warn users if sse flows are received without streaming, refs #4469 (#5249)

CHANGELOG.md

@@ -6,6 +6,8 @@
   ([#5227](https://github.com/mitmproxy/mitmproxy/issues/5227), @mhils)
 * Console Performance Improvements
   ([#3427](https://github.com/mitmproxy/mitmproxy/issues/3427), @BkPHcgQL3V)
+* Warn users if server side event responses are received without streaming.
+  ([#4469](https://github.com/mitmproxy/mitmproxy/issues/4469), @mhils)
 * Add flatpak support to the browser addon
   ([#5200](https://github.com/mitmproxy/mitmproxy/issues/5200), @pauloromeira)
 * Add example addon to dump contents to files based on a filter expression 

docs/src/content/overview-features.md

@@ -358,7 +358,8 @@ By default, mitmproxy will read an entire request/response, perform any
 indicated manipulations on it, and then send the message on to the other party.
 This can be problematic when downloading or uploading large files. When
 streaming is enabled, message bodies are not buffered on the proxy but instead
-sent directly to the server/client. HTTP headers are still fully buffered before
+sent directly to the server/client. This currently means that the message body
+will not be accessible within mitmproxy. HTTP headers are still fully buffered before
 being sent.
 
 Request/response streaming is enabled by specifying a size cutoff in the

mitmproxy/addons/server_side_events.py

@@ -0,0 +1,19 @@
+from mitmproxy import ctx, http
+
+
+class ServerSideEvents:
+    """
+    Server-Side Events are currently swallowed if there's no streaming,
+    see https://github.com/mitmproxy/mitmproxy/issues/4469.
+
+    Until this bug is fixed, this addon warns the user about this.
+    """
+
+    def response(self, flow: http.HTTPFlow):
+        assert flow.response
+        is_sse = flow.response.headers.get("content-type", "").startswith("text/event-stream")
+        if is_sse and not flow.response.stream:
+            ctx.log.warn(
+                "mitmproxy currently does not support server side events. As a workaround, you can enable response "
+                "streaming for such flows: https://github.com/mitmproxy/mitmproxy/issues/4469"
+            )

test/mitmproxy/addons/test_server_side_events.py

@@ -0,0 +1,12 @@
+from mitmproxy.addons.server_side_events import ServerSideEvents
+from mitmproxy.test import taddons
+from mitmproxy.test.tflow import tflow
+
+
+async def test_simple():
+    s = ServerSideEvents()
+    with taddons.context() as tctx:
+        f = tflow(resp=True)
+        f.response.headers["content-type"] = "text/event-stream"
+        s.response(f)
+        await tctx.master.await_log("mitmproxy currently does not support server side events.")

test/mitmproxy/tools/console/test_common.py

@@ -39,6 +39,7 @@ def test_format_keyvals():
 
 
 def test_truncated_text():
+    urwid.set_encoding("utf8")
     half_width_text = common.TruncatedText("Half-width", [])
     full_width_text = common.TruncatedText("ＦＵＬＬ－ＷＩＤＴＨ", [])
     assert half_width_text.render((10,))