Ingress incorrectly adds Content-Encoding: deflate breaking streaming responses

[tomquist]

Describe the issue you are experiencing

The Supervisor ingress proxy incorrectly adds Content-Encoding: deflate to streaming responses when the original browser request contains Accept-Encoding: gzip, deflate, br, zstd headers, even when the add-on returns uncompressed content. This breaks Server-Sent Events (SSE) and chunked streaming because browsers buffer the entire response to decompress it, only delivering data after the connection closes.

Root cause:

In supervisor/api/ingress.py, the _response_header() function strips Content-Encoding from the add-on's response:

def _response_header(response: aiohttp.ClientResponse) -> CIMultiDict[str]:
    for name, value in response.headers.items():
        if name in (hdrs.CONTENT_ENCODING, ...):
            continue  # Strips Content-Encoding from add-on response
        headers.add(name, value)

Then in _handle_request(), when creating a web.StreamResponse, aiohttp's automatic compression middleware sees the original Accept-Encoding header and automatically adds Content-Encoding: deflate even though the actual body from the add-on is uncompressed:

response = web.StreamResponse(status=result.status, headers=headers)
response.content_type = content_type
await response.prepare(request)  # aiohttp adds Content-Encoding: deflate here

Impact:

When browsers receive Content-Encoding: deflate, they buffer the entire response to decompress it, even though the content is not actually compressed. This means:

• SSE events only appear after the connection closes (not in real-time)
• Chunked streaming responses don't stream - they arrive all at once at the end
• Real-time interactive features (chat, progress updates, etc.) are completely broken

The Accept-Encoding header is fully controlled by the browser, so there is no workaround I'm aware of.

What type of installation are you running?

Home Assistant Supervised

Which operating system are you running on?

Home Assistant Operating System

Steps to reproduce the issue

1. Create an add-on that serves SSE (Server-Sent Events) or chunked streaming responses
2. Configure the add-on with nginx that explicitly disables compression (gzip off;)
3. Configure the add-on to use ingress
4. Open the add-on UI in a browser (which sends Accept-Encoding: gzip, deflate, br, zstd)
5. Connect to an SSE endpoint or streaming endpoint
6. Observe that data only appears after the connection closes, not in real-time as chunks arrive
7. Browser Network tab shows Content-Encoding: deflate but content is not actually compressed.
8. No SSE events arrive until the connection is closed, at which points all events arrive at the same time

Anything in the Supervisor logs that might be useful for us?

No specific errors logged - the issue is silent but breaks streaming functionality completely.

System information

System Information

version	core-2026.2.0.dev202601060246
installation_type	Home Assistant Supervised
dev	true
hassio	true
docker	true
container_arch	aarch64
user	root
virtualenv	false
python_version	3.13.11
os_name	Linux
os_version	6.12.54-linuxkit
arch	aarch64
timezone	Europe/Berlin
config_dir	/config

Home Assistant Cloud

logged_in	false
can_reach_cert_server	ok
can_reach_cloud_auth	ok
can_reach_cloud	ok

Home Assistant Supervisor

host_os	null
update_channel	dev
supervisor_version	supervisor-2026.01.0.dev0601
agent_version	1.6.0
docker_version	29.1.3
disk_total	910.7 GB
disk_used	197.7 GB
nameservers
healthy	true
supported	failed to load: Unsupported
host_connectivity	null
supervisor_connectivity	true
ntp_synchronized	null
virtualization	null
supervisor_api	ok
version_api	ok
installed_addons	OpenCode Manager (latest)

Dashboards

dashboards	2
resources	0
views	0
mode	storage

Network Configuration

adapters	lo (disabled), eth0 (enabled, default, auto), docker0 (disabled), hassio (disabled), veth684358c (disabled), veth9e82aa0 (disabled), veth1ced439 (disabled), veth16e6297 (disabled), vethdca2e1a (disabled), vethd408f9c (disabled)
ipv4_addresses	lo (127.0.0.1/8), eth0 (172.17.0.2/16), docker0 (172.18.0.1/16), hassio (172.30.32.1/23), veth684358c (), veth9e82aa0 (), veth1ced439 (), veth16e6297 (), vethdca2e1a (), vethd408f9c ()
ipv6_addresses	lo (::1/128), eth0 (), docker0 (fe80::b082:b9ff:fe7c:5ae5/64), hassio (fd0c:ac1e:2100::1/48, fe80::f81e:abff:feec:41dc/64), veth684358c (fe80::58e6:3bff:fe70:c5f0/64), veth9e82aa0 (fe80::bc4e:b9ff:fea6:2934/64), veth1ced439 (fe80::34b5:56ff:fe50:30cd/64), veth16e6297 (fe80::50da:f4ff:fedb:ad64/64), vethdca2e1a (fe80::f4d0:aaff:fe51:ee2f/64), vethd408f9c (fe80::3452:bcff:feba:4d54/64)
announce_addresses	172.17.0.2

Recorder

oldest_recorder_run	January 6, 2026 at 9:26 PM
current_recorder_run	January 6, 2026 at 10:26 PM
estimated_db_size	0.58 MiB
database_engine	sqlite
database_version	3.49.2

Supervisor diagnostics

config_entry-hassio-01KEAK98JAX5YQF8K1X391DAS8.json

Additional information

Context: I'm building an Add-On that spins up a headless OpenCode server with a web interface to use AI to assist in writing config files. There were a couple of obstacles with Ingress, but for this one, I couldn't come up with a workaround.

[tomquist]

My suggestion for a fix is to preserve Content-Encoding: identity from backends. In the _response_header() function, modify it to preserve Content-Encoding: identity:

def _response_header(response: aiohttp.ClientResponse) -> CIMultiDict[str]:
    """Create response header."""
    headers = CIMultiDict[str]()

    for name, value in response.headers.items():
        if name in (
            hdrs.TRANSFER_ENCODING,
            hdrs.CONTENT_LENGTH,
            hdrs.CONTENT_TYPE,
        ):
            continue
        # Preserve Content-Encoding: identity to prevent auto-compression
        if name == hdrs.CONTENT_ENCODING and value.lower() != "identity":
            continue
        headers.add(name, value)

    return headers

This lets backends signal "don't compress" by sending Content-Encoding: identity, gives add-ons explicit control, and existing add-ons that don't set Content-Encoding will continue working

[tomquist]

Turns out this is actually a bug in Home Assistant core, which compresses the content-type text/event-stream unconditionally:
https://github.com/home-assistant/core/blob/ce234d69a72a2df8a6826ab3308513d48d7a8890/homeassistant/components/hassio/http.py#L265-L277

This gets called unconditionally here:
https://github.com/home-assistant/core/blob/ce234d69a72a2df8a6826ab3308513d48d7a8890/homeassistant/components/hassio/ingress.py#L217-L223

I think this issue should be transferred to Home Assistant Core. There are two solutions:

1. Disable compression for content type text/event-stream
2. Disable compression if the header X-Accel-Buffering is set to no

Solution 2. is probably a bit of a hack because the header is more about buffering than about compression (although the two concepts overlap since deflate decompression can only be done with buffering)/