FS Plugin

Native filesystem plugin for justjavac/webview applications.

It exposes a handle-based API under window.MoonBitPlugins.fs and is intended to be installed through Webview::install_plugin(...).

This is a reusable MoonBit module, so applications can add it as a dependency and install it without wiring command bindings manually.

Install

import {
  "plugins/fs",
  "justjavac/webview",
}

fn main {
  let webview = @webview.Webview::new(debug=1)
  webview.install_plugin(@fs.plugin())
  webview.run()
}

JavaScript API

All fs commands resolve to CommandResponse:

const response = await window.MoonBitPlugins.fs.open({
  path: "demo.txt",
  mode: "w+b",
});

if (response.status === "ok") {
  console.log(response.payload);
} else {
  console.error(response.error);
}

If you want the native absolute path before opening a file, resolve it first:

const resolved = await window.MoonBitPlugins.fs.resolvePath({
  path: "demo.txt",
});

Commands

• fs.open({ path, mode }) Returns { handle }.
• fs.read({ handle, size }) Returns { content, bytes_read, eof }.
• fs.write({ handle, content }) Returns { bytes_written }.
• fs.seek({ handle, offset, whence }) whence is "set", "current", or "end".
• fs.fstat({ handle }) Returns { path, size, position, eof, exists, is_file, is_dir }.
• fs.flush({ handle }) Flushes buffered writes.
• fs.close({ handle }) Closes the open handle.
• fs.exists({ path }) Returns { exists }.
• fs.resolvePath({ path }) Returns { path } with the native absolute path for the given input.
• fs.readDir({ path }) Returns { entries }.
• fs.removeFile({ path }) Returns { removed }.

Events

The plugin emits an activity event after successful operations:

window.MoonBitPlugins.fs["@@onEvent"]("activity", (event) => {
  console.log(event);
});

Event payload shape:

{
  operation: "open" | "read" | "write" | "seek" | "fstat" | "flush" | "close" | "readDir" | "removeFile",
  path: string | null,
  handle: number | null,
  bytes: number | null
}

Notes

• This plugin currently targets the native backend.
• This plugin exposes direct host filesystem access. Only use it with trusted, local HTML/JavaScript content; do not install it in webviews that navigate to untrusted or remote pages.
• Use relative paths like demo.txt for portable examples across macOS, Linux, and Windows.
• Resolve relative paths with fs.resolvePath({ path }) when the UI should display the actual absolute location chosen by the native runtime.
• open stores the resolved absolute path for each handle, so fstat({ handle }) reports an absolute path.
• read and write use UTF-8 text payloads.
• fstat is handle-based; if you also want path-based metadata, add a separate stat command.