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fix: backfill tool call data in chat stream conversion #2306

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fix: backfill tool call data in chat stream conversion #2306

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67 changes: 67 additions & 0 deletions backend/internal/pkg/apicompat/chatcompletions_responses_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -685,6 +685,73 @@ func TestResponsesEventToChatChunks_ToolCallDelta(t *testing.T) {
assert.Equal(t, 0, *tc.Index, "first tool arg delta must still use index 0")
}

func TestResponsesEventToChatChunks_ToolCallBackfillsNameFromArgumentsDone(t *testing.T) {
state := NewResponsesEventToChatState()
state.Model = "gpt-4o"
state.SentRole = true

chunks := ResponsesEventToChatChunks(&ResponsesStreamEvent{
Type: "response.output_item.added",
OutputIndex: 1,
Item: &ResponsesOutput{
Type: "function_call",
CallID: "call_backfill_1",
},
}, state)
require.Len(t, chunks, 1)
require.Len(t, chunks[0].Choices[0].Delta.ToolCalls, 1)
assert.Equal(t, "", chunks[0].Choices[0].Delta.ToolCalls[0].Function.Name)

chunks = ResponsesEventToChatChunks(&ResponsesStreamEvent{
Type: "response.function_call_arguments.done",
OutputIndex: 1,
CallID: "call_backfill_1",
Name: "get_weather",
Arguments: `{"city":"NYC"}`,
}, state)
require.Len(t, chunks, 1)
tc := chunks[0].Choices[0].Delta.ToolCalls[0]
require.NotNil(t, tc.Index)
assert.Equal(t, 0, *tc.Index)
assert.Equal(t, "get_weather", tc.Function.Name)
assert.Equal(t, `{"city":"NYC"}`, tc.Function.Arguments)
}

func TestResponsesEventToChatChunks_ToolCallBackfillsNameFromOutputItemDone(t *testing.T) {
state := NewResponsesEventToChatState()
state.Model = "gpt-4o"
state.SentRole = true

chunks := ResponsesEventToChatChunks(&ResponsesStreamEvent{
Type: "response.output_item.added",
OutputIndex: 2,
Item: &ResponsesOutput{
Type: "function_call",
CallID: "call_backfill_2",
},
}, state)
require.Len(t, chunks, 1)
require.Len(t, chunks[0].Choices[0].Delta.ToolCalls, 1)
assert.Equal(t, "", chunks[0].Choices[0].Delta.ToolCalls[0].Function.Name)

chunks = ResponsesEventToChatChunks(&ResponsesStreamEvent{
Type: "response.output_item.done",
OutputIndex: 2,
Item: &ResponsesOutput{
Type: "function_call",
CallID: "call_backfill_2",
Name: "get_time",
Arguments: `{"tz":"UTC"}`,
},
}, state)
require.Len(t, chunks, 1)
tc := chunks[0].Choices[0].Delta.ToolCalls[0]
require.NotNil(t, tc.Index)
assert.Equal(t, 0, *tc.Index)
assert.Equal(t, "get_time", tc.Function.Name)
assert.Equal(t, `{"tz":"UTC"}`, tc.Function.Arguments)
}

func TestResponsesEventToChatChunks_Completed(t *testing.T) {
state := NewResponsesEventToChatState()
state.Model = "gpt-4o"
Expand Down
74 changes: 74 additions & 0 deletions backend/internal/pkg/apicompat/responses_to_chatcompletions.go
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Original file line number Diff line number Diff line change
Expand Up @@ -131,6 +131,8 @@ type ResponsesEventToChatState struct {
Finalized bool // true after finish chunk has been emitted
NextToolCallIndex int // next sequential tool_call index to assign
OutputIndexToToolIndex map[int]int // Responses output_index → Chat tool_calls index
OutputIndexNameSent map[int]bool
OutputIndexArgsSeen map[int]bool
IncludeUsage bool
Usage *ChatUsage
}
Expand All @@ -141,6 +143,8 @@ func NewResponsesEventToChatState() *ResponsesEventToChatState {
ID: generateChatCmplID(),
Created: time.Now().Unix(),
OutputIndexToToolIndex: make(map[int]int),
OutputIndexNameSent: make(map[int]bool),
OutputIndexArgsSeen: make(map[int]bool),
}
}

