ses/src/module-instance.js

Hardened JavaScript for Fearless Cooperation

/** @import {ModuleExportsNamespace} from '../types.js' */

import { assert } from './error/assert.js';
import { getDeferredExports } from './module-proxy.js';
import {
  ReferenceError,
  SyntaxError,
  TypeError,
  arrayForEach,
  arrayIncludes,
  arrayPush,
  arraySome,
  arraySort,
  create,
  defineProperty,
  entries,
  freeze,
  isArray,
  keys,
  mapGet,
  weakmapGet,
  reflectHas,
  assign,
} from './commons.js';
import { compartmentEvaluate } from './compartment-evaluate.js';

const { quote: q } = assert;

export const makeVirtualModuleInstance = (
  compartmentPrivateFields,
  moduleSource,
  compartment,
  moduleAliases,
  moduleSpecifier,
  resolvedImports,
) => {
  const { exportsProxy, exportsTarget, activate } = getDeferredExports(
    compartment,
    weakmapGet(compartmentPrivateFields, compartment),
    moduleAliases,
    moduleSpecifier,
  );

  const notifiers = create(null);

  if (moduleSource.exports) {
    if (
      !isArray(moduleSource.exports) ||
      arraySome(moduleSource.exports, name => typeof name !== 'string')
    ) {
      throw TypeError(
        `SES virtual module source "exports" property must be an array of strings for module ${moduleSpecifier}`,
      );
    }
    arrayForEach(moduleSource.exports, name => {
      let value = exportsTarget[name];
      const updaters = [];

      const get = () => value;

      const set = newValue => {
        value = newValue;
        for (const updater of updaters) {
          updater(newValue);
        }
      };

      defineProperty(exportsTarget, name, {
        get,
        set,
        enumerable: true,
        configurable: false,
      });

      notifiers[name] = update => {
        arrayPush(updaters, update);
        update(value);
      };
    });
    // This is enough to support import * from cjs - the '*' field doesn't need to be in exports nor exportsTarget because import will only ever access it via notifiers
    notifiers['*'] = update => {
      update(exportsTarget);
    };
  }

  const localState = {
    activated: false,
  };
  return freeze({
    notifiers,
    exportsProxy,
    execute() {
      if (reflectHas(localState, 'errorFromExecute')) {
        throw localState.errorFromExecute;
      }
      if (!localState.activated) {
        activate();
        localState.activated = true;
        try {
          // eslint-disable-next-line @endo/no-polymorphic-call
          moduleSource.execute(exportsTarget, compartment, resolvedImports);
        } catch (err) {
          localState.errorFromExecute = err;
          throw err;
        }
      }
    },
  });
};

// `makeModuleInstance` takes a module's compartment record, the live import
// namespace, and a global object; and produces a module instance.
// The module instance carries the proxied module exports namespace (the
// "exports"), notifiers to update the module's internal import namespace, and
// an idempotent execute function.
// The module exports namespace is a proxy to the proxied exports namespace
// that the execution of the module instance populates.
export const makeModuleInstance = (
  privateFields,
  moduleAliases,
  moduleRecord,
  importedInstances,
) => {
  const {
    compartment,
    moduleSpecifier,
    moduleSource,
    importMeta: moduleRecordMeta,
  } = moduleRecord;
  const {
    reexports: exportAlls = [],
    __syncModuleProgram__: functorSource,
    __fixedExportMap__: fixedExportMap = {},
    __liveExportMap__: liveExportMap = {},
    __reexportMap__: reexportMap = {},
    __needsImport__: needsImport = false,
    __needsImportMeta__: needsImportMeta = false,
    __syncModuleFunctor__,
  } = moduleSource;

  const compartmentFields = weakmapGet(privateFields, compartment);

  const { __shimTransforms__, resolveHook, importMetaHook, compartmentImport } =
    compartmentFields;

  const { exportsProxy, exportsTarget, activate } = getDeferredExports(
    compartment,
    compartmentFields,
    moduleAliases,
    moduleSpecifier,
  );

  // {_exportName_: getter} module exports namespace
  // object (eventually proxied).
  const exportsProps = create(null);

  // {_localName_: accessor} proxy traps for moduleLexicals and live bindings.
  // The moduleLexicals object is frozen and the corresponding properties of
  // moduleLexicals must be immutable, so we copy the descriptors.
  const moduleLexicals = create(null);

  // {_localName_: init(initValue) -> initValue} used by the
  // rewritten code to initialize exported fixed bindings.
  const onceVar = create(null);

