我正在使用NestJS为openai聊天完成API编写转发服务。我想对原始流进行转换，然后将流转发到客户端。
代码如下所示，它位于一个nestJS控制器中

const completion = await openai.createChatCompletion(
  {
    model: 'gpt-3.5-turbo',
    messages: messages,
    n: 1,
    stream: true,
    max_tokens: 4000,
  },
  { responseType: 'stream' },
);

class TransformerStream extends Transform {
  _transform(chunk, encoding, callback) {
    // If I directly forward the chunk like this, the client can receive chunk by chunk
    this.push(chunk)
    // However, if I use string, the client can't receive chunk by chunk.
    // My original code is to transform the chunk to string and do some transformation, to simplify the question, just use 'data: ping\n' here
    this.push('data: ping\n', 'utf8')
    callback()
  }
}

const transformer = new TransformerStream()
completion.data.pipe(transformer).pipe(res)

我使用axios从客户端请求API，并尝试使用onDownloadProgress逐块接收它

axios.post('/api/chat', body, {
  responseType: 'stream',
  onDownloadProgress: progress => {
    console.log(progress)
  }
} )

总之，当我直接从openAI API发送缓冲区块时，可以多次记录进度。但是当我发送字符串时，它只能被记录一次。