feat: Add support to invoke PostResponse plugins

cmd/epp/main.go

@@ -211,6 +211,7 @@ func run() error {
 			scorers,
 			picker.NewMaxScorePicker(),
 			[]plugins.PostSchedule{},
+			[]plugins.PostResponse{},
 			schedConfigOpts...)
 		scheduler = scheduling.NewSchedulerWithConfig(datastore, schedulerConfig)
 	}

pkg/epp/handlers/response.go

@@ -21,6 +21,7 @@ import (
 	"encoding/json"
 	"strings"
 
+	configPb "github.com/envoyproxy/go-control-plane/envoy/config/core/v3"
 	extProcPb "github.com/envoyproxy/go-control-plane/envoy/service/ext_proc/v3"
 	"sigs.k8s.io/controller-runtime/pkg/log"
 	"sigs.k8s.io/gateway-api-inference-extension/pkg/epp/metrics"
@@ -98,6 +99,58 @@ func (s *StreamingServer) HandleResponseBodyModelStreaming(
 	}
 }
 
+func (s *StreamingServer) HandleResponseHeaders(ctx context.Context, reqCtx *RequestContext, resp *extProcPb.ProcessingRequest_ResponseHeaders) (*RequestContext, error) {
+	for _, header := range resp.ResponseHeaders.Headers.Headers {
+		if header.RawValue != nil {
+			reqCtx.Response.Headers[header.Key] = string(header.RawValue)
+		} else {
+			reqCtx.Response.Headers[header.Key] = header.Value
+		}
+	}
+
+	reqCtx, err := s.director.HandleResponse(ctx, reqCtx)
+
+	return reqCtx, err
+}
+
+func (s *StreamingServer) generateResponseHeaderResponse(reqCtx *RequestContext) *extProcPb.ProcessingResponse {
+	return &extProcPb.ProcessingResponse{
+		Response: &extProcPb.ProcessingResponse_ResponseHeaders{
+			ResponseHeaders: &extProcPb.HeadersResponse{
+				Response: &extProcPb.CommonResponse{
+					HeaderMutation: &extProcPb.HeaderMutation{
+						SetHeaders: s.generateResponseHeaders(reqCtx),
+					},
+				},
+			},
+		},
+	}
+}
+
+func (s *StreamingServer) generateResponseHeaders(reqCtx *RequestContext) []*configPb.HeaderValueOption {
+	// can likely refactor these two bespoke headers to be updated in PostDispatch, to centralize logic.
+	headers := []*configPb.HeaderValueOption{
+		{
+			Header: &configPb.HeaderValue{
+				// This is for debugging purpose only.
+				Key:      "x-went-into-resp-headers",
+				RawValue: []byte("true"),
+			},
+		},
+	}
+
+	// include all headers
+	for key, value := range reqCtx.Response.Headers {
+		headers = append(headers, &configPb.HeaderValueOption{
+			Header: &configPb.HeaderValue{
+				Key:      key,
+				RawValue: []byte(value),
+			},
+		})
+	}
+	return headers
+}
+
 // Example message if "stream_options": {"include_usage": "true"} is included in the request:
 // data: {"id":"...","object":"text_completion","created":1739400043,"model":"food-review-0","choices":[],
 // "usage":{"prompt_tokens":7,"total_tokens":17,"completion_tokens":10}}
@@ -112,8 +165,8 @@ func (s *StreamingServer) HandleResponseBodyModelStreaming(
 func parseRespForUsage(
 	ctx context.Context,
 	responseText string,
-) Response {
-	response := Response{}
+) ResponseBody {
+	response := ResponseBody{}
 	logger := log.FromContext(ctx)
 
 	lines := strings.Split(responseText, "\n")
@@ -136,7 +189,7 @@ func parseRespForUsage(
 	return response
 }
 
-type Response struct {
+type ResponseBody struct {
 	Usage Usage `json:"usage"`
 }
 

pkg/epp/handlers/server.go

@@ -23,7 +23,6 @@ import (
 	"strings"
 	"time"
 
-	configPb "github.com/envoyproxy/go-control-plane/envoy/config/core/v3"
 	extProcPb "github.com/envoyproxy/go-control-plane/envoy/service/ext_proc/v3"
 	envoyTypePb "github.com/envoyproxy/go-control-plane/envoy/type/v3"
 	"github.com/go-logr/logr"
@@ -49,6 +48,7 @@ func NewStreamingServer(destinationEndpointHintMetadataNamespace, destinationEnd
 
 type Director interface {
 	HandleRequest(ctx context.Context, reqCtx *RequestContext) (*RequestContext, error)
+	HandleResponse(ctx context.Context, reqCtx *RequestContext) (*RequestContext, error)
 	GetRandomPod() *backend.Pod
 }
 
