@expo/fingerprint

A library to generate a fingerprint from a React Native project

Table of Contents

• API Usage
• CLI Usage
• Customizations
  • .fingerprintignore file
  • fingerprint.config.js file
• Limitations

API Usage

import * as Fingerprint from '@expo/fingerprint';

await Fingerprint.createFingerprintAsync('/projectRoot');

createFingerprintAsync

Create a fingerprint from project

function createFingerprintAsync(projectRoot: string, options?: Options): Promise<Fingerprint>;

Example:

const fingerprint = await createFingerprintAsync('/app');
console.log(fingerprint);

{
  "sources": [
    {
      "type": "file",
      "filePath": "app.json",
      "reasons": ["expoConfig"],
      "hash": "378083de0c6e6bb6caf8fb72df658b0b26fb29ef"
    },
    {
      "type": "file",
      "filePath": "eas.json",
      "reasons": ["easBuild"],
      "hash": "f723802b6ea916d1a6c4767b2299cc81ddb22eb4"
    },
    {
      "type": "dir",
      "filePath": "node_modules/expo",
      "reasons": ["expoAutolinkingIos", "expoAutolinkingAndroid", "bareRncliAutolinking"],
      "hash": "1faee4057fa943300905750b51c3b0cbf05f4b0d"
    }
  ],
  "hash": "bf8a3b08935f056270b1688333b02f1ef5fa25bf"
}

createProjectHashAsync

Create a native hash value from project

function createProjectHashAsync(projectRoot: string, options?: Options): Promise<string>;

Example:

const hash = await createProjectHashAsync('/app');
console.log(hash);

bf8a3b08935f056270b1688333b02f1ef5fa25bf

diffFingerprintChangesAsync

Diff the given fingerprint with the current project fingerprint state

function diffFingerprintChangesAsync(
  fingerprint: Fingerprint,
  projectRoot: string,
  options?: Options
): Promise<FingerprintSource[]>;

Example:

const fingerprint = {
  sources: [
    {
      type: 'file',
      filePath: 'app.json',
      reasons: ['expoConfig'],
      hash: '378083de0c6e6bb6caf8fb72df658b0b26fb29ef',
    },
    {
      type: 'file',
      filePath: 'eas.json',
      reasons: ['easBuild'],
      hash: 'f723802b6ea916d1a6c4767b2299cc81ddb22eb4',
    },
    {
      type: 'dir',
      filePath: 'node_modules/expo',
      reasons: ['expoAutolinkingIos', 'expoAutolinkingAndroid', 'bareRncliAutolinking'],
      hash: '1faee4057fa943300905750b51c3b0cbf05f4b0d',
    },
  ],
  hash: 'bf8a3b08935f056270b1688333b02f1ef5fa25bf',
};
const result = await diffFingerprintChangesAsync(fingerprint, '/app');
console.log(result);

[
  {
    "op": "removed",
    "source": {
      "type": "file",
      "filePath": "./assets/icon.png",
      "reasons": ["expoConfigExternalFile"],
      "hash": "3f71f5a8458c06b83424cc33e1f2481f601199ea"
    }
  },
  {
    "op": "added",
    "source": {
      "type": "dir",
      "filePath": "ios",
      "reasons": ["bareNativeDir"],
      "hash": "2420400e6140a4ccfc350fc483b26efdfc26ddac"
    }
  },
  {
    "op": "changed",
    "source": {
      "type": "contents",
      "id": "expoConfig",
      "contents": "{\"ios\":{\"bundleIdentifier\":\"com.test\",\"supportsTablet\":true},\"name\":\"test\",\"platforms\":[\"ios\"],\"slug\":\"test\"}",
      "reasons": ["expoConfig"],
      "hash": "dd2a3ebb872b097f9c1e33780fb8db8688848fa0"
    }
  }
]

diffFingerprints

Find the diff between two fingerprints

function diffFingerprints(
  fingerprint1: Fingerprint,
  fingerprint2: Fingerprint
): FingerprintSource[];

CLI Usage

Generate a fingerprint for a given project

npx @expo/fingerprint /path/to/projectRoot

Generate a fingerprint for a given project and write it to a file

npx @expo/fingerprint /path/to/projectRoot > fingerprint.json

Compare a fingerprint with the current project state

npx @expo/fingerprint /path/to/projectRoot fingerprint.json

Customizations

Include or exclude extra files to ignored paths in the .fingerprintignore file

Our default ignore paths, found here DEFAULT_IGNORE_PATHS, make hashing fast and keep hashing results stable. If the default setup does not fit your workflow, you can add a .fingerprintignore file in your project root. It works like .gitignore but with some slight differences: We use minimatch for pattern matching with the limitations.

