add support for response dynamic metadata (#1027)

* add support for response dynamic metadata

Signed-off-by: zirain <zirain2009@gmail.com>

* address Colin's comment

Signed-off-by: zirain <zirain2009@gmail.com>

---------

Signed-off-by: zirain <zirain2009@gmail.com>

Author: zirain

go.mod

@@ -12,6 +12,7 @@ require (
 	github.com/envoyproxy/go-control-plane/ratelimit v0.1.1-0.20250812085011-4cf7e8485428
 	github.com/go-kit/log v0.2.1
 	github.com/golang/mock v1.6.0
+	github.com/google/go-cmp v0.7.0
 	github.com/google/uuid v1.6.0
 	github.com/gorilla/mux v1.8.1
 	github.com/grpc-ecosystem/go-grpc-middleware v1.4.0

src/service/ratelimit.go

@@ -10,13 +10,15 @@ import (
 	"go.opentelemetry.io/otel"
 	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/trace"
+	"google.golang.org/protobuf/types/known/structpb"
 
 	"github.com/envoyproxy/ratelimit/src/settings"
 	"github.com/envoyproxy/ratelimit/src/stats"
 
 	"github.com/envoyproxy/ratelimit/src/utils"
 
 	core "github.com/envoyproxy/go-control-plane/envoy/config/core/v3"
+	ratelimitv3 "github.com/envoyproxy/go-control-plane/envoy/extensions/common/ratelimit/v3"
 	pb "github.com/envoyproxy/go-control-plane/envoy/service/ratelimit/v3"
 	logger "github.com/sirupsen/logrus"
 	"golang.org/x/net/context"
@@ -38,18 +40,19 @@ type RateLimitServiceServer interface {
 }
 
 type service struct {
-	configLock                  sync.RWMutex
-	configUpdateEvent           <-chan provider.ConfigUpdateEvent
-	config                      config.RateLimitConfig
-	cache                       limiter.RateLimitCache
-	stats                       stats.ServiceStats
-	health                      *server.HealthChecker
-	customHeadersEnabled        bool
-	customHeaderLimitHeader     string
-	customHeaderRemainingHeader string
-	customHeaderResetHeader     string
-	customHeaderClock           utils.TimeSource
-	globalShadowMode            bool
+	configLock                     sync.RWMutex
+	configUpdateEvent              <-chan provider.ConfigUpdateEvent
+	config                         config.RateLimitConfig
+	cache                          limiter.RateLimitCache
+	stats                          stats.ServiceStats
+	health                         *server.HealthChecker
+	customHeadersEnabled           bool
+	customHeaderLimitHeader        string
+	customHeaderRemainingHeader    string
+	customHeaderResetHeader        string
+	customHeaderClock              utils.TimeSource
+	globalShadowMode               bool
+	responseDynamicMetadataEnabled bool
 }
 
 func (this *service) SetConfig(updateEvent provider.ConfigUpdateEvent, healthyWithAtLeastOneConfigLoad bool) {
@@ -84,6 +87,7 @@ func (this *service) SetConfig(updateEvent provider.ConfigUpdateEvent, healthyWi
 
 	rlSettings := settings.NewSettings()
 	this.globalShadowMode = rlSettings.GlobalShadowMode
+	this.responseDynamicMetadataEnabled = rlSettings.ResponseDynamicMetadata
 
 	if rlSettings.RateLimitResponseHeadersEnabled {
 		this.customHeadersEnabled = true
@@ -239,10 +243,72 @@ func (this *service) shouldRateLimitWorker(
 		this.stats.GlobalShadowMode.Inc()
 	}
 
+	// If response dynamic data enabled, set dynamic data on response.
+	if this.responseDynamicMetadataEnabled {
+		response.DynamicMetadata = ratelimitToMetadata(request)
+	}
+
 	response.OverallCode = finalCode
 	return response
 }
 
