pass request_buffer_queue_size argument to HttpProtocol (#1717)

* pass request_buffer_queue_size argument to HttpProtocol

* fix to use simultaneously only one task to put body to stream buffer

* add a test code for REQUEST_BUFFER_QUEUE_SIZE

tests/test_request_buffer_queue_size.py

@@ -0,0 +1,36 @@
+import io
+
+from sanic.response import text
+
+data = "abc" * 10_000_000
+
+
+def test_request_buffer_queue_size(app):
+    default_buf_qsz = app.config.get("REQUEST_BUFFER_QUEUE_SIZE")
+    qsz = 1
+    while qsz == default_buf_qsz:
+        qsz += 1
+    app.config.REQUEST_BUFFER_QUEUE_SIZE = qsz
+
+    @app.post("/post", stream=True)
+    async def post(request):
+        assert request.stream.buffer_size == qsz
+        print("request.stream.buffer_size =", request.stream.buffer_size)
+
+        bio = io.BytesIO()
+        while True:
+            bdata = await request.stream.read()
+            if not bdata:
+                break
+            bio.write(bdata)
+
+            head = bdata[:3].decode("utf-8")
+            tail = bdata[3:][-3:].decode("utf-8")
+            print(head, "...", tail)
+
+        bio.seek(0)
+        return text(bio.read().decode("utf-8"))
+
+    request, response = app.test_client.post("/post", data=data)
+    assert response.status == 200
+    assert response.text == data