python/aqmp: add configurable read buffer limit

QMP can transmit some pretty big messages, and the default limit of 64KB
isn't sufficient. Make sure that we can configure it.

Reported-by: G S Niteesh Babu <niteesh.gs@gmail.com>
Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 20210915162955.333025-11-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>

python/qemu/aqmp/protocol.py

@@ -189,6 +189,9 @@ class AsyncProtocol(Generic[T]):
     #: Logger object for debugging messages from this connection.
     logger = logging.getLogger(__name__)
 
+    # Maximum allowable size of read buffer
+    _limit = (64 * 1024)
+
     # -------------------------
     # Section: Public interface
     # -------------------------
@@ -452,6 +455,7 @@ class AsyncProtocol(Generic[T]):
                 port=address[1],
                 ssl=ssl,
                 backlog=1,
+                limit=self._limit,
             )
         else:
             coro = asyncio.start_unix_server(
@@ -459,6 +463,7 @@ class AsyncProtocol(Generic[T]):
                 path=address,
                 ssl=ssl,
                 backlog=1,
+                limit=self._limit,
             )
 
         server = await coro     # Starts listening
@@ -482,9 +487,18 @@ class AsyncProtocol(Generic[T]):
         self.logger.debug("Connecting to %s ...", address)
 
         if isinstance(address, tuple):
-            connect = asyncio.open_connection(address[0], address[1], ssl=ssl)
+            connect = asyncio.open_connection(
+                address[0],
+                address[1],
+                ssl=ssl,
+                limit=self._limit,
+            )
         else:
-            connect = asyncio.open_unix_connection(path=address, ssl=ssl)
+            connect = asyncio.open_unix_connection(
+                path=address,
+                ssl=ssl,
+                limit=self._limit,
+            )
         self._reader, self._writer = await connect
 
         self.logger.debug("Connected.")