feat: Make WebSocket Reader/Writer (#5001)

[trebler]

Resolves #5001

[CLAassistant]

All committers have signed the CLA.

[ry]

LGTM - nice tests!

[keroxp]

@ry Why this merged? WebSocket and TCP are totally different protocol layer. And also this R/W implementation ignores ping/pong/close frame. This abstraction is not good. If use case described in #5001 is needed, one should do that or use readFrame/ writeFrame in ws modules.

[keroxp]

copyBytes ignores overflowed data of src. It seems to discard data in frames, doesn't it?.

[trebler]

I think you are right. Would something like this make sense instead?

#readBacklog = new Uint8Array();

  async read(p: Uint8Array): Promise<number | null> {
    for await (const ev of this.receive()) {
      if (ev instanceof Uint8Array) {
        const copiedFromBacklog = Math.min(
          this.#readBacklog.byteLength,
          p.byteLength,
        );

        p.set(this.#readBacklog.subarray(0, copiedFromBacklog));

        this.#readBacklog = this.#readBacklog.subarray(copiedFromBacklog);

        if (copiedFromBacklog === p.byteLength) {
          this.#readBacklog = concat(this.#readBacklog, ev);
          return copiedFromBacklog;
        }

        const diff = p.byteLength - copiedFromBacklog;
        const copy = Math.min(diff, ev.byteLength);

        p.set(ev.subarray(0, copy), copiedFromBacklog);

        if (copy < ev.byteLength) {
          this.#readBacklog = concat(this.#readBacklog, ev.subarray(copy));
        }

        return copiedFromBacklog + copy;
      }
    }

    if (this.#readBacklog.byteLength) {
      const copiedFromBacklog = copyBytes(this.#readBacklog, p);
      this.#readBacklog = this.#readBacklog.subarray(copiedFromBacklog);

      return copiedFromBacklog;
    }

    return null;
  }

[trebler]

And also this R/W implementation ignores ping/pong/close frame.

@keroxp, the purpose was to only handle data frames / messages. ping/pong/close are "technical" frames. E.g., if one wanted to pipe all WS messages to/from a file, DB, TCP socket, one would want to only read/write "useful" information (being messages).

[ry]

Why this merged?

@keroxp Negligence on my part. Now that you raise the point, I agree that Reader/Writer isn't the right abstraction for a frame oriented protocol. Let's revert it.