refactor(epp): unexport RequestContext protocol and response state (llm-d#2457)

The stream state machine, drop reason, and response-phase bookkeeping
fields have no users outside the handlers package. Unexporting them
gives the ext_proc protocol state a compile-time boundary, making the
struct split proposed in llm-d#1189 unnecessary. Also deletes the request
trailer response field and constants, which were never assigned.

Signed-off-by: Luke Van Drie <lukevandrie@google.com>

Author: LukeAVanDrie

pkg/epp/handlers/response.go

@@ -50,19 +50,19 @@ func (s *StreamingServer) HandleResponseBody(ctx context.Context, reqCtx *Reques
 
 	fairnessID, priority := extractFairnessAndPriority(reqCtx)
 
-	reqCtx.ResponseSize += len(responseBytes)
+	reqCtx.responseSize += len(responseBytes)
 
-	if reqCtx.FirstTokenTimestamp.IsZero() && len(responseBytes) > 0 {
-		reqCtx.FirstTokenTimestamp = time.Now()
+	if reqCtx.firstTokenTimestamp.IsZero() && len(responseBytes) > 0 {
+		reqCtx.firstTokenTimestamp = time.Now()
 	}
 
 	if reqCtx.modelServerStreaming && len(responseBytes) > 0 {
 		now := time.Now()
-		if !reqCtx.LastChunkReceivedTimestamp.IsZero() {
-			itl := now.Sub(reqCtx.LastChunkReceivedTimestamp).Seconds()
+		if !reqCtx.lastChunkReceivedTimestamp.IsZero() {
+			itl := now.Sub(reqCtx.lastChunkReceivedTimestamp).Seconds()
 			metrics.RecordInterTokenLatency(ctx, reqCtx.IncomingModelName, reqCtx.TargetModelName, fairnessID, priority, itl)
 		}
-		reqCtx.LastChunkReceivedTimestamp = now
+		reqCtx.lastChunkReceivedTimestamp = now
 	}
 
 	var parsedResp *fwkrh.ParsedResponse
@@ -91,11 +91,11 @@ func (s *StreamingServer) HandleResponseBody(ctx context.Context, reqCtx *Reques
 		}
 	}
 	if endOfStream {
-		metrics.RecordNormalizedTimePerOutputToken(ctx, reqCtx.IncomingModelName, reqCtx.TargetModelName, fairnessID, priority, reqCtx.RequestReceivedTimestamp, reqCtx.ResponseCompleteTimestamp, reqCtx.Usage.CompletionTokens)
-		metrics.RecordRequestLatencies(ctx, reqCtx.IncomingModelName, reqCtx.TargetModelName, fairnessID, priority, reqCtx.RequestReceivedTimestamp, reqCtx.ResponseCompleteTimestamp)
-		metrics.RecordResponseSizes(reqCtx.IncomingModelName, reqCtx.TargetModelName, fairnessID, priority, reqCtx.ResponseSize)
-		metrics.RecordRequestTTFT(ctx, reqCtx.IncomingModelName, reqCtx.TargetModelName, fairnessID, priority, reqCtx.modelServerStreaming, reqCtx.RequestReceivedTimestamp, reqCtx.FirstTokenTimestamp)
-		metrics.RecordRequestTPOT(ctx, reqCtx.IncomingModelName, reqCtx.TargetModelName, fairnessID, priority, reqCtx.modelServerStreaming, reqCtx.RequestReceivedTimestamp, reqCtx.FirstTokenTimestamp, reqCtx.ResponseCompleteTimestamp, reqCtx.Usage.CompletionTokens)
+		metrics.RecordNormalizedTimePerOutputToken(ctx, reqCtx.IncomingModelName, reqCtx.TargetModelName, fairnessID, priority, reqCtx.RequestReceivedTimestamp, reqCtx.responseCompleteTimestamp, reqCtx.Usage.CompletionTokens)
+		metrics.RecordRequestLatencies(ctx, reqCtx.IncomingModelName, reqCtx.TargetModelName, fairnessID, priority, reqCtx.RequestReceivedTimestamp, reqCtx.responseCompleteTimestamp)
+		metrics.RecordResponseSizes(reqCtx.IncomingModelName, reqCtx.TargetModelName, fairnessID, priority, reqCtx.responseSize)
+		metrics.RecordRequestTTFT(ctx, reqCtx.IncomingModelName, reqCtx.TargetModelName, fairnessID, priority, reqCtx.modelServerStreaming, reqCtx.RequestReceivedTimestamp, reqCtx.firstTokenTimestamp)
+		metrics.RecordRequestTPOT(ctx, reqCtx.IncomingModelName, reqCtx.TargetModelName, fairnessID, priority, reqCtx.modelServerStreaming, reqCtx.RequestReceivedTimestamp, reqCtx.firstTokenTimestamp, reqCtx.responseCompleteTimestamp, reqCtx.Usage.CompletionTokens)
 	}
 	return s.director.HandleResponseBody(ctx, reqCtx, endOfStream)
 }

pkg/epp/handlers/response_test.go

@@ -291,7 +291,7 @@ func TestHandleResponseBodyWithoutSchedulingRequest(t *testing.T) {
 		TargetModelName:           "target-model",
 		Priority:                  3,
 		RequestReceivedTimestamp:  timeBaseline,
-		ResponseCompleteTimestamp: timeBaseline.Add(time.Second),
+		responseCompleteTimestamp: timeBaseline.Add(time.Second),
 		Response: &Response{
 			Headers: map[string]string{},
 		},
@@ -642,7 +642,7 @@ func TestResponseSizeAccumulation(t *testing.T) {
 				endOfStream := i == len(tt.chunks)-1
 				server.HandleResponseBody(ctx, reqCtx, chunk, endOfStream)
 			}
-			assert.Equal(t, tt.wantResponseSize, reqCtx.ResponseSize)
+			assert.Equal(t, tt.wantResponseSize, reqCtx.responseSize)
 		})
 	}
 }