module: Set dynamic import callback

.eslintignore

@@ -2,6 +2,7 @@ lib/internal/v8.js
 lib/internal/v8_prof_polyfill.js
 lib/punycode.js
 test/addons/??_*
+test/es-module/test-esm-dynamic-import.js
 test/fixtures
 test/message/esm_display_syntax_error.mjs
 tools/eslint

lib/internal/loader/Loader.js

@@ -1,8 +1,12 @@
 'use strict';
 
-const { getURLFromFilePath } = require('internal/url');
+const path = require('path');
+const { getURLFromFilePath, URL } = require('internal/url');
 
-const { createDynamicModule } = require('internal/loader/ModuleWrap');
+const {
+  createDynamicModule,
+  setImportModuleDynamicallyCallback
+} = require('internal/loader/ModuleWrap');
 
 const ModuleMap = require('internal/loader/ModuleMap');
 const ModuleJob = require('internal/loader/ModuleJob');
@@ -24,6 +28,13 @@ function getURLStringForCwd() {
   }
 }
 
+function normalizeReferrerURL(referrer) {
+  if (typeof referrer === 'string' && path.isAbsolute(referrer)) {
+    return getURLFromFilePath(referrer).href;
+  }
+  return new URL(referrer).href;
+}
+
 /* A Loader instance is used as the main entry point for loading ES modules.
  * Currently, this is a singleton -- there is only one used for loading
  * the main module and everything in its dependency graph. */
@@ -129,6 +140,12 @@ class Loader {
     const module = await job.run();
     return module.namespace();
   }
+
+  static registerImportDynamicallyCallback(loader) {
+    setImportModuleDynamicallyCallback(async (referrer, specifier) => {
+      return loader.import(specifier, normalizeReferrerURL(referrer));
+    });
+  }
 }
 Loader.validFormats = ['esm', 'cjs', 'builtin', 'addon', 'json', 'dynamic'];
 Object.setPrototypeOf(Loader.prototype, null);

lib/internal/loader/ModuleWrap.js

@@ -1,6 +1,9 @@
 'use strict';
 
-const { ModuleWrap } = internalBinding('module_wrap');
+const {
+  ModuleWrap,
+  setImportModuleDynamicallyCallback
+} = internalBinding('module_wrap');
 const debug = require('util').debuglog('esm');
 const ArrayJoin = Function.call.bind(Array.prototype.join);
 const ArrayMap = Function.call.bind(Array.prototype.map);
@@ -59,5 +62,6 @@ const createDynamicModule = (exports, url = '', evaluate) => {
 
 module.exports = {
   createDynamicModule,
+  setImportModuleDynamicallyCallback,
   ModuleWrap
 };

lib/module.js

@@ -472,6 +472,7 @@ Module._load = function(request, parent, isMain) {
           ESMLoader.hook(hooks);
         }
       }
+      Loader.registerImportDynamicallyCallback(ESMLoader);
       await ESMLoader.import(getURLFromFilePath(request).pathname);
     })()
     .catch((e) => {

src/env.h

@@ -332,6 +332,7 @@ class ModuleWrap;
   V(vm_parsing_context_symbol, v8::Symbol)                                    \
   V(url_constructor_function, v8::Function)                                   \
   V(write_wrap_constructor_function, v8::Function)                            \
+  V(host_import_module_dynamically_callback, v8::Function)                    \
 
 class Environment;
 

src/module_wrap.cc

@@ -558,6 +558,62 @@ void ModuleWrap::Resolve(const FunctionCallbackInfo<Value>& args) {
   args.GetReturnValue().Set(result.FromJust().ToObject(env));
 }
 
+static MaybeLocal<Promise> ImportModuleDynamically(
+    Local<Context> context,
+    Local<v8::ScriptOrModule> referrer,
+    Local<String> specifier) {
+  Isolate* iso = context->GetIsolate();
+  Environment* env = Environment::GetCurrent(context);
+  v8::EscapableHandleScope handle_scope(iso);
+
+  if (env->context() != context) {
+    auto maybe_resolver = Promise::Resolver::New(context);
+    Local<Promise::Resolver> resolver;
+    if (maybe_resolver.ToLocal(&resolver)) {
+      // TODO(jkrems): Turn into proper error object w/ code
+      Local<Value> error = v8::Exception::Error(
+        OneByteString(iso, "import() called outside of main context"));
+      if (resolver->Reject(context, error).IsJust()) {
+        return handle_scope.Escape(resolver.As<Promise>());
+      }
+    }
+    return MaybeLocal<Promise>();
+  }
+
+  Local<Function> import_callback =
+    env->host_import_module_dynamically_callback();
+  Local<Value> import_args[] = {
+    referrer->GetResourceName(),
+    Local<Value>(specifier)
+  };
+  MaybeLocal<Value> maybe_result = import_callback->Call(context,
+                                                         v8::Undefined(iso),
+                                                         2,
+                                                         import_args);
+
+  Local<Value> result;
+  if (maybe_result.ToLocal(&result)) {
+    return handle_scope.Escape(result.As<Promise>());
+  }
+  return MaybeLocal<Promise>();
+}
+
+void ModuleWrap::SetImportModuleDynamicallyCallback(
+    const FunctionCallbackInfo<Value>& args) {
+  Isolate* iso = args.GetIsolate();
+  Environment* env = Environment::GetCurrent(args);
+  HandleScope handle_scope(iso);
+  if (!args[0]->IsFunction()) {
+    env->ThrowError("first argument is not a function");
+    return;
+  }
+
+  Local<Function> import_callback = args[0].As<Function>();
+  env->set_host_import_module_dynamically_callback(import_callback);
+
+  iso->SetHostImportModuleDynamicallyCallback(ImportModuleDynamically);
+}
+
 void ModuleWrap::Initialize(Local<Object> target,
                             Local<Value> unused,
                             Local<Context> context) {
@@ -575,6 +631,9 @@ void ModuleWrap::Initialize(Local<Object> target,
 
   target->Set(FIXED_ONE_BYTE_STRING(isolate, "ModuleWrap"), tpl->GetFunction());
   env->SetMethod(target, "resolve", node::loader::ModuleWrap::Resolve);
+  env->SetMethod(target,
+                 "setImportModuleDynamicallyCallback",
+                 node::loader::ModuleWrap::SetImportModuleDynamicallyCallback);
 }
 
