Pausable response streams (#1179)

* This commit adds handlers for the asyncio/uvloop protocol callbacks for pause_writing and resume_writing.
These are needed for the correct functioning of built-in tcp flow-control provided by uvloop and asyncio.
This is somewhat of a breaking change, because the `write` function in user streaming callbacks now must be `await`ed.
This is necessary because it is possible now that the http protocol may be paused, and any calls to write may need to wait on an async event to be called to become unpaused.

Updated examples and tests to reflect this change.

This change does not apply to websocket connections. A change to websocket connections may be required to match this change.

* Fix a couple of PEP8 errors caused by previous rebase.

* update docs

add await syntax to response.write in response-streaming docs.

* remove commented out code from a test file

tests/test_request_stream.py

@@ -83,7 +83,7 @@ def test_request_stream_app():
                 body = await request.stream.get()
                 if body is None:
                     break
-                response.write(body.decode('utf-8'))
+                await response.write(body.decode('utf-8'))
         return stream(streaming)
 
     @app.put('/_put')
@@ -100,7 +100,7 @@ def test_request_stream_app():
                 body = await request.stream.get()
                 if body is None:
                     break
-                response.write(body.decode('utf-8'))
+                await response.write(body.decode('utf-8'))
         return stream(streaming)
 
     @app.patch('/_patch')
@@ -117,7 +117,7 @@ def test_request_stream_app():
                 body = await request.stream.get()
                 if body is None:
                     break
-                response.write(body.decode('utf-8'))
+                await response.write(body.decode('utf-8'))
         return stream(streaming)
 
     assert app.is_request_stream is True
@@ -177,7 +177,7 @@ def test_request_stream_handle_exception():
                 body = await request.stream.get()
                 if body is None:
                     break
-                response.write(body.decode('utf-8'))
+                await response.write(body.decode('utf-8'))
         return stream(streaming)
 
     # 404
@@ -231,7 +231,7 @@ def test_request_stream_blueprint():
                 body = await request.stream.get()
                 if body is None:
                     break
-                response.write(body.decode('utf-8'))
+                await response.write(body.decode('utf-8'))
         return stream(streaming)
 
     @bp.put('/_put')
@@ -248,7 +248,7 @@ def test_request_stream_blueprint():
                 body = await request.stream.get()
                 if body is None:
                     break
-                response.write(body.decode('utf-8'))
+                await response.write(body.decode('utf-8'))
         return stream(streaming)
 
     @bp.patch('/_patch')
@@ -265,7 +265,7 @@ def test_request_stream_blueprint():
                 body = await request.stream.get()
                 if body is None:
                     break
-                response.write(body.decode('utf-8'))
+                await response.write(body.decode('utf-8'))
         return stream(streaming)
 
     app.blueprint(bp)
@@ -380,7 +380,7 @@ def test_request_stream():
                 body = await request.stream.get()
                 if body is None:
                     break
-                response.write(body.decode('utf-8'))
+                await response.write(body.decode('utf-8'))
         return stream(streaming)
 
     @app.get('/get')

tests/test_response.py

@@ -10,6 +10,7 @@ from random import choice
 
 from sanic import Sanic
 from sanic.response import HTTPResponse, stream, StreamingHTTPResponse, file, file_stream, json
+from sanic.server import HttpProtocol
 from sanic.testing import HOST, PORT
 from unittest.mock import MagicMock
 
@@ -30,9 +31,10 @@ def test_response_body_not_a_string():
 
 
 async def sample_streaming_fn(response):
-    response.write('foo,')
+    await response.write('foo,')
     await asyncio.sleep(.001)
-    response.write('bar')
+    await response.write('bar')
+
 
 
 def test_method_not_allowed():
@@ -189,20 +191,30 @@ def test_stream_response_includes_chunked_header():
 
 def test_stream_response_writes_correct_content_to_transport(streaming_app):
     response = StreamingHTTPResponse(sample_streaming_fn)
-    response.transport = MagicMock(asyncio.Transport)
+    response.protocol = MagicMock(HttpProtocol)
+    response.protocol.transport = MagicMock(asyncio.Transport)
+
+    async def mock_drain():
+        pass
+
+    def mock_push_data(data):
+        response.protocol.transport.write(data)
+
+    response.protocol.push_data = mock_push_data
+    response.protocol.drain = mock_drain
 
     @streaming_app.listener('after_server_start')
     async def run_stream(app, loop):
         await response.stream()
-        assert response.transport.write.call_args_list[1][0][0] == (
+        assert response.protocol.transport.write.call_args_list[1][0][0] == (
             b'4\r\nfoo,\r\n'
         )
 
-        assert response.transport.write.call_args_list[2][0][0] == (
+        assert response.protocol.transport.write.call_args_list[2][0][0] == (
             b'3\r\nbar\r\n'
         )
 
-        assert response.transport.write.call_args_list[3][0][0] == (
+        assert response.protocol.transport.write.call_args_list[3][0][0] == (
             b'0\r\n\r\n'
         )