dependency redirection

An application may need to ship patched versions of modules or to prevent modules from allowing all modules access to all other modules. Redirection can be used by intercepting attempts to load the modules wishing to be replaced.

{
  "resources": {
    "./app/checked.js": {
      "dependencies": {
        "fs": true,
        "os": "./app/node_modules/alt-os",
        "http": { "import": true }
      }
    }
  }
}

The dependencies are keyed by the requested specifier string and have values of either true, null, a string pointing to a module to be resolved, or a conditions object.

The specifier string does not perform any searching and must match exactly 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 are used to find the module.

If the value of the redirection is a string, it is resolved relative to the manifest and then immediately used without searching.

Any specifier string for which resolution is attempted and that is not listed in the dependencies results in an error according to the policy.

Redirection does not prevent access to APIs through means such as direct access to require.cache or through module.constructor which allow access to loading modules. Policy redirection only affects 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 preceding example, "http" is allowed when the "import" condition is part of loading it.

A value of null for the resolved value causes the resolution to fail. This can be used to ensure some kinds of dynamic access are explicitly prevented.

Unknown values for the resolved module location cause failures but are not guaranteed to be forward compatible.