2. Build a persistent store for artifact downloads

The RAILGUN proof generation system uses large artifact files. Because of the size and number of these files, which cover a variety of use cases, we recommend against packaging them directly into your application. This would increase the application size by 50MB+.

Instead, Wallet SDK will automatically download these artifact files when required and persist them for further use. The ArtifactStore module manages downloads and persistence of these assets.

As a dApp developer, you only need to provide a file storage mechanism that the ArtifactStore will use to 1) check file existence, 2) store assets, 3) retrieve assets.

Example: ArtifactStore using localForage (browser)

// create-artifact-store.ts
import { ArtifactStore } from '@railgun-community/wallet';
import localforage from 'localforage';

export const createArtifactStore = (): ArtifactStore => {
  return new ArtifactStore(
    async (path: string) => {
      return localforage.getItem(path);
    },
    async (dir: string, path: string, item: string | Buffer) => {
      await localforage.setItem(path, item);
    },
    async (path: string) => (await localforage.getItem(path)) != null,
  );
}

Example: ArtifactStore using custom directory and fs filesystem (node.js)

import { ArtifactStore } from '@railgun-community/wallet';
import fs from 'fs';

const createDownloadDirPath = (documentsDir: string, path: string) => {
  return `${documentsDir}/${path}`;
};

export const createArtifactStore = (documentsDir: string): ArtifactStore => {
  const getFile = async (path: string) => {
    return fs.promises.readFile(createDownloadDirPath(documentsDir, path));
  };

  const storeFile = async (
    dir: string,
    path: string,
    item: string | Buffer,
  ) => {
    await fs.promises.mkdir(createDownloadDirPath(documentsDir, dir), {
      recursive: true,
    });
    await fs.promises.writeFile(
      createDownloadDirPath(documentsDir, path),
      item,
    );
  };

  const fileExists = (path: string): Promise<boolean> => {
    return new Promise(resolve => {
      fs.promises
        .access(createDownloadDirPath(documentsDir, path))
        .then(() => resolve(true))
        .catch(() => resolve(false));
    });
  };

  return new ArtifactStore(getFile, storeFile, fileExists);
};

Use createArtifactStore when calling startRailgunEngine from Step 1.