fallback: pass object_pairs_hook a list of pairs (#744)

Author: youdie006

msgpack/fallback.py

@@ -529,15 +529,15 @@ def _unpack(self, execute=EX_CONSTRUCT):
                     self._unpack(EX_SKIP)
                 return
             if self._object_pairs_hook is not None:
-
-                def _gen():
-                    for _ in range(n):
-                        key = self._unpack(EX_CONSTRUCT)
-                        if self._strict_map_key and type(key) not in (str, bytes):
-                            raise ValueError("%s is not allowed for map key" % str(type(key)))
-                        yield key, self._unpack(EX_CONSTRUCT)
-
-                ret = self._object_pairs_hook(_gen())
+                # Pass a list, as the C extension does, so the whole map is
+                # consumed even if the hook does not iterate it.
+                pairs = []
+                for _ in range(n):
+                    key = self._unpack(EX_CONSTRUCT)
+                    if self._strict_map_key and type(key) not in (str, bytes):
+                        raise ValueError("%s is not allowed for map key" % str(type(key)))
+                    pairs.append((key, self._unpack(EX_CONSTRUCT)))
+                ret = self._object_pairs_hook(pairs)
             else:
                 ret = {}
                 for _ in range(n):

test/test_obj.py

@@ -41,6 +41,18 @@ def test_decode_pairs_hook():
     assert unpacked[1] == prod_sum
 
 
+def test_decode_pairs_hook_receives_list():
+    def reject_duplicate_keys(pairs):
+        keys = [k for k, _ in pairs]
+        assert len(keys) == len(set(keys))
+        return dict(pairs)
+
+    packed = packb([{"a": 1, "b": 2}, 3])
+    assert unpackb(packed, object_pairs_hook=reject_duplicate_keys) == [{"a": 1, "b": 2}, 3]
+    assert unpackb(packed, object_pairs_hook=lambda pairs: pairs[0]) == [("a", 1), 3]
+    assert unpackb(packed, object_pairs_hook=lambda pairs: None) == [None, 3]
+
+
 def test_only_one_obj_hook():
     with raises(TypeError):
         unpackb(b"", object_hook=lambda x: x, object_pairs_hook=lambda x: x)