Can't create really long funnels due to GET limitation

[timgl]

Bug description

We've had a user create a funnel with Korean characters and 17 steps, which causes this issue:

Expected behavior

We should send requests to api/insight/funnel using POST instead of GET.

How to reproduce

Environment

• PostHog Cloud
• self-hosted PostHog, version/commit: please provide

Additional context

Thank you for your bug report – we love squashing them!

[alexkim205]

How to Reproduce

1. Create a filter with a loooot of steps. See this one.
2. Check network request
3. Verify we get same long request error -> Request Line is too large (4216 > 4094)

Note: This bug only occurs in Self-Hosted and Cloud setups
This limitation doesn't exist in local dev setup because there is no gunicorn layer in local dev that limits the number of chars in our requests docs. It's probably why we didn't notice the bug. An example pipeline on localhost whose request is ~6000 chars long works correctly.

Solution A - Tim's solution

Change GET to POST endpoint.

Pros

• No restriction on limit
• Secure

Cons

• Involves deep code change (frontend and backend stack)
• Confusing API (acts like a GET, looks like a POST)

Solution B - Change gunicorn limit_request_line config <-- Chose this one b/c pro's are stronger and con's can be mitigated

Change limit_request_line to 0 (unlimited) or 8190 (max).

Pros

• Doesn't involve deep code change
• API method stays consistent with action

Cons

• Unlimited request length is a security risk for DDOS attacks. Can mitigate by setting to 8190.

Next Steps

1. Write test. Run tests in self hosted env which will fail.
2. Make fix (choose A or B above).
3. Testing
4. PR and merge