HttpServletResponse::sendRedirect(String) broken in JSPs (EE10)

[MuffinTheMan]

I believe we found another bug while testing our upgrade to EE10 (Java 21) on App Engine Standard.

If we attempt a redirect from a JSP (via HttpServletResponse::sendRedirect(String) like response.sendRedirect("/some-path");), it works properly locally but crashes when running via our deployed App Engine application (with an error like: Request failed: Unexpected Error: java.io.IOException: written 2 > 0 content-length). When sending a redirect from a non-JSP HttpServlet, there are no issues; so it appears to be an issue specific to handling redirects from JSPs.

This can be reproduced with my sample web app: https://github.com/MuffinTheMan/appengine-standard-ee10-sample/tree/3-redirects (see the README.md for instructions--I have been testing with a custom runtime built from this commit: 0f190e8 due to #316).

From the README:

Broken

• Navigate to /redirect-test
  • Local App: redirected to /jsp
  • Deployed App: the browser displays an error like Request failed: Unexpected Error: java.io.IOException: written 2 > 0 content-length

Working

• Navigate to /redirect
  • Local App: redirected to /jsp
  • Deployed App: redirected to /jsp

[ludoch]

I assume the runtime code used is from head, right?

[MuffinTheMan]

@ludoch the latest commit in my local version from which I had built the jars was 0f190e8

However, I just checked out the latest appengine-java-standard:main and built new jars to test. Same issue with the latest.

[lachlan-roberts]

I think this is a bug in Jetty 12 EE10, I will open a PR to fix.