fix(restQL): header comparison must be case insensitive

[wedneyyuri]

This is required to be compliant with the HTTP/1.1 spec

Reference: https://www.envoyproxy.io/docs/envoy/latest/configuration/http/http_conn_man/header_casing#:~:text=When%20handling%20HTTP%2F1.1%2C%20Envoy,rely%20on%20specific%20header%20casing.

[caiorcferreira]

Thanks, this is a nice corner case to catch!

My only suggestion is to used strings.EqualFold instead of strings.ToLower as it is more efficient, and strings operations in Go in a hot path like this code can have a significant impact on the GC pressure under high load.

Reference on the strings.EqualFold: https://www.digitalocean.com/community/questions/how-to-efficiently-compare-strings-in-go

[wedneyyuri]

Hi @caiorcferreira thanks for your suggestion, but I don't see a way to use strings.EqualFold here. In this snippet code we're not looping over the keys of disallowedHeaders.

[caiorcferreira]

Sorry, I should have been more clear. In this case, changing disallowedHeaders to a slice and looping over it using strings.EqualFold should beat strings.ToLower overall, since each time it's called it will perform an allocation since strings are immutable in Go, even with the added time complexity because, usually, m >>> n, where m is the quantity of request headers and n is the quantity of disallowedHeaders.

[wedneyyuri]

Thanks for your support, I made the requested changes :v:

[caiorcferreira]

Nice catch! Thanks for your contribution.