Add non-streaming response to approximate prefix cache.

pkg/epp/handlers/server.go

@@ -115,6 +115,7 @@ type Request struct {
 }
 type Response struct {
 	Headers map[string]string
+	Body    []byte
 }
 type StreamRequestState int
 
@@ -303,6 +304,7 @@ func (s *StreamingServer) Process(srv extProcPb.ExternalProcessor_ProcessServer)
 						break
 					}
 
+					reqCtx.Response.Body = body
 					reqCtx, responseErr = s.HandleResponseBody(ctx, reqCtx, responseBody)
 					if responseErr != nil {
 						if logger.V(logutil.DEBUG).Enabled() {

pkg/epp/requestcontrol/director.go

@@ -280,14 +280,15 @@ func (d *Director) HandleResponseBodyStreaming(ctx context.Context, reqCtx *hand
 
 // HandleResponseBodyComplete is called when the response body is fully received.
 func (d *Director) HandleResponseBodyComplete(ctx context.Context, reqCtx *handlers.RequestContext) (*handlers.RequestContext, error) {
-	logger := log.FromContext(ctx).WithValues("stage", "bodyChunk")
+	requestID := reqCtx.Request.Headers[requtil.RequestIdHeaderKey]
+	logger := log.FromContext(ctx).WithValues("stage", "bodyChunk", requtil.RequestIdHeaderKey, requestID)
 	logger.V(logutil.DEBUG).Info("Entering HandleResponseBodyComplete")
-	response := &Response{
-		RequestId: reqCtx.Request.Headers[requtil.RequestIdHeaderKey],
-		Headers:   reqCtx.Response.Headers,
+	llmResponse, err := schedulingtypes.NewLLMResponseFromBytes(reqCtx.Response.Body)
+	if err != nil {
+		logger.Error(err, "HandleResponseBodyComplete: failed to convert the response to LLMResponse.")
+		return reqCtx, err
 	}
-
-	d.runResponseCompletePlugins(ctx, reqCtx.SchedulingRequest, response, reqCtx.TargetPod)
+	d.runResponseCompletePlugins(ctx, reqCtx.SchedulingRequest, llmResponse, reqCtx.TargetPod)
 
 	logger.V(logutil.DEBUG).Info("Exiting HandleResponseBodyComplete")
 	return reqCtx, nil
@@ -337,7 +338,7 @@ func (d *Director) runResponseStreamingPlugins(ctx context.Context, request *sch
 	}
 }
 
-func (d *Director) runResponseCompletePlugins(ctx context.Context, request *schedulingtypes.LLMRequest, response *Response, targetPod *backend.Pod) {
+func (d *Director) runResponseCompletePlugins(ctx context.Context, request *schedulingtypes.LLMRequest, response *schedulingtypes.LLMResponse, targetPod *backend.Pod) {
 	loggerDebug := log.FromContext(ctx).V(logutil.DEBUG)
 	for _, plugin := range d.requestControlPlugins.responseCompletePlugins {
 		loggerDebug.Info("Running ResponseComplete plugin", "plugin", plugin.TypedName())

pkg/epp/requestcontrol/director_test.go

@@ -696,6 +696,27 @@ func TestDirector_HandleResponseComplete(t *testing.T) {
 	mockSched := &mockScheduler{}
 	director := NewDirectorWithConfig(ds, mockSched, nil, NewConfig().WithResponseCompletePlugins(pc1))
 
+	chatCompletionJSON := `{
+		"choices": [
+			{
+				"message": {
+					"role": "assistant",
+					"content": "Hello!"
+				},
+				"finish_reason": "stop"
+			}
+		],
+		"usage": {
+			"prompt_tokens": 1,
+			"completion_tokens": 2,
+			"total_tokens": 3
+		}
+	}`
+	wantLLMResponse, err := schedulingtypes.NewLLMResponseFromBytes([]byte(chatCompletionJSON))
+	if err != nil {
+		t.Fatalf("NewLLMResponseFromBytes failed with error: %v", err)
+	}
+
 	reqCtx := &handlers.RequestContext{
 		Request: &handlers.Request{
 			Headers: map[string]string{
@@ -704,24 +725,22 @@ func TestDirector_HandleResponseComplete(t *testing.T) {
 		},
 		Response: &handlers.Response{
 			Headers: map[string]string{"X-Test-Complete-Header": "CompleteValue"},
+			Body:    []byte(chatCompletionJSON),
 		},
 		TargetPod: &backend.Pod{NamespacedName: types.NamespacedName{Namespace: "namespace1", Name: "test-pod-name"}},
 	}
 
