policy: support conditions for redirects

Author: bmeck

doc/api/policy.md

@@ -124,24 +124,25 @@ replaced.
 
 ```json
 {
-  "builtins": [],
   "resources": {
     "./app/checked.js": {
       "dependencies": {
         "fs": true,
-        "os": "./app/node_modules/alt-os"
+        "os": "./app/node_modules/alt-os",
+        "http": { "import": true }
       }
     }
   }
 }
 ```
 
-The dependencies are keyed by the requested string specifier and have values
-of either `true` or a string pointing to a module that will be resolved.
+The dependencies are keyed by the requested specifier string and have values
+of either `true`, `null`, a string pointing to a module that will be resolved,
+or a conditions object.
 
 The specifier string does not perform any searching and must match exactly
-what is provided to the `require()`. Therefore, multiple specifiers may be
-needed in the policy if `require()` uses multiple different strings to point
+what is provided to the `require()` or `import`. Therefore, multiple specifiers
+may be needed in the policy if it uses multiple different strings to point
 to the same module (such as excluding the extension).
 
 If the value of the redirection is `true` the default searching algorithms will
@@ -150,20 +151,31 @@ be used to find the module.
 If the value of the redirection is a string, it will be resolved relative to
 the manifest and then immediately be used without searching.
 
-Any specifier string that is `require()`ed and not listed in the dependencies
-will result in an error according to the policy.
+Any specifier string that is attempted to resolved and not listed in the
+dependencies will result in an error according to the policy.
 
 Redirection will not prevent access to APIs through means such as direct access
 to `require.cache` and/or through `module.constructor` which allow access to
-loading modules. Policy redirection only affect specifiers to `require()`.
-Other means such as to prevent undesired access to APIs through variables are
-necessary to lock down that path of loading modules.
+loading modules. Policy redirection only affect specifiers to `require()` and
+`import`. Other means such as to prevent undesired access to APIs through
+variables are necessary to lock down that path of loading modules.
 
 A boolean value of `true` for the dependencies map can be specified to allow a
 module to load any specifier without redirection. This can be useful for local
 development and may have some valid usage in production, but should be used
 only with care after auditing a module to ensure its behavior is valid.
 
+Similar to `"exports"` in `package.json` dependencies can also be specified to
+be objects containing conditions which branch how dependencies are loaded. In
+the above example `"http"` will be allowed when the `"import"` condition is
+part of loading it.
+
+A value of `null` for the resolved value will cause the resolution to fail.
+This can be used to ensure some kinds dynamic access are explicitly prevented.
+
+Unknown values for the resolved module location will cause failure, but are
+not guaranteed to be forwards compatible.
+
 #### Example: Patched dependency
 
 Redirected dependencies can provide attenuated or modified functionality as fits

lib/internal/errors.js

@@ -1215,7 +1215,8 @@ E('ERR_MANIFEST_ASSERT_INTEGRITY',
     return msg;
   }, Error);
 E('ERR_MANIFEST_DEPENDENCY_MISSING',
-  'Manifest resource %s does not list %s as a dependency specifier',
+  'Manifest resource %s does not list %s as a dependency specifier for ' +
+  'conditions: %s',
   Error);
 E('ERR_MANIFEST_INTEGRITY_MISMATCH',
   'Manifest resource %s has multiple entries but integrity lists do not match',

lib/internal/modules/cjs/helpers.js

@@ -1,9 +1,11 @@
 'use strict';
 
 const {
+  ArrayPrototypeJoin,
   ObjectDefineProperty,
   ObjectPrototypeHasOwnProperty,
   SafeMap,
+  SafeSet,
 } = primordials;
 const {
   ERR_MANIFEST_DEPENDENCY_MISSING,
@@ -16,10 +18,16 @@ const path = require('path');
 const { pathToFileURL, fileURLToPath } = require('internal/url');
 const { URL } = require('url');
 
+const { getOptionValue } = require('internal/options');
+const userConditions = getOptionValue('--conditions');
+
 let debug = require('internal/util/debuglog').debuglog('module', (fn) => {
   debug = fn;
 });
 
