Function transform

packages/client/src/upload.ts:213–217

(chunk, _encoding, callback)

          const fileStream = createReadStream(names[0]);
          const counter = new Transform({
            transform(chunk, _encoding, callback) {
              uploadProgress.bytesUploaded += chunk.length;
              uploadProgress.emit('progress');
              callback(null, chunk);
            },
          });
          fileStream.on('error', err => counter.destroy(err));
          counter.on('close', () => fileStream.destroy());