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
36656	`GZipMiddleware` drops content from async streaming responses	Adam Johnson	Adam Johnson	"0bd2c0c9015b53c41394a1c0989afbfd94dc2830 (#33735) expanded `GzipMiddleware` to support async streaming responses. But it does so with a faulty `gzip_wrapper()` that compresses chunks as individual files, rather than as a continuous stream. As a result, only the first chunk is decompressible, and browsers drop the rest of the response, even as they stay connected and download all the data.

The solution is to use a streaming approach with `GzipFile`, as is already done for sync responses in `compress_sequence()`.

Additionally, the sync approach currently starts by sending an empty chunk to flush the headers. I think that may be necessary for async responses too, since the first content chunk may take an arbitrary amount of time to be generated.

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`, only the header will appear, and the rest of the response will be dropped.

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

import asyncio
import os
import sys

from django.conf import settings
from django.core.asgi import get_asgi_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__,
    # Use Daphne for async runserver
    INSTALLED_APPS=[
        ""daphne"",
    ],
    ASGI_APPLICATION=f""{__name__}.app"",
    # Only gzip middleware
    MIDDLEWARE=[
        ""django.middleware.gzip.GZipMiddleware"",
    ],
)


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

    return StreamingHttpResponse(stream())


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

app = get_asgi_application()

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

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