StreamResponse and Response implement MutableMapping interface

CHANGES/2246.feature

@@ -0,0 +1 @@
+StreamResponse and Response are now MutableMappings.

aiohttp/web_response.py

@@ -1,3 +1,4 @@
+import collections
 import datetime
 import enum
 import json
@@ -33,7 +34,7 @@ class ContentCoding(enum.Enum):
 ############################################################
 
 
-class StreamResponse(HeadersMixin):
+class StreamResponse(collections.MutableMapping, HeadersMixin):
 
     _length_check = True
 
@@ -49,6 +50,7 @@ def __init__(self, *, status=200, reason=None, headers=None):
         self._payload_writer = None
         self._eof_sent = False
         self._body_length = 0
+        self._state = {}
 
         if headers is not None:
             self._headers = CIMultiDict(headers)
@@ -439,6 +441,21 @@ def __repr__(self):
         return "<{} {} {}>".format(self.__class__.__name__,
                                    self.reason, info)
 
+    def __getitem__(self, key):
+        return self._state[key]
+
+    def __setitem__(self, key, value):
+        self._state[key] = value
+
+    def __delitem__(self, key):
+        del self._state[key]
+
+    def __len__(self):
+        return len(self._state)
+
+    def __iter__(self):
+        return iter(self._state)
+
 
 class Response(StreamResponse):
 

docs/web_advanced.rst

@@ -284,6 +284,17 @@ This is mostly useful for :ref:`aiohttp-web-middlewares` and
 :ref:`aiohttp-web-signals` handlers to store data for further processing by the
 next handlers in the chain.
 
+:class:`aiohttp.web.StreamResponse` and :class:`aiohttp.web.Response` objects
+also support :class:`collections.abc.MutableMapping` interface. This is useful
+when you want to share data with signals and middlewares once all the work in
+the handler is done::
+
+    async def handler(request):
+      [ do all the work ]
+      response['my_metric'] = 123
+      return response
+
+
 To avoid clashing with other *aiohttp* users and third-party libraries, please
 choose a unique key name for storing data.
 

docs/web_reference.rst

@@ -505,6 +505,16 @@ The common case for sending an answer from
    def handler(request):
        return Response("All right!")
 
+Response classes are :obj:`dict` like objects,
+allowing them to be used for :ref:`sharing
+data<aiohttp-web-data-sharing>` among :ref:`aiohttp-web-middlewares`
+and :ref:`aiohttp-web-signals` handlers::
+
+   resp['key'] = value
+
+.. versionadded:: 3.0
+
+   Dict-like interface support.
 
 StreamResponse
 ^^^^^^^^^^^^^^

tests/test_web_response.py

@@ -1,3 +1,4 @@
+import collections
 import datetime
 import json
 import re
@@ -76,6 +77,34 @@ def test_stream_response_ctor():
     assert resp.task is req.task
 
 
+def test_stream_response_is_mutable_mapping():
+    resp = StreamResponse()
+    assert isinstance(resp, collections.MutableMapping)
+    resp['key'] = 'value'
+    assert 'value' == resp['key']
+
+
+def test_stream_response_delitem():
+    resp = StreamResponse()
+    resp['key'] = 'value'
+    del resp['key']
+    assert 'key' not in resp
+
+
+def test_stream_response_len():
+    resp = StreamResponse()
+    assert len(resp) == 0
+    resp['key'] = 'value'
+    assert len(resp) == 1
+
+
+def test_request_iter():
+    resp = StreamResponse()
+    resp['key'] = 'value'
+    resp['key2'] = 'value2'
+    assert set(resp) == {'key', 'key2'}
+
+
 def test_content_length():
     resp = StreamResponse()
     assert resp.content_length is None