@@ -91,6 +91,8 @@ type RequestContext struct {
 	RequestState         StreamRequestState
 	modelServerStreaming bool
 
+	Response *Response
+
 	reqHeaderResp  *extProcPb.ProcessingResponse
 	reqBodyResp    *extProcPb.ProcessingResponse
 	reqTrailerResp *extProcPb.ProcessingResponse
@@ -104,6 +106,9 @@ type Request struct {
 	Headers map[string]string
 	Body    map[string]interface{}
 }
+type Response struct {
+	Headers map[string]string
+}
 type StreamRequestState int
 
 const (
@@ -131,6 +136,9 @@ func (s *StreamingServer) Process(srv extProcPb.ExternalProcessor_ProcessServer)
 			Headers: make(map[string]string),
 			Body:    make(map[string]interface{}),
 		},
+		Response: &Response{
+			Headers: make(map[string]string),
+		},
 	}
 
 	var body []byte
@@ -229,25 +237,13 @@ func (s *StreamingServer) Process(srv extProcPb.ExternalProcessor_ProcessServer)
 				}
 			}
 			reqCtx.RequestState = ResponseRecieved
-			reqCtx.respHeaderResp = &extProcPb.ProcessingResponse{
-				Response: &extProcPb.ProcessingResponse_ResponseHeaders{
-					ResponseHeaders: &extProcPb.HeadersResponse{
-						Response: &extProcPb.CommonResponse{
-							HeaderMutation: &extProcPb.HeaderMutation{
-								SetHeaders: []*configPb.HeaderValueOption{
-									{
-										Header: &configPb.HeaderValue{
-											// This is for debugging purpose only.
-											Key:      "x-went-into-resp-headers",
-											RawValue: []byte("true"),
-										},
-									},
-								},
-							},
-						},
-					},
-				},
+
+			var responseErr error
+			reqCtx, responseErr = s.HandleResponseHeaders(ctx, reqCtx, v)
+			if responseErr != nil {
+				logger.V(logutil.DEFAULT).Error(responseErr, "Failed to process response headers", "request", req)
 			}
+			reqCtx.respHeaderResp = s.generateResponseHeaderResponse(reqCtx)
 
 		case *extProcPb.ProcessingRequest_ResponseBody:
 			if reqCtx.modelServerStreaming {

pkg/epp/requestcontrol/director.go

@@ -31,10 +31,12 @@ import (
 	schedulingtypes "sigs.k8s.io/gateway-api-inference-extension/pkg/epp/scheduling/types"
 	errutil "sigs.k8s.io/gateway-api-inference-extension/pkg/epp/util/error"
 	logutil "sigs.k8s.io/gateway-api-inference-extension/pkg/epp/util/logging"
+	requtil "sigs.k8s.io/gateway-api-inference-extension/pkg/epp/util/request"
 )
 
 type Scheduler interface {
 	Schedule(ctx context.Context, b *schedulingtypes.LLMRequest) (result *schedulingtypes.Result, err error)
+	OnResponse(ctx context.Context, resp *schedulingtypes.LLMResponse, targetPodName string)
 }
 
 type Director struct {
@@ -84,6 +86,7 @@ func (d *Director) HandleRequest(ctx context.Context, reqCtx *handlers.RequestCo
 
 	llmReq := &schedulingtypes.LLMRequest{
 		TargetModel: reqCtx.ResolvedTargetModel,
+		RequestId:   reqCtx.Request.Headers[requtil.RequestIdHeaderKey],
 		Critical:    modelObj.Spec.Criticality != nil && *modelObj.Spec.Criticality == v1alpha2.Critical,
 		Prompt:      prompt,
 		Headers:     reqCtx.Request.Headers,
@@ -137,6 +140,20 @@ func (d *Director) PostDispatch(ctx context.Context, reqCtx *handlers.RequestCon
 	return reqCtx, nil
 }
 
+func (d *Director) HandleResponse(ctx context.Context, reqCtx *handlers.RequestContext) (*handlers.RequestContext, error) {
+	logger := log.FromContext(ctx)
+
+	llmResp := &schedulingtypes.LLMResponse{
+		RequestId: reqCtx.Request.Headers[requtil.RequestIdHeaderKey],
+		Headers:   reqCtx.Response.Headers,
+	}
+	logger.V(logutil.DEBUG).Info("LLM response assembled", "response", llmResp)
+
+	d.scheduler.OnResponse(ctx, llmResp, reqCtx.TargetPod)
+
+	return reqCtx, nil
+}
+
 func (d *Director) GetRandomPod() *backend.Pod {
 	pods := d.datastore.PodGetAll()
 	if len(pods) == 0 {

