dotfiles/bin/ssh-fwd

#!/bin/bash -e

shopt -s expand_aliases
[[ $TERM = xterm-kitty ]] && alias ssh='kitty +kitten ssh'

# Variables
ssh=ssh
declare -a args

# Display the usage
function usage {
    cat << EOF
Usage: $(basename "$0") SSH_HOST LOCAL_PORT DISTANT_PORT [TARGET] [-- SSH_OPTIONS]
EOF
}

# Show an error
function error {
    >&2 usage
    exit "${1:-1}"
}

# Check if TCP port number is free
port_is_free() {
    ! lsof -i -P -n | grep -q ':'"${1}"' (LISTEN)'
}

# Arguments
while [[ -n $* ]]; do
    case "$1" in
        "--")
            shift
            ssh_options=("$@")
            set --
        ;;
        *)
            args+=("$1")
            shift
        ;;
    esac
done

# Checking the validity of the args
[[ -z ${args[2]} ]] && error 1
[[ -z ${args[3]} ]] && args[3]=localhost

# Command building
ssh_com=(
    "$ssh"
    "${ssh_options[@]}"
    -f
    -N
    -L "${args[1]}:${args[3]}:${args[2]}"
    "${args[0]}"
)

# Debug
#echo "${ssh_com[@]}"
#exit 0

# Execution
set -x
if port_is_free "${args[1]}"; then
    "${ssh_com[@]}"
else
    echo "Port is not free, skipping."
fi