vfs.registerProvider

vfs.registerProvider(entry): void

Registers a provider that --vfs-mount can select for a source it recognizes, so a file format Node.js has no built-in provider for can still be mounted.

A source is claimed by the first provider whose canHandle() returns true. Registered providers are consulted before the built-in ones, newest registration first, and are offered directories as well as files, so a registered provider can back, wrap, or vet any source. If none claims the source, the built-in providers handle it: a directory with RealFSProvider, and a file whose bytes are a ZIP archive with ZipProvider.

Providers must be registered before the mounts are created. Register from a module preloaded with --require or --import:

// provider.js, preloaded with --require
const fs = require('node:fs');
const vfs = require('node:vfs');

const MAGIC = Buffer.from('CUSTOMFMT');

vfs.registerProvider({
  name: 'customfmt',
  canHandle(path, stats) {
    if (!stats.isFile()) return false;
    const head = Buffer.alloc(MAGIC.length);
    const fd = fs.openSync(path, 'r');
    try {
      fs.readSync(fd, head, 0, MAGIC.length, 0);
    } finally {
      fs.closeSync(fd);
    }
    return head.equals(MAGIC);
  },
  create(path) {
    return new MyCustomProvider(path);
  },
});

$ node --experimental-vfs --require ./provider.js \
       --vfs-load archive.customfmt