# Params:
#   $1: The URL of the Envoy tar.gz to be downloaded.
#   $2: The full path of the output binary.
#   $3: Non-versioned name to use
function download_envoy_if_necessary () {
  if [[ ! -f "$2" ]] ; then
    # Enter the output directory.
    mkdir -p "$(dirname "$2")"
    pushd "$(dirname "$2")"

    # Download and extract the binary to the output directory.
    echo "Downloading ${SIDECAR}: $1 to $2"