Custom Adapter

If the built-in BareResourceFetcher and ExpoResourceFetcher don't fit your needs, you can implement your own adapter and plug it into React Native ExecuTorch. This is useful if you want to use a different download library, fetch from a private server, or add custom caching logic.

The ResourceFetcherAdapter interface

Your adapter must implement the ResourceFetcherAdapter interface exported from react-native-executorch. This interface defines every method which is used under the hood by React Native ExecuTorch:

import {
  ResourceFetcherAdapter,
  ResourceSource,
} from 'react-native-executorch';

interface ResourceFetcherAdapter {
  fetch(
    callback: (downloadProgress: number) => void,
    ...sources: ResourceSource[]
  ): Promise<string[] | null>;

  readAsString(path: string): Promise<string>;
}

fetch

This is the core method called by every model hook and module whenever it needs to resolve a model or resource to a local file path.

• callback — called with a progress value between 0 and 1 as downloads proceed. Called with 1 when complete.
• ...sources — one or more ResourceSource values:
  • string — a remote URL or an absolute local file path.
  • number — a bundled asset reference from require('./model.pte').
  • object — an inline JS object (e.g. a tokenizer config) that should be JSON-serialized and written to disk. Your adapter is responsible for stringifying it and saving it as a file, then returning the local path. This allows callers to pass configs inline instead of hosting them at a URL.
• Returns an array of absolute local file paths (without file:// prefix), one per source, in the same order. Return null if the fetch was intentionally interrupted (e.g. cancelled by the user).

readAsString

Called internally to read configuration files (e.g. tokenizer configs) that were previously downloaded via fetch.

• path — absolute path to the file on disk.
• Returns the file contents as a UTF-8 string.

Registering your adapter

Pass your adapter to initExecutorch at the entry point of your app, before any other library API is called:

import { initExecutorch } from 'react-native-executorch';
import { MyCustomFetcher } from './MyCustomFetcher';

initExecutorch({ resourceFetcher: MyCustomFetcher });

Any model hook or module used after this point will route all resource fetching through your adapter.