Work around bug in AWS API Gateway.

Fix #1065.

Author: aaugustin

docs/project/changelog.rst

@@ -38,6 +38,10 @@ Improvements
   the :attr:`~legacy.protocol.WebSocketCommonProtocol.path` attribute of
   the first argument.
 
+* Worked around a `bug in AWS API Gateway`_ that websockets 10.0 triggers.
+
+.. _bug in AWS API Gateway: https://github.com/aaugustin/websockets/issues/1065
+
 * Mirrored the entire :class:`~asyncio.Server` API
   in :class:`~server.WebSocketServer`.
 

docs/topics/compression.rst

@@ -77,8 +77,8 @@ usage for both sides.
 
 * **Window Bits** controls the size of the compression context. It must be
   an integer between 9 (lowest memory usage) and 15 (best compression).
-  websockets defaults to 12. Setting it to 8 is possible but rejected by some
-  versions of zlib.
+  websockets defaults to 12 for servers and 15 for clients. Setting it to 8
+  is possible but rejected by some versions of zlib.
 
 :mod:`zlib` offers additional parameters for tuning compression. They control
 the trade-off between compression rate and CPU and memory usage for the
@@ -101,10 +101,20 @@ Unless mentioned otherwise, websockets uses the defaults of
 Tuning compression
 ------------------
 
-By default, websockets enables compression with conservative settings that
-optimize memory usage at the cost of a slightly worse compression rate: Window
-Bits = 12 and Memory Level = 5. This strikes a good balance for small messages
-that are typical of WebSocket servers.
+By default, for servers, websockets enables compression with conservative
+settings that optimize memory usage at the cost of a slightly worse
+compression rate: Window Bits = 12 and Memory Level = 5. This strikes a good
+balance for small messages that are typical of WebSocket servers.
+
+For clients, websockets enables compression but leaves settings up to the
+server. This is for a bad reason: providing compression settings triggers a
+`bug in AWS API Gateway`_ and, since there's no realistic way to file a bug
+against AWS, affected users end up filing bugs against websockets. Optimizing
+memory usage is less critical for clients because it's uncommon to open
+thousands of client connections in a program. This makes it acceptable not to
+perform the same optimization as for servers.
+
+.. _bug in AWS API Gateway: https://github.com/aaugustin/websockets/issues/1065
 
 Here's how various compression settings affect memory usage of a single
 connection on a 64-bit system, as well a benchmark of compressed size and

src/websockets/extensions/permessage_deflate.py

@@ -448,8 +448,6 @@ def enable_client_permessage_deflate(
     ):
         extensions = list(extensions) + [
             ClientPerMessageDeflateFactory(
-                server_max_window_bits=12,
-                client_max_window_bits=12,
                 compress_settings={"memLevel": 5},
             )
         ]