#36293: Extend `django.utils.text.compress_sequence()` to optionally flush data
written to compressed file
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Reporter: huoyinghui | Owner: (none)
Type: New feature | Status: closed
Component: HTTP handling | Version: dev
Severity: Normal | Resolution: needsinfo
Keywords: gzip flush | Triage Stage: Unreviewed
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by huoyinghui):
I’ve already resolved this in my own project by subclassing GZipMiddleware
to skip compression for responses with Content-Type: text/event-stream.
However, I believe this is a common enough use case that it deserves
better support at the framework level.
SSE relies on real-time delivery, and buffering caused by gzip (especially
under the 17KB threshold) can introduce noticeable latency on the client
side. Developers may not immediately realize gzip is the cause, leading to
unnecessary debugging time.
It would be helpful if Django could:
1. Document this behavior and its impact on SSE;
2. Automatically skip compression for text/event-stream
responses;
3. Or offer a more explicit way to opt-out of compression per
response.
Supporting this natively would improve the developer experience and better
accommodate streaming use cases.
Here’s my test case:
def test_sse_middleware_skipped(self):
from django.middleware.gzip import GZipMiddleware
from django.http import StreamingHttpResponse
class DummyRequest:
META = {"HTTP_ACCEPT_ENCODING": "gzip"}
def event_stream():
for i in range(3):
yield f"data: {i}\n\n".encode("utf-8")
time.sleep(1)
response = StreamingHttpResponse(event_stream(), content_type="text
/event-stream")
middleware = GZipMiddleware(lambda req: response)
result = middleware(DummyRequest())
first_chunk = next(result.streaming_content)
self.assertFalse(first_chunk.startswith(b"\x1f\x8b"), "SSE response
should not be gzipped")
Test results:
• Case 1: flush_each=True
✅ The client receives each event promptly — no visible delay.
• Case 2: flush_each=False (default gzip behavior)
⚠️ All events are buffered and maybe delivered only after ~17KB, which
defeats SSE’s purpose. The client appears stuck until buffer threshold is
reached.
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Ticket URL: <https://code.djangoproject.com/ticket/36293#comment:6>
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