feat: add stream mode support (#282)

Signed-off-by: akisaya <akikevinsama@gmail.com>
Co-authored-by: Xunzhuo <bitliu@tencent.com>

Author: AkisAya

src/semantic-router/pkg/extproc/request_handler.go

@@ -33,6 +33,43 @@ func serializeOpenAIRequest(req *openai.ChatCompletionNewParams) ([]byte, error)
 	return json.Marshal(req)
 }
 
+// extractStreamParam extracts the stream parameter from the original request body
+func extractStreamParam(originalBody []byte) bool {
+	var requestMap map[string]interface{}
+	if err := json.Unmarshal(originalBody, &requestMap); err != nil {
+		return false
+	}
+
+	if streamValue, exists := requestMap["stream"]; exists {
+		if stream, ok := streamValue.(bool); ok {
+			return stream
+		}
+	}
+	return false
+}
+
+// serializeOpenAIRequestWithStream converts request back to JSON, preserving the stream parameter from original request
+func serializeOpenAIRequestWithStream(req *openai.ChatCompletionNewParams, hasStreamParam bool) ([]byte, error) {
+	// First serialize the SDK object
+	sdkBytes, err := json.Marshal(req)
+	if err != nil {
+		return nil, err
+	}
+
+	// If original request had stream parameter, add it back
+	if hasStreamParam {
+		var sdkMap map[string]interface{}
+		if err := json.Unmarshal(sdkBytes, &sdkMap); err == nil {
+			sdkMap["stream"] = true
+			if modifiedBytes, err := json.Marshal(sdkMap); err == nil {
+				return modifiedBytes, nil
+			}
+		}
+	}
+
+	return sdkBytes, nil
+}
+
 // addSystemPromptToRequestBody adds a system prompt to the beginning of the messages array in the JSON request body
 func addSystemPromptToRequestBody(requestBody []byte, systemPrompt string) ([]byte, error) {
 	if systemPrompt == "" {
@@ -166,7 +203,7 @@ type RequestContext struct {
 	ProcessingStartTime time.Time
 
 	// Streaming detection
-	ExpectStreamingResponse bool // set from request Accept header
+	ExpectStreamingResponse bool // set from request Accept header or stream parameter
 	IsStreamingResponse     bool // set from response Content-Type
 
 	// TTFT tracking
@@ -207,6 +244,7 @@ func (r *OpenAIRouter) handleRequestHeaders(v *ext_proc.ProcessingRequest_Reques
 	if accept, ok := ctx.Headers["accept"]; ok {
 		if strings.Contains(strings.ToLower(accept), "text/event-stream") {
 			ctx.ExpectStreamingResponse = true
+			observability.Infof("Client expects streaming response based on Accept header")
 		}
 	}
 
@@ -246,6 +284,13 @@ func (r *OpenAIRouter) handleRequestBody(v *ext_proc.ProcessingRequest_RequestBo
 	// Save the original request body
 	ctx.OriginalRequestBody = v.RequestBody.GetBody()
 
+	// Extract stream parameter from original request and update ExpectStreamingResponse if needed
+	hasStreamParam := extractStreamParam(ctx.OriginalRequestBody)
+	if hasStreamParam {
+		observability.Infof("Original request contains stream parameter: true")
+		ctx.ExpectStreamingResponse = true // Set this if stream param is found
+	}
+
 	// Parse the OpenAI request using SDK types
 	openAIRequest, err := parseOpenAIRequest(ctx.OriginalRequestBody)
 	if err != nil {
@@ -499,8 +544,8 @@ func (r *OpenAIRouter) handleModelRouting(openAIRequest *openai.ChatCompletionNe
 				// Modify the model in the request
 				openAIRequest.Model = openai.ChatModel(matchedModel)
 
-				// Serialize the modified request
-				modifiedBody, err := serializeOpenAIRequest(openAIRequest)
+				// Serialize the modified request with stream parameter preserved
+				modifiedBody, err := serializeOpenAIRequestWithStream(openAIRequest, ctx.ExpectStreamingResponse)
 				if err != nil {
 					observability.Errorf("Error serializing modified request: %v", err)
 					metrics.RecordRequestError(actualModel, "serialization_error")
@@ -758,8 +803,8 @@ func (r *OpenAIRouter) handleToolSelection(openAIRequest *openai.ChatCompletionN
 
 // updateRequestWithTools updates the request body with the selected tools
 func (r *OpenAIRouter) updateRequestWithTools(openAIRequest *openai.ChatCompletionNewParams, response **ext_proc.ProcessingResponse, ctx *RequestContext) error {
-	// Re-serialize the request with modified tools
-	modifiedBody, err := serializeOpenAIRequest(openAIRequest)
+	// Re-serialize the request with modified tools and preserved stream parameter
+	modifiedBody, err := serializeOpenAIRequestWithStream(openAIRequest, ctx.ExpectStreamingResponse)
 	if err != nil {
 		return err
 	}