fix(openai): harden Chat-to-Responses compatibility (#5772)

Add a shared Responses-to-Chat stream state machine and use it from the OpenAI relay path. Preserve assistant text alongside tool calls, bind tool argument deltas by output_index, map incomplete finish reasons, support reasoning/custom tool events, and buffer upstream SSE for non-stream Chat clients.

Add deterministic service tests and relay SSE tests for the conversion path.

Related to #5745.

relay/channel/openai/chat_via_responses.go

@@ -1,6 +1,7 @@
 package openai
 
 import (
+	"bufio"
 	"fmt"
 	"io"
 	"net/http"
@@ -13,31 +14,12 @@ import (
 	relaycommon "github.com/QuantumNous/new-api/relay/common"
 	"github.com/QuantumNous/new-api/relay/helper"
 	"github.com/QuantumNous/new-api/service"
+	"github.com/QuantumNous/new-api/service/openaicompat"
 	"github.com/QuantumNous/new-api/types"
 
 	"github.com/gin-gonic/gin"
 )
 
-func responsesStreamIndexKey(itemID string, idx *int) string {
-	if itemID == "" {
-		return ""
-	}
-	if idx == nil {
-		return itemID
-	}
-	return fmt.Sprintf("%s:%d", itemID, *idx)
-}
-
-func stringDeltaFromPrefix(prev string, next string) string {
-	if next == "" {
-		return ""
-	}
-	if prev != "" && strings.HasPrefix(next, prev) {
-		return next[len(prev):]
-	}
-	return next
-}
-
 func OaiResponsesToChatHandler(c *gin.Context, info *relaycommon.RelayInfo, resp *http.Response) (*dto.Usage, *types.NewAPIError) {
 	if resp == nil || resp.Body == nil {
 		return nil, types.NewOpenAIError(fmt.Errorf("invalid response"), types.ErrorCodeBadResponse, http.StatusInternalServerError)
@@ -90,6 +72,109 @@ func OaiResponsesToChatHandler(c *gin.Context, info *relaycommon.RelayInfo, resp
 	return usage, nil
 }
 
