Fix the mapping stream add() function (#59)

The sorting should be only on the runlist index. Blanket sorting on all the
tuple fields will fail as filehandles/BinaryIO is not sortable.

dissect/util/stream.py

@@ -281,9 +281,11 @@ def add(self, offset: int, size: int, fh: BinaryIO, file_offset: int = 0) -> Non
             size: The size that this mapped fh spans in the stream.
             fh: The file-like object to map.
             file_offset: The offset in the fh to start from.
+
+        Note that there is no check on overlapping offsets and/or sizes.
         """
         self._runs.append((offset, size, fh, file_offset))
-        self._runs = sorted(self._runs)
+        self._runs = sorted(self._runs, key=lambda run: run[0])
         self._buf = None
         self.size = self._runs[-1][0] + self._runs[-1][1]
 

tests/test_stream.py

@@ -96,6 +96,20 @@ def test_mapping_stream() -> None:
     assert fh.read(1) == b""
 
 
+def test_mapping_stream_same_offset() -> None:
+    buffers = [
+        io.BytesIO(b"\x01" * 512),
+        io.BytesIO(b"\x02" * 512),
+    ]
+    fh = stream.MappingStream()
+    # Add them in different orders to test if sorting works
+    fh.add(0, 1024, buffers[0])
+    fh.add(0, 1024, buffers[1])  # This should not raise an exception in add()
+
+    assert fh._runs[0][2] == buffers[0]
+    assert fh._runs[1][2] == buffers[1]
+
+
 def test_runlist_stream() -> None:
     buf = io.BytesIO(b"\x01" * 512 + b"\x02" * 512 + b"\x03" * 512)
     fh = stream.RunlistStream(buf, [(0, 32), (32, 16), (48, 48)], 1536, 16)