Fix Chunked Transport-Encoding in ASGI streaming response

In ASGI-mode, don't do sanic-side response chunk encoding, leave that to the ASGI-response-transport
Don't set content-length when using chunked-encoding in ASGI mode, this is incompatible with ASGI Chunked Transport-Encoding.

(cherry picked from commit c0839afdde)

sanic/app.py

@@ -1474,3 +1474,4 @@ class Sanic:
         self.asgi = True
         asgi_app = await ASGIApp.create(self, scope, receive, send)
         await asgi_app()
+    _asgi_single_callable = True  # We conform to ASGI 3.0 single-callable

sanic/asgi.py

@@ -309,13 +309,17 @@ class ASGIApp:
         callback = None if self.ws else self.stream_callback
         await handler(self.request, None, callback)
 
+    _asgi_single_callable = True  # We conform to ASGI 3.0 single-callable
+
     async def stream_callback(self, response: HTTPResponse) -> None:
         """
         Write the response.
         """
         headers: List[Tuple[bytes, bytes]] = []
         cookies: Dict[str, str] = {}
+        content_length: List[str] = []
         try:
+            content_length = response.headers.popall("content-length", [])
             cookies = {
                 v.key: v
                 for _, v in list(
@@ -348,10 +352,17 @@ class ASGIApp:
             ]
 
         response.asgi = True
-
-        if "content-length" not in response.headers and not isinstance(
-            response, StreamingHTTPResponse
-        ):
+        is_streaming = isinstance(response, StreamingHTTPResponse)
+        if is_streaming and getattr(response, "chunked", False):
+            # disable sanic chunking, this is done at the ASGI-server level
+            response.chunked = False
+            # content-length header is removed to signal to the ASGI-server
+            # to use automatic-chunking if it supports it
+        elif len(content_length) > 0:
+            headers += [
+                (b"content-length", str(content_length[0]).encode("latin-1"))
+            ]
+        elif not is_streaming:
             headers += [
                 (b"content-length", str(len(response.body)).encode("latin-1"))
             ]

sanic/response.py

@@ -80,6 +80,8 @@ class StreamingHTTPResponse(BaseHTTPResponse):
         if type(data) != bytes:
             data = self._encode_body(data)
 
+        # `chunked` will always be False in ASGI-mode, even if the underlying
+        # ASGI Transport implements Chunked transport. That does it itself.
         if self.chunked:
             await self.protocol.push_data(b"%x\r\n%b\r\n" % (len(data), data))
         else:

tests/test_response.py

@@ -235,7 +235,7 @@ def test_chunked_streaming_returns_correct_content(streaming_app):
 @pytest.mark.asyncio
 async def test_chunked_streaming_returns_correct_content_asgi(streaming_app):
     request, response = await streaming_app.asgi_client.get("/")
-    assert response.text == "4\r\nfoo,\r\n3\r\nbar\r\n0\r\n\r\n"
+    assert response.text == "foo,bar"
 
 
 def test_non_chunked_streaming_adds_correct_headers(non_chunked_streaming_app):