Protection against too many deprecation warnings

[jpountz]

As highlighted in #33479, triggering too many deprecation warnings may have bad consequences with proxies. While this particular issue could be fixed easily by checking all fields up-front in order to trigger only one deprecation warning per request rather than one per field per request, it would be nice to have better protection against this in practice, so that we won't break users if we ever make a similar mistake again.

One solution that was proposed was to limit the number of deprecation warnings to some configurable limit, which some of us were not happy with due to the fact that it would silently ignore some warnings. As a consequence a second proposal was made so that if the limit is N then we only emit N-1 deprecation warnings and reserve the last one to add a new warning that would say that due to the high number of deprecation warnings, some of them were ignored.

[elasticmachine]

Pinging @elastic/es-core-infra

[jpountz]

We like the idea of using one warning to say something like "X warnings have been ignored because they would make the number or size of warning headers exceed the configured limit". Now the question is: if we have a limit of 10 warnings, should we have 9 actual warnings plus this one, or 10 actual warnings plus this one? We didn't have enough time to reach consensus on that one. Opinions?

[tomcallahan]

Removing the discuss label as we've previously agreed to iron out the rest of this discussion on the issue here.

[dvisztempacct]

This can also cause the elasticsearch-js to blow up.

Here is a reproduction in case it is useful. I was filing an issue accidentally against elasticsearch-js when I realized my mistake and came here to find this issue.

https://gist.github.com/dvisztempacct/54a4d208903ea9eb84b44b9a6a1cb7fe

It breaks not only the Node.js HTTP response header decoder but also the one in Wireshark.

[gwbrown]

There is still an open question from this comment:

if we have a limit of 10 warnings, should we have 9 actual warnings plus this one, or 10 actual warnings plus this one?

However, this is broadly something we would like to do and tweaking the exact behavior will be trivial. We can move ahead with an implementation whenever someone has time to implement this.