dosubot[bot] commented on issue #38420: URL: https://github.com/apache/superset/issues/38420#issuecomment-4001321162
<!-- Answer --> This issue appears related to the webhook notification feature added in [PR #36127](https://github.com/apache/superset/pull/36127). There's a related discussion with the same Mattermost errors: [#38283](https://github.com/apache/superset/discussions/38283). **Root cause of the errors:** 1. **413 (Request body too large)**: The PNG/PDF attachments are being sent directly to Mattermost's Incoming Webhook, which has payload size limits. Mattermost webhooks aren't designed to receive large binary file uploads. 2. **400 (multipart/form-data decode failure)**: Mattermost Incoming Webhooks expect `application/json` payloads, but Superset is sending `multipart/form-data` to include the file attachments. This is a fundamental incompatibility. **The core issue**: Mattermost Incoming Webhooks are not suitable for receiving file attachments (PNG/PDF). They only accept JSON text payloads. To send files to Mattermost, you'd need to use the [Mattermost Files API](https://api.mattermost.com/#tag/files) instead of webhooks, which requires authentication tokens rather than webhook URLs. **Workarounds:** - Use **text-only** report format if webhook notifications to Mattermost are needed - Use **email** notifications for PNG/PDF reports - Use **Slack** integration (which properly handles file uploads via the SDK) if you have a Mattermost-Slack bridge This may warrant a documentation update or feature enhancement to clarify that webhook endpoints receiving file attachments need to support `multipart/form-data` and accept sufficiently large payloads. <!-- Dosu Comment Footer --> *To reply, just mention [@dosu](https://go.dosu.dev/dosubot).* --- <sup>How did I do? [Good](https://app.dosu.dev/response-feedback/9e84c5ea-bfa1-41bb-9470-1cc6c21ff479?feedback_type=great_response) | [Irrelevant](https://app.dosu.dev/response-feedback/9e84c5ea-bfa1-41bb-9470-1cc6c21ff479?feedback_type=irrelevant_answer) | [Incorrect](https://app.dosu.dev/response-feedback/9e84c5ea-bfa1-41bb-9470-1cc6c21ff479?feedback_type=incorrect_sources) | [Verbose](https://app.dosu.dev/response-feedback/9e84c5ea-bfa1-41bb-9470-1cc6c21ff479?feedback_type=too_verbose) | [Hallucination](https://app.dosu.dev/response-feedback/9e84c5ea-bfa1-41bb-9470-1cc6c21ff479?feedback_type=hallucination) | [Report 🐛](https://app.dosu.dev/response-feedback/9e84c5ea-bfa1-41bb-9470-1cc6c21ff479?feedback_type=bug_report) | [Other](https://app.dosu.dev/response-feedback/9e84c5ea-bfa1-41bb-9470-1cc6c21ff479?feedback_type=other)</sup> [](https://app.dosu.dev/a28d3c7e-a9d3-459e-9fb6-3a6f9ff4f357/ask?utm_source=github) [](https://cursor.com/link/prompt?text=This%20issue%20appears%20related%20to%20the%20webhook%20notification%20feature%20added%20in%20%5BPR%20%2336127%5D%28https%3A//github.com/apache/superset/pull/36127%29.%20There%27s%20a%20related%20discussion%20with%20the%20same%20Mattermost%20errors%3A%20%5B%2338283%5D%28https%3A//github.com/apache/superset/discussions/38283%29.%0A%0A%2A%2ARoot%20cause%20of%20the%20errors%3A%2A%2A%0A%0A1.%20%2A%2A413%20%28Request%20body%20too%20large%29%2A%2A%3A%20The%20PNG/PDF%20attachments%20are%20being%20sent%20directly%20to%20Mattermost%27s%20Incoming%20Webhook%2C%20which%20has%20payload%20size%20limits.%20Mattermost%20webhooks%20aren%27t%20designed%20to%20receive%20large%20binary%20file%20uploads.%0A%0A2.%20%2A%2A400%20%28multipart/form-data%20decode%20failure% 29%2A%2A%3A%20Mattermost%20Incoming%20Webhooks%20expect%20%60application/json%60%20payloads%2C%20but%20Superset%20is%20sending%20%60multipart/form-data%60%20to%20include%20the%20file%20attachments.%20This%20is%20a%20fundamental%20incompatibility.%0A%0A%2A%2AThe%20core%20issue%2A%2A%3A%20Mattermost%20Incoming%20Webhooks%20are%20not%20suitable%20for%20receiving%20file%20attachments%20%28PNG/PDF%29.%20They%20only%20accept%20JSON%20text%20payloads.%20To%20send%20files%20to%20Mattermost%2C%20you%27d%20need%20to%20use%20the%20%5BMattermost%20Files%20API%5D%28https%3A//api.mattermost.com/%23tag/files%29%20instead%20of%20webhooks%2C%20which%20requires%20authentication%20tokens%20rather%20than%20webhook%20URLs.%0A%0A%2A%2AWorkarounds%3A%2A%2A%0A-%20Use%20%2A%2Atext-only%2A%2A%20report%20format%20if%20webhook%20notifications%20to%20Mattermost%20are%20needed%0A-%20Use%20%2A%2Aemail%2A%2A%20notifications%20for%20PNG/PDF%20reports%0A-%20Use%20%2A%2ASlack%2A%2A%20integration%20%28which%20properly %20handles%20file%20uploads%20via%20the%20SDK%29%20if%20you%20have%20a%20Mattermost-Slack%20bridge%0A%0AThis%20may%20warrant%20a%20documentation%20update%20or%20feature%20enhancement%20to%20clarify%20that%20webhook%20endpoints%20receiving%20file%20attachments%20need%20to%20support%20%60multipart/form-data%60%20and%20accept%20sufficiently%20large%20payloads.) [](https://go.dosu.dev/discord-bot) [](https://twitter.com/intent/tweet?text=%40dosu_ai%20helped%20me%20solve%20this%20issue!&url=https%3A//github.com/apache/superset/issues/38420) -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