+func OaiResponsesToChatBufferedStreamHandler(c *gin.Context, info *relaycommon.RelayInfo, resp *http.Response) (*dto.Usage, *types.NewAPIError) {
+	if resp == nil || resp.Body == nil {
+		return nil, types.NewOpenAIError(fmt.Errorf("invalid response"), types.ErrorCodeBadResponse, http.StatusInternalServerError)
+	}
+	defer service.CloseResponseBodyGracefully(resp)
+
+	accumulator := openaicompat.NewResponsesBufferedAccumulator()
+	var finalResponse *dto.OpenAIResponsesResponse
+	var streamErr *types.NewAPIError
+
+	scanner := helper.NewStreamScanner(resp.Body)
+	scanner.Split(bufio.ScanLines)
+	for scanner.Scan() {
+		line := scanner.Text()
+		if len(line) < 6 || line[:5] != "data:" {
+			continue
+		}
+		data := line[5:]
+		data = strings.TrimSpace(data)
+		if data == "" || data == "[DONE]" {
+			if data == "[DONE]" {
+				break
+			}
+			continue
+		}
+
+		var streamResp dto.ResponsesStreamResponse
+		if err := common.UnmarshalJsonStr(data, &streamResp); err != nil {
+			logger.LogError(c, "failed to unmarshal buffered responses stream event: "+err.Error())
+			streamErr = types.NewOpenAIError(err, types.ErrorCodeBadResponseBody, http.StatusInternalServerError)
+			break
+		}
+		accumulator.ProcessEvent(&streamResp)
+		switch streamResp.Type {
+		case "response.completed", "response.done", "response.incomplete":
+			finalResponse = streamResp.Response
+			if streamResp.Type == "response.incomplete" {
+				if finalResponse == nil {
+					finalResponse = &dto.OpenAIResponsesResponse{}
+				}
+				if len(finalResponse.Status) == 0 {
+					finalResponse.Status = []byte(`"incomplete"`)
+				}
+			}
+		case "response.failed", "response.error":
+			if streamResp.Response != nil {
+				if oaiErr := streamResp.Response.GetOpenAIError(); oaiErr != nil && oaiErr.Type != "" {
+					streamErr = types.WithOpenAIError(*oaiErr, http.StatusInternalServerError)
+					break
+				}
+			}
+			streamErr = types.NewOpenAIError(fmt.Errorf("responses stream error: %s", streamResp.Type), types.ErrorCodeBadResponse, http.StatusInternalServerError)
+		}
+		if streamErr != nil || finalResponse != nil {
+			break
+		}
+	}
+	if streamErr != nil {
+		return nil, streamErr
+	}
+	if err := scanner.Err(); err != nil {
+		return nil, types.NewOpenAIError(err, types.ErrorCodeBadResponse, http.StatusInternalServerError)
+	}
+	if finalResponse == nil {
+		finalResponse = &dto.OpenAIResponsesResponse{
+			ID:        helper.GetResponseID(c),
+			CreatedAt: int(time.Now().Unix()),
+			Model:     info.UpstreamModelName,
+			Status:    []byte(`"completed"`),
+		}
+	}
+	accumulator.SupplementResponseOutput(finalResponse)
+
+	chatId := helper.GetResponseID(c)
+	chatResp, usage, err := service.ResponsesResponseToChatCompletionsResponse(finalResponse, chatId)
+	if err != nil {
+		return nil, types.NewOpenAIError(err, types.ErrorCodeBadResponseBody, http.StatusInternalServerError)
+	}
+	if usage == nil || usage.TotalTokens == 0 {
+		text := service.ExtractOutputTextFromResponses(finalResponse)
+		usage = service.ResponseText2Usage(c, text, info.UpstreamModelName, info.GetEstimatePromptTokens())
+		chatResp.Usage = *usage
+	}
+
+	var responseBody []byte
+	switch info.RelayFormat {
+	case types.RelayFormatClaude:
+		claudeResp := service.ResponseOpenAI2Claude(chatResp, info)
+		responseBody, err = common.Marshal(claudeResp)
+	case types.RelayFormatGemini:
+		geminiResp := service.ResponseOpenAI2Gemini(chatResp, info)
+		responseBody, err = common.Marshal(geminiResp)
+	default:
+		responseBody, err = common.Marshal(chatResp)
+	}
+	if err != nil {
+		return nil, types.NewOpenAIError(err, types.ErrorCodeJsonMarshalFailed, http.StatusInternalServerError)
+	}
+
+	service.IOCopyBytesGracefully(c, resp, responseBody)
+	return usage, nil
+}
+
 func OaiResponsesToChatStreamHandler(c *gin.Context, info *relaycommon.RelayInfo, resp *http.Response) (*dto.Usage, *types.NewAPIError) {
 	if resp == nil || resp.Body == nil {
 		return nil, types.NewOpenAIError(fmt.Errorf("invalid response"), types.ErrorCodeBadResponse, http.StatusInternalServerError)
@@ -99,44 +184,28 @@ func OaiResponsesToChatStreamHandler(c *gin.Context, info *relaycommon.RelayInfo
 
 	responseId := helper.GetResponseID(c)
 	createAt := time.Now().Unix()
-	model := info.UpstreamModelName
-
-	var (
-		usage       = &dto.Usage{}
-		outputText  strings.Builder
-		usageText   strings.Builder
-		sentStart   bool
-		sentStop    bool
-		sawToolCall bool
-		streamErr   *types.NewAPIError
-	)
-
-	toolCallIndexByID := make(map[string]int)
-	toolCallNameByID := make(map[string]string)
-	toolCallArgsByID := make(map[string]string)
-	toolCallNameSent := make(map[string]bool)
-	toolCallCanonicalIDByItemID := make(map[string]string)
-	hasSentReasoningSummary := false
-	needsReasoningSummarySeparator := false
-	//reasoningSummaryTextByKey := make(map[string]string)
+	state := openaicompat.NewResponsesToChatStreamState(info.UpstreamModelName, false)
+	state.ID = responseId
+	state.Created = createAt
+	streamErr := (*types.NewAPIError)(nil)
 
 	if info.RelayFormat == types.RelayFormatClaude && info.ClaudeConvertInfo == nil {
 		info.ClaudeConvertInfo = &relaycommon.ClaudeConvertInfo{LastMessagesType: relaycommon.LastMessageTypeNone}
 	}
 
