ngtcp2 for Nim

Wrapper around the ngtcp2 C library for Nim.

Updating to a newer version

Follow these steps when updating the wrapper to a newer version of ngtcp2:

1. update the git submodule in sources/ to point to the new version
2. run build.sh (requires Nim and CMake to be installed)
3. update the version in ngtcp2.nimble
4. commit the changes