Description

There is performance issue with sentry-raven and sentry-ruby gems.

In some cases different middlewares assign to env hash some large objects.
I.e. grape expose his routing in env['grape.routing_args'] https://github.com/ruby-grape/grape/blob/02d7113d09eb9fcb4264c841d1fdd305e3e8adb5/lib/grape/util/env.rb#L22

In large applications it may be havy hash object. So when sentry try to cast this with #to_s that causes to large CPU consumption. I.e. in our application it takes around 45 sec to perform and almost 100% CPU load).
And the result just throwed away because this is not headers that needs to be in the event.

There are some demo that emulates this issue https://gist.github.com/moofkit/e1bf1ca0d3186aa7f9b89d3c3ee7fc58
You can try it with

$ make start
$ make test
> time curl 'http://localhost:9292/exception'
{"error":"An error ocurred"}       10.11 real         0.00 user         0.00 sys

Why it takes 10 secs of 5 is covered in this issue #777

So, this little patch postpone Object#to_s after all headers checks in both sentry-raven and sentry-ruby gems