Convert message IO to work w/ a RawConnection.

libp2p/io/exceptions.py

@@ -0,0 +1,10 @@
+class MsgioException(Exception):
+    pass
+
+
+class MissingLengthException(MsgioException):
+    pass
+
+
+class MissingMessageException(MsgioException):
+    pass

libp2p/io/msgio.py

@@ -1,4 +1,6 @@
-import asyncio
+from libp2p.network.connection.raw_connection_interface import IRawConnection
+
+from .exceptions import MissingLengthException, MissingMessageException
 
 SIZE_LEN_BYTES = 4
 
@@ -10,7 +12,13 @@ def encode(msg_bytes: bytes) -> bytes:
     return len_prefix + msg_bytes
 
 
-async def read_next_message(reader: asyncio.StreamReader) -> bytes:
+async def read_next_message(reader: IRawConnection) -> bytes:
-    len_bytes = await reader.readexactly(SIZE_LEN_BYTES)
+    len_bytes = await reader.read(SIZE_LEN_BYTES)
+    if len(len_bytes) != SIZE_LEN_BYTES:
+        raise MissingLengthException()
     len_int = int.from_bytes(len_bytes, "big")
-    return await reader.readexactly(len_int)
+    next_msg = await reader.read(len_int)
+    if len(next_msg) != len_int:
+        # TODO makes sense to keep reading until this condition is true?
+        raise MissingMessageException()
+    return next_msg