pkg/epp/scheduling/config.go

@@ -23,13 +23,14 @@ import (
 
 // NewSchedulerConfig creates a new SchedulerConfig object with the given plugins.
 func NewSchedulerConfig(preSchedulePlugins []plugins.PreSchedule, filters []plugins.Filter, scorers map[plugins.Scorer]int,
-	picker plugins.Picker, postSchedulePlugins []plugins.PostSchedule, opts ...ConfigOption) *SchedulerConfig {
+	picker plugins.Picker, postSchedulePlugins []plugins.PostSchedule, postResponsePlugins []plugins.PostResponse, opts ...ConfigOption) *SchedulerConfig {
 	config := &SchedulerConfig{
 		preSchedulePlugins:  preSchedulePlugins,
 		filters:             filters,
 		scorers:             scorers,
 		picker:              picker,
 		postSchedulePlugins: postSchedulePlugins,
+		postResponsePlugins: postResponsePlugins,
 	}
 	for _, opt := range opts {
 		opt(config)
@@ -44,6 +45,7 @@ type SchedulerConfig struct {
 	scorers             map[plugins.Scorer]int // map from scorer to weight
 	picker              plugins.Picker
 	postSchedulePlugins []plugins.PostSchedule
+	postResponsePlugins []plugins.PostResponse
 }
 
 type ConfigOption func(*SchedulerConfig)

pkg/epp/scheduling/plugins/filter/filter_test.go

@@ -21,6 +21,7 @@ import (
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
+	"github.com/google/uuid"
 	k8stypes "k8s.io/apimachinery/pkg/types"
 	"sigs.k8s.io/gateway-api-inference-extension/pkg/epp/backend"
 	backendmetrics "sigs.k8s.io/gateway-api-inference-extension/pkg/epp/backend/metrics"
@@ -170,7 +171,7 @@ func TestFilter(t *testing.T) {
 
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
-			ctx := types.NewSchedulingContext(context.Background(), test.req, test.input)
+			ctx := types.NewSchedulingContext(context.Background(), test.req, nil, test.input)
 			got := test.filter.Filter(ctx, test.input)
 
 			if diff := cmp.Diff(test.output, got); diff != "" {
@@ -205,6 +206,7 @@ func TestLoRASoftAffinityDistribution(t *testing.T) {
 	// Create a test request and pods
 	req := &types.LLMRequest{
 		TargetModel: testAffinityModel,
+		RequestId:   uuid.NewString(),
 	}
 
 	// Test setup: One affinity pod and one available pod
@@ -226,7 +228,7 @@ func TestLoRASoftAffinityDistribution(t *testing.T) {
 			},
 		},
 	}
-	ctx := types.NewSchedulingContext(context.Background(), req, pods)
+	ctx := types.NewSchedulingContext(context.Background(), req, nil, pods)
 
 	// Run the filter function multiple times and count the results
 	affinityCount := 0

pkg/epp/scheduling/plugins/prefix/plugin_test.go

@@ -27,7 +27,7 @@ func TestPrefixPlugin(t *testing.T) {
 		TargetModel: "test-model1",
 		Prompt:      "aaaaaa",
 	}
-	ctx := types.NewSchedulingContext(context.Background(), req1, pods)
+	ctx := types.NewSchedulingContext(context.Background(), req1, nil, pods)
 	plugin.PreSchedule(ctx)
 	state, err := plugin.getPrefixState(ctx.CycleState)
 	assert.NoError(t, err)
@@ -51,7 +51,7 @@ func TestPrefixPlugin(t *testing.T) {
 		TargetModel: "test-model2",
 		Prompt:      "bbbbbb",
 	}
-	ctx = types.NewSchedulingContext(context.Background(), req2, pods)
+	ctx = types.NewSchedulingContext(context.Background(), req2, nil, pods)
 	plugin.PreSchedule(ctx)
 	state, err = plugin.getPrefixState(ctx.CycleState)
 	assert.NoError(t, err)
@@ -74,7 +74,7 @@ func TestPrefixPlugin(t *testing.T) {
 		TargetModel: "test-model1",
 		Prompt:      "aaaabbbb",
 	}
-	ctx = types.NewSchedulingContext(context.Background(), req3, pods)
+	ctx = types.NewSchedulingContext(context.Background(), req3, nil, pods)
 	plugin.PreSchedule(ctx)
 	state, err = plugin.getPrefixState(ctx.CycleState)
 	assert.NoError(t, err)
@@ -96,7 +96,7 @@ func TestPrefixPlugin(t *testing.T) {
 		TargetModel: "test-model-new",
 		Prompt:      "aaaabbbb",
 	}
-	ctx = types.NewSchedulingContext(context.Background(), req4, pods)
+	ctx = types.NewSchedulingContext(context.Background(), req4, nil, pods)
 	plugin.PreSchedule(ctx)
 	state, err = plugin.getPrefixState(ctx.CycleState)
 	assert.NoError(t, err)
@@ -118,7 +118,7 @@ func TestPrefixPlugin(t *testing.T) {
 		TargetModel: "test-model1",
 		Prompt:      "aaaabbbbcccc",
 	}
-	ctx = types.NewSchedulingContext(context.Background(), req5, pods)
+	ctx = types.NewSchedulingContext(context.Background(), req5, nil, pods)
 	plugin.PreSchedule(ctx)
 	state, err = plugin.getPrefixState(ctx.CycleState)
 	assert.NoError(t, err)

