fix: responses argument type

core/relay/adaptor/openai/chat.go

@@ -1397,7 +1397,7 @@ func ConvertResponsesToChatCompletionResponse(
 							Type:  relaymodel.ToolChoiceTypeFunction,
 							Function: relaymodel.Function{
 								Name:      outputItem.Name,
-								Arguments: outputItem.Arguments,
+								Arguments: outputItem.Arguments.String(),
 							},
 						},
 					},

core/relay/adaptor/openai/gemini.go

@@ -1010,7 +1010,7 @@ func ConvertResponsesToGeminiResponse(
 			if outputItem.Name != "" {
 				var args map[string]any
 				if outputItem.Arguments != "" {
-					err := sonic.Unmarshal([]byte(outputItem.Arguments), &args)
+					err := sonic.UnmarshalString(outputItem.Arguments.String(), &args)
 					if err == nil {
 						candidate.Content.Parts = append(
 							candidate.Content.Parts,
@@ -1257,7 +1257,7 @@ func (s *geminiStreamState) handleFunctionCallArgumentsDone(
 
 	// Parse arguments
 	var args map[string]any
-	if err := sonic.UnmarshalString(event.Arguments, &args); err != nil {
+	if err := sonic.UnmarshalString(event.Arguments.String(), &args); err != nil {
 		return false
 	}
 

core/relay/adaptor/openai/response_test.go

@@ -309,6 +309,49 @@ func TestResponseStreamHandlerFlushesLifecycleEventsOnOfficialTextStreamOrder(t
 	assert.Contains(t, output, "response.completed")
 }
 
+func TestResponseStreamHandlerAcceptsObjectFunctionCallArguments(t *testing.T) {
+	t.Parallel()
+	gin.SetMode(gin.TestMode)
+
+	recorder := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(recorder)
+	c.Request = httptest.NewRequestWithContext(
+		t.Context(),
+		http.MethodPost,
+		"/v1/responses",
+		nil,
+	)
+
+	body := strings.Join([]string{
+		"event: response.output_item.added",
+		`data: {"type":"response.output_item.added","output_index":0,"item":{"id":"fc_123","type":"function_call","call_id":"call_123","name":"search","arguments":{},"status":"in_progress"}}`,
+		"",
+		"event: response.function_call_arguments.done",
+		`data: {"type":"response.function_call_arguments.done","item_id":"fc_123","output_index":0,"arguments":{"query":"spawn tool"},"sequence_number":1}`,
+		"",
+		"event: response.output_item.done",
+		`data: {"type":"response.output_item.done","output_index":0,"item":{"id":"fc_123","type":"function_call","call_id":"call_123","name":"search","arguments":{"query":"spawn tool"},"status":"completed"}}`,
+		"",
+		"event: response.completed",
+		`data: {"type":"response.completed","response":{"id":"resp_tool","object":"response","created_at":1,"status":"completed","model":"gpt-5.5","output":[{"id":"fc_123","type":"function_call","call_id":"call_123","name":"search","arguments":{"query":"spawn tool"},"status":"completed"}],"parallel_tool_calls":true,"store":false,"usage":{"input_tokens":1,"output_tokens":1,"total_tokens":2}}}`,
+		"",
+	}, "\n")
+	resp := &http.Response{
+		StatusCode: http.StatusOK,
+		Body:       io.NopCloser(bytes.NewBufferString(body)),
+		Header:     make(http.Header),
+	}
+
+	result, err := ResponseStreamHandler(&meta.Meta{}, &responseTestStore{}, c, resp)
+	require.Nil(t, err)
+	assert.Equal(t, "resp_tool", result.UpstreamID)
+	assert.Equal(t, model.ZeroNullInt64(2), result.Usage.TotalTokens)
+
+	output := recorder.Body.String()
+	assert.Contains(t, output, `"arguments":{"query":"spawn tool"}`)
+	assert.Contains(t, output, `"type":"response.completed"`)
+}
+
 func TestResponseStreamHandlerStartsBufferTimeoutFromFirstDelayedEvent(t *testing.T) {
 	responseStreamInitialBufferTimeoutTestMu.Lock()
 	defer responseStreamInitialBufferTimeoutTestMu.Unlock()

core/relay/model/response.go

@@ -1,9 +1,41 @@
 package model
 
 import (
+	"slices"
+
+	"github.com/bytedance/sonic"
 	"github.com/labring/aiproxy/core/model"
 )
 
