improve no-op qos error response

Author: Pascal van Leeuwen

qos/noop/context.go

@@ -11,14 +11,6 @@ import (
 	"github.com/buildwithgrove/path/protocol"
 )
 
-// clientRespMsgNoProtocolEndpoints is the error message sent to clients when
-// the underlying protocol fails to register any endpoint responses with the NoOp QoS service.
-// This can occur due to:
-//   - User error: invalid service ID in the request's HTTP header
-//   - Protocol error: selected endpoint failed to provide a valid response
-//   - System timeout: no endpoints responded within the allowed time window
-const clientRespMsgNoProtocolEndpoints = "NoOp QoS service error: No responses received from any service endpoints. Please verify your service ID and retry."
-
 // requestContext implements all the functionality required by gateway.RequestQoSContext interface.
 var _ gateway.RequestQoSContext = &requestContext{}
 
@@ -45,7 +37,7 @@ type requestContext struct {
 
 	// presetFailureResponse, if set, is used to return a preconstructed response to the user.
 	// This is used by the conductor of the requestContext instance, e.g. if reading the HTTP request's body fails.
-	presetFailureResponse *HTTPResponse
+	presetFailureResponse pathhttp.HTTPResponse
 }
 
 // GetServicePayload returns the payload to be sent to a service endpoint.
@@ -68,7 +60,10 @@ func (rc *requestContext) GetServicePayloads() []protocol.Payload {
 // UpdateWithResponse is NOT safe for concurrent use
 // Implements the gateway.RequestQoSContext interface.
 func (rc *requestContext) UpdateWithResponse(endpointAddr protocol.EndpointAddr, endpointSerializedResponse []byte) {
-	rc.receivedResponses = append(rc.receivedResponses, endpointResponse{EndpointAddr: endpointAddr, ResponseBytes: endpointSerializedResponse})
+	rc.receivedResponses = append(rc.receivedResponses, endpointResponse{
+		EndpointAddr:  endpointAddr,
+		ResponseBytes: endpointSerializedResponse,
+	})
 }
 
 // GetHTTPResponse returns a user-facing response that fulfills the pathhttp.HTTPResponse interface.
@@ -81,10 +76,7 @@ func (rc *requestContext) GetHTTPResponse() pathhttp.HTTPResponse {
 	}
 
 	if len(rc.receivedResponses) == 0 {
-		return &HTTPResponse{
-			httpStatusCode: http.StatusOK,
-			payload:        []byte(clientRespMsgNoProtocolEndpoints),
-		}
+		return getNoEndpointResponse()
 	}
 
 	return &HTTPResponse{

qos/noop/errors.go

@@ -0,0 +1,50 @@
+package noop
+
+import (
+	"fmt"
+	"net/http"
+
+	pathhttp "github.com/buildwithgrove/path/network/http"
+)
+
+const (
+	// errTemplate is the template for the error response to ensure
+	// that the error response is returned in a valid JSON format.
+	errTemplate = `{"error":"%s","msg":"%s"}`
+
+	// clientRespMsgNoProtocolEndpoints is the error message sent to clients when
+	// the underlying protocol fails to register any endpoint responses with the NoOp QoS service.
+	// This can occur due to:
+	//   - User error: invalid service ID in the request's HTTP header
+	//   - Protocol error: selected endpoint failed to provide a valid response
+	//   - System timeout: no endpoints responded within the allowed time window
+	clientRespMsgNoProtocolEndpoints = "no-op qos service error: no responses received from any service endpoints"
+
+	// clientRespMsgRequestProcessingError is the error message sent to clients when
+	// the NoOp QoS service encounters an error while reading the request body.
+	// This can occur due to:
+	//   - User error: invalid request body caused the an error reading the request body
+	clientRespMsgRequestProcessingError = "no-op qos service error: error processing the request"
+)
+
+// formatJSONError creates a JSON formatted error response with the provided error and message.
+func formatJSONError(message string, err error) []byte {
+	return []byte(fmt.Sprintf(errTemplate, err.Error(), message))
+}
+
+// getRequestProcessingError creates a HTTP response for request processing errors.
+func getRequestProcessingError(err error) pathhttp.HTTPResponse {
+	return &HTTPResponse{
+		httpStatusCode: http.StatusBadRequest,
+		payload:        formatJSONError(clientRespMsgRequestProcessingError, err),
+	}
+}
+
+// getNoEndpointResponse creates a HTTP response for no endpoint responses.
+func getNoEndpointResponse() pathhttp.HTTPResponse {
+	err := fmt.Errorf("no protocol endpoint responses")
+	return &HTTPResponse{
+		httpStatusCode: http.StatusInternalServerError,
+		payload:        formatJSONError(clientRespMsgNoProtocolEndpoints, err),
+	}
+}

qos/noop/noop.go

@@ -56,10 +56,7 @@ func (NoOpQoS) GetRequiredQualityChecks(_ protocol.EndpointAddr) []gateway.Reque
 // The returned requestContext will returns a user-facing HTTP request with the supplied error when it GetHTTPResponse method is called.
 func requestContextFromError(err error) *requestContext {
 	return &requestContext{
-		presetFailureResponse: &HTTPResponse{
-			httpStatusCode: http.StatusOK,
-			payload:        []byte(fmt.Sprintf("Error processing the request: %v", err)),
-		},
+		presetFailureResponse: getRequestProcessingError(err),
 	}
 }