Extract HTML5 SSE helpers

services/api-server/src/api_server/html5_sse.py

@@ -0,0 +1,19 @@
+from __future__ import annotations
+
+from collections.abc import Iterator
+
+
+def html5_sse_event(event: str, fragment: str) -> str:
+    data = "\n".join(f"data: {line}" for line in fragment.splitlines())
+    return f"event: {event}\nretry: 5000\n{data}\n\n"
+
+
+def html5_sse_if_changed(last_fragments: dict[str, str], event: str, fragment: str) -> Iterator[str]:
+    if last_fragments.get(event) == fragment:
+        return
+    last_fragments[event] = fragment
+    yield html5_sse_event(event, fragment)
+
+
+def html5_sse_comment(message: str) -> str:
+    return f": {message}\n\n"