+var nullBytes = []byte("null")
+
+type ResponseArguments string
+
+func (a *ResponseArguments) UnmarshalJSON(data []byte) error {
+	var s string
+	if err := sonic.ConfigDefault.Unmarshal(data, &s); err == nil {
+		*a = ResponseArguments(s)
+		return nil
+	}
+
+	if slices.Equal(data, nullBytes) {
+		*a = ""
+		return nil
+	}
+
+	*a = ResponseArguments(data)
+
+	return nil
+}
+
+func (a ResponseArguments) MarshalJSON() ([]byte, error) {
+	return sonic.ConfigDefault.Marshal(string(a))
+}
+
+func (a ResponseArguments) String() string {
+	return string(a)
+}
+
 // InputItemType represents the type of an input item
 type InputItemType = string
 
@@ -179,15 +211,15 @@ type OutputContent struct {
 
 // OutputItem represents an output item in a response
 type OutputItem struct {
-	ID        string          `json:"id"`
-	Type      string          `json:"type"`
-	Status    ResponseStatus  `json:"status,omitempty"`
-	Role      string          `json:"role,omitempty"`
-	Content   []OutputContent `json:"content,omitempty"`
-	Arguments string          `json:"arguments,omitempty"` // For function_call type
-	CallID    string          `json:"call_id,omitempty"`   // For function_call type
-	Name      string          `json:"name,omitempty"`      // For function_call type
-	Summary   any             `json:"summary,omitempty"`   // For reasoning type: []SummaryPart or string
+	ID        string            `json:"id"`
+	Type      string            `json:"type"`
+	Status    ResponseStatus    `json:"status,omitempty"`
+	Role      string            `json:"role,omitempty"`
+	Content   []OutputContent   `json:"content,omitempty"`
+	Arguments ResponseArguments `json:"arguments,omitempty"` // For function_call type
+	CallID    string            `json:"call_id,omitempty"`   // For function_call type
+	Name      string            `json:"name,omitempty"`      // For function_call type
+	Summary   any               `json:"summary,omitempty"`   // For reasoning type: []SummaryPart or string
 }
 
 // InputContent represents content in an input item
@@ -333,18 +365,18 @@ type InputItemList struct {
 
 // ResponseStreamEvent represents a server-sent event for response streaming
 type ResponseStreamEvent struct {
-	Type           string         `json:"type"`
-	Response       *Response      `json:"response,omitempty"`
-	Error          *OpenAIError   `json:"error,omitempty"`
-	OutputIndex    *int           `json:"output_index,omitempty"`
-	Item           *OutputItem    `json:"item,omitempty"`
-	ItemID         string         `json:"item_id,omitempty"`
-	ContentIndex   *int           `json:"content_index,omitempty"`
-	Part           *OutputContent `json:"part,omitempty"`      // For content_part events
-	Delta          string         `json:"delta,omitempty"`     // For text.delta, function_call_arguments.delta
-	Text           string         `json:"text,omitempty"`      // For text content
-	Arguments      string         `json:"arguments,omitempty"` // For function_call_arguments.done
-	SequenceNumber int            `json:"sequence_number,omitempty"`
+	Type           string            `json:"type"`
+	Response       *Response         `json:"response,omitempty"`
+	Error          *OpenAIError      `json:"error,omitempty"`
+	OutputIndex    *int              `json:"output_index,omitempty"`
+	Item           *OutputItem       `json:"item,omitempty"`
+	ItemID         string            `json:"item_id,omitempty"`
+	ContentIndex   *int              `json:"content_index,omitempty"`
+	Part           *OutputContent    `json:"part,omitempty"`      // For content_part events
+	Delta          string            `json:"delta,omitempty"`     // For text.delta, function_call_arguments.delta
+	Text           string            `json:"text,omitempty"`      // For text content
+	Arguments      ResponseArguments `json:"arguments,omitempty"` // For function_call_arguments.done
+	SequenceNumber int               `json:"sequence_number,omitempty"`
 }
 
 func (r *Response) ToolUsageWebSearchCallCount() int64 {