 }  // namespace loader

src/module_wrap.h

@@ -39,6 +39,8 @@ class ModuleWrap : public BaseObject {
   static void GetUrl(v8::Local<v8::String> property,
                      const v8::PropertyCallbackInfo<v8::Value>& info);
   static void Resolve(const v8::FunctionCallbackInfo<v8::Value>& args);
+  static void SetImportModuleDynamicallyCallback(
+      const v8::FunctionCallbackInfo<v8::Value>& args);
   static v8::MaybeLocal<v8::Module> ResolveCallback(
       v8::Local<v8::Context> context,
       v8::Local<v8::String> specifier,

test/es-module/test-esm-dynamic-import.js

@@ -0,0 +1,113 @@
+// Flags: --experimental-modules --harmony-dynamic-import
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const { URL } = require('url');
+const vm = require('vm');
+
+common.crashOnUnhandledRejection();
+
+const relativePath = './test-esm-ok.mjs';
+const absolutePath = require.resolve('./test-esm-ok.mjs');
+const targetURL = new URL('file:///');
+targetURL.pathname = absolutePath;
+
+function expectErrorProperty(result, propertyKey, value) {
+  Promise.resolve(result)
+    .catch(common.mustCall(error => {
+      assert.equal(error[propertyKey], value);
+    }));
+}
+
+function expectMissingModuleError(result) {
+  expectErrorProperty(result, 'code', 'MODULE_NOT_FOUND');
+}
+
+function expectInvalidUrlError(result) {
+  expectErrorProperty(result, 'code', 'ERR_INVALID_URL');
+}
+
+function expectInvalidReferrerError(result) {
+  expectErrorProperty(result, 'code', 'ERR_INVALID_URL');
+}
+
+function expectInvalidProtocolError(result) {
+  expectErrorProperty(result, 'code', 'ERR_INVALID_PROTOCOL');
+}
+
+function expectInvalidContextError(result) {
+  expectErrorProperty(result,
+    'message', 'import() called outside of main context');
+}
+
+function expectOkNamespace(result) {
+  Promise.resolve(result)
+    .then(common.mustCall(ns => {
+      // Can't deepStrictEqual because ns isn't a normal object
+      assert.deepEqual(ns, { default: true });
+    }));
+}
+
+function expectFsNamespace(result) {
+  Promise.resolve(result)
+    .then(common.mustCall(ns => {
+      assert.equal(typeof ns.default.writeFile, 'function');
+    }));
+}
+
+// For direct use of import expressions inside of CJS or ES modules, including
+// via eval, all kinds of specifiers should work without issue.
+(function testScriptOrModuleImport() {
+  // Importing another file, both direct & via eval
+  // expectOkNamespace(import(relativePath));
+  expectOkNamespace(eval.call(null, `import("${relativePath}")`));
+  expectOkNamespace(eval(`import("${relativePath}")`));
+  expectOkNamespace(eval.call(null, `import("${targetURL}")`));
+
+  // Importing a built-in, both direct & via eval
+  expectFsNamespace(import("fs"));
+  expectFsNamespace(eval('import("fs")'));
+  expectFsNamespace(eval.call(null, 'import("fs")'));
+
+  expectMissingModuleError(import("./not-an-existing-module.mjs"));
+  // TODO(jkrems): Right now this doesn't hit a protocol error because the
+  // module resolution step already rejects it. These arguably should be
+  // protocol errors.
+  expectMissingModuleError(import("node:fs"));
+  expectMissingModuleError(import('http://example.com/foo.js'));
+})();
+
+// vm.runInThisContext:
+// * Supports built-ins, always
+// * Supports imports if the script has a known defined origin
+(function testRunInThisContext() {
+  // Succeeds because it's got an valid base url
+  expectFsNamespace(vm.runInThisContext(`import("fs")`, {
+    filename: __filename,
+  }));
+  expectOkNamespace(vm.runInThisContext(`import("${relativePath}")`, {
+    filename: __filename,
+  }));
+  // Rejects because it's got an invalid referrer URL.
+  // TODO(jkrems): Arguably the first two (built-in + absolute URL) could work
+  // with some additional effort.
+  expectInvalidReferrerError(vm.runInThisContext('import("fs")'));
+  expectInvalidReferrerError(vm.runInThisContext(`import("${targetURL}")`));
+  expectInvalidReferrerError(vm.runInThisContext(`import("${relativePath}")`));
+})();
+
+// vm.runInNewContext is currently completely unsupported, pending well-defined
+// semantics for per-context/realm module maps in node.
+(function testRunInNewContext() {
+  // Rejects because it's running in the wrong context
+  expectInvalidContextError(
+    vm.runInNewContext(`import("${targetURL}")`, undefined, {
+      filename: __filename,
+    })
+  );
+
+  // Rejects because it's running in the wrong context
+  expectInvalidContextError(vm.runInNewContext(`import("fs")`, undefined, {
+    filename: __filename,
+  }));
+})();