esm: support loading data URLs

Co-Authored-By: Jan Olaf Krems <jan.krems@gmail.com>

Author: bmeck

doc/api/esm.md

@@ -312,13 +312,38 @@ There are four types of specifiers:
 Bare specifiers, and the bare specifier portion of deep import specifiers, are
 strings; but everything else in a specifier is a URL.
 
-Only `file://` URLs are supported. A specifier like
+Only `file:` and `data:` URLs are supported. A specifier like
 `'https://example.com/app.js'` may be supported by browsers but it is not
 supported in Node.js.
 
 Specifiers may not begin with `/` or `//`. These are reserved for potential
 future use. The root of the current volume may be referenced via `file:///`.
 
+#### `data:` Imports
+
+<!-- YAML
+added: REPLACEME
+-->
+
+[`data:` URLs][] are supported for importing with the following MIME types:
+
+* `text/javascript` for ES Modules
+* `application/json` for JSON
+* `application/wasm` for WASM.
+
+`data:` URLs only resolve [_Bare specifiers_][Terminology] for builtin modules
+and [_Absolute specifiers_][Terminology]. Resolving
+[_Relative specifiers_][Terminology] will not work because `data:` is not a
+[special scheme][]. For example, attempting to load `./foo`
+from `data:text/javascript,import "./foo";` will fail to resolve since there
+is no concept of relative resolution for `data:` URLs. An example of a `data:`
+URLs being used is:
+
+```mjs
+import 'data:text/javascript,console.log("hello!");'
+import _ from 'data:application/json,"world!"'
+```
+
 ## import.meta
 
