An alternative implementation of heroku's start-stunnel script that works for rails console

with-stunnel

#!/usr/bin/env bash
#
# This script builds on top of Heroku's stunnel wrapper script [1]
# and provides a simplified implementation with fewer moving parts,
# fewer processes, and most importantly, one that works well with
# any commands being wrapped.
#
# To use this wrapper, make sure you've installed the stunnel redis buildpack,
# then simply prefix the command you wish to run with it.
#
# 'Procfile' example:
#
#     web: bin/with-stunnel bundle exec puma
#
# 'heroku run' example:
#
#     $ heroku run -a myapp-staging 'export REDIS_STUNNEL_URLS="MY_REDIS_URL"; bin/with-stunnel rails console' 
#
# NOTE: It's recommended that you set the REDIS_STUNNEL_URLS config
#       var for your Heroku app to ensure that the correct Redis URLs
#       will be proxied.
# 
# [1](https://github.com/heroku/heroku-buildpack-redis/blob/master/bin/start-stunnel)
#


# Re-use Heroku's start-stunnel script.
# We only care about the config-gen() and the main() functions there.
#
if [[ -e bin/start-stunnel ]]; then
    source bin/start-stunnel

else # assume the stunnel redis buildpack is not installed.
    exec "$@"
fi

# Re-define the run-stunnel function to work around the issue with
# running commands that reads from stdin (e.g., 'rails console'),
# and to simplify the implementation.
#
run-stunnel () {

    # Generate stunnel config files and update redis url env vars
    config-gen

    # Start stunnel in a subshell and wait for it to terminate, after which
    # we kill the wrapped command process.
    (
        stunnel4 vendor/stunnel/stunnel.conf < /dev/null
        kill -SIGTERM -$$
        # NOTE: $$ expands to the PID of this process (with-stunnel)
    ) &

    exec "$@"
    #
    # NOTE: If the wrapped command (this process) exits, then Heroku sends
    #       SIGTERM to all processes, and the dyno terminates.
    #
}

main "$@"