Python: Model remote flow sources for the websockets library

[joefarebrother]

Models remote flow sources for the websockets library.
Currently omitted are handlers set up via route maps, e.g. with websockets.asyncio.router.route; these would require a little more complex handling of dataflow through classes of werkzeug.routing.

[Copilot]

Pull request overview

This PR adds modeling for remote flow sources in the websockets PyPI package. The implementation provides taint tracking for WebSocket server connections through handler parameters and their methods like recv() and recv_streaming().

• Models websocket handlers registered via serve and unix_serve functions in both asyncio and sync variants
• Implements taint tracking for ServerConnection instances and their message-receiving methods
• Adds comprehensive test coverage for both synchronous and asynchronous websocket handlers

Reviewed changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
python/ql/lib/semmle/python/frameworks/Websockets.qll	New framework modeling file that defines websocket handlers, ServerConnection instances, and taint propagation rules
python/ql/lib/semmle/python/Frameworks.qll	Imports the new Websockets framework module
python/ql/lib/change-notes/2025-12-01-websockets.md	Documents the addition of remote flow source modeling for websockets
python/ql/test/library-tests/frameworks/websockets/taint_test_sync.py	Test file for synchronous websocket taint tracking scenarios
python/ql/test/library-tests/frameworks/websockets/taint_test_asyncio.py	Test file for asynchronous websocket taint tracking scenarios
python/ql/test/library-tests/frameworks/websockets/response_test.py	Test file covering various handler registration patterns including route handlers
python/ql/test/library-tests/frameworks/websockets/InlineTaintTest.ql	QL test query for inline taint test framework
python/ql/test/library-tests/frameworks/websockets/InlineTaintTest.expected	Expected results file (auto-generated)
python/ql/test/library-tests/frameworks/websockets/ConceptsTest.ql	QL test query for concepts test framework
python/ql/test/library-tests/frameworks/websockets/ConceptsTest.expected	Expected results file for concepts test

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[Copilot]

The HandlerParam class should extend RemoteFlowSource::Range to properly model websocket handler parameters as remote flow sources, similar to how other frameworks like Pyramid and Tornado model their handler parameters. This class should also implement the getSourceType() method to return an appropriate description like "websockets handler parameter".

Suggested change

	private class HandlerParam extends DataFlow::Node, InstanceSource {
	HandlerParam() { exists(WebSocketHandler h | this = DataFlow::parameterNode(h.getArg(0))) }
	private class HandlerParam extends RemoteFlowSource::Range, InstanceSource {
	HandlerParam() { exists(WebSocketHandler h | this = DataFlow::parameterNode(h.getArg(0))) }
	override string getSourceType() { result = "websockets handler parameter" }

[joefarebrother]

This parameter is already classified as a remote flow source due to WebSocketHandler being RequestHandler.

[Copilot]

The documentation references WebSocket::instance() but the correct predicate name is ServerConnection::instance(). This should be updated to match the actual module and predicate structure.

Suggested change

	* Use the predicate `WebSocket::instance()` to get references to instances of `websockets.asyncio.ServerConnection` and `websockets.sync.ServerConnection`.
	* Use the predicate `ServerConnection::instance()` to get references to instances of `websockets.asyncio.ServerConnection` and `websockets.sync.ServerConnection`.