-	sendChatChunk := func(chunk *dto.ChatCompletionsStreamResponse) bool {
-		if chunk == nil {
+	sendChatChunk := func(chunk dto.ChatCompletionsStreamResponse) bool {
+		if len(chunk.Choices) == 0 && chunk.Usage == nil {
 			return true
 		}
 		if info.RelayFormat == types.RelayFormatOpenAI {
-			if err := helper.ObjectData(c, chunk); err != nil {
+			if err := helper.ObjectData(c, &chunk); err != nil {
 				streamErr = types.NewOpenAIError(err, types.ErrorCodeBadResponse, http.StatusInternalServerError)
 				return false
 			}
 			return true
 		}
 
-		chunkData, err := common.Marshal(chunk)
+		chunkData, err := common.Marshal(&chunk)
 		if err != nil {
 			streamErr = types.NewOpenAIError(err, types.ErrorCodeJsonMarshalFailed, http.StatusInternalServerError)
 			return false
@@ -148,154 +217,6 @@ func OaiResponsesToChatStreamHandler(c *gin.Context, info *relaycommon.RelayInfo
 		return true
 	}
 
-	sendStartIfNeeded := func() bool {
-		if sentStart {
-			return true
-		}
-		if !sendChatChunk(helper.GenerateStartEmptyResponse(responseId, createAt, model, nil)) {
-			return false
-		}
-		sentStart = true
-		return true
-	}
-
-	//sendReasoningDelta := func(delta string) bool {
-	//	if delta == "" {
-	//		return true
-	//	}
-	//	if !sendStartIfNeeded() {
-	//		return false
-	//	}
-	//
-	//	usageText.WriteString(delta)
-	//	chunk := &dto.ChatCompletionsStreamResponse{
-	//		Id:      responseId,
-	//		Object:  "chat.completion.chunk",
-	//		Created: createAt,
-	//		Model:   model,
-	//		Choices: []dto.ChatCompletionsStreamResponseChoice{
-	//			{
-	//				Index: 0,
-	//				Delta: dto.ChatCompletionsStreamResponseChoiceDelta{
-	//					ReasoningContent: &delta,
-	//				},
-	//			},
-	//		},
-	//	}
-	//	if err := helper.ObjectData(c, chunk); err != nil {
-	//		streamErr = types.NewOpenAIError(err, types.ErrorCodeBadResponse, http.StatusInternalServerError)
-	//		return false
-	//	}
-	//	return true
-	//}
-
-	sendReasoningSummaryDelta := func(delta string) bool {
-		if delta == "" {
-			return true
-		}
-		if needsReasoningSummarySeparator {
-			if strings.HasPrefix(delta, "\n\n") {
-				needsReasoningSummarySeparator = false
-			} else if strings.HasPrefix(delta, "\n") {
-				delta = "\n" + delta
-				needsReasoningSummarySeparator = false
-			} else {
-				delta = "\n\n" + delta
-				needsReasoningSummarySeparator = false
-			}
-		}
-		if !sendStartIfNeeded() {
-			return false
-		}
-
-		usageText.WriteString(delta)
-		chunk := &dto.ChatCompletionsStreamResponse{
-			Id:      responseId,
-			Object:  "chat.completion.chunk",
-			Created: createAt,
-			Model:   model,
-			Choices: []dto.ChatCompletionsStreamResponseChoice{
-				{
-					Index: 0,
-					Delta: dto.ChatCompletionsStreamResponseChoiceDelta{
-						ReasoningContent: &delta,
-					},
-				},
-			},
-		}
-		if !sendChatChunk(chunk) {
-			return false
-		}
-		hasSentReasoningSummary = true
-		return true
-	}
-
-	sendToolCallDelta := func(callID string, name string, argsDelta string) bool {
-		if callID == "" {
-			return true
-		}
-		if outputText.Len() > 0 {
-			// Prefer streaming assistant text over tool calls to match non-stream behavior.
-			return true
-		}
-		if !sendStartIfNeeded() {
-			return false
-		}
-
-		idx, ok := toolCallIndexByID[callID]
-		if !ok {
-			idx = len(toolCallIndexByID)
-			toolCallIndexByID[callID] = idx
-		}
-		if name != "" {
-			toolCallNameByID[callID] = name
-		}
-		if toolCallNameByID[callID] != "" {
-			name = toolCallNameByID[callID]
-		}
-
-		tool := dto.ToolCallResponse{
-			ID:   callID,
-			Type: "function",
-			Function: dto.FunctionResponse{
-				Arguments: argsDelta,
-			},
-		}
-		tool.SetIndex(idx)
-		if name != "" && !toolCallNameSent[callID] {
-			tool.Function.Name = name
-			toolCallNameSent[callID] = true
-		}
-
-		chunk := &dto.ChatCompletionsStreamResponse{
-			Id:      responseId,
-			Object:  "chat.completion.chunk",
-			Created: createAt,
-			Model:   model,
-			Choices: []dto.ChatCompletionsStreamResponseChoice{
-				{
-					Index: 0,
-					Delta: dto.ChatCompletionsStreamResponseChoiceDelta{
-						ToolCalls: []dto.ToolCallResponse{tool},
-					},
-				},
-			},
-		}
-		if !sendChatChunk(chunk) {
-			return false
-		}
-		sawToolCall = true
-
-		// Include tool call data in the local builder for fallback token estimation.
-		if tool.Function.Name != "" {
-			usageText.WriteString(tool.Function.Name)
-		}
-		if argsDelta != "" {
-			usageText.WriteString(argsDelta)
-		}
-		return true
-	}
-
 	helper.StreamScannerHandler(c, resp, info, func(data string, sr *helper.StreamResult) {
 		if streamErr != nil {
 			sr.Stop(streamErr)
@@ -309,193 +230,7 @@ func OaiResponsesToChatStreamHandler(c *gin.Context, info *relaycommon.RelayInfo
 			return
 		}
 
