id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
36655	GZipMiddleware buffers streaming responses	Adam Johnson	Adam Johnson	"Currently, `GZipMiddleware`, via `compress_sequence()`, buffers the entire response before sending it to the client. This can cause issues for clients that expect to receive data in chunks, such as those using Server-Sent Events (SSE) or WebSockets.

This issue was reported to me in the django-browser-reload project back in [https://github.com/adamchainz/django-browser-reload/pull/161 Issue #161 (2023)], where a contributor fixed it with a workaround, and I didn't think to investigate. Now, while implementing [https://github.com/adamchainz/django-http-compression django-http-compression], I have realized that it’s a proper bug that can be fixed by adding a call to `zfile.flush()`, as done in its [https://github.com/adamchainz/django-http-compression/pull/8 PR #8].

To reproduce the issue, use the app below, which can be run with `uv run --script`. If you comment out `GzipMiddleware` and load the page in a browser, you will see the numbers incrementing every second. If you include `GzipMiddleware`, the page will never load. Adding the `zfile.flush()` call in `compress_sequence()` fixes the issue.

{{{#!python
#!/usr/bin/env uv run --script
# /// script
# requires-python = "">=3.14""
# dependencies = [
#     ""django"",
# ]
# ///
from __future__ import annotations

import os
import sys
import time

from django.conf import settings
from django.core.wsgi import get_wsgi_application
from django.http import StreamingHttpResponse
from django.urls import path

settings.configure(
    # Dangerous: disable host header validation
    ALLOWED_HOSTS=[""*""],
    # Use DEBUG=1 to enable debug mode
    DEBUG=(os.environ.get(""DEBUG"", """") == ""1""),
    # Make this module the urlconf
    ROOT_URLCONF=__name__,
    # Only gzip middleware
    MIDDLEWARE=[
        ""django.middleware.gzip.GZipMiddleware"",
    ],
)


def clock(request):
    def stream():
        yield ""<h1>Clock</h1>\n""
        count = 1
        while True:
            yield f""<p>{count}</p>\n""
            count += 1
            time.sleep(1)

    return StreamingHttpResponse(stream())


urlpatterns = [
    path("""", clock),
]

app = get_wsgi_application()

if __name__ == ""__main__"":
    from django.core.management import execute_from_command_line

    execute_from_command_line(sys.argv)
}}}"	Bug	closed	HTTP handling	dev	Normal	duplicate			Unreviewed	0	0	0	0	0	0