[image-utils] add env variable to disable sharp resolution

.github/workflows/test.yml

@@ -32,6 +32,7 @@ jobs:
             dev-server,
             expo-cli,
             expo-codemod,
+            image-utils,
             json-file,
             metro-config,
             package-manager,

packages/image-utils/README.md

@@ -1,3 +1,13 @@
 # `@expo/image-utils`
 
-A library for image processing functionality in Expo CLI. It uses `sharp` for image processing if it's available through a global `sharp-cli` installation. Otherwise it uses `jimp`, a Node library with no native dependencies, and warns the user that they may want to install `sharp-cli` for faster image processing.
+A library for image processing functionality in Expo CLI. It uses `sharp` for image processing if it's available through a global `sharp-cli` installation. Otherwise it uses `jimp`, a Node library with no native dependencies, and warns the user that they may want to install `sharp-cli` for faster image processing.
+
+## Advanced Configuration
+
+This package can be configured using the following environment variables.
+
+### EXPO_IMAGE_UTILS_NO_SHARP
+
+When truthy, this will force global `sharp-cli` resolution methods like `isAvailableAsync()` and `findSharpInstanceAsync()` to fail. Other processes can use this to fallback on Jimp for image modifications. By default this is falsy (undefined).
+
+`findSharpInstanceAsync()` will throw an error if disabled because it shouldn't be invoked if `isAvailableAsync()` returns `false`.

packages/image-utils/jest.config.js

@@ -0,0 +1,7 @@
+const path = require('path');
+
+module.exports = {
+  preset: '../../jest/unit-test-config',
+  rootDir: path.resolve(__dirname),
+  displayName: require('./package').name,
+};

packages/image-utils/package.json

@@ -6,6 +6,7 @@
   "scripts": {
     "watch": "tsc --watch",
     "build": "tsc",
+    "test": "jest",
     "prepare": "yarn run clean && yarn build",
     "clean": "rimraf build ./tsconfig.tsbuildinfo"
   },

packages/image-utils/src/__tests__/sharp-test.ts

@@ -0,0 +1,21 @@
+beforeEach(() => {
+  delete process.env.EXPO_IMAGE_UTILS_NO_SHARP;
+});
+
+// Test that the environment variable can be used to disable sharp-cli for easier testing of image generation.
+describe('isAvailableAsync', () => {
+  it(`can be disabled using an environment variable`, async () => {
+    process.env.EXPO_IMAGE_UTILS_NO_SHARP = '1';
+    const { isAvailableAsync } = require('../sharp');
+    expect(await isAvailableAsync()).toBe(false);
+  });
+});
+describe('findSharpInstanceAsync', () => {
+  it(`will throw an error if sharp-cli is disabled in the environment`, async () => {
+    process.env.EXPO_IMAGE_UTILS_NO_SHARP = '1';
+    const { findSharpInstanceAsync } = require('../sharp');
+    expect(findSharpInstanceAsync()).rejects.toThrowError(
+      'sharp-cli has been disabled with the environment variable'
+    );
+  });
+});

packages/image-utils/src/sharp.ts

@@ -1,6 +1,7 @@
 import semver from 'semver';
 import spawnAsync from '@expo/spawn-async';
 import resolveFrom from 'resolve-from';
+import { boolish } from 'getenv';
 import { Options, SharpCommandOptions, SharpGlobalOptions } from './sharp.types';
 
 const SHARP_HELP_PATTERN = /\n\nSpecify --help for available options/g;
@@ -25,7 +26,16 @@ export async function resizeBufferAsync(buffer: Buffer, sizes: number[]): Promis
   return resizedBuffers;
 }
 
+const isSharpDisabled = boolish('EXPO_IMAGE_UTILS_NO_SHARP', false);
+
+/**
+ * Returns `true` if a global sharp instance can be found.
+ * This functionality can be overridden with `process.env.EXPO_IMAGE_UTILS_NO_SHARP=1`.
+ */
 export async function isAvailableAsync(): Promise<boolean> {
+  if (isSharpDisabled) {
+    return false;
+  }
   try {
     return !!(await findSharpBinAsync());
   } catch (_) {
@@ -127,7 +137,16 @@ async function findSharpBinAsync(): Promise<string> {
   return _sharpBin;
 }
 
+/**
+ * Returns the instance of `sharp` installed by the global `sharp-cli` package.
+ * This method will throw errors if the `sharp` instance cannot be found, these errors can be circumvented by ensuring `isAvailableAsync()` resolves to `true`.
+ */
 export async function findSharpInstanceAsync(): Promise<any | null> {
+  if (isSharpDisabled) {
+    throw new Error(
+      'Global instance of sharp-cli cannot be retrieved because sharp-cli has been disabled with the environment variable `EXPO_IMAGE_UTILS_NO_SHARP`'
+    );
+  }
   if (_sharpInstance) {
     return _sharpInstance;
   }