# Write patch file with open(patch_file, 'wb') as f_patch: # Header: magic bytes + old size + new size f_patch.write(b'XD3P') f_patch.write(old_len.to_bytes(8, 'little')) f_patch.write(new_len.to_bytes(8, 'little')) for op in patch_ops: if op[0] == 'COPY': f_patch.write(b'\x01') # opcode COPY f_patch.write(op[1].to_bytes(8, 'little')) # position f_patch.write(op[2].to_bytes(4, 'little')) # length else: # ADD f_patch.write(b'\x02') # opcode ADD f_patch.write(bytes([op[1]])) # single byte
with open(patch_file, 'rb') as f_patch: # Read header magic = f_patch.read(4) if magic != b'XD3P': raise ValueError("Invalid patch file format") old_len = int.from_bytes(f_patch.read(8), 'little') new_len = int.from_bytes(f_patch.read(8), 'little') if len(old_data) != old_len: raise ValueError("Old file size mismatch") # Reconstruct new data new_data = bytearray() while len(new_data) < new_len: opcode = f_patch.read(1) if not opcode: break if opcode[0] == 0x01: # COPY pos = int.from_bytes(f_patch.read(8), 'little') length = int.from_bytes(f_patch.read(4), 'little') new_data.extend(old_data[pos:pos+length]) elif opcode[0] == 0x02: # ADD byte = f_patch.read(1) new_data.extend(byte) else: raise ValueError("Unknown opcode in patch") # Write output with open(output_file, 'wb') as f_out: f_out.write(new_data)
old_len = len(old_data) new_len = len(new_data)
print(f"Patch created: {patch_file}") print(f"Operations: {len(patch_ops)}") if == " main ": if len(sys.argv) != 4: print("Usage: python make_xdelta_patch.py <old_file> <new_file> <patch_file>") sys.exit(1) create_patch(sys.argv[1], sys.argv[2], sys.argv[3]) 2. Patch applicator (reconstructs new file from old + patch) # xdeltapatcher.py import sys def apply_patch(old_file, patch_file, output_file): with open(old_file, 'rb') as f_old: old_data = f_old.read()
# Simple patch format: copy from old or add new bytes patch_ops = [] i = 0 while i < new_len: # Try to find longest match in old data best_match_len = 0 best_match_pos = 0 search_len = min(1024, new_len - i) for j in range(max(0, i - 1024), min(old_len, i + 1024)): # Simple forward matching match_len = 0 while (i + match_len < new_len and j + match_len < old_len and new_data[i + match_len] == old_data[j + match_len]): match_len += 1 if match_len > best_match_len and match_len >= 4: best_match_len = match_len best_match_pos = j if best_match_len >= 4: # COPY command patch_ops.append(('COPY', best_match_pos, best_match_len)) i += best_match_len else: # ADD command (single byte) patch_ops.append(('ADD', new_data[i])) i += 1
It applies a binary patch (generated by comparing an old file and a new file) to recreate the new file from the old one. # make_xdelta_patch.py import sys def create_patch(old_file, new_file, patch_file): with open(old_file, 'rb') as f_old, open(new_file, 'rb') as f_new: old_data = f_old.read() new_data = f_new.read()
