wait_port.sh

# Small function that checks if a TCP port on localhost is open.
#
# Timeout after 10 attempts.
#
# Usage: wait_port <port>
wait_port() (
  local i=0 port=$1
  echo "waiting on port $port"
  # Bash has a magic filesystem that can be used to do basic TCP.
  #
  # Use 127.0.0.1 instead of "localhost" to avoid resolution issues I observed
  # inside of the container.
  while ! exec 3<>"/dev/tcp/127.0.0.1/$port"; do
    sleep 0.1
    ((i += 1))
    if [[ $i == 10 ]]; then
      echo "error: timeout"
      return 1
    fi
  done
)