zulip/zulip

channel: Handle 500s from the server more naturally

Open

#6,296 opened on Aug 28, 2017

View on GitHub
 (12 comments) (0 reactions) (0 assignees)Python (19,672 stars) (7,339 forks)batch import
area: apiarea: productionbughelp wanted

Description

Right now, if the server 500s on a JSON request from a client in a way that doesn't return valid JSON, we get this sort of JS exception sent back to the server.

Message:
Unexpected token < in JSON at position 0

Stacktrace:
SyntaxError: Unexpected token < in JSON at position 0
    at JSON.parse (<anonymous>)

    at Object.a.xhr_error_message (static/min/app.f993cb5274ab.js:1331:372)
       = static/js/channel.js line 110 column 27

    at error (static/min/app.f993cb5274ab.js:2062:742)
       = static/js/reactions.js line 25 column 28

I think we should fix this in 2 ways;

  • Make it ~impossible for an invalid-JSON response to come back from channel.js (e.g. have a set of 500 error pages for API URLs that are in JSON format), and mostly not change this code. This probably involves changes to both our nginx configuration (for "unexpected errors" where Django isn't even running). And then there's a probably simpler piece of changing zerver/middleware.py to handle unexpected exceptions in JSON style API routes at the Django level.
  • Make channel.js catch this exception and provide a more clear error message for what's happening (perhaps including the invalid JSON it received) in the report, via blueslip.error or something.

Contributor guide

Tech stack
javascriptpythondjango
Domain
backendfrontend
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
needs maintainer response
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
JavaScriptPythonDjangoHTTP error handling
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
Start by examining the frontend error handling in `static/js/channel.js` around line 110 where JSON.parse is called. The goal is to catch SyntaxError and report via blueslip.error. For backend, inspect `zerver/middleware.py` to ensure JSON API routes return JSON even on 500 errors. Also consider nginx configuration to return JSON for certain error codes. The issue has 12 comments discussing approaches; read comments #5 and #8 for proposed solutions and maintainer feedback.