-	_, err := director.HandleResponseBodyComplete(ctx, reqCtx)
+	_, err = director.HandleResponseBodyComplete(ctx, reqCtx)
 	if err != nil {
 		t.Fatalf("HandleResponseBodyComplete() returned unexpected error: %v", err)
 	}
 
-	if diff := cmp.Diff("test-req-id-for-complete", pc1.lastRespOnComplete.RequestId); diff != "" {
-		t.Errorf("Scheduler.OnComplete RequestId mismatch (-want +got):\n%s", diff)
-	}
-	if diff := cmp.Diff(reqCtx.Response.Headers, pc1.lastRespOnComplete.Headers); diff != "" {
-		t.Errorf("Scheduler.OnComplete Headers mismatch (-want +got):\n%s", diff)
-	}
 	if diff := cmp.Diff("namespace1/test-pod-name", pc1.lastTargetPodOnComplete); diff != "" {
 		t.Errorf("Scheduler.OnComplete TargetPodName mismatch (-want +got):\n%s", diff)
 	}
+	if diff := cmp.Diff(wantLLMResponse, pc1.lastRespOnComplete); diff != "" {
+		t.Errorf("Scheduler.OnComplete response body mismatch (-want +got):\n%s", diff)
+	}
 }
 
 const (
@@ -744,7 +763,7 @@ type testResponseStreaming struct {
 
 type testResponseComplete struct {
 	tn                      plugins.TypedName
-	lastRespOnComplete      *Response
+	lastRespOnComplete      *schedulingtypes.LLMResponse
 	lastTargetPodOnComplete string
 }
 
@@ -788,7 +807,7 @@ func (p *testResponseStreaming) ResponseStreaming(_ context.Context, _ *scheduli
 	p.lastTargetPodOnStreaming = targetPod.NamespacedName.String()
 }
 
-func (p *testResponseComplete) ResponseComplete(_ context.Context, _ *schedulingtypes.LLMRequest, response *Response, targetPod *backend.Pod) {
+func (p *testResponseComplete) ResponseComplete(_ context.Context, _ *schedulingtypes.LLMRequest, response *schedulingtypes.LLMResponse, targetPod *backend.Pod) {
 	p.lastRespOnComplete = response
 	p.lastTargetPodOnComplete = targetPod.NamespacedName.String()
 }

pkg/epp/requestcontrol/plugins.go

@@ -55,5 +55,5 @@ type ResponseStreaming interface {
 // ResponseComplete is called by the director after the complete response is sent.
 type ResponseComplete interface {
 	plugins.Plugin
-	ResponseComplete(ctx context.Context, request *types.LLMRequest, response *Response, targetPod *backend.Pod)
+	ResponseComplete(ctx context.Context, request *types.LLMRequest, response *types.LLMResponse, targetPod *backend.Pod)
 }

pkg/epp/scheduling/framework/plugins/multi/prefix/plugin.go

@@ -17,6 +17,7 @@ limitations under the License.
 package prefix
 
 import (
+	"bytes"
 	"context"
 	"encoding/binary"
 	"encoding/json"
@@ -28,6 +29,7 @@ import (
 	k8stypes "k8s.io/apimachinery/pkg/types"
 	"sigs.k8s.io/controller-runtime/pkg/log"
 
+	"sigs.k8s.io/gateway-api-inference-extension/pkg/epp/backend"
 	backendmetrics "sigs.k8s.io/gateway-api-inference-extension/pkg/epp/backend/metrics"
 	"sigs.k8s.io/gateway-api-inference-extension/pkg/epp/metrics"
 	"sigs.k8s.io/gateway-api-inference-extension/pkg/epp/plugins"
@@ -117,6 +119,12 @@ var _ plugins.StateData = &SchedulingContextState{}
 type SchedulingContextState struct {
 	// PrefixHashes is a list of prefix hashes of the request prompt broken into blocks.
 	PrefixHashes []BlockHash
+	// RestBytes is the trailing bytes that not able to fill in a full block and left over.
+	// If not empty, this will be used as the starting block for the following response that will
+	// be added to the response as well. This happens especially at the multi-turn scenario.
+	RestBytes []byte
+	// BlockSize is the block size used to caculate the hash of the request/response.
+	BlockSize int
 	// A map of server to its longest prefix cache match length.
 	PrefixCacheServers map[ServerID]int
 }
@@ -192,10 +200,13 @@ func (p *Plugin) WithName(name string) *Plugin {
 
