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Docs | Val Town

Permission errors

Some NPM and Deno modules will produce an error like this:

{
  "error": "Requires read access to <exec_path>, run again with the --allow-read flag"
}

Vals run in a sandbox with limited access: we use Deno’s permissions system to limit access to anything that could allow one val to read data from another, or otherwise compromise security.

NPM modules, on the other hand, often do unexpected and dangerous things, like downloading other code at runtime, accessing your environment variables, reading files from disk, and more. This unrestricted access is the root cause of many security issues for Node.js.

Allowed permissions

Vals have access to the following:

  • The network (--allow-net)
  • The environment, which in this case only means your secrets (--allow-env)

They don’t have access to:

  • The filesystem (--allow-read and --allow-write)
  • Dynamic libraries (--allow-ffi)
  • System information (--allow-sys)

Workarounds

Use esm.sh

If you’re having problems using an NPM module because of permission issues, you can often import the package from esm.sh instead of NPM to quickly resolve the issue. For example:

import garminConnect from "npm:garmin-connect";
import garminConnect from "https://esm.sh/garmin-connect";

esm.sh transpiles code in order to run cleanly on Deno.

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