core: split out _internal_receive()

This is needed for libssh2.

mitogen/core.py

@@ -1036,6 +1036,16 @@ class Stream(BasicStream):
     def construct(self):
         pass
 
+    def _internal_receive(self, broker, buf):
+        if self._input_buf and self._input_buf_len < 128:
+            self._input_buf[0] += buf
+        else:
+            self._input_buf.append(buf)
+
+        self._input_buf_len += len(buf)
+        while self._receive_one(broker):
+            pass
+
     def on_receive(self, broker):
         """Handle the next complete message on the stream. Raise
         :py:class:`StreamError` on failure."""
@@ -1045,14 +1055,7 @@ class Stream(BasicStream):
         if not buf:
             return self.on_disconnect(broker)
 
-        if self._input_buf and self._input_buf_len < 128:
+        self._internal_receive(broker, buf)
-            self._input_buf[0] += buf
-        else:
-            self._input_buf.append(buf)
-
-        self._input_buf_len += len(buf)
-        while self._receive_one(broker):
-            pass
 
     HEADER_FMT = '>LLLLLL'
     HEADER_LEN = struct.calcsize(HEADER_FMT)