Filesystem capability

This example lets a renderer request host file operations through the filesystem extension. The backend grants a specific directory and operation scope; the page exercises that grant through the command bridge.

18_extension_fs · Source files: main.mbt, fs.html

Behavior

The page exposes read, write and directory operations. The native entry registers the fs capability with a PermissionRoot and an operation allowlist.

async fn main {
  @proton.html("18 extension fs", resource, width=960, height=720, debug=true)
  ..capability(
    @fs.capability([
      @fs.PermissionRoot(".", [
        "read_file", "write_file", "exists", "kind", "size", "readdir", "mkdir",
        "remove", "rmdir", "rename", "realpath",
      ]),
    ]),
  )
  ..identifier("dev.proton.18-extension-fs")
  .run_or_abort()
}

Implementation

The backend installs the filesystem extension and chooses both its root and allowed operations. The renderer supplies a path and operation, but cannot grant itself a wider root. A missing file and an unauthorized operation are separate failure cases.

This example grants write/delete access for demonstration. In an application, narrow the list to the required operations and use a deliberate data directory. The page's HTML and JavaScript demonstrate the raw extension bridge; MoonBit frontends can use typed descriptors.

Run

After completing source checkout and runtime setup, run from the repository root:

moon -C examples run 18_extension_fs --target native

Limits and interpretation

The example grants write and deletion operations under its working directory. Use a disposable directory for experiments; production apps should grant only their required paths and operations.