+func ratelimitToMetadata(req *pb.RateLimitRequest) *structpb.Struct {
+	fields := make(map[string]*structpb.Value)
+
+	// Domain
+	fields["domain"] = structpb.NewStringValue(req.Domain)
+
+	// Descriptors
+	descriptorsValues := make([]*structpb.Value, 0, len(req.Descriptors))
+	for _, descriptor := range req.Descriptors {
+		s := descriptorToStruct(descriptor)
+		if s == nil {
+			continue
+		}
+		descriptorsValues = append(descriptorsValues, structpb.NewStructValue(s))
+	}
+	fields["descriptors"] = structpb.NewListValue(&structpb.ListValue{
+		Values: descriptorsValues,
+	})
+
+	// HitsAddend
+	if hitsAddend := req.GetHitsAddend(); hitsAddend != 0 {
+		fields["hitsAddend"] = structpb.NewNumberValue(float64(hitsAddend))
+	}
+
+	return &structpb.Struct{Fields: fields}
+}
+
+func descriptorToStruct(descriptor *ratelimitv3.RateLimitDescriptor) *structpb.Struct {
+	if descriptor == nil {
+		return nil
+	}
+
+	fields := make(map[string]*structpb.Value)
+
+	// Entries
+	entriesValues := make([]*structpb.Value, 0, len(descriptor.Entries))
+	for _, entry := range descriptor.Entries {
+		val := fmt.Sprintf("%s=%s", entry.GetKey(), entry.GetValue())
+		entriesValues = append(entriesValues, structpb.NewStringValue(val))
+	}
+	fields["entries"] = structpb.NewListValue(&structpb.ListValue{
+		Values: entriesValues,
+	})
+
+	// Limit
+	if descriptor.GetLimit() != nil {
+		fields["limit"] = structpb.NewStringValue(descriptor.Limit.String())
+	}
+
+	// HitsAddend
+	if hitsAddend := descriptor.GetHitsAddend(); hitsAddend != nil {
+		fields["hitsAddend"] = structpb.NewNumberValue(float64(hitsAddend.GetValue()))
+	}
+
+	return &structpb.Struct{Fields: fields}
+}
+
 func (this *service) rateLimitLimitHeader(descriptor *pb.RateLimitResponse_DescriptorStatus) *core.HeaderValue {
 	// Limit header only provides the mandatory part from the spec, the actual limit
 	// the optional quota policy is currently not provided

src/service/ratelimit_test.go

@@ -0,0 +1,61 @@
+package ratelimit
+
+import (
+	"testing"
+
+	ratelimitv3 "github.com/envoyproxy/go-control-plane/envoy/extensions/common/ratelimit/v3"
+	pb "github.com/envoyproxy/go-control-plane/envoy/service/ratelimit/v3"
+	"github.com/google/go-cmp/cmp"
+	"github.com/stretchr/testify/require"
+	"google.golang.org/protobuf/encoding/protojson"
+	"google.golang.org/protobuf/testing/protocmp"
+	"google.golang.org/protobuf/types/known/structpb"
+)
+
+func TestRatelimitToMetadata(t *testing.T) {
+	cases := []struct {
+		name     string
+		req      *pb.RateLimitRequest
+		expected string
+	}{
+		{
+			name: "Single descriptor with single entry",
+			req: &pb.RateLimitRequest{
+				Domain: "fake-domain",
+				Descriptors: []*ratelimitv3.RateLimitDescriptor{
+					{
+						Entries: []*ratelimitv3.RateLimitDescriptor_Entry{
+							{
+								Key:   "key1",
+								Value: "val1",
+							},
+						},
+					},
+				},
+			},
+			expected: `{
+    "descriptors": [
+        {
+            "entries": [
+                "key1=val1"
+            ]
+        }
+    ],
+    "domain": "fake-domain"
+}`,
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			got := ratelimitToMetadata(tc.req)
+			expected := &structpb.Struct{}
+			err := protojson.Unmarshal([]byte(tc.expected), expected)
+			require.NoError(t, err)
+
+			if diff := cmp.Diff(got, expected, protocmp.Transform()); diff != "" {
+				t.Errorf("diff: %s", diff)
+			}
+		})
+	}
+}

src/settings/settings.go

@@ -210,6 +210,8 @@ type Settings struct {
 	// Should the ratelimiting be running in Global shadow-mode, ie. never report a ratelimit status, unless a rate was provided from envoy as an override
 	GlobalShadowMode bool `envconfig:"SHADOW_MODE" default:"false"`
 
+	ResponseDynamicMetadata bool `envconfig:"RESPONSE_DYNAMIC_METADATA" default:"false"`
+
 	// Allow merging of multiple yaml files referencing the same domain
 	MergeDomainConfigurations bool `envconfig:"MERGE_DOMAIN_CONFIG" default:"false"`