GCS 上のファイルをアトミックに mv する

atomic_file_mv.ts

import { Bucket, File } from '@google-cloud/storage';

type AtomicFileMvReturnType = [{ src: File; dest: File }, Error | undefined];
const atomicFileMv = async (
  bucket: Bucket,
  srcPath: string,
  destPath: string
): Promise<AtomicFileMvReturnType> => {
  const src = bucket.file(srcPath, { generation: 0 });
  const dest = bucket.file(destPath, { generation: 0 });

  if (!(await src.exists()).pop()) {
    return [{ src, dest }, new Error('no such source file')];
  }

  if ((await dest.exists()).pop()) {
    return [{ src, dest }, new Error('already file exists')];
  }

  const writeableStream = dest.createWriteStream();
  const finishWriteDestFile = (resolve: (arg: AtomicFileMvReturnType) => void) => {
    src.delete((srcDeleteError) => {
      if (!srcDeleteError) {
        resolve([{ src, dest }, undefined]);
        return;
      }

      // rollback
      dest.delete(() => {
        resolve([{ src, dest }, srcDeleteError]);
      });
    });
  };

  return new Promise<AtomicFileMvReturnType>((resolve) => {
    src.createReadStream().pipe(
      writeableStream
        .on('finish', () => finishWriteDestFile(resolve))
        .on('error', (err) => {
          dest.deleteResumableCache();
          resolve([{ src, dest }, err]);
        })
    );
  });
};