ChatCompletionAccumulator.AddChunk panics when tool_call's index is not equal to slice index #464
Description
Problem
Hi team, I encountered a panic when using this SDK to handle my own model's response.
panic: runtime error: index out of range [-1]
goroutine 1 [running]:
github.com/openai/openai-go.(*ChatCompletion).accumulateDelta(_, {{0x1400014e1c7, 0x17}, {0x14000158008, 0x1, 0x1}, 0x688b2f81, {0x1400014e21f, 0x29}, {0x1400014e1ea, ...}, ...})
/Users/du/go/pkg/mod/github.com/openai/[email protected]/streamaccumulator.go:129 +0xabc
github.com/openai/openai-go.(*ChatCompletionAccumulator).AddChunk(_, {{0x1400014e1c7, 0x17}, {0x14000158008, 0x1, 0x1}, 0x688b2f81, {0x1400014e21f, 0x29}, {0x1400014e1ea, ...}, ...})
/Users/du/go/pkg/mod/github.com/openai/[email protected]/streamaccumulator.go:40 +0x64Cause
After reviewing the source code, I found that accumulateDelta assumes the index value of the tool_call is equal to the index where the tool_call is present in the Go slice. This assumption seems to cause the panic when the index is out of order or negative (e.g., -1). It's unclear whether this is an issue with the SDK's implementation or if our model's response isn't compatible with OpenAI's expected format.
Here’s the relevant code snippet:
// func (cc *ChatCompletion) accumulateDelta(chunk ChatCompletionChunk) bool
for j := range delta.Delta.ToolCalls {
deltaTool := &delta.Delta.ToolCalls[j]
choice.Message.ToolCalls = expandToFit(choice.Message.ToolCalls, int(deltaTool.Index))
tool := &choice.Message.ToolCalls[deltaTool.Index]
if deltaTool.ID != "" {
tool.ID = deltaTool.ID
}
if deltaTool.Type != "" {
tool.Type = constant.Function(deltaTool.Type)
}
tool.Function.Name += deltaTool.Function.Name
tool.Function.Arguments += deltaTool.Function.Arguments
}Reproduce
Here is a minimal example to reproduce the issue. In this example, the tool_calls includes a tool_call with an invalid index value of -1:
package main
import (
"encoding/json"
"github.com/openai/openai-go"
)
func main() {
acc := openai.ChatCompletionAccumulator{}
chunk := openai.ChatCompletionChunk{}
str := "{\"id\":\"gen-1753952129163910909\",\"object\":\"chat.completion.chunk\",\"created\":1753952129,\"model\":\"model\",\"choices\":[{\"index\":0,\"delta\":{\"role\":null,\"content\":null,\"reasoning_content\":null,\"tool_calls\":[{\"id\":\"call_goVJu3KUQtuahQuqW6wgzQ\",\"index\":-1,\"type\":\"function\",\"function\":{\"name\":\"doc_search\",\"arguments\":\"\"}}]},\"logprobs\":null,\"finish_reason\":null,\"matched_stop\":null}],\"usage\":null}"
err := json.Unmarshal([]byte(str), &chunk)
if err != nil {
println(err)
}
acc.AddChunk(chunk)
}