How do I change status and headers when streaming with lambda and function url?

Hello,

I'm new to working with AWS Lambda and streaming HTTP responses. I've been following this tutorial and specifically the "Create a response streaming function (AWS CloudFormation)" section. In that section, they use awslambda.HttpResponseStream.from to add metadata to the stream. However, when I implemented a similar Lambda handler, the result was not what I expected. Instead of adding the metadata to the response, it concatenated it with the response body.

Here's the code I used:

export const handler = awslambda.streamifyResponse(
  async (ev: APIGatewayProxyEventV2, stream: ResponseStream) => {
    const metadata = {
      status: 404,
      headers: {
        'Content-Type': 'text/html',
        'Cache-Control': 'no-cache',
      },
    }

    stream = awslambda.HttpResponseStream.from(stream, metadata)
    stream.setContentType('text/html')

    stream.write('Not found!')
    await new Promise((resolve) => setTimeout(resolve, 1000))
    stream.write('text1')
    await new Promise((resolve) => setTimeout(resolve, 1000))
    stream.write('text2')
    await new Promise((resolve) => setTimeout(resolve, 1000))
    stream.end()
  },
)

My goal is to change the response status and headers dynamically within the Lambda function. Is there a way to achieve this? I would appreciate any guidance or suggestions.

Thank you in advance!