Correct handling of UTF-8 data?

[robn]

It has been seen that when a UTF-8 encoded character is present in a label (specifically ★ - U+02605 - BLACK STAR), a Plack server handling serving the output from the ->format method directly (not using the internal ->psgi method) is truncated by a few bytes. This suggests something isn't coping with a mismatch in octet vs character lengths.

The problem was actually seen in something using Prometheus::Tiny::Shared, so the "problem" could exist anywhere in:

• shared cached freeze/thaw
• metric insertion
• output formatting
• the surrounding web server

If possible, we should ensure that P::T's internal PSGI handler does the right thing here. If it does turn out to be entirely an application-level concern, then we should perhaps document some guidance for users. At the very least, I'd like to understand the problem.