-		switch streamResp.Type {
-		case "response.created":
-			if streamResp.Response != nil {
-				if streamResp.Response.Model != "" {
-					model = streamResp.Response.Model
-				}
-				if streamResp.Response.CreatedAt != 0 {
-					createAt = int64(streamResp.Response.CreatedAt)
-				}
-			}
-
-		//case "response.reasoning_text.delta":
-		//if !sendReasoningDelta(streamResp.Delta) {
-		//	sr.Stop(streamErr)
-		//	return
-		//}
-
-		//case "response.reasoning_text.done":
-
-		case "response.reasoning_summary_text.delta":
-			if !sendReasoningSummaryDelta(streamResp.Delta) {
-				sr.Stop(streamErr)
-				return
-			}
-
-		case "response.reasoning_summary_text.done":
-			if hasSentReasoningSummary {
-				needsReasoningSummarySeparator = true
-			}
-
-		//case "response.reasoning_summary_part.added", "response.reasoning_summary_part.done":
-		//	key := responsesStreamIndexKey(strings.TrimSpace(streamResp.ItemID), streamResp.SummaryIndex)
-		//	if key == "" || streamResp.Part == nil {
-		//		break
-		//	}
-		//	// Only handle summary text parts, ignore other part types.
-		//	if streamResp.Part.Type != "" && streamResp.Part.Type != "summary_text" {
-		//		break
-		//	}
-		//	prev := reasoningSummaryTextByKey[key]
-		//	next := streamResp.Part.Text
-		//	delta := stringDeltaFromPrefix(prev, next)
-		//	reasoningSummaryTextByKey[key] = next
-		//	if !sendReasoningSummaryDelta(delta) {
-		//		sr.Stop(streamErr)
-		//		return
-		//	}
-
-		case "response.output_text.delta":
-			if !sendStartIfNeeded() {
-				sr.Stop(streamErr)
-				return
-			}
-
-			if streamResp.Delta != "" {
-				outputText.WriteString(streamResp.Delta)
-				usageText.WriteString(streamResp.Delta)
-				delta := streamResp.Delta
-				chunk := &dto.ChatCompletionsStreamResponse{
-					Id:      responseId,
-					Object:  "chat.completion.chunk",
-					Created: createAt,
-					Model:   model,
-					Choices: []dto.ChatCompletionsStreamResponseChoice{
-						{
-							Index: 0,
-							Delta: dto.ChatCompletionsStreamResponseChoiceDelta{
-								Content: &delta,
-							},
-						},
-					},
-				}
-				if !sendChatChunk(chunk) {
-					sr.Stop(streamErr)
-					return
-				}
-			}
-
-		case "response.output_item.added", "response.output_item.done":
-			if streamResp.Item == nil {
-				break
-			}
-			if streamResp.Item.Type != "function_call" {
-				break
-			}
-
-			itemID := strings.TrimSpace(streamResp.Item.ID)
-			callID := strings.TrimSpace(streamResp.Item.CallId)
-			if callID == "" {
-				callID = itemID
-			}
-			if itemID != "" && callID != "" {
-				toolCallCanonicalIDByItemID[itemID] = callID
-			}
-			name := strings.TrimSpace(streamResp.Item.Name)
-			if name != "" {
-				toolCallNameByID[callID] = name
-			}
-
-			newArgs := streamResp.Item.ArgumentsString()
-			prevArgs := toolCallArgsByID[callID]
-			argsDelta := ""
-			if newArgs != "" {
-				if strings.HasPrefix(newArgs, prevArgs) {
-					argsDelta = newArgs[len(prevArgs):]
-				} else {
-					argsDelta = newArgs
-				}
-				toolCallArgsByID[callID] = newArgs
-			}
-
-			if !sendToolCallDelta(callID, name, argsDelta) {
-				sr.Stop(streamErr)
-				return
-			}
