Text Streaming with StreamResponse Class

In some cases it's too hard to use generators to implement response streaming. Vovk.ts introduces StreamResponse class inherited from Response class that uses TransformStream#readable as body and adds required HTTP headers. It's a lower-level API that is used behind the scenes to implement generator logic described at previous section. Service method at this case is implemented as a regular function that accepts StreamResponse instance as a pointer to send messages manually.

There is what the streaming service might look like:

import type { StreamResponse } from 'vovk';
 
export type Token = { message: string };
 
export default class StreamService {
  static async streamTokens(resp: StreamResponse<Token>) {
    const tokens: Token[] = [
      { message: 'Hello,' },
      { message: ' World' },
      { message: '!' },
    ];
 
    for (const token of tokens) {
      await new Promise((resolve) => setTimeout(resolve, 300));
      resp.send(token);
    }
 
    resp.close();
  }
}

As you can see tokens are sent using StreamResponse#send method and, when the stream is completed, it needs to be closed with StreamResponse#close.

The Controller Class returns an instance of StreamResponse and the streaming is performed a floating Promise above the return statement.

import { prefix, get, StreamResponse, type VovkRequest } from 'vovk';
import StreamService, { type Token } from './StreamService';
 
@prefix('stream')
export default class StreamController {
  @get('tokens')
  static async streamTokens() {
    const resp = new StreamResponse<Token>();
 
    void StreamService.streamTokens(resp);
 
    return resp;
  }
}

StreamResponse class also provides throw methods that safely closes the stream and makes the client to re-throw the received error.

await resp.throw(new Error('Stream error'));

Live Text Streaming Example with StreamResponse Class

import type { StreamResponse } from 'vovk';
 
export type Token = { message: string };
 
export default class StreamService {
  static async streamTokens(resp: StreamResponse<Token>) {
    const tokens: Token[] = [
      { message: 'Hello,' },
      { message: ' World' },
      { message: ' from' },
      { message: ' Stream' },
      { message: '!' },
    ];
 
    for (const token of tokens) {
      resp.send(token);
      await new Promise((resolve) => setTimeout(resolve, 300));
    }
 
    await resp.close();
  }
}

Source code (opens in a new tab)