[aayush-kapoor]

Background

#14722

Some OpenAI-compatible providers send the first tool_calls delta with an id and function.arguments but without function.name, then provide function.name in a subsequent delta. The StreamingToolCallTracker previously threw AI_InvalidResponseDataError on the first delta because it required function.name to be present immediately.

Summary

added a small buffering layer in front of the tracker that:

• holds onto deltas (per index) until function.name is seen
• while buffering, it accumulates id, arguments, and extra_content
• when function.name shows up, it forwards a single combined delta to StreamingToolCallTracker.processDelta
• once forwarded, the tool-call index is marked as forwarded and all subsequent deltas (argument-only chunks) pass straight through to the tracker unchanged.

Manual Verification

verified by running this repro before and after the fix

repro:

import { createOpenAICompatible } from '@ai-sdk/openai-compatible';
import { streamText, tool } from 'ai';
import { z } from 'zod';
import { run } from '../../lib/run';

const encoder = new TextEncoder();

const chunks = [
  {
    choices: [
      {
        finish_reason: null,
        index: 0,
        delta: { role: 'assistant', content: null },
      },
    ],
  },
  {
    choices: [
      {
        finish_reason: null,
        index: 0,
        delta: {
          tool_calls: [
            {
              index: 0,
              id: 'call_123',
              type: 'function',
              function: { arguments: '' },
            },
          ],
        },
      },
    ],
  },
  {
    choices: [
      {
        finish_reason: null,
        index: 0,
        delta: {
          tool_calls: [
            {
              index: 0,
              id: 'call_123',
              type: 'function',
              function: { name: 'bash', arguments: '{' },
            },
          ],
        },
      },
    ],
  },
  {
    choices: [
      {
        finish_reason: null,
        index: 0,
        delta: {
          tool_calls: [
            { index: 0, function: { arguments: '"command"' } },
          ],
        },
      },
    ],
  },
  {
    choices: [
      {
        finish_reason: null,
        index: 0,
        delta: {
          tool_calls: [
            { index: 0, function: { arguments: ': "ls -la"}' } },
          ],
        },
      },
    ],
  },
  {
    choices: [
      {
        finish_reason: 'tool_calls',
        index: 0,
        delta: {},
      },
    ],
  },
];

const openaiCompatible = createOpenAICompatible({
  name: 'late-tool-name-repro',
  baseURL: 'https://example.test/v1',
  apiKey: 'test-key',
  fetch: async () =>
    new Response(
      new ReadableStream({
        start(controller) {
          for (const chunk of chunks) {
            controller.enqueue(
              encoder.encode(`data: ${JSON.stringify(chunk)}\n\n`),
            );
          }

          controller.enqueue(encoder.encode('data: [DONE]\n\n'));
          controller.close();
        },
      }),
      {
        headers: {
          'content-type': 'text/event-stream',
        },
      },
    ),
});

run(async () => {
  const result = streamText({
    model: openaiCompatible.chatModel('mock-model'),
    prompt: 'Run ls -la.',
    maxRetries: 0,
    toolChoice: 'required',
    tools: {
      bash: tool({
        description: 'Run a shell command.',
        inputSchema: z.object({
          command: z.string(),
        }),
        execute: async input => input,
      }),
    },
  });

  try {
    for await (const part of result.fullStream) {
      console.log(part.type, part);
    }
  } catch (error) {
    console.error('\nReproduced error:');
    console.error(error);
    process.exitCode = 1;
  }
});

Checklist

• All commits are signed (PRs with unsigned commits cannot be merged)
• Tests have been added / updated (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)
• A patch changeset for relevant packages has been added (for bug fixes / features - run pnpm changeset in the project root)
• I have reviewed this pull request (self-review)

Related Issues

fixes #14722