Function createBlobReaderStream

lib/internal/blob.js:443–532

(reader)

}

function createBlobReaderStream(reader) {
  return new lazyReadableStream({
    type: 'bytes',
    start(c) {
      // There really should only be one read at a time so using an
      // array here is purely defensive.
      this.pendingPulls = [];
      // Register a wakeup callback that the C++ side can invoke
      // when new data is available after a STATUS_BLOCK.
      reader.setWakeup(() => {
        if (this.pendingPulls.length > 0) {
          this.readNext(c);
        }
      });
    },
    pull(c) {
      const { promise, resolve, reject } = PromiseWithResolvers();
      this.pendingPulls.push({ resolve, reject });
      this.readNext(c);
      return promise;
    },
    readNext(c) {
      reader.pull((status, buffer) => {
        // If pendingPulls is empty here, the stream had to have
        // been canceled, and we don't really care about the result.
        // We can simply exit.
        if (this.pendingPulls.length === 0) {
          return;
        }
        if (status === 0) {
          // EOS
          c.close();
          // This is to signal the end for byob readers
          // see https://streams.spec.whatwg.org/#example-rbs-pull
          c.byobRequest?.respond(0);
          const pending = this.pendingPulls.shift();
          pending.resolve();
          return;
        } else if (status < 0) {
          // The read could fail for many different reasons when reading
          // from a non-memory resident blob part (e.g. file-backed blob).
          // The error details the system error code.
          const error =
            lazyDOMException('The blob could not be read',
                             'NotReadableError');
          const pending = this.pendingPulls.shift();
          c.error(error);
          pending.reject(error);
          return;
        } else if (status === 2) {
          // STATUS_BLOCK: No data available yet. The wakeup callback
          // registered in start() will re-invoke readNext when data
          // arrives.
          return;
        }
        // ReadableByteStreamController.enqueue errors if we submit a
        // 0-length buffer. We need to check for that here.
        if (buffer !== undefined && buffer.byteLength !== 0) {