Expand All @@ -156,6 +160,10 @@ func ResponsesEventToChatChunks(evt *ResponsesStreamEvent, state *ResponsesEvent
return resToChatHandleOutputItemAdded(evt, state)
case "response.function_call_arguments.delta":
return resToChatHandleFuncArgsDelta(evt, state)
case "response.function_call_arguments.done":
return resToChatHandleFuncArgsDone(evt, state)
case "response.output_item.done":
return resToChatHandleOutputItemDone(evt, state)
case "response.reasoning_summary_text.delta":
return resToChatHandleReasoningDelta(evt, state)
case "response.reasoning_summary_text.done":
Expand Down Expand Up @@ -248,6 +256,7 @@ func resToChatHandleOutputItemAdded(evt *ResponsesStreamEvent, state *ResponsesE
idx := state.NextToolCallIndex
state.OutputIndexToToolIndex[evt.OutputIndex] = idx
state.NextToolCallIndex++
state.OutputIndexNameSent[evt.OutputIndex] = strings.TrimSpace(evt.Item.Name) != ""

return []ChatCompletionsChunk{makeChatDeltaChunk(state, ChatDelta{
ToolCalls: []ChatToolCall{{
Expand All @@ -270,6 +279,7 @@ func resToChatHandleFuncArgsDelta(evt *ResponsesStreamEvent, state *ResponsesEve
if !ok {
return nil
}
state.OutputIndexArgsSeen[evt.OutputIndex] = true

return []ChatCompletionsChunk{makeChatDeltaChunk(state, ChatDelta{
ToolCalls: []ChatToolCall{{
Expand All @@ -281,6 +291,70 @@ func resToChatHandleFuncArgsDelta(evt *ResponsesStreamEvent, state *ResponsesEve
})}
}

func resToChatHandleFuncArgsDone(evt *ResponsesStreamEvent, state *ResponsesEventToChatState) []ChatCompletionsChunk {
idx, ok := state.OutputIndexToToolIndex[evt.OutputIndex]
if !ok {
return nil
}

delta := ChatToolCall{Index: &idx}
if evt.CallID != "" {
delta.ID = evt.CallID
}

if name := strings.TrimSpace(evt.Name); name != "" && !state.OutputIndexNameSent[evt.OutputIndex] {
delta.Function.Name = name
state.OutputIndexNameSent[evt.OutputIndex] = true
}

if evt.Arguments != "" && !state.OutputIndexArgsSeen[evt.OutputIndex] {
delta.Function.Arguments = evt.Arguments
state.OutputIndexArgsSeen[evt.OutputIndex] = true
}

if delta.ID == "" && delta.Function.Name == "" && delta.Function.Arguments == "" {
return nil
}

return []ChatCompletionsChunk{makeChatDeltaChunk(state, ChatDelta{
ToolCalls: []ChatToolCall{delta},
})}
}

func resToChatHandleOutputItemDone(evt *ResponsesStreamEvent, state *ResponsesEventToChatState) []ChatCompletionsChunk {
if evt.Item == nil || evt.Item.Type != "function_call" {
return nil
}

idx, ok := state.OutputIndexToToolIndex[evt.OutputIndex]
if !ok {
return nil
}

delta := ChatToolCall{Index: &idx}
if evt.Item.CallID != "" {
delta.ID = evt.Item.CallID
}

if name := strings.TrimSpace(evt.Item.Name); name != "" && !state.OutputIndexNameSent[evt.OutputIndex] {
delta.Function.Name = name
state.OutputIndexNameSent[evt.OutputIndex] = true
}

if evt.Item.Arguments != "" && !state.OutputIndexArgsSeen[evt.OutputIndex] {
delta.Function.Arguments = evt.Item.Arguments
state.OutputIndexArgsSeen[evt.OutputIndex] = true
}

if delta.ID == "" && delta.Function.Name == "" && delta.Function.Arguments == "" {
return nil
}

return []ChatCompletionsChunk{makeChatDeltaChunk(state, ChatDelta{
ToolCalls: []ChatToolCall{delta},
})}
}

func resToChatHandleReasoningDelta(evt *ResponsesStreamEvent, state *ResponsesEventToChatState) []ChatCompletionsChunk {
if evt.Delta == "" {
return nil
Expand Down
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