Silly question, but shouldn't elang have some good & highly concurrent http libraries?
Because of preemptive nature of Erlang, doing lengthy work in those functions can destabilise the system (the "magic value" is said to be around 1ms). That is because C functions can't be preempted in the middle of execution like Erlang ones can.
Using dirty schedulers lifts this time limitation, but gives a higher constant overhead when calling a function on a dirty scheduler, since it means switching OS thread. This tradeoff, however, is perfectly acceptable for a lot of cases.
And yes, Erlang has good & highly concurrent HTTP libraries implemented in Erlang.
There's also work on supporting writing NIFs in Rust, which gives some degree of additional safety. The relevant project would be: https://github.com/hansihe/rustler
Disclaimer: I wrote the Buoy (https://github.com/lpgauth/buoy)