 // Score returns the scoring result for the given list of pods based on context.
 func (p *Plugin) Score(ctx context.Context, cycleState *types.CycleState, request *types.LLMRequest, pods []types.Pod) map[types.Pod]float64 {
+	blockSize := getBlockSize(pods, p.config.DefaultBlockSize)
 	// pre score step, hashing prompt and find longest prefix match.
-	hashes := hashPrompt(ctx, request, getBlockSize(pods, p.config.DefaultBlockSize), p.config.MaxPrefixBlocksToMatch)
+	hashes, restBytes := hashPrompt(ctx, request, blockSize, p.config.MaxPrefixBlocksToMatch)
 	state := &SchedulingContextState{
 		PrefixHashes:       hashes,
+		RestBytes:          restBytes,
+		BlockSize:          blockSize,
 		PrefixCacheServers: p.matchLongestPrefix(ctx, hashes),
 	}
 
@@ -226,7 +237,6 @@ func (p *Plugin) PreRequest(ctx context.Context, request *types.LLMRequest, sche
 	targetPod := primaryProfileResult.TargetPods[0].GetPod() // get the first pod of the primary profile
 
 	state, err := plugins.ReadPluginStateKey[*SchedulingContextState](p.pluginState, request.RequestId, plugins.StateKey(p.TypedName().String()))
-	p.pluginState.Delete(request.RequestId) // delete the state explicitly after completing using it
 	if err != nil {
 		log.FromContext(ctx).Error(err, "failed to read prefix plugin state", "requestID", request.RequestId)
 		return
@@ -244,9 +254,7 @@ func (p *Plugin) PreRequest(ctx context.Context, request *types.LLMRequest, sche
 
 	total := len(state.PrefixHashes)
 	matchLen := state.PrefixCacheServers[ServerID(targetPod.NamespacedName)]
-
-	blockSize := getBlockSize(primaryProfileResult.TargetPods, p.config.DefaultBlockSize)
-	metrics.RecordPrefixCacheMatch(matchLen*blockSize, total*blockSize)
+	metrics.RecordPrefixCacheMatch(matchLen*state.BlockSize, total*state.BlockSize)
 }
 
 // matchLongestPrefix returns a map of servers and length of prefix that each server caches.
@@ -301,47 +309,59 @@ func (m *Plugin) CleanUpInactivePods(ctx context.Context, handle plugins.Handle)
 // hashPrompt divides the prompt into blocks and calculate the prefix cache for each block.
 // hash[0] is calculated including the model name and cache_salt(if provided), since different models generally don't share prefix cache.
 // For block i, hash(i) = hash(block i content, hash(i-1)).
-func hashPrompt(ctx context.Context, request *types.LLMRequest, cacheBlockSize int, maxPrefixBlocks int) []BlockHash {
+// Also return the extra string.
+func hashPrompt(ctx context.Context, request *types.LLMRequest, cacheBlockSize int, maxPrefixBlocks int) ([]BlockHash, []byte) {
 	loggerDebug := log.FromContext(ctx).V(logutil.DEBUG)
 	if request == nil || request.Body == nil {
 		loggerDebug.Info("Request or request data is nil, skipping hashing")
-		return nil
+		return nil, nil
 	}
 
 	userInput, err := getUserInputBytes(request)
 	if err != nil {
 		loggerDebug.Error(err, "Failed to get user input bytes")
-		return nil
+		return nil, nil
 	}
+	prevBlockHash := defaultPrevBlock(request)
+	return hashInputWithPrevBlockHash(ctx, prevBlockHash, 0, userInput, cacheBlockSize, maxPrefixBlocks)
+}
 
-	if len(userInput) < cacheBlockSize {
-		loggerDebug.Info("Request body too small for prefix cache", "size", len(userInput), "block size", cacheBlockSize)
-		return nil
-	}
-	if len(userInput) > cacheBlockSize*maxPrefixBlocks {
-		loggerDebug.Info("Truncating input", "size", len(userInput), "max prefix blocks", maxPrefixBlocks, "block size", cacheBlockSize)
-		userInput = userInput[:maxPrefixBlocks*cacheBlockSize]
-	}
-	// Split the body into blocks of size cacheBlockSize.
-	// If the last block is smaller than cacheBlockSize, it will be ignored.
-	res := make([]BlockHash, 0, len(userInput)/cacheBlockSize)
-	// Add the model to the first block hash so that different models have different hashes even with the same body.
+func defaultPrevBlock(request *types.LLMRequest) BlockHash {
 	h := xxhash.New()
+	// Add the model to the first block hash so that different models have different hashes even with the same body.
 	_, _ = h.Write([]byte(request.TargetModel))
 	if cacheSalt := request.Body.CacheSalt(); cacheSalt != "" {
 		_, _ = h.Write([]byte(cacheSalt))
 	}
 
