[3.11] gh-111112: Avoid potential confusion in TCP server example. (GH-111113) (...

gh-111112: Avoid potential confusion in TCP server example. (GH-111113)

Improve misleading TCP server docs and example.

socket.recv(), as documented by the Python reference documentation,
returns at most `bufsize` bytes, and the underlying TCP protocol means
there is no guaranteed correspondence between what is sent by the client
and what is received by the server.

This conflation could mislead readers into thinking that TCP is
datagram-based or has similar semantics, which will likely appear to
work for simple cases, but introduce difficult to reproduce bugs.
(cherry picked from commit a79a27242f75fc33416d4d135a4a542898d140e5)

Co-authored-by: Aidan Holm <alfh@google.com>

diff --git a/Doc/library/socketserver.rst b/Doc/library/socketserver.rst
index 7540375b8d1f50a9aa00ace1262d3cc7af7a717f..5e92332c5f195c8ca20b4cf30c3836411e8130ac 100644 (file)
--- a/Doc/library/socketserver.rst
+++ b/Doc/library/socketserver.rst
@@ -488,7 +488,7 @@ This is the server side::
        def handle(self):
            # self.request is the TCP socket connected to the client
            self.data = self.request.recv(1024).strip()
-           print("{} wrote:".format(self.client_address[0]))
+           print("Received from {}:".format(self.client_address[0]))
            print(self.data)
            # just send back the same data, but upper-cased
            self.request.sendall(self.data.upper())
@@ -519,8 +519,9 @@ objects that simplify communication by providing the standard file interface)::
 
 The difference is that the ``readline()`` call in the second handler will call
 ``recv()`` multiple times until it encounters a newline character, while the
-single ``recv()`` call in the first handler will just return what has been sent
-from the client in one ``sendall()`` call.
+single ``recv()`` call in the first handler will just return what has been
+received so far from the client's ``sendall()`` call (typically all of it, but
+this is not guaranteed by the TCP protocol).
 
 
 This is the client side::