Keep only the current WebSocket message in the secrets proxy

deploy/proxy/swap.py

@@ -216,5 +216,10 @@ async def swap(self, flow: http.HTTPFlow, found: list[tuple[str, str]]) -> None:
     def responseheaders(self, flow: http.HTTPFlow) -> None:
         flow.response.stream = True
 
+    def websocket_message(self, flow: http.HTTPFlow) -> None:
+        """mitmproxy keeps every message of a connection for its life. Only the
+        current one is kept: the dumper reads it after this hook."""
+        del flow.websocket.messages[:-1]
+
 
 addons = [Swap()]

src/secrets_exchange/tests/test_swap.py

@@ -652,6 +652,14 @@ def test_responses_stream(swap: ModuleType) -> None:
     assert flow.response.stream is True
 
 
+def test_a_websocket_keeps_only_the_current_message(swap: ModuleType) -> None:
+    flow = SimpleNamespace(websocket=SimpleNamespace(messages=["earlier", "current"]))
+
+    swap.Swap().websocket_message(flow)
+
+    assert flow.websocket.messages == ["current"]
+
+
 async def test_the_exchange_client_reads_the_answers(swap: ModuleType) -> None:
     exchange = swap.Exchange("http://exchange.test/")
     fetched: list[Any] = []