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Reading UI Message Streams

UIMessage streams are useful outside of traditional chat use cases. You can consume them for terminal UIs, custom stream processing on the client, or React Server Components (RSC). The readUIMessageStream helper transforms a stream of UIMessageChunk objects into an AsyncIterableStream of UIMessage objects, allowing you to process messages as they’re being constructed.

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Basic Usage

import { readUIMessageStream, streamText } from 'ai';
import { openai } from '@ai-sdk/openai';

async function main() {
  const result = streamText({
    model: openai('gpt-4-turbo'),
    prompt: 'Write a short story about a robot.',
  });

  for await (const uiMessage of readUIMessageStream({
    stream: result.toUIMessageStream(),
  })) {
    console.log('Current message state:', uiMessage);
  }
}

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Tool Calls Integration

Handle streaming responses that include tool calls: 
import { readUIMessageStream, streamText, tool } from 'ai';
import { openai } from '@ai-sdk/openai';
import { z } from 'zod';

async function handleToolCalls() {
  const result = streamText({
    model: openai('gpt-4-turbo'),
    tools: {
      weather: tool({
        description: 'Get the weather in a location',
        inputSchema: z.object({
          location: z.string().describe('The location to get the weather for'),
        }),
        execute: ({ location }) => ({
          location,
          temperature: 72 + Math.floor(Math.random() * 21) - 10,
        }),
      }),
    },
    prompt: 'What is the weather in Tokyo?',
  });

  for await (const uiMessage of readUIMessageStream({
    stream: result.toUIMessageStream(),
  })) {
    // Handle different part types
    uiMessage.parts.forEach(part => {
      switch (part.type) {
        case 'text':
          console.log('Text:', part.text);
          break;
        case 'tool-call':
          console.log('Tool called:', part.toolName, 'with args:', part.args);
          break;
        case 'tool-result':
          console.log('Tool result:', part.result);
          break;
      }
    });
  }
}

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Resuming Conversations

Resume streaming from a previous message state: 
import { readUIMessageStream, streamText } from 'ai';
import { openai } from '@ai-sdk/openai';

async function resumeConversation(lastMessage: UIMessage) {
  const result = streamText({
    model: openai('gpt-4-turbo'),
    messages: [
      { role: 'user', content: 'Continue our previous conversation.' },
    ],
  });

  // Resume from the last message
  for await (const uiMessage of readUIMessageStream({
    stream: result.toUIMessageStream(),
    message: lastMessage, // Resume from this message
  })) {
    console.log('Resumed message:', uiMessage);
  }
}