index.md

casfs

casfs is a Content Addressable Storage (CAS) abstraction over a file system. It has no folders nor files. Instead, it has blobs which are identified by their content.

Essentially, it provides two main operations: put and get. The put operation takes a blob and stores it in the underlying file system and returns the blob's hash digest. The get operation takes a hash and returns the blob, which matches the hash digest, if it exists.

Usage

casfs on top of Node.js fs module

casfs builds on top of crudfs, and crudfs—in turn—builds on top of File System Access API.

import * as fs from 'fs';
import { nodeToFsa } from 'memfs/lib/node-to-fsa';
import { FsaCrud } from 'memfs/lib/fsa-to-crud';

const fsa = nodeToFsa(fs, '/path/to/folder', {mode: 'readwrite'});
const crud = new FsaCrud(fsa);
const cas = new CrudCas(crud, {hash});

The hash is a function which computes a hash digest string from a Uint8Array blob. Here is how one could look like:

import { createHash } from 'crypto';

const hash = async (blob: Uint8Array): Promise<string> => {
  const shasum = createHash('sha1');
  shasum.update(blob);
  return shasum.digest('hex');
};

Now that you have a cas instance, you can use it to put and get blobs.

const blob = new Uint8Array([1, 2, 3]);

const hash = await cas.put(blob);
console.log(hash); // 9dc58b6d4e8eefb5a3c3e0c9f4a1a0b1b2b3b4b5

const blob2 = await cas.get(hash);

You can also delete blobs:

await cas.del(hash);

And retrieve information about blobs:

const info = await cas.info(hash);