+        
+        # Looping through file block headers to find scene header
+        for block_code, offset in self._block_offsets.items():
+            if block_code.startswith("SC"):
+                print(f"Found scene block at offset {offset}!")
 
-            # File identifier, 8-byte string; should always be "BLENDER"
-            self.identifier = self.stream.read(7).decode("utf-8")
+    def _read_block_offsets(self):
+        """
+        Cache the offset to each file block.
+        """
 
-            # Pointer size, 1-byte char; '-' indicates 8 bytes, '_' indicates 4
-            self.pointer_size = 8 if self.stream.read(1).decode("utf-8") == "-" else 4
+        block_offsets = {}
+        self.seek(self._block_start)
+        while True:
+            # File block code; identifies type of data
+            block_code = self.read(4).decode("utf-8")
+            # Empty string indicates EOF.
+            if block_code == "":
+                break
+            block_offsets[block_code] = self.tell()
+            # Size of file block, after this header
+            block_size = int.from_bytes(self.read(4), self.endianness)
+            
+            # Skip rest of file header.
+            self.seek(self.pointer_size + 8, io.SEEK_CUR)
+            # Skip to next file block.
+            self.seek(block_size, io.SEEK_CUR)
 
-            # Endianness, 1-byte char; 'v' indicates little endian, 'V' indicates big
-            self.endianness = "little" if self.stream.read(1).decode("utf-8") == "v" else "big"
+        return block_offsets
 
-            # Blender version, 3-byte int; v2.93 is represented as 293, and so on
-            self.version = int(self.stream.read(3))
+    def read_header(self):
+        self.seek(0)
 
-            # Looping through file block headers to find scene header
-            # TODO: Implement proper error handling if the target file block does not exist.
-            while True:
+        # File identifier, 8-byte string; should always be "BLENDER"
+        self.identifier = self.read(7).decode("utf-8")
 
-                # File block code; identifies type of data
-                code = self.stream.read(4).decode("utf-8")
+        # Pointer size, 1-byte char; '-' indicates 8 bytes, '_' indicates 4
+        self.pointer_size = 8 if self.read(1).decode("utf-8") == "-" else 4
 
-                # Size of file block, after this header
-                size = int.from_bytes(self.stream.read(4), self.endianness)
+        # Endianness, 1-byte char; 'v' indicates little endian, 'V' indicates big
+        self.endianness = "little" if self.read(1).decode("utf-8") == "v" else "big"
 
-                # Seeking to end of file block header
-                self.stream.seek(8+self.pointer_size+size, 1)
-
-                # Scene file block codes will always begin with "SC"
-                if code.startswith("SC"):
-                    # TODO: Acquire SDNA index of scene data, to be found in DNA1 file block
-                    # SDNA index occurs directly following file block size in header
-                    # and is pointer_size bytes long
-                    break
-                
-                # Seeking to the start of the next file block
-                self.stream.seek(8+self.pointer_size+size, 1)
+        # Blender version, 3-byte int; v2.93 is represented as 293, and so on
+        self.version = int(self.read(3))