[LoadTesting][Tooling] Support load testing via config (#460)

## Summary

Support load testing via config

Author: adshmh

protocol/shannon/config.go

@@ -73,6 +73,11 @@ type (
 		GatewayPrivateKeyHex    string               `yaml:"gateway_private_key_hex"`
 		OwnedAppsPrivateKeysHex []string             `yaml:"owned_apps_private_keys_hex"`
 		ServiceFallback         []ServiceFallback    `yaml:"service_fallback"`
+		// Optional.
+		// Puts the Gateway in LoadTesting mode if specified.
+		// All relays will be sent to a fixed URL.
+		// Allows measuring performance of PATH and full node(s) in isolation.
+		LoadTestingConfig *LoadTestingConfig `yaml:"load_testing_config"`
 	}
 
 	// TODO_TECHDEBT(@adshmh): Make configuration and implementation explicit:
@@ -88,6 +93,18 @@ type (
 		// regardless of the health of the protocol endpoints.
 		SendAllTraffic bool `yaml:"send_all_traffic"`
 	}
+
+	// Load testing configuration.
+	// Used to track Gateway's performance when using "perfect" endpoints.
+	// If specified:
+	// - Directs all relays to the specified backend service URL
+	// - No protocol or fallback endpoint used.
+	// - Assumes high throughput backend service (e.g. nginx with a fixed response)
+	LoadTestingConfig struct {
+		// The URL to use for sending relays.
+		BackendServiceURL string `yaml:"backend_service_url"`
+		// TODO_UPNEXT(@adshmh): Support using a fixed URL for a Shannon endpoint/RelayMiner during load testing.
+	}
 )
 
 func (gc GatewayConfig) Validate() error {

protocol/shannon/context.go

@@ -100,6 +100,14 @@ type requestContext struct {
 
 	// fallbackEndpoints is used to retrieve a fallback endpoint by an endpoint address.
 	fallbackEndpoints map[protocol.EndpointAddr]endpoint
+
+	// Optional.
+	// Puts the Gateway in LoadTesting mode if specified.
+	// All relays will be sent to a fixed URL.
+	// Allows measuring performance of PATH and full node(s) in isolation.
+	// Applies to Single Relay ONLY
+	// No parallel requests for a single relay in load testing mode.
+	loadTestingConfig *LoadTestingConfig
 }
 
 // HandleServiceRequest:
@@ -338,6 +346,13 @@ func (rc *requestContext) executeRelayRequestStrategy(payload protocol.Payload)
 	rc.hydrateLogger("executeRelayRequestStrategy")
 
 	switch {
+
+	// ** Priority 0: Load testing mode **
+	// Use the configured load testing backend server.
+	case rc.loadTestingConfig != nil:
+		rc.logger.Debug().Msg("LoadTesting Mode: Sending relay to the load test backend server")
+		return rc.sendProtocolRelay(payload)
+
 	// ** Priority 1: Check Endpoint type **
 	// Direct fallback endpoint
 	// - Bypasses protocol validation and Shannon network
@@ -524,14 +539,25 @@ func (rc *requestContext) sendProtocolRelay(payload protocol.Payload) (protocol.
 		return defaultResponse, fmt.Errorf("SHOULD NEVER HAPPEN: failed to marshal relay request: %w", err)
 	}
 
+	// TODO_UPNEXT(@adshmh): parse the LoadTesting server's URL in-advance.
+	var targetServerURL string
+	switch {
+	// LoadTesting mode: use the fixed URL.
+	case rc.loadTestingConfig != nil:
+		targetServerURL = rc.loadTestingConfig.BackendServiceURL
+	// Default: use the selected endoint's URL
+	default:
+		targetServerURL = selectedEndpoint.PublicURL()
+	}
+
 	// TODO_TECHDEBT(@adshmh): Add a new struct to track details about the HTTP call.
 	// It should contain at-least:
 	// - endpoint payload
 	// - HTTP status code
 	// Use the new struct to pass data around for logging/metrics/etc.
 	//
 	// Send the HTTP request to the protocol endpoint.
-	httpRelayResponseBz, httpStatusCode, err := rc.sendHTTPRequest(payload, selectedEndpoint.PublicURL(), relayRequestBz)
+	httpRelayResponseBz, httpStatusCode, err := rc.sendHTTPRequest(payload, targetServerURL, relayRequestBz)
 	if err != nil {
 		return defaultResponse, err
 	}
@@ -541,6 +567,17 @@ func (rc *requestContext) sendProtocolRelay(payload protocol.Payload) (protocol.
 		return defaultResponse, fmt.Errorf("%w %w: %d", errSendHTTPRelay, errEndpointNon2XXHTTPStatusCode, httpStatusCode)
 	}
 
+	// LoadTesting mode: return the backend server's response as-is.
+	if rc.loadTestingConfig != nil {
+		return protocol.Response{
+			Bytes:          httpRelayResponseBz,
+			HTTPStatusCode: httpStatusCode,
+			// Intentionally leaving the endpoint address empty.
+			// Ensuring to sanctions/invalidation rules apply to LoadTesting backend server
+			EndpointAddr: "",
+		}, nil
+	}
+
 	// Validate and process the response
 	response, err := rc.validateAndProcessResponse(httpRelayResponseBz)
 	if err != nil {

protocol/shannon/protocol.go

@@ -74,6 +74,12 @@ type Protocol struct {
 	// Each service can have a SendAllTraffic flag to send all traffic to
 	// fallback endpoints, regardless of the health of the protocol endpoints.
 	serviceFallbackMap map[protocol.ServiceID]serviceFallback
+
+	// Optional.
+	// Puts the Gateway in LoadTesting mode if specified.
+	// All relays will be sent to a fixed URL.
+	// Allows measuring performance of PATH and full node(s) in isolation.
+	loadTestingConfig *LoadTestingConfig
 }
 
 // serviceFallback holds the fallback information for a service,
@@ -123,6 +129,9 @@ func NewProtocol(
 
 		// serviceFallbacks contains the fallback information for each service.
 		serviceFallbackMap: config.getServiceFallbackMap(),
+
+		// load testing config, if specified.
+		loadTestingConfig: config.LoadTestingConfig,
 	}
 
 	return protocolInstance, nil
@@ -334,6 +343,7 @@ func (p *Protocol) BuildHTTPRequestContextForEndpoint(
 		relayRequestSigner: permittedSigner,
 		httpClient:         p.httpClient,
 		fallbackEndpoints:  fallbackEndpoints,
+		loadTestingConfig:  p.loadTestingConfig,
 	}, protocolobservations.Observations{}, nil
 }