Here's how to use .fingerprintignore: To skip a whole folder but keep some files, you can do this:

# Ignore the entire /app/ios folder
/app/ios/**/*

# But still keep /app/ios/Podfile and /app/ios/Podfile.lock
!/app/ios/Podfile
!/app/ios/Podfile.lock

fingerprint.config.js

You can customize the fingerprinting behavior by creating a fingerprint.config.js file in your project root. This file allows you to specify custom configurations, such as skipping certain fingerprint sources, adding extra fingerprint sources, or enabling debug mode.

Below is an example fingerprint.config.js configuration, assuming you have @expo/fingerprint installed as a direct dependency:

/** @type {import('@expo/fingerprint').Config} */
const config = {
  sourceSkips: [
    'ExpoConfigRuntimeVersionIfString',
    'ExpoConfigVersions',
    'PackageJsonAndroidAndIosScriptsIfNotContainRun',
  ],
};
module.exports = config;

If you are using @expo/fingerprint through expo (where @expo/fingerprint is installed as a transitive dependency), you can import fingerprint from expo/fingerprint:

/** @type {import('expo/fingerprint').Config} */
const config = {
  sourceSkips: [
    'ExpoConfigRuntimeVersionIfString',
    'ExpoConfigVersions',
    'PackageJsonAndroidAndIosScriptsIfNotContainRun',
  ],
};
module.exports = config;

For supported configurations, you can refer to the source code and SourceSkips.ts for supported SourceSkips.

Limitations

Limited support for config-plugins raw functions

When using config-plugins with raw functions, it's essential to be aware of certain limitations, particularly in the context of fingerprinting. Expo makes its best effort to generate fingerprints for changes made through config-plugins; however, raw functions pose specific challenges. Raw functions are not serializable as fingerprints, which means they cannot be directly used for generating unique hashes.

To work around this limitation, Expo employs one of the following strategies to create serializable fingerprints for raw functions:

1. Using Function.name: Expo utilizes the Function.name property if available for named raw functions. This property provides a recognizable name for the function, which can be used as a fingerprint property.

2. Using withAnonymous: For anonymous raw functions without a Function.name, Expo resorts to using 'withAnonymous' as the fingerprint property. This is a generic identifier for anonymous functions.

Here's an example to illustrate these concepts:

// In app.config.js
const { withInfoPlist } = require('expo/config-plugins');

const withMyPlugin = (config) => {
  return withInfoPlist(config, (config) => {
    config.modResults.NSLocationWhenInUseUsageDescription = 'Allow $(PRODUCT_NAME) to use your location';
    return config;
  });
};

export default ({ config }) => {
  config.plugins ||= [];
  config.plugins.push(withMyPlugin);
  config.plugins.push((config) => config);
  return config;
};`

In this example, Expo will use ['withMyPlugin', 'withAnonymous'] as plugin properties for fingerprint hashing.

It's important to note that due to this design, if you make changes to the implementation of raw config-plugins functions, such as altering the Info.plist value within 'withMyPlugin', the fingerprint will still generate the same hash value. To ensure unique fingerprints when modifying config-plugins implementations, consider the following options:

• Avoid Anonymous Functions: Avoid using anonymous raw config-plugins functions. Instead, use named functions whenever possible, and ensure that their names remain consistent as long as the implementation changes.

• Use Local config-plugins: Alternatively, you can create local config-plugins as separate modules, each with its own export. This approach allows you to specify a different function name when making changes to the config-plugins implementations.

  Here's an example of using a local config-plugin:

  // In ./plugins/withMyPlugin.js
  const { withInfoPlist } = require('expo/config-plugins');
  
  const withMyPlugin = (config) => {
    return withInfoPlist(config, (config) => {
      config.modResults.NSLocationWhenInUseUsageDescription =
        'Allow $(PRODUCT_NAME) to use your location';
      return config;
    });
  };
  
  module.exports = withMyPlugin;

  // in app.json
  {
    "expo": {
      // ...
      "plugins": "./plugins/withMyPlugin"
    }
  }

By following these guidelines, you can effectively manage changes to config-plugins and ensure that fingerprinting remains consistent and reliable.