How to handle errors when streaming from backend.

[Pascaltib]

How can you handle errors in the backend when returning stream as a response with toDataStreamResponse()?

try {

	const result = streamText({
		model: aiSdkOpenAI(GPT_VERSION),
		messages: reqMessages
	})

	return result.toDataStreamResponse()
} catch (err) {
	// TODO: THIS DOES NOT WORK
	console.error(err)
	throw err
}

In this example, how can I capture any errors?

If I use the example in the documentation it will work and will log the error but the text will no longer be streamed.

try {

	const result = streamText({
		model: aiSdkOpenAI(GPT_VERSION),
		messages: reqMessages
	})

        for await (const part of result.fullStream) {
		switch (part.type) {
			// ... handle other part types

			case 'error': {
				const error = part.error
                                 // This works
				console.error(error)
				break
			}
		}
	}

	return result.toDataStreamResponse()
} catch (err) {
	// TODO: THIS DOES NOT WORK
	console.error(err)
	throw err
}

[defless]

you need to throw an error in your switch case to catch it:

  for await (const part of result.fullStream) {
    switch (part.type) {
      case 'error': {
        const error = part.error;
        throw error;
      }
    }
  }

and in the catch:

return new Response(error, { status: 500 });

[Pascaltib]

Hey defless thanks for trying to help. Although as I mentioned when I use the for loop (the second example I posted), the text is no longer streamed even if there are no errors present. The error handling actually does work. I just can't get both to work at the same time.

[lgrammel]

You can change / log error messages using the following: https://sdk.vercel.ai/docs/ai-sdk-ui/chatbot#error-messages