-	prevBlockHash := BlockHash(h.Sum64())
-	for i := 0; i+cacheBlockSize <= len(userInput); i += cacheBlockSize {
+	return BlockHash(h.Sum64())
+}
+
+func hashInputWithPrevBlockHash(ctx context.Context, prevBlockHash BlockHash, prevBlockLength int, input []byte, cacheBlockSize int, maxPrefixBlocks int) ([]BlockHash, []byte) {
+	loggerDebug := log.FromContext(ctx).V(logutil.DEBUG)
+	if len(input)+prevBlockLength < cacheBlockSize {
+		loggerDebug.Info("Request body too small for prefix cache", "size", len(input), "block size", cacheBlockSize)
+		return nil, input
+	}
+	if len(input)+prevBlockLength > cacheBlockSize*maxPrefixBlocks {
+		loggerDebug.Info("Truncating input", "size", len(input), "max prefix blocks", maxPrefixBlocks, "block size", cacheBlockSize)
+		input = input[:(maxPrefixBlocks*cacheBlockSize - prevBlockLength)]
+	}
+	// Split the body into blocks of size cacheBlockSize.
+	// If the last block is smaller than cacheBlockSize, it will be ignored.
+	res := make([]BlockHash, 0, len(input)/cacheBlockSize)
+	lastOffSet := 0
+	h := xxhash.New()
+	for i := 0; i+cacheBlockSize <= len(input); i += cacheBlockSize {
 		h.Reset()
-		_, _ = h.Write(userInput[i : i+cacheBlockSize])
+		_, _ = h.Write(input[i : i+cacheBlockSize])
 		_, _ = h.Write(toBytes(prevBlockHash))
 		res = append(res, BlockHash(h.Sum64()))
 
 		prevBlockHash = res[len(res)-1]
+		lastOffSet = i + cacheBlockSize
 	}
-	return res
+	return res, input[lastOffSet:]
 }
 
 func toBytes(i BlockHash) []byte {
@@ -356,7 +376,39 @@ func getUserInputBytes(request *types.LLMRequest) ([]byte, error) {
 	}
 
 	// must be chat-completions request at this point, return bytes of entire messages
-	return json.Marshal(request.Body.ChatCompletions.Messages)
+	return types.MarshalMessagesToJSON(request.Body.ChatCompletions.Messages...)
+}
+
+func (p *Plugin) ResponseComplete(ctx context.Context, request *types.LLMRequest, response *types.LLMResponse, targetPod *backend.Pod) {
+	state, err := plugins.ReadPluginStateKey[*SchedulingContextState](p.pluginState, request.RequestId, plugins.StateKey(p.TypedName().String()))
+	if err != nil {
+		log.FromContext(ctx).Error(err, "failed to read prefix plugin state", "requestID", request.RequestId)
+		return
+	}
+	p.pluginState.Delete(request.RequestId) // delete the state explicitly after completing using it.
+
+	reponseForKVCache, err := response.FirstChoiceContent()
+	if err != nil {
+		log.FromContext(ctx).Error(err, "failed to get first choice content", "requestID", request.RequestId)
+		return
+	}
+	var input bytes.Buffer
+	input.Write(state.RestBytes)
+	input.Write(reponseForKVCache)
+
+	server := ServerID(targetPod.NamespacedName)
+	prevBlockHash := defaultPrevBlock(request)
+	prevBlockHashLength := 0
+	if len(state.PrefixHashes) > 0 {
+		prevBlockHash = state.PrefixHashes[len(state.PrefixHashes)-1]
+		prevBlockHashLength = len(state.PrefixHashes)
+	}
+	hashBlocks, _ := hashInputWithPrevBlockHash(ctx, prevBlockHash, prevBlockHashLength, input.Bytes(), state.BlockSize, p.config.MaxPrefixBlocksToMatch)
+	p.wg.Add(1)
+	go func() {
+		p.indexer.Add(hashBlocks, server)
+		p.wg.Done()
+	}()
 }
 
 func getBlockSize(pods []types.Pod, defaultBlockSize int) int {