pkg/epp/scheduling/plugins/scorer/kvcache_test.go

@@ -82,7 +82,7 @@ func TestKvCacheScorer(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			ctx := types.NewSchedulingContext(context.Background(), &types.LLMRequest{}, tt.pods)
+			ctx := types.NewSchedulingContext(context.Background(), &types.LLMRequest{}, nil, tt.pods)
 			scorer := &KVCacheScorer{}
 			scores := scorer.Score(ctx, tt.pods)
 

pkg/epp/scheduling/plugins/scorer/queue_test.go

@@ -73,7 +73,7 @@ func TestQueueScorer(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			ctx := types.NewSchedulingContext(context.Background(), &types.LLMRequest{}, tt.pods)
+			ctx := types.NewSchedulingContext(context.Background(), &types.LLMRequest{}, nil, tt.pods)
 			scores := scorer.Score(ctx, tt.pods)
 
 			for i, pod := range tt.pods {

pkg/epp/scheduling/scheduler.go

@@ -84,6 +84,7 @@ func NewSchedulerWithConfig(datastore Datastore, config *SchedulerConfig) *Sched
 		scorers:             config.scorers,
 		picker:              config.picker,
 		postSchedulePlugins: config.postSchedulePlugins,
+		postResponsePlugins: config.postResponsePlugins,
 	}
 }
 
@@ -94,6 +95,7 @@ type Scheduler struct {
 	scorers             map[plugins.Scorer]int // map from scorer to its weight
 	picker              plugins.Picker
 	postSchedulePlugins []plugins.PostSchedule
+	postResponsePlugins []plugins.PostResponse
 }
 
 type Datastore interface {
@@ -113,7 +115,7 @@ func (s *Scheduler) Schedule(ctx context.Context, req *types.LLMRequest) (*types
 	// Snapshot pod metrics from the datastore to:
 	// 1. Reduce concurrent access to the datastore.
 	// 2. Ensure consistent data during the scheduling operation of a request.
-	sCtx := types.NewSchedulingContext(ctx, req, types.ToSchedulerPodMetrics(s.datastore.PodGetAll()))
+	sCtx := types.NewSchedulingContext(ctx, req, nil, types.ToSchedulerPodMetrics(s.datastore.PodGetAll()))
 	loggerDebug.Info(fmt.Sprintf("Scheduling a request, Metrics: %+v", sCtx.PodsSnapshot))
 
 	s.runPreSchedulePlugins(sCtx)
@@ -211,3 +213,32 @@ func (s *Scheduler) runPostSchedulePlugins(ctx *types.SchedulingContext, res *ty
 		metrics.RecordSchedulerPluginProcessingLatency(plugins.PostSchedulePluginType, plugin.Name(), time.Since(before))
 	}
 }
+
+// OnResponse is invoked during the processing of a response from an inference pod. It will invoke
+// any defined plugins that process the response.
+func (s *Scheduler) OnResponse(ctx context.Context, resp *types.LLMResponse, targetPodName string) {
+	// Snapshot pod metrics from the datastore to:
+	// 1. Reduce concurrent access to the datastore.
+	// 2. Ensure consistent data during the scheduling operation of a request.
+	pods := types.ToSchedulerPodMetrics(s.datastore.PodGetAll())
+	var targetPod types.Pod
+	for _, pod := range pods {
+		if pod.GetPod().NamespacedName.String() == targetPodName {
+			targetPod = pod
+			break
+		}
+	}
+
+	sCtx := types.NewSchedulingContext(ctx, nil, resp, pods)
+
+	s.runPostResponsePlugins(sCtx, targetPod)
+}
+
+func (s *Scheduler) runPostResponsePlugins(ctx *types.SchedulingContext, targetPod types.Pod) {
+	for _, plugin := range s.postResponsePlugins {
+		ctx.Logger.V(logutil.DEBUG).Info("Running post-response plugin", "plugin", plugin.Name())
+		before := time.Now()
+		plugin.PostResponse(ctx, targetPod)
+		metrics.RecordSchedulerPluginProcessingLatency(plugins.PostResponsePluginType, plugin.Name(), time.Since(before))
+	}
+}