How to read bytes response from web serial api writer

Question

I'm trying to work with Web Serial API. I want to write bytes to device and read bytes response from it.

I can write bytes as well as string to device - here everything working as expected. I can read bytes and string from device - here I have problems. Examples are showing that you can create a while(true) loop and the stream will return { value, done } flags. But I didn't find what actually done flag means. When I'm connecting to device and start this loop, it never ends.

    while (this.port.readable) {
      try {
        while (true) {
          const { value, done } = await this.reader.read();
          if (value) {
            getChunk(value);
          }
          if (done) {
            break;
          }
        }
      } catch (error) {
        console.error("Serial port reading error: " + error);
      } finally {
        this.reader.releaseLock();
      }
    }

I did find some suggestions with pipeTo function but it only operates in examples on string responses, in addition it don't work in my case:

const textEncoder = new TextEncoderStream();
const writableStreamClosed = textEncoder.readable.pipeTo(this.port.writable);
const writer = textEncoder.writable.getWriter();

await writer.write("help");

Uncaught (in promise) TypeError: Failed to execute 'pipeTo' on 'ReadableStream': Cannot pipe to a locked stream

So to sum up. How can I write bytes to device via serial API and receive back response from it.

Thanks in advance.

Answer 1

Ok, I did write my own function that reads given number of bytes. Maybe this will help someone.

public async readBytes(numberOfBytes: number): Promise<Uint8Array> {
    let bytes: Uint8Array = new Uint8Array(numberOfBytes);
    let readBytes: number = 0;
    let finished: boolean = false;

    try {
      while (true) {
        const { value, done } = await this.reader.read();
        if (value) {
          let chunk: Uint8Array = value;

          if (readBytes === 0 && chunk[0] === SerialService.FAIL) {
            return bytes;
          }

          for (let i = 0; i < chunk.length; i++) {
            bytes[i] = chunk[i];
            readBytes++;

            if (readBytes >= numberOfBytes) {
              finished = true;
            }
          }
        }
        if (done || finished) {
          break;
        }
      }
    } catch (error) {
      console.error("Serial port reading error: " + error);
    }

    return bytes;
  }