@push.rocks/webstream/ts/convert.ts

A cross-platform streaming package designed for node and web environments.

export interface IDuplexStream {
  read(): any;
  write(chunk: any, callback?: (error?: Error | null) => void): boolean;
  on(event: string, listener: (...args: any[]) => void): this;
  once(event: string, listener: (...args: any[]) => void): this;
  end(callback?: () => void): void;
  destroy(error?: Error): void;
}

export interface IReadableStreamOptions {
  highWaterMark?: number;
}

export interface IWritableStreamOptions {
  highWaterMark?: number;
}

export function convertDuplexToWebStream(duplex: IDuplexStream): { readable: ReadableStream, writable: WritableStream } {
  const readable = new ReadableStream({
    start(controller) {
      duplex.on('readable', () => {
        let chunk;
        while (null !== (chunk = duplex.read())) {
          controller.enqueue(chunk);
        }
      });

      duplex.on('end', () => {
        controller.close();
      });
    },
    cancel(reason) {
      duplex.destroy(new Error(reason));
    }
  });

  const writable = new WritableStream({
    write(chunk) {
      return new Promise<void>((resolve, reject) => {
        const isBackpressured = !duplex.write(chunk, (error) => {
          if (error) {
            reject(error);
          } else {
            resolve();
          }
        });

        if (isBackpressured) {
          duplex.once('drain', resolve);
        }
      });
    },
    close() {
      return new Promise<void>((resolve, reject) => {
        duplex.end(resolve);
      });
    },
    abort(reason) {
      duplex.destroy(new Error(reason));
    }
  });

  return { readable, writable };
}