func readKey()

in hack/self-hosted/main.go [39:84]
40 lines of code
7 McCabe index (conditional complexity)

func readKey(filename string) ([]byte, error) {
	var response []byte
	content, err := ioutil.ReadFile(filename)
	if err != nil {
		return response, errors.WithMessage(err, "error reading file")
	}

	block, _ := pem.Decode(content)
	if block == nil {
		return response, errors.Errorf("Error decoding PEM file %s", filename)
	}

	pubKey, err := x509.ParsePKIXPublicKey(block.Bytes)
	if err != nil {
		return response, errors.Wrapf(err, "Error parsing key content of %s", filename)
	}
	switch pubKey.(type) {
	case *rsa.PublicKey:
	default:
		return response, errors.New("Public key was not RSA")
	}

	var alg jose.SignatureAlgorithm
	switch pubKey.(type) {
	case *rsa.PublicKey:
		alg = jose.RS256
	default:
		return response, fmt.Errorf("invalid public key type %T, must be *rsa.PrivateKey", pubKey)
	}

	kid, err := keyIDFromPublicKey(pubKey)
	if err != nil {
		return response, err
	}

	var keys []jose.JSONWebKey
	keys = append(keys, jose.JSONWebKey{
		Key:       pubKey,
		KeyID:     kid,
		Algorithm: string(alg),
		Use:       "sig",
	})

	keyResponse := KeyResponse{Keys: keys}
	return json.MarshalIndent(keyResponse, "", "    ")
}