[paymentservice] support range feature flag for simulated slowness

This also adds support for range feature flags in the feature flag
service and its API.

docker-compose.yml

@@ -414,6 +414,7 @@ services:
       - OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE
       - OTEL_RESOURCE_ATTRIBUTES
       - OTEL_SERVICE_NAME=paymentservice
+      - FEATURE_FLAG_GRPC_SERVICE_ADDR
     depends_on:
       otelcol:
         condition: service_started

pb/demo.proto

@@ -276,6 +276,18 @@ service FeatureFlagService {
    */
   rpc EvaluateProbabilityFeatureFlag(EvaluateProbabilityFeatureFlagRequest) returns (EvaluateProbabilityFeatureFlagResponse) {}
 
+  /*
+   * A convenience function to fetch a triplet of feature flag values that represent a range of values. For example, for
+   * simulating increased request latencies in a service, the triplet of feature flags to be created would be
+   * - serviceNameSimulateSlowness: on/off switch or probability for the feature (value is >= 0 & <= 1),
+   * - serviceNameSimulateSlownessLowerBound: the lower bound in milliseconds for the additional delay,
+   * - serviceNameSimulateSlownessUpperBound: the upper bound in milliseconds for the additional delay.
+   * That is, the feature flag API assumes that there are additional feature flag values with the suffix "LowerBound" and
+   * "UpperBound" when a range feature flag with a particular name is requested. In case the feature is enabled, but one or both
+   * of lower/upper bound does not exist, the arbitrary defaults for the lower and upper bound are 0 and 1000 respectively.
+   */
+  rpc GetRangeFeatureFlag(RangeFeatureFlagRequest) returns (RangeFeatureFlagResponse) {}
+
   /* Creates a new feature flag. */
   rpc CreateFlag(CreateFlagRequest) returns (CreateFlagResponse) {}
 
@@ -303,6 +315,18 @@ message EvaluateProbabilityFeatureFlagResponse {
   bool enabled = 1;
 }
 
+message RangeFeatureFlagRequest {
+  string name = 1;
+  string nameLowerBound = 2;
+  string nameUpperBound = 3;
+}
+
+message RangeFeatureFlagResponse {
+  bool enabled = 1;
+  float lowerBound = 2;
+  float upperBound = 3;
+}
+
 message GetFeatureFlagValueRequest {
   string name = 1;
 }

regenerate-grpc-code.sh

@@ -37,7 +37,6 @@ EOF
   exit 1
 }
 
-
 command -v protoc >/dev/null 2>&1 || {
   cat <<EOF >&2
 protoc needs to be installed but it isn't.
@@ -74,7 +73,7 @@ popd > /dev/null
 
 echo "Regenerating Java code in src/adservice based on demo.proto"
 pushd src/adservice > /dev/null
-./gradlew  generateProto
+./gradlew generateProto
 popd > /dev/null
 
 echo "Recompiling Erlang code in src/featureflagservice based on demo.proto"