-
-		case "response.function_call_arguments.delta":
-			itemID := strings.TrimSpace(streamResp.ItemID)
-			callID := toolCallCanonicalIDByItemID[itemID]
-			if callID == "" {
-				callID = itemID
-			}
-			if callID == "" {
-				break
-			}
-			toolCallArgsByID[callID] += streamResp.Delta
-			if !sendToolCallDelta(callID, "", streamResp.Delta) {
-				sr.Stop(streamErr)
-				return
-			}
-
-		case "response.function_call_arguments.done":
-
-		case "response.completed":
-			if streamResp.Response != nil {
-				if streamResp.Response.Model != "" {
-					model = streamResp.Response.Model
-				}
-				if streamResp.Response.CreatedAt != 0 {
-					createAt = int64(streamResp.Response.CreatedAt)
-				}
-				if streamResp.Response.Usage != nil {
-					if streamResp.Response.Usage.InputTokens != 0 {
-						usage.PromptTokens = streamResp.Response.Usage.InputTokens
-						usage.InputTokens = streamResp.Response.Usage.InputTokens
-					}
-					if streamResp.Response.Usage.OutputTokens != 0 {
-						usage.CompletionTokens = streamResp.Response.Usage.OutputTokens
-						usage.OutputTokens = streamResp.Response.Usage.OutputTokens
-					}
-					if streamResp.Response.Usage.TotalTokens != 0 {
-						usage.TotalTokens = streamResp.Response.Usage.TotalTokens
-					} else {
-						usage.TotalTokens = usage.PromptTokens + usage.CompletionTokens
-					}
-					if streamResp.Response.Usage.InputTokensDetails != nil {
-						usage.PromptTokensDetails.CachedTokens = streamResp.Response.Usage.InputTokensDetails.CachedTokens
-						usage.PromptTokensDetails.ImageTokens = streamResp.Response.Usage.InputTokensDetails.ImageTokens
-						usage.PromptTokensDetails.AudioTokens = streamResp.Response.Usage.InputTokensDetails.AudioTokens
-					}
-					if streamResp.Response.Usage.CompletionTokenDetails.ReasoningTokens != 0 {
-						usage.CompletionTokenDetails.ReasoningTokens = streamResp.Response.Usage.CompletionTokenDetails.ReasoningTokens
-					}
-				}
-			}
-
-			if !sendStartIfNeeded() {
-				sr.Stop(streamErr)
-				return
-			}
-			if !sentStop {
-				if info.RelayFormat == types.RelayFormatClaude && info.ClaudeConvertInfo != nil {
-					info.ClaudeConvertInfo.Usage = usage
-				}
-				finishReason := "stop"
-				if sawToolCall && outputText.Len() == 0 {
-					finishReason = "tool_calls"
-				}
-				stop := helper.GenerateStopResponse(responseId, createAt, model, finishReason)
-				if !sendChatChunk(stop) {
-					sr.Stop(streamErr)
-					return
-				}
-				sentStop = true
-			}
-
-		case "response.error", "response.failed":
+		if streamResp.Type == "response.error" || streamResp.Type == "response.failed" {
 			if streamResp.Response != nil {
 				if oaiErr := streamResp.Response.GetOpenAIError(); oaiErr != nil && oaiErr.Type != "" {
 					streamErr = types.WithOpenAIError(*oaiErr, http.StatusInternalServerError)
@@ -506,8 +241,19 @@ func OaiResponsesToChatStreamHandler(c *gin.Context, info *relaycommon.RelayInfo
 			streamErr = types.NewOpenAIError(fmt.Errorf("responses stream error: %s", streamResp.Type), types.ErrorCodeBadResponse, http.StatusInternalServerError)
 			sr.Stop(streamErr)
 			return
+		}
 
