Make recv buffer size a class attribute.

This supports overriding it by subclassing, rather than monkey-patching.

Also use a more realistic value in the docs.

docs/howto/sansio.rst

@@ -133,7 +133,7 @@ When reaching the end of the data stream, call the protocol's
 For example, if ``sock`` is a :obj:`~socket.socket`::
 
     try:
-        data = sock.recv(4096)
+        data = sock.recv(65536)
     except OSError:  # socket closed
         data = b""
     if data:

src/websockets/sync/connection.py

@@ -23,8 +23,6 @@
 
 logger = logging.getLogger(__name__)
 
-BUFSIZE = 65536
-
 
 class Connection:
     """
@@ -39,6 +37,8 @@ class Connection:
 
     """
 
+    recv_bufsize = 65536
+
     def __init__(
         self,
         socket: socket.socket,
@@ -525,7 +525,7 @@ def recv_events(self) -> None:
                 try:
                     if self.close_deadline is not None:
                         self.socket.settimeout(self.close_deadline.timeout())
-                    data = self.socket.recv(BUFSIZE)
+                    data = self.socket.recv(self.recv_bufsize)
                 except Exception as exc:
                     if self.debug:
                         self.logger.debug("error while receiving data", exc_info=True)