Findings so far.
From Nov 2018 - Apr 2024, many users encountered a 408 Request Time-out error like mine, but with slightly different wording:
Internal Server Error ("error parsing HTTP 408 response body: invalid character '<' looking for beginning of value: "<html><body><h1>408 Request Time-out</h1>\nYour browser didn't send a complete request in time.\n</body></html>\n"")
In Nov 2024, a user encountered the exact same error as me.
| Date | Identical error | Similar error | Thread | Reported solution |
|---|---|---|---|---|
| 20 Nov 2018 | N | Y | HA instance not loading on outside network | Unresolved |
| 09 Nov 2019 | N | Y | Can't install DuckDns addon | Unresolved |
| 24 Nov 2019 | N | Y | Unable to update hassio and/or install addons | - Set MTU size to 900 in HA OS; or - Move HA OS server from WLAN behind firewall, to Ethernet connection in front of firewall |
| 17 Aug 2020 | N | Y | Unable to install any addon. Pull image timeout. · Issue #1933 · home-assistant/supervisor · GitHub | Unresolved |
| 07 Feb 2021 | N | Y | Issue installing Home Assistant on raspberry pi 4 - Never finished preparing | Unresolved |
| 27 Aug 2021 | N | Y | Trying to install add-ons fails with an error apparently relating to a time-out · Issue #3081 · home-assistant/supervisor · GitHub | Problem may be due to MTU size conflict with Docker CDN? If Home Assistant is on Armbian, fix by enabling MTU probing: sudo sysctl -w net.ipv4.tcp_mtu_probing=1 |
| 03 Aug 2021 | N | Y | Official add-ons won't install | Unresolved |
| 13 Dec 2022 | N | Y | Cannot install any core or add-on updates | Fix MTU and MSS clamping (unclear how), and avoid Google’s misuse of DF flag by changing DNS provider from Google to Cloudflare |
| 30 Mar 2023 | N | Y | Can't add-on file editor | Unresolved |
| 14 Sep 2023 | N | Y | Addons not accessible or starting after move to SSD Boot and restore from backup | - Change ISP package; or - Remove ethernet loop, if present |
| 23 Sep 2023 | N | Y | Not able to download Add-ons | Change DNS provider & reboot router |
| 05 Apr 2024 | N | Y | Cannot install Mosquitto addon, reason may be that I used MQTT integration before | Put HA server in front of firewall |
| 05 Nov 2024 | Y | N | How to install adds on in HA green - server error | Unresolved |
Hypothesis
If we assume all the above bug reports were caused by the same underlying issue, which seems to be to do with network connectivity, we can infer that:
- Between 5 Apr 2024 - 5 Nov 2024, a string or statement in HA or one of its dependencies was substituted as follows, changing the way HA reported this error to the user:
s/error parsing HTTP 408 response body: invalid character '<' looking for beginning of value/unknown/ - Individual instances of the error might be resolvable through network configuration changes.
When time permits, I will test this hypothesis on my install and report back.
Tentative conclusion
Subject to corroboration of hypothesis above:
Home Assistant should probably check, at install time, for any network configurations that conflict with its expectations, and automatically adjust its expectations (e.g. MTU size) to avoid inconveniencing the user later on. If it cannot do so, it should warn the user to make the necessary changes manually.