 * {Object}
@@ -869,6 +894,8 @@ $ node --experimental-modules --es-module-specifier-resolution=node index
 success!
 ```
 
+[Terminology]: #esm_terminology
+[`data:` URLs]: https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/Data_URIs
 [`export`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/export
 [`import`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import
 [`import()`]: #esm_import-expressions
@@ -877,6 +904,7 @@ success!
 [CommonJS]: modules.html
 [ECMAScript-modules implementation]: https://github.com/nodejs/modules/blob/master/doc/plan-for-new-modules-implementation.md
 [Node.js EP for ES Modules]: https://github.com/nodejs/node-eps/blob/master/002-es-modules.md
+[special scheme]: https://url.spec.whatwg.org/#special-scheme
 [WHATWG JSON modules specification]: https://html.spec.whatwg.org/#creating-a-json-module-script
 [ES Module Integration Proposal for Web Assembly]: https://github.com/webassembly/esm-integration
 [dynamic instantiate hook]: #esm_dynamic_instantiate_hook

lib/internal/modules/esm/default_resolve.js

@@ -12,7 +12,7 @@ const typeFlag = getOptionValue('--input-type');
 const experimentalWasmModules = getOptionValue('--experimental-wasm-modules');
 const { resolve: moduleWrapResolve,
         getPackageType } = internalBinding('module_wrap');
-const { pathToFileURL, fileURLToPath } = require('internal/url');
+const { URL, pathToFileURL, fileURLToPath } = require('internal/url');
 const { ERR_INPUT_TYPE_NOT_ALLOWED,
         ERR_UNKNOWN_FILE_EXTENSION } = require('internal/errors').codes;
 
@@ -45,12 +45,32 @@ if (experimentalWasmModules)
   extensionFormatMap['.wasm'] = legacyExtensionFormatMap['.wasm'] = 'wasm';
 
 function resolve(specifier, parentURL) {
+  try {
+    const parsed = new URL(specifier);
+    if (parsed.protocol === 'data:') {
+      const [ , mime ] = /^([^/]+\/[^;,]+)(;base64)?,/.exec(parsed.pathname) || [ null, null, null ];
+      const format = ({
+        '__proto__': null,
+        'text/javascript': 'module',
+        'application/json': 'json',
+        'application/wasm': experimentalWasmModules ? 'wasm' : null
+      })[mime] || null;
+      return {
+        url: specifier,
+        format
+      };
+    }
+  } catch {}
   if (NativeModule.canBeRequiredByUsers(specifier)) {
     return {
       url: specifier,
       format: 'builtin'
     };
   }
+  if (parentURL && parentURL.startsWith('data:')) {
+    // This is gonna blow up, we want the error
+    new URL(specifier, parentURL);
+  }
 
   const isMain = parentURL === undefined;
   if (isMain)

lib/internal/modules/esm/loader.js

@@ -102,9 +102,12 @@ class Loader {
       }
     }
 
-    if (format !== 'dynamic' && !url.startsWith('file:'))
+    if (format !== 'dynamic' &&
+      !url.startsWith('file:') &&
+      !url.startsWith('data:')
+    )
       throw new ERR_INVALID_RETURN_PROPERTY(
-        'file: url', 'loader resolve', 'url', url
+        'file: or data: url', 'loader resolve', 'url', url
       );
 
     return { url, format };

lib/internal/modules/esm/translators.js

@@ -9,6 +9,8 @@ const {
   StringPrototype
 } = primordials;
 
+const { Buffer } = require('buffer');
+
 const {
   stripBOM,
   loadNativeModule
@@ -23,6 +25,8 @@ const { debuglog } = require('internal/util/debuglog');
 const { promisify } = require('internal/util');
 const esmLoader = require('internal/process/esm_loader');
 const {
+  ERR_INVALID_URL,
+  ERR_INVALID_URL_SCHEME,
   ERR_UNKNOWN_BUILTIN_MODULE
 } = require('internal/errors').codes;
 const readFileAsync = promisify(fs.readFile);
@@ -33,6 +37,31 @@ const debug = debuglog('esm');
 const translators = new SafeMap();
 exports.translators = translators;
 
+const DATA_URL_PATTERN = /^[^/]+\/[^,;]+(;base64)?,([\s\S]*)$/;
+function getSource(url) {
+  const parsed = new URL(url);
+  if (parsed.protocol === 'file:') {
+    return readFileAsync(parsed);
+  } else if (parsed.protocol === 'data:') {
+    const match = DATA_URL_PATTERN.exec(parsed.pathname);
+    if (!match) {
+      throw new ERR_INVALID_URL(url);
+    }
+    const [ , base64, body ] = match;
+    return Buffer.from(body, base64 ? 'base64' : 'utf8');
+  } else {
+    throw new ERR_INVALID_URL_SCHEME(['file', 'data']);
+  }
+}
+
+function errPath(url) {
+  const parsed = new URL(url);
+  if (parsed.protocol === 'file:') {
+    return fileURLToPath(parsed);
+  }
+  return url;
+}
+
 function initializeImportMeta(meta, { url }) {
   meta.url = url;
 }
@@ -44,7 +73,7 @@ async function importModuleDynamically(specifier, { url }) {
 
 // Strategy for loading a standard JavaScript module
 translators.set('module', async function moduleStrategy(url) {
-  const source = `${await readFileAsync(new URL(url))}`;
+  const source = `${await getSource(url)}`;
   debug(`Translating StandardModule ${url}`);
   const { ModuleWrap, callbackMap } = internalBinding('module_wrap');
   const module = new ModuleWrap(source, url);
@@ -111,26 +140,32 @@ translators.set('builtin', async function builtinStrategy(url) {
 translators.set('json', async function jsonStrategy(url) {
   debug(`Translating JSONModule ${url}`);
   debug(`Loading JSONModule ${url}`);
-  const pathname = fileURLToPath(url);
-  const modulePath = isWindows ?