-		default:
+		chunks, err := openaicompat.ResponsesStreamEventToChatChunks(&streamResp, state)
+		if err != nil {
+			streamErr = types.NewOpenAIError(err, types.ErrorCodeBadResponse, http.StatusInternalServerError)
+			sr.Stop(streamErr)
+			return
+		}
+		for _, chunk := range chunks {
+			if !sendChatChunk(chunk) {
+				sr.Stop(streamErr)
+				return
+			}
 		}
 	})
 
@@ -515,30 +261,22 @@ func OaiResponsesToChatStreamHandler(c *gin.Context, info *relaycommon.RelayInfo
 		return nil, streamErr
 	}
 
+	usage := state.Usage
 	if usage.TotalTokens == 0 {
-		usage = service.ResponseText2Usage(c, usageText.String(), info.UpstreamModelName, info.GetEstimatePromptTokens())
+		usage = service.ResponseText2Usage(c, state.UsageText(), info.UpstreamModelName, info.GetEstimatePromptTokens())
+		state.Usage = usage
 	}
 
-	if !sentStart {
-		if !sendChatChunk(helper.GenerateStartEmptyResponse(responseId, createAt, model, nil)) {
-			return nil, streamErr
-		}
+	if info.RelayFormat == types.RelayFormatClaude && info.ClaudeConvertInfo != nil {
+		info.ClaudeConvertInfo.Usage = usage
 	}
-	if !sentStop {
-		if info.RelayFormat == types.RelayFormatClaude && info.ClaudeConvertInfo != nil {
-			info.ClaudeConvertInfo.Usage = usage
-		}
-		finishReason := "stop"
-		if sawToolCall && outputText.Len() == 0 {
-			finishReason = "tool_calls"
-		}
-		stop := helper.GenerateStopResponse(responseId, createAt, model, finishReason)
-		if !sendChatChunk(stop) {
+	for _, chunk := range openaicompat.FinalizeResponsesToChatStream(state) {
+		if !sendChatChunk(chunk) {
 			return nil, streamErr
 		}
 	}
 	if info.RelayFormat == types.RelayFormatOpenAI && info.ShouldIncludeUsage && usage != nil {
-		if err := helper.ObjectData(c, helper.GenerateFinalUsageResponse(responseId, createAt, model, *usage)); err != nil {
+		if err := helper.ObjectData(c, helper.GenerateFinalUsageResponse(responseId, state.Created, state.Model, *usage)); err != nil {
 			return nil, types.NewOpenAIError(err, types.ErrorCodeBadResponse, http.StatusInternalServerError)
 		}
 	}

