Decode as LLSD when in quirks mode too

In addition to assuming that outgoing content should be presented as LLSD,
quirks mode should also assume that incoming content is LLSD unless
told otherwise.

llsd_asgi/middleware.py

@@ -47,7 +47,9 @@ async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
         headers = MutableHeaders(scope=scope)
 
         try:
-            self.parse = _CONTENT_TYPE_TO_PARSE[headers.get("content-type")]
+            self.parse = _CONTENT_TYPE_TO_PARSE[
+                headers.get("content-type", "application/llsd+xml" if self.quirks else None)
+            ]
             self.should_decode_from_llsd_to_json = True
         except KeyError:
             self.should_decode_from_llsd_to_json = False

tests/test_middleware.py

@@ -150,7 +150,7 @@ async def lifespan_only_app(scope: Scope, receive: Receive, send: Send) -> None:
     "accept",
     [(None), ("*/*"), ("text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,*/*;q=0.8")],
 )
-async def test_quirks(accept: str) -> None:
+async def test_quirks_encode(accept: str) -> None:
     app = LLSDMiddleware(JSONResponse({"message": "Hello, world!"}), quirks=True)
 
     async with httpx.AsyncClient(app=app, base_url="http://testserver") as client:
@@ -166,6 +166,25 @@ async def test_quirks(accept: str) -> None:
         assert llsd.parse_xml(r.content) == {"message": "Hello, world!"}
 
 
+@pytest.mark.asyncio
+async def test_quirks_decode():
+    async def app(scope: Scope, receive: Receive, send: Send) -> None:
+        request = Request(scope, receive=receive)
+        data = await request.json()
+        message = data["message"]
+        text = f"message={message!r}"
+
+        response = PlainTextResponse(text)
+        await response(scope, receive, send)
+
+    app = LLSDMiddleware(app, quirks=True)
+
+    async with httpx.AsyncClient(app=app, base_url="http://testserver") as client:
+        r = await client.post("/", content=llsd.format_xml({"message": "Hello, world!"}))
+        assert r.status_code == 200
+        assert r.text == "message='Hello, world!'"
+
+
 @pytest.mark.asyncio
 @pytest.mark.parametrize(
     "accept",