+// TODO: Use this set when resolving pkg#exports conditions in loader.js.
+const cjsConditions = new SafeSet(['require', 'node', ...userConditions]);
+
 function loadNativeModule(filename, request) {
   const mod = NativeModule.map.get(filename);
   if (mod) {
@@ -38,11 +46,12 @@ function makeRequireFunction(mod, redirects) {
 
   let require;
   if (redirects) {
-    const { resolve, reaction } = redirects;
     const id = mod.filename || mod.id;
-    require = function require(path) {
+    const conditions = cjsConditions;
+    const { resolve, reaction } = redirects;
+    require = function require(specifier) {
       let missing = true;
-      const destination = resolve(path);
+      const destination = resolve(specifier, conditions);
       if (destination === true) {
         missing = false;
       } else if (destination) {
@@ -66,9 +75,13 @@ function makeRequireFunction(mod, redirects) {
         }
       }
       if (missing) {
-        reaction(new ERR_MANIFEST_DEPENDENCY_MISSING(id, path));
+        reaction(new ERR_MANIFEST_DEPENDENCY_MISSING(
+          id,
+          specifier,
+          ArrayPrototypeJoin([...conditions], ', ')
+        ));
       }
-      return mod.require(path);
+      return mod.require(specifier);
     };
   } else {
     require = function require(path) {
@@ -168,6 +181,7 @@ function normalizeReferrerURL(referrer) {
 
 module.exports = {
   addBuiltinLibsToObject,
+  cjsConditions,
   loadNativeModule,
   makeRequireFunction,
   normalizeReferrerURL,

lib/internal/modules/cjs/loader.js

@@ -47,7 +47,6 @@ const {
   RegExpPrototypeTest,
   SafeMap,
   SafeWeakMap,
-  SafeSet,
   String,
   StringPrototypeIndexOf,
   StringPrototypeMatch,
@@ -76,6 +75,7 @@ const {
   makeRequireFunction,
   normalizeReferrerURL,
   stripBOM,
+  cjsConditions,
   loadNativeModule
 } = require('internal/modules/cjs/helpers');
 const { getOptionValue } = require('internal/options');
@@ -85,7 +85,6 @@ const manifest = getOptionValue('--experimental-policy') ?
   require('internal/process/policy').manifest :
   null;
 const { compileFunction } = internalBinding('contextify');
-const userConditions = getOptionValue('--conditions');
 
 // Whether any user-provided CJS modules had been loaded (executed).
 // Used for internal assertions.
@@ -1002,7 +1001,6 @@ Module._load = function(request, parent, isMain) {
   return module.exports;
 };
 
-const cjsConditions = new SafeSet(['require', 'node', ...userConditions]);
 Module._resolveFilename = function(request, parent, isMain, options) {
   if (NativeModule.canBeRequiredByUsers(request)) {
     return request;

lib/internal/modules/esm/resolve.js

@@ -31,6 +31,9 @@ const {
   Stats,
 } = require('fs');
 const { getOptionValue } = require('internal/options');
+const manifest = getOptionValue('--experimental-policy') ?
+  require('internal/process/policy').manifest :
+  null;
 const { sep, relative } = require('path');
 const preserveSymlinks = getOptionValue('--preserve-symlinks');
 const preserveSymlinksMain = getOptionValue('--preserve-symlinks-main');
@@ -42,6 +45,7 @@ const {
   ERR_INVALID_MODULE_SPECIFIER,
   ERR_INVALID_PACKAGE_CONFIG,
   ERR_INVALID_PACKAGE_TARGET,
+  ERR_MANIFEST_DEPENDENCY_MISSING,
   ERR_MODULE_NOT_FOUND,
   ERR_PACKAGE_IMPORT_NOT_DEFINED,
   ERR_PACKAGE_PATH_NOT_EXPORTED,
@@ -764,6 +768,27 @@ function resolveAsCommonJS(specifier, parentURL) {
 
 function defaultResolve(specifier, context = {}, defaultResolveUnused) {
   let { parentURL, conditions } = context;
+  if (manifest) {
+    const redirects = manifest.getRedirector(parentURL);
+    if (redirects) {
+      const { resolve, reaction } = redirects;
+      const destination = resolve(specifier, new SafeSet(conditions));
+      let missing = true;
+      if (destination === true) {
+        missing = false;
+      } else if (destination) {
+        const href = destination.href;
+        return { url: href };
+      }
+      if (missing) {
+        reaction(new ERR_MANIFEST_DEPENDENCY_MISSING(
+          parentURL,
+          specifier,
+          ArrayPrototypeJoin([...conditions], ', '))
+        );
+      }
+    }
+  }
   let parsed;
   try {
     parsed = new URL(specifier);

