Hono: bodyLimit() can be bypassed for chunked / unknown-length requests

Summary

bodyLimit() does not reliably enforce maxSize for requests without a usable Content-Length (e.g. Transfer-Encoding: chunked). Oversized requests can reach handlers and return 200 instead of 413.

Details

For chunked / unknown-length requests, bodyLimit() wraps the body in a stream that counts bytes asynchronously, then runs the handler before the size decision is final. The 413 is only applied afterwards by checking c.error.

This lets the limit be bypassed when:

• the handler does not read the body,
• the handler reads only the first chunk(s) and returns, or
• the handler reads the body but swallows the read error in try/catch.

In all three cases the handler returns 200 before the limit check completes (or its result is observed).

The fix is to enforce the size decision before next() runs, instead of retrofitting the response via c.error afterwards.

Impact

Applications relying on bodyLimit() as a hard boundary can be bypassed: oversized chunked requests can reach handler logic and return successful responses. Per-request data exposure is bounded by maxSize, but the documented guarantee — "oversized requests are rejected before business logic runs" — does not hold.

Credits

• @lalalala5678 (slow chunked / early return variants)
• @Jvr2022 (error handling bypass)