  // {_localName_: update(newValue)} used by the rewritten code to
  // both initialize and update live bindings.
  const liveVar = create(null);

  const importMeta = create(null);
  if (moduleRecordMeta) {
    assign(importMeta, moduleRecordMeta);
  }
  if (needsImportMeta && importMetaHook) {
    importMetaHook(moduleSpecifier, importMeta);
  }

  /** @type {(fullSpecifier: string) => Promise<ModuleExportsNamespace>} */
  let dynamicImport;
  if (needsImport) {
    /** @param {string} importSpecifier */
    dynamicImport = async importSpecifier =>
      compartmentImport(resolveHook(importSpecifier, moduleSpecifier));
  }

  // {_localName_: [{get, set, notify}]} used to merge all the export updaters.
  const localGetNotify = create(null);

  // {[importName: string]: notify(update(newValue))} Used by code that imports
  // one of this module's exports, so that their update function will
  // be notified when this binding is initialized or updated.
  const notifiers = create(null);

  arrayForEach(entries(fixedExportMap), ([fixedExportName, [localName]]) => {
    let fixedGetNotify = localGetNotify[localName];
    if (!fixedGetNotify) {
      // fixed binding state
      let value;
      let tdz = true;
      /** @type {null | Array<(value: any) => void>} */
      let optUpdaters = [];

      // tdz sensitive getter
      const get = () => {
        if (tdz) {
          throw ReferenceError(`binding ${q(localName)} not yet initialized`);
        }
        return value;
      };

      // leave tdz once
      const init = freeze(initValue => {
        // init with initValue of a declared const binding, and return
        // it.
        if (!tdz) {
          throw TypeError(
            `Internal: binding ${q(localName)} already initialized`,
          );
        }
        value = initValue;
        const updaters = optUpdaters;
        optUpdaters = null;
        tdz = false;
        for (const updater of updaters || []) {
          updater(initValue);
        }
        return initValue;
      });

      // If still tdz, register update for notification later.
      // Otherwise, update now.
      const notify = updater => {
        if (updater === init) {
          // Prevent recursion.
          return;
        }
        if (tdz) {
          arrayPush(optUpdaters || [], updater);
        } else {
          updater(value);
        }
      };

      // Need these for additional exports of the local variable.
      fixedGetNotify = {
        get,
        notify,
      };
      localGetNotify[localName] = fixedGetNotify;
      onceVar[localName] = init;
    }

    exportsProps[fixedExportName] = {
      get: fixedGetNotify.get,
      set: undefined,
      enumerable: true,
      configurable: false,
    };

    notifiers[fixedExportName] = fixedGetNotify.notify;
  });

  arrayForEach(
    entries(liveExportMap),
    ([liveExportName, [localName, setProxyTrap]]) => {
      let liveGetNotify = localGetNotify[localName];
      if (!liveGetNotify) {
        // live binding state
        let value;
        let tdz = true;
        const updaters = [];

        // tdz sensitive getter
        const get = () => {
          if (tdz) {
            throw ReferenceError(
              `binding ${q(liveExportName)} not yet initialized`,
            );
          }
          return value;
        };

        // This must be usable locally for the translation of initializing
        // a declared local live binding variable.
        //
        // For reexported variable, this is also an update function to
        // register for notification with the downstream import, which we
        // must assume to be live. Thus, it can be called independent of
        // tdz but always leaves tdz. Such reexporting creates a tree of
        // bindings. This lets the tree be hooked up even if the imported
        // module instance isn't initialized yet, as may happen in cycles.
        const update = freeze(newValue => {
          value = newValue;
          tdz = false;
          for (const updater of updaters) {
            updater(newValue);
          }
        });

        // tdz sensitive setter
        const set = newValue => {
          if (tdz) {
            throw ReferenceError(`binding ${q(localName)} not yet initialized`);
          }
          value = newValue;
          for (const updater of updaters) {
            updater(newValue);
          }
        };

        // Always register the updater function.
        // If not in tdz, also update now.
        const notify = updater => {
          if (updater === update) {
            // Prevent recursion.
            return;
          }
          arrayPush(updaters, updater);
          if (!tdz) {
            updater(value);
          }
        };

        liveGetNotify = {
          get,
          notify,
        };

        localGetNotify[localName] = liveGetNotify;
        if (setProxyTrap) {
          defineProperty(moduleLexicals, localName, {
            get,
            set,
            enumerable: true,
            configurable: false,
          });
        }
        liveVar[localName] = update;
      }

      exportsProps[liveExportName] = {
        get: liveGetNotify.get,
        set: undefined,
        enumerable: true,
        configurable: false,
      };

      notifiers[liveExportName] = liveGetNotify.notify;
    },
  );

  const notifyStar = update => {
    update(exportsTarget);
  };
  notifiers['*'] = notifyStar;