relay/channel/openai/chat_via_responses_test.go

@@ -0,0 +1,128 @@
+package openai
+
+import (
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/QuantumNous/new-api/common"
+	"github.com/QuantumNous/new-api/constant"
+	relaycommon "github.com/QuantumNous/new-api/relay/common"
+	"github.com/QuantumNous/new-api/types"
+	"github.com/gin-gonic/gin"
+	"github.com/stretchr/testify/require"
+)
+
+func newResponsesChatTestContext(t *testing.T, body string, isStream bool) (*gin.Context, *httptest.ResponseRecorder, *http.Response, *relaycommon.RelayInfo) {
+	t.Helper()
+
+	recorder := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(recorder)
+	c.Request = httptest.NewRequest(http.MethodPost, "/v1/chat/completions", nil)
+	c.Set(common.RequestIdKey, "responses-test")
+
+	resp := &http.Response{
+		StatusCode: http.StatusOK,
+		Body:       io.NopCloser(strings.NewReader(body)),
+		Header:     http.Header{"Content-Type": []string{"text/event-stream"}},
+	}
+	info := &relaycommon.RelayInfo{
+		ChannelMeta:        &relaycommon.ChannelMeta{UpstreamModelName: "gpt-test"},
+		IsStream:           isStream,
+		RelayFormat:        types.RelayFormatOpenAI,
+		ShouldIncludeUsage: true,
+		DisablePing:        true,
+	}
+	return c, recorder, resp, info
+}
+
+func TestOaiResponsesToChatStreamHandlerConvertsSSEOrderAndUsage(t *testing.T) {
+	oldMode := gin.Mode()
+	gin.SetMode(gin.TestMode)
+	t.Cleanup(func() { gin.SetMode(oldMode) })
+
+	oldTimeout := constant.StreamingTimeout
+	constant.StreamingTimeout = 30
+	t.Cleanup(func() { constant.StreamingTimeout = oldTimeout })
+
+	body := strings.Join([]string{
+		`data: {"type":"response.created","response":{"id":"resp_1","model":"gpt-test","created_at":1710000000}}`,
+		`data: {"type":"response.output_text.delta","delta":"hello"}`,
+		`data: {"type":"response.output_item.added","output_index":1,"item":{"type":"function_call","id":"fc_1","call_id":"call_1","name":"lookup"}}`,
+		`data: {"type":"response.function_call_arguments.delta","output_index":1,"delta":"{\"q\":\"x\"}"}`,
+		`data: {"type":"response.completed","response":{"status":"completed","usage":{"input_tokens":2,"output_tokens":3,"total_tokens":5}}}`,
+		`data: [DONE]`,
+		``,
+	}, "\n")
+
+	c, recorder, resp, info := newResponsesChatTestContext(t, body, true)
+
+	usage, err := OaiResponsesToChatStreamHandler(c, info, resp)
+	require.Nil(t, err)
+	require.NotNil(t, usage)
+	require.Equal(t, 2, usage.PromptTokens)
+	require.Equal(t, 3, usage.CompletionTokens)
+	require.Equal(t, 5, usage.TotalTokens)
+
+	got := recorder.Body.String()
+	require.Equal(t, "text/event-stream", recorder.Header().Get("Content-Type"))
+	require.Contains(t, got, `"role":"assistant"`)
+	require.Contains(t, got, `"content":"hello"`)
+	require.Contains(t, got, `"name":"lookup"`)
+	require.Contains(t, got, `"arguments":"{\"q\":\"x\"}"`)
+	require.Contains(t, got, `"finish_reason":"tool_calls"`)
+	require.Contains(t, got, `"usage":{"prompt_tokens":2,"completion_tokens":3,"total_tokens":5`)
+	require.Contains(t, got, `data: [DONE]`)
+	requireOrderedSubstrings(t, got,
+		`"role":"assistant"`,
+		`"content":"hello"`,
+		`"name":"lookup"`,
+		`"arguments":"{\"q\":\"x\"}"`,
+		`"finish_reason":"tool_calls"`,
+		`"usage":{"prompt_tokens":2,"completion_tokens":3,"total_tokens":5`,
+		`data: [DONE]`,
+	)
+}
+
+func TestOaiResponsesToChatBufferedStreamHandlerReturnsJSONFromSSE(t *testing.T) {
+	oldMode := gin.Mode()
+	gin.SetMode(gin.TestMode)
+	t.Cleanup(func() { gin.SetMode(oldMode) })
+
+	body := strings.Join([]string{
+		`data: {"type":"response.output_text.delta","delta":"buffered text"}`,
+		`data: {"type":"response.output_item.added","output_index":0,"item":{"type":"function_call","id":"fc_1","call_id":"call_1","name":"lookup"}}`,
+		`data: {"type":"response.function_call_arguments.delta","output_index":0,"delta":"{\"q\":\"x\"}"}`,
+		`data: {"type":"response.done","response":{"model":"gpt-test","status":"completed","usage":{"input_tokens":1,"output_tokens":2,"total_tokens":3}}}`,
+		`data: [DONE]`,
+		``,
+	}, "\n")
+
+	c, recorder, resp, info := newResponsesChatTestContext(t, body, false)
+
+	usage, err := OaiResponsesToChatBufferedStreamHandler(c, info, resp)
+	require.Nil(t, err)
+	require.NotNil(t, usage)
+	require.Equal(t, 3, usage.TotalTokens)
+
+	got := recorder.Body.String()
+	require.NotContains(t, got, `data:`)
+	require.Contains(t, got, `"object":"chat.completion"`)
+	require.Contains(t, got, `"content":"buffered text"`)
+	require.Contains(t, got, `"name":"lookup"`)
+	require.Contains(t, got, `"arguments":"{\"q\":\"x\"}"`)
+	require.Contains(t, got, `"finish_reason":"tool_calls"`)
+}
+
+func requireOrderedSubstrings(t *testing.T, s string, parts ...string) {
+	t.Helper()
+
+	offset := 0
+	for _, part := range parts {
+		idx := strings.Index(s[offset:], part)
+		require.NotEqualf(t, -1, idx, "missing %q after byte offset %d", part, offset)
+		offset += idx + len(part)
+	}
+}