-    StringPrototype.replace(pathname, winSepRegEx, '\\') : pathname;
-  let module = CJSModule._cache[modulePath];
-  if (module && module.loaded) {
-    const exports = module.exports;
-    return createDynamicModule([], ['default'], url, (reflect) => {
-      reflect.exports.default.set(exports);
-    });
+  const pathname = url.startsWith('file:') ? fileURLToPath(url) : null;
+  let modulePath;
+  let module;
+  if (pathname) {
+    modulePath = isWindows ?
+      StringPrototype.replace(pathname, winSepRegEx, '\\') : pathname;
+    module = CJSModule._cache[modulePath];
+    if (module && module.loaded) {
+      const exports = module.exports;
+      return createDynamicModule([], ['default'], url, (reflect) => {
+        reflect.exports.default.set(exports);
+      });
+    }
   }
-  const content = await readFileAsync(pathname, 'utf-8');
-  // A require call could have been called on the same file during loading and
-  // that resolves synchronously. To make sure we always return the identical
-  // export, we have to check again if the module already exists or not.
-  module = CJSModule._cache[modulePath];
-  if (module && module.loaded) {
-    const exports = module.exports;
-    return createDynamicModule(['default'], url, (reflect) => {
-      reflect.exports.default.set(exports);
-    });
+  const content = `${await getSource(url)}`;
+  if (pathname) {
+    // A require call could have been called on the same file during loading and
+    // that resolves synchronously. To make sure we always return the identical
+    // export, we have to check again if the module already exists or not.
+    module = CJSModule._cache[modulePath];
+    if (module && module.loaded) {
+      const exports = module.exports;
+      return createDynamicModule(['default'], url, (reflect) => {
+        reflect.exports.default.set(exports);
+      });
+    }
   }
   try {
     const exports = JsonParse(stripBOM(content));
@@ -143,10 +178,12 @@ translators.set('json', async function jsonStrategy(url) {
     // parse error instead of just manipulating the original error message.
     // That would allow to add further properties and maybe additional
     // debugging information.
-    err.message = pathname + ': ' + err.message;
+    err.message = errPath(url) + ': ' + err.message;
     throw err;
   }
-  CJSModule._cache[modulePath] = module;
+  if (pathname) {
+    CJSModule._cache[modulePath] = module;
+  }
   return createDynamicModule([], ['default'], url, (reflect) => {
     debug(`Parsing JSONModule ${url}`);
     reflect.exports.default.set(module.exports);
@@ -155,14 +192,13 @@ translators.set('json', async function jsonStrategy(url) {
 
 // Strategy for loading a wasm module
 translators.set('wasm', async function(url) {
-  const pathname = fileURLToPath(url);
-  const buffer = await readFileAsync(pathname);
+  const buffer = await getSource(url);
   debug(`Translating WASMModule ${url}`);
   let compiled;
   try {
     compiled = await WebAssembly.compile(buffer);
   } catch (err) {
-    err.message = pathname + ': ' + err.message;
+    err.message = errPath(url) + ': ' + err.message;
     throw err;
   }
 

test/es-module/test-esm-data-urls.js

@@ -0,0 +1,63 @@
+// Flags: --experimental-modules
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+function createURL(mime, body) {
+  return `data:${mime},${body}`;
+}
+function createBase64URL(mime, body) {
+  return `data:${mime};base64,${Buffer.from(body).toString('base64')}`;
+}
+(async () => {
+  {
+    const body = 'export default {a:"aaa"};';
+    const plainESMURL = createURL('text/javascript', body);
+    const ns = await import(plainESMURL);
+    assert.deepStrictEqual(Object.keys(ns), ['default']);
+    assert.deepStrictEqual(ns.default.a, 'aaa');
+    const importerOfURL = createURL(
+      'text/javascript',
+      `export {default as default} from ${JSON.stringify(plainESMURL)}`
+    );
+    assert.strictEqual(
+      (await import(importerOfURL)).default,
+      ns.default
+    );
+    const base64ESMURL = createBase64URL('text/javascript', body);
+    assert.notStrictEqual(
+      await import(base64ESMURL),
+      ns
+    );
+  }
+  {
+    const body = 'export default import.meta.url;';
+    const plainESMURL = createURL('text/javascript', body);
+    const ns = await import(plainESMURL);
+    assert.deepStrictEqual(Object.keys(ns), ['default']);
+    assert.deepStrictEqual(ns.default, plainESMURL);
+  }
+  {
+    const body = '{"x": 1}';
+    const plainESMURL = createURL('application/json', body);
+    const ns = await import(plainESMURL);
+    assert.deepStrictEqual(Object.keys(ns), ['default']);
+    assert.deepStrictEqual(ns.default.x, 1);
+  }
+  {
+    const body = '{"default": 2}';
+    const plainESMURL = createURL('application/json', body);
+    const ns = await import(plainESMURL);
+    assert.deepStrictEqual(Object.keys(ns), ['default']);
+    assert.deepStrictEqual(ns.default.default, 2);
+  }
+  {
+    const body = 'null';
+    const plainESMURL = createURL('invalid', body);
+    try {
+      await import(plainESMURL);
+      common.mustNotCall()();
+    } catch (e) {
+      assert.strictEqual(e.code, 'ERR_INVALID_RETURN_PROPERTY_VALUE');
+    }
+  }
+})().then(common.mustCall());