lib/internal/policy/manifest.js

@@ -7,11 +7,15 @@ const {
   ObjectCreate,
   ObjectEntries,
   ObjectFreeze,
+  ObjectKeys,
   ObjectSetPrototypeOf,
   RegExpPrototypeTest,
   SafeMap,
   uncurryThis,
 } = primordials;
+const {
+  compositeKey
+} = require('internal/util/compositekey');
 const {
   canBeRequiredByUsers
 } = require('internal/bootstrap/loaders').NativeModule;
@@ -70,13 +74,21 @@ class Manifest {
    */
   #integrities = new SafeMap();
   /**
-   * @type {Map<string, (specifier: string) => true | URL>}
+   * @type {
+      Map<
+        string,
+        (specifier: string, conditions: Set<string>) => true | null | URL
+      >
+    }
    *
    * Used to find where a dependency is located.
    *
    * This stores functions to lazily calculate locations as needed.
    * `true` is used to signify that the location is not specified
    * by the manifest and default resolution should be allowed.
+   *
+   * The functions return `null` to signify that a dependency is
+   * not found
    */
   #dependencies = new SafeMap();
   /**
@@ -158,36 +170,83 @@ class Manifest {
         dependencyMap = ObjectCreate(null);
       }
       if (typeof dependencyMap === 'object' && !ArrayIsArray(dependencyMap)) {
+        function searchDependencies(target, conditions) {
+          if (
+            target &&
+            typeof target === 'object' &&
+            !ArrayIsArray(target)
+          ) {
+            const keys = ObjectKeys(target);
+            for (let i = 0; i < keys.length; i++) {
+              const key = keys[i];
+              if (conditions.has(key)) {
+                const ret = searchDependencies(target[key], conditions);
+                if (ret != null) {
+                  return ret;
+                }
+              }
+            }
+          } else if (typeof target === 'string') {
+            return target;
+          } else if (target === true) {
+            return target;
+          } else {
+            throw new ERR_MANIFEST_INVALID_RESOURCE_FIELD(
+              resourceHREF,
+              'dependencies');
+          }
+          return null;
+        }
+        // This is used so we don't traverse this every time
+        // in theory we can delete parts of the dep map once this is populated
+        const localMappings = new SafeMap();
         /**
-         * @returns {true | URL}
+         * @returns {true | null | URL}
          */
-        const dependencyRedirectList = (toSpecifier) => {
-          if (toSpecifier in dependencyMap !== true) {
+        const dependencyRedirectList = (specifier, conditions) => {
+          const key = compositeKey([localMappings, specifier, ...conditions]);
+          if (localMappings.has(key)) {
+            return localMappings.get(key);
+          }
+          if (specifier in dependencyMap !== true) {
+            localMappings.set(key, null);
             return null;
           }
-          const to = dependencyMap[toSpecifier];
-          if (to === true) {
+          const target = searchDependencies(
+            dependencyMap[specifier],
+            conditions);
+          if (target === true) {
+            localMappings.set(key, true);
             return true;
           }
-          if (parsedURLs.has(to)) {
-            return parsedURLs.get(to);
-          } else if (canBeRequiredByUsers(to)) {
-            const href = `node:${to}`;
+          if (typeof target !== 'string') {
+            localMappings.set(key, null);
+            return null;
+          }
+          if (parsedURLs.has(target)) {
+            const parsed = parsedURLs.get(target);
+            localMappings.set(key, parsed);
+            return parsed;
+          } else if (canBeRequiredByUsers(target)) {
+            const href = `node:${target}`;
             const resolvedURL = new URL(href);
-            parsedURLs.set(to, resolvedURL);
+            parsedURLs.set(target, resolvedURL);
             parsedURLs.set(href, resolvedURL);
+            localMappings.set(key, resolvedURL);
             return resolvedURL;
-          } else if (RegExpPrototypeTest(kRelativeURLStringPattern, to)) {
-            const resolvedURL = new URL(to, manifestURL);
+          } else if (RegExpPrototypeTest(kRelativeURLStringPattern, target)) {
+            const resolvedURL = new URL(target, manifestURL);
             const href = resourceURL.href;
-            parsedURLs.set(to, resolvedURL);
+            parsedURLs.set(target, resolvedURL);
             parsedURLs.set(href, resolvedURL);
+            localMappings.set(key, resolvedURL);
             return resolvedURL;
           }
-          const resolvedURL = new URL(to);
-          const href = resourceURL.href;
-          parsedURLs.set(to, resolvedURL);
+          const resolvedURL = new URL(target);
+          const href = resolvedURL.href;
+          parsedURLs.set(target, resolvedURL);
           parsedURLs.set(href, resolvedURL);
+          localMappings.set(key, resolvedURL);
           return resolvedURL;
         };
         dependencies.set(resourceHREF, dependencyRedirectList);
@@ -208,7 +267,10 @@ class Manifest {
     const dependencies = this.#dependencies;
     if (dependencies.has(requester)) {
       return {
-        resolve: (to) => dependencies.get(requester)(`${to}`),
+        resolve: (specifier, conditions) => dependencies.get(requester)(
+          `${specifier}`,
+          conditions
+        ),
         reaction: this.#reaction
       };
     }