use new response error for client's error encoder

command/daemon/command.go

@@ -93,6 +93,7 @@ func (c *command) Execute(cmd *cobra.Command, args []string) {
 		serverConfig.ListenAddress = Flags.Server.Listen.Address
 		serverConfig.Logger = c.logger
 		serverConfig.RequestFuncs = customServer.RequestFuncs()
+		serverConfig.Router = customServer.Router()
 		serverConfig.ServiceName = customServer.ServiceName()
 
 		newServer, err = server.New(serverConfig)

server/error.go

@@ -21,6 +21,9 @@ func errorDomain(err error) string {
 }
 
 func errorMessage(err error) string {
+	if err == nil {
+		return ""
+	}
 	switch kitErr := err.(type) {
 	case kithttp.Error:
 		switch errgoErr := kitErr.Err.(type) {

server/response_error.go

@@ -0,0 +1,86 @@
+package server
+
+import (
+	microerror "github.com/giantswarm/microkit/error"
+	kithttp "github.com/go-kit/kit/transport/http"
+)
+
+// ResponseErrorConfig represents the configuration used to create a new
+// response error.
+type ResponseErrorConfig struct {
+	// Settings.
+	Underlying error
+}
+
+// DefaultResponseErrorConfig provides a default configuration to create a new
+// response error by best effort.
+func DefaultResponseErrorConfig() ResponseErrorConfig {
+	return ResponseErrorConfig{
+		// Settings.
+		Underlying: nil,
+	}
+}
+
+// New creates a new configured response error.
+func NewResponseError(config ResponseErrorConfig) (ResponseError, error) {
+	// Settings.
+	if config.Underlying == nil {
+		return nil, microerror.MaskAnyf(invalidConfigError, "underlying must not be empty")
+	}
+
+	newResponseError := &responseError{
+		// Internals.
+		code:    CodeUnknownError,
+		message: errorMessage(config.Underlying),
+
+		// Settings.
+		underlying: config.Underlying,
+	}
+
+	return newResponseError, nil
+}
+
+type responseError struct {
+	// Internals.
+	code    string
+	message string
+
+	// Settings.
+	underlying error
+}
+
+func (e *responseError) Code() string {
+	return e.code
+}
+
+func (e *responseError) Error() string {
+	return e.underlying.Error()
+}
+
+func (e *responseError) Message() string {
+	return e.message
+}
+
+func (e *responseError) IsEndpoint() bool {
+	switch u := e.underlying.(type) {
+	case kithttp.Error:
+		switch u.Domain {
+		case kithttp.DomainEncode:
+			return true
+		case kithttp.DomainDecode:
+			return true
+		case kithttp.DomainDo:
+			return true
+		}
+	}
+
+	return false
+}
+
+func (e *responseError) SetCode(code string) {
+	e.code = code
+}
+
+func (e *responseError) SetMessage(message string) {
+	e.message = message
+}