expo-asset/src/AssetSources.ts

An Expo universal module to download assets and pass them into other APIs

import type { PackagerAsset } from '@react-native/assets-registry/registry';
import { Platform } from 'expo-modules-core';
import { PixelRatio, NativeModules } from 'react-native';

import AssetSourceResolver from './AssetSourceResolver';
import { getManifest2, manifestBaseUrl } from './PlatformUtils';

// @docsMissing
export type AssetMetadata = Pick<
  PackagerAsset,
  'httpServerLocation' | 'name' | 'hash' | 'type' | 'scales' | 'width' | 'height'
> & {
  uri?: string;
  fileHashes?: string[];
  fileUris?: string[];
};

export type AssetSource = {
  uri: string;
  hash: string;
};

/**
 * Selects the best file for the given asset (ex: choosing the best scale for images) and returns
 * a { uri, hash } pair for the specific asset file.
 *
 * If the asset isn't an image with multiple scales, the first file is selected.
 */
export function selectAssetSource(meta: AssetMetadata): AssetSource {
  // This logic is based on that of AssetSourceResolver, with additional support for file hashes and
  // explicitly provided URIs
  const scale = AssetSourceResolver.pickScale(meta.scales, PixelRatio.get());
  const index = meta.scales.findIndex((s) => s === scale);
  const hash = meta.fileHashes ? (meta.fileHashes[index] ?? meta.fileHashes[0]) : meta.hash;

  // Allow asset processors to directly provide the URL to load
  const uri = meta.fileUris ? (meta.fileUris[index] ?? meta.fileUris[0]) : meta.uri;
  if (uri) {
    return { uri: resolveUri(uri), hash };
  }

  const fileScale = scale === 1 ? '' : `@${scale}x`;
  const fileExtension = meta.type ? `.${encodeURIComponent(meta.type)}` : '';
  const suffix = `/${encodeURIComponent(meta.name)}${fileScale}${fileExtension}`;
  const params = new URLSearchParams({
    platform: Platform.OS,
    hash: meta.hash,
  });

  // For assets with a specified absolute URL, we use the existing origin instead of prepending the
  // development server or production CDN URL origin
  if (/^https?:\/\//.test(meta.httpServerLocation)) {
    const uri = meta.httpServerLocation + suffix + '?' + params;
    return { uri, hash };
  }

  // For assets during development using manifest2, we use the development server's URL origin
  const manifest2 = getManifest2();

  const devServerUrl = manifest2?.extra?.expoGo?.developer
    ? 'http://' + manifest2.extra.expoGo.debuggerHost
    : null;
  if (devServerUrl) {
    const baseUrl = new URL(meta.httpServerLocation + suffix, devServerUrl);

    baseUrl.searchParams.set('platform', Platform.OS);
    baseUrl.searchParams.set('hash', meta.hash);
    return {
      uri: baseUrl.href,
      hash,
    };
  }

  // Temporary fallback for loading assets in Expo Go home
  if (NativeModules['ExponentKernel']) {
    return { uri: `https://classic-assets.eascdn.net/~assets/${encodeURIComponent(hash)}`, hash };
  }

  // In correctly configured apps, we arrive here if the asset is locally available on disk due to
  // being managed by expo-updates, and `getLocalAssetUri(hash)` must return a local URI for this
  // hash. Since the asset is local, we don't have a remote URL and specify an invalid URL (an empty
  // string) as a placeholder.
  return { uri: '', hash };
}

/**
 * Resolves the given URI to an absolute URI. If the given URI is already an absolute URI, it is
 * simply returned. Otherwise, if it is a relative URI, it is resolved relative to the manifest's
 * base URI.
 */
export function resolveUri(uri: string): string {
  // `manifestBaseUrl` is always an absolute URL or `null`.
  return manifestBaseUrl ? new URL(uri, manifestBaseUrl).href : uri;
}