Add a serviceworker (#234)

* Add a serviceworker

* rename + fix random extra character

* Fixing worker typings

* Fixing types properly this time.

* Once of those rare cases where this matters.

* Naming the things.

* Move registration to the app (so we can use snackbar later)

* Moving SW plugin later so it picks up things like HTML

* MVP service worker

* Two stage-service worker

* Fix prerendering by conditionally awaiting Custom Elements polyfill.

* Fix icon 404's

* add doc comment to autoswplugin

* Fix type

config/auto-sw-plugin.js

@@ -0,0 +1,156 @@
+const util = require('util');
+const minimatch = require('minimatch');
+const SingleEntryPlugin = require('webpack/lib/SingleEntryPlugin');
+const WebWorkerTemplatePlugin = require('webpack/lib/webworker/WebWorkerTemplatePlugin');
+const ParserHelpers = require('webpack/lib/ParserHelpers');
+
+const NAME = 'auto-sw-plugin';
+const JS_TYPES = ['auto', 'esm', 'dynamic'];
+
+/**
+ * Automatically finds and bundles Service Workers by looking for navigator.serviceWorker.register(..).
+ * An Array of webpack assets is injected into the Service Worker bundle as a `BUILD_ASSETS` global.
+ * Hidden and `.map` files are excluded by default, and this can be customized using the include & exclude options.
+ * @example
+ *  // webpack config
+ *  plugins: [
+ *    new AutoSWPlugin({
+ *      exclude: [
+ *        '**\/.*',     // don't expose hidden files (default)
+ *        '**\/*.map',  // don't precache sourcemaps (default)
+ *        'index.html'  // don't cache the page itself
+ *      ]
+ *    })
+ *  ]
+ * @param {Object} [options={}]
+ * @param {string[]} [options.exclude]  Minimatch pattern(s) of which assets to omit from BUILD_ASSETS.
+ * @param {string[]} [options.include]  Minimatch pattern(s) of assets to allow in BUILD_ASSETS.
+ */
+module.exports = class AutoSWPlugin {
+  constructor(options) {
+    this.options = Object.assign({
+      exclude: [
+        '**/*.map',
+        '**/.*'
+      ]
+    }, options || {});
+  }
+
+  apply(compiler) {
+    const serviceWorkers = [];
+
+    compiler.hooks.emit.tapPromise(NAME, compilation => this.emit(compiler, compilation, serviceWorkers));
+
+    compiler.hooks.normalModuleFactory.tap(NAME, (factory) => {
+      for (const type of JS_TYPES) {
+        factory.hooks.parser.for(`javascript/${type}`).tap(NAME, parser => {
+          let counter = 0;
+
+          const processRegisterCall = expr => {
+            const dep = parser.evaluateExpression(expr.arguments[0]);
+
+            if (!dep.isString()) {
+              parser.state.module.warnings.push({
+                message: 'navigator.serviceWorker.register() will only be bundled if passed a String literal.'
+              });
+              return false;
+            }
+
+            const filename = dep.string;
+            const outputFilename = this.options.filename || 'serviceworker.js'
+            const context = parser.state.current.context;
+            serviceWorkers.push({
+              outputFilename,
+              filename,
+              context
+            });
+
+            const id = `__webpack__serviceworker__${++counter}`;
+            ParserHelpers.toConstantDependency(parser, id)(expr.arguments[0]);
+            return ParserHelpers.addParsedVariableToModule(parser, id, '__webpack_public_path__ + ' + JSON.stringify(outputFilename));
+          };
+
+          parser.hooks.call.for('navigator.serviceWorker.register').tap(NAME, processRegisterCall);
+          parser.hooks.call.for('self.navigator.serviceWorker.register').tap(NAME, processRegisterCall);
+          parser.hooks.call.for('window.navigator.serviceWorker.register').tap(NAME, processRegisterCall);
+        });
+      }
+    });
+  }
+
+  createFilter(list) {
+    const filters = [].concat(list);
+    for (let i=0; i<filters.length; i++) {
+      if (typeof filters[i] === 'string') {
+        filters[i] = minimatch.filter(filters[i]);
+      }
+    }
+    return filters;
+  }
+
+  async emit(compiler, compilation, serviceWorkers) {
+    let assetMapping = Object.keys(compilation.assets);
+    if (this.options.include) {
+      const filters = this.createFilter(this.options.include);
+      assetMapping = assetMapping.filter(filename => {
+        for (const filter of filters) {
+          if (filter(filename)) return true;
+        }
+        return false;
+      });
+    }
+    if (this.options.exclude) {
+      const filters = this.createFilter(this.options.exclude);
+      assetMapping = assetMapping.filter(filename => {
+        for (const filter of filters) {
+          if (filter(filename)) return false;
+        }
+        return true;
+      });
+    }
+    await Promise.all(serviceWorkers.map(
+      (serviceWorker, index) => this.compileServiceWorker(compiler, compilation, serviceWorker, index, assetMapping)
+    ));
+  }
+
+  async compileServiceWorker(compiler, compilation, options, index, assetMapping) {
+    const entryFilename = options.filename;
+
+    const chunkFilename = compiler.options.output.chunkFilename.replace(/\.([a-z]+)$/i, '.serviceworker.$1');
+    const workerOptions = {
+      filename: options.outputFilename, // chunkFilename.replace(/\.?\[(?:chunkhash|contenthash|hash)(:\d+(?::\d+)?)?\]/g, ''),
+      chunkFilename: this.options.chunkFilename || chunkFilename,
+      globalObject: 'self'
+    };
+
+    const childCompiler = compilation.createChildCompiler(NAME, { filename: workerOptions.filename });
+    (new WebWorkerTemplatePlugin(workerOptions)).apply(childCompiler);
+
+    /* The duplication DefinePlugin ends up causing is problematic (it doesn't hoist injections), so we'll do it manually. */
+    // (new DefinePlugin({
+    //   BUILD_ASSETS: JSON.stringify(assetMapping)
+    // })).apply(childCompiler);
+    (new SingleEntryPlugin(options.context, entryFilename, workerOptions.filename)).apply(childCompiler);
+
+    const subCache = `subcache ${__dirname} ${entryFilename} ${index}`;
+    let childCompilation;
+    childCompiler.hooks.compilation.tap(NAME, c => {
+      childCompilation = c;
+      if (childCompilation.cache) {
+        if (!childCompilation.cache[subCache]) childCompilation.cache[subCache] = {};
+        childCompilation.cache = childCompilation.cache[subCache];
+      }
+    });
+
+    await (util.promisify(childCompiler.runAsChild.bind(childCompiler)))();
+
+    const original = childCompilation.assets[workerOptions.filename].source();
+    const source = `var BUILD_ASSETS=${JSON.stringify(assetMapping)};\n${original}`;
+    childCompilation.assets[workerOptions.filename] = {
+      source: () => source,
+      size: () => Buffer.byteLength(source, 'utf8')
+    };
+
+    Object.assign(compilation.assets, childCompilation.assets);
+  }
+};