Simplify detecting available HTTP client

http() {

  local method="$1"

  local url="$2"

  local file="$3"

  [ -n "$url" ] || return 1

  [ -n "$2" ] || return 1

  shift 1

  local http_client

  if [ -n "${RUBY_BUILD_HTTP_CLIENT}" ]; then

    http_client="http_${method}_${RUBY_BUILD_HTTP_CLIENT}"

  else

    if type aria2c &>/dev/null; then

      http_client="http_${method}_aria2c"

    elif type curl &>/dev/null; then

      http_client="http_${method}_curl"

    elif type wget &>/dev/null; then

      http_client="http_${method}_wget"

    else

      echo "error: please install \`aria2c\`, \`curl\` or \`wget\` and try again" >&2

      exit 1

    fi

  RUBY_BUILD_HTTP_CLIENT="${RUBY_BUILD_HTTP_CLIENT:-$(detect_http_client)}"

  [ -n "$RUBY_BUILD_HTTP_CLIENT" ] || return 1

  "http_${method}_${RUBY_BUILD_HTTP_CLIENT}" "$@"

}

detect_http_client() {

  local client

  for client in aria2c curl wget; do

    if type "$client" &>/dev/null; then

      echo "$client"

      return

    fi

  "${http_client}" "$url" "$file"

  done

  echo "error: please install \`aria2c\`, \`curl\`, or \`wget\` and try again" >&2

  return 1

}

http_head_aria2c() {