  // Per the calling convention for the moduleFunctor generated from
  // an ESM, the `imports` function gets called once up front
  // to populate or arrange the population of imports and reexports.
  // The generated code produces an `updateRecord`: the means for
  // the linker to update the imports and exports of the module.
  // The updateRecord must conform to moduleAnalysis.imports
  // updateRecord = Map<specifier, importUpdaters>
  // importUpdaters = Map<importName, [update(newValue)*]>
  function imports(updateRecord) {
    // By the time imports is called, the importedInstances should already be
    // initialized with module instances that satisfy
    // imports.
    // importedInstances = Map[_specifier_, { notifiers, module, execute }]
    // notifiers = { [importName: string]: notify(update(newValue))}

    // export * cannot export default.
    const candidateAll = create(null);
    candidateAll.default = false;
    for (const [specifier, importUpdaters] of updateRecord) {
      const instance = mapGet(importedInstances, specifier);
      // The module instance object is an internal literal, does not bind this,
      // and never revealed outside the SES shim.
      // There are two instantiation sites for instances and they are both in
      // this module.
      // eslint-disable-next-line @endo/no-polymorphic-call
      instance.execute(); // bottom up cycle tolerant
      const { notifiers: importNotifiers } = instance;
      for (const [importName, updaters] of importUpdaters) {
        const importNotify = importNotifiers[importName];
        if (!importNotify) {
          throw SyntaxError(
            `The requested module '${specifier}' does not provide an export named '${importName}'`,
          );
        }
        for (const updater of updaters) {
          importNotify(updater);
        }
      }
      if (arrayIncludes(exportAlls, specifier)) {
        // Make all these imports candidates.
        // Note names don't change in reexporting all
        for (const [importAndExportName, importNotify] of entries(
          importNotifiers,
        )) {
          if (candidateAll[importAndExportName] === undefined) {
            candidateAll[importAndExportName] = importNotify;
          } else {
            // Already a candidate: remove ambiguity.
            candidateAll[importAndExportName] = false;
          }
        }
      }
      if (reexportMap[specifier]) {
        // Make named reexports candidates too.
        for (const [localName, exportedName] of reexportMap[specifier]) {
          candidateAll[exportedName] = importNotifiers[localName];
        }
      }
    }

    for (const [exportName, notify] of entries(candidateAll)) {
      if (!notifiers[exportName] && notify !== false) {
        notifiers[exportName] = notify;

        // exported live binding state
        let value;
        const update = newValue => (value = newValue);
        notify(update);
        exportsProps[exportName] = {
          get() {
            return value;
          },
          set: undefined,
          enumerable: true,
          configurable: false,
        };
      }
    }

    // Sort the module exports namespace as per spec.
    // The module exports namespace will be wrapped in a module namespace
    // exports proxy which will serve as a "module exports namespace exotic
    // object".
    // Sorting properties is not generally reliable because some properties may
    // be symbols, and symbols do not have an inherent relative order, but
    // since all properties of the exports namespace must be keyed by a string
    // and the string must correspond to a valid identifier, sorting these
    // properties works for this specific case.
    arrayForEach(arraySort(keys(exportsProps)), k =>
      defineProperty(exportsTarget, k, exportsProps[k]),
    );

    freeze(exportsTarget);
    activate();
  }

  let optFunctor;
  if (__syncModuleFunctor__ !== undefined) {
    optFunctor = __syncModuleFunctor__;
  } else {
    optFunctor = compartmentEvaluate(compartmentFields, functorSource, {
      globalObject: compartment.globalThis,
      transforms: __shimTransforms__,
      __moduleShimLexicals__: moduleLexicals,
    });
  }
  let didThrow = false;
  let thrownError;
  function execute() {
    if (optFunctor) {
      // uninitialized
      const functor = optFunctor;
      optFunctor = null;
      // initializing - call with `this` of `undefined`.
      try {
        functor(
          freeze({
            imports: freeze(imports),
            onceVar: freeze(onceVar),
            liveVar: freeze(liveVar),
            import: dynamicImport,
            importMeta,
          }),
        );
      } catch (e) {
        didThrow = true;
        thrownError = e;
      }
      // initialized
    }
    if (didThrow) {
      throw thrownError;
    }
  }

  return freeze({
    notifiers,
    exportsProxy,
    execute,
  });
};