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Sharing Files with Hyperdrive

This walkthrough will guide you through using Hyperdrive either as a standalone module or using Hyperspace. We recommend that you first read the Getting Started guides for the approach you intend to take.

You might also want to read the Hypercore walkthrough, as Hyperdrive is built on top of Hypercores. In fact, it uses two: one for storing the file metadata and another for storing the file content.

Introduction

Hyperdrives are file archives which mimic the posix interface. The include a number of useful features:

  • Sparse Downloading: By default, readers only download the portions of files they need, on demand. You can stream media from friends without jumping through hoops! Seeking is snappy and there's no buffering.
  • Fast Lookups: File metadata is stored in a distributed trie structure, meaning files can be located with minimal network lookups.
  • Version Controlled: Files are versioned by default, making it easy to see historical changes and prevent data loss.
  • Version Tagging: You can assign string names to Hyperdrive versions and store these within the drive, making it straightforward to switch between semantically-meaningful versions.

As with Hypercores, a Hyperdrive can only have a single writer on a single machine; the creator of the Hyperdrive is the only person who can modify to it, because they're the only one with the private key. That said, the writer can replicate to many readers, in a manner similar to BitTorrent.

In this walkthrough, we'll create hyperdrives using standalone modules and Hyperspace (step 1). We'll then demonstrate the basic APIs (step 2) and then learn about versioning (step 3).

Walkthrough

If you want to follow along with the code, setup the walkthrough repo:

git clone https://github.com/hypercore-protocol/walkthroughs.git
cd walkthroughs/hyperdrive
npm install

Step 1a: Using standalone modules

To create or load a hyperdrive as a standalone module, you follow this simple pattern:

const Hyperdrive = require('hyperdrive')
const drive = new Hyperdrive('./storage-path') // get or create drive at given path

If a drive exists at the path you provide, it will be loaded. If no drive exists, one will be created.

You can load a specific drive within your storage by supplying a key. This will only load the drive, so if no data exists locally yet then it will instantiate as an empty read-only drive waiting to pull data from the network:

const drive = new Hyperdrive('./storage-path', Buffer.from(key, 'hex')) // load

You can also force creation of a new drive by passing null for the key:

const drive = new Hyperdrive('./storage-path', null) // create new

You can read details such as the key or writability of a drive after 'ready' has been emitted:

drive.ready(err => {
if (err) throw err

console.log(drive.key) // the drive's public key, used to identify it
console.log(drive.discoveryKey) // the drive's discovery key for the DHT
console.log(drive.writable) // do we possess the private key of this drive?
console.log(drive.version) // what is the version-number of this drive?
console.log(drive.peers) // list of the peers currently replicating this drive
})

// if you prefer promises you can use:
await drive.promises.ready()

If you want to load a drive in-memory, you can use the random-access-memory (RAM) interface. The walkthrough code uses RAM to avoid writing to your device.

const ram = require('random-access-memory')
const drive1 = new Hyperdrive(ram, null) // create
const drive2 = new Hyperdrive(ram, Buffer.from(key, 'hex')) // load

Run this step (full code):

node step-1a.js

Step 1b: Using Hyperspace

Creating and loading hyperdrives using Hyperspace is not much different from using standalone modules. We'll assume you've created a Hyperspace client interface (see Getting Started with Hyperspace).

Rather than passing a path into hyperdrive(), you pass a "corestore" instance.

const drive1 = new Hyperdrive(client.corestore(), null) // create
const drive2 = new Hyperdrive(client.corestore(), Buffer.from(key, 'hex')) // load

The rest works the same as before.

If you want to load a drive in-memory and use hyperspace, you can use the hyperspace "simulator." The walkthrough code uses the simulator to avoid writing to your device.

const createHyperspaceSimulator = require('hyperspace/simulator')
const { client, cleanup } = await createHyperspaceSimulator()

const drive1 = new Hyperdrive(client.corestore(), null) // create
const drive2 = new Hyperdrive(client.corestore(), Buffer.from(key, 'hex')) // load

await cleanup() // shut down the simulator

Run this step (full code):

node step-1b.js

Step 2: Reading and writing files

Many of the APIs for reading and writing files mimic the NodeJS "fs" API. This should hopefully make this code look familiar. Hyperdrive's default interface is callback based, but a promises API exists under .promises so we'll use that.

Here are a number of common methods:

await drive.promises.writeFile('/hello.txt', 'World')

const st = await drive.promises.stat('/hello.txt')
console.log(st.isDirectory()) // => false
console.log(st.isFile()) // => true
console.log(st.size) // => 5
console.log(st.blocks) // 1 (the number of blocks in the content hypercore)

await drive.promises.readFile('/hello.txt', 'utf8') // => 'World'
await drive.promises.readdir('/') // => ['hello.txt']
await drive.promises.readdir('/', {recursive: true, includeStats: true})
// => [{name: 'hello.txt', stat: Stat(...)}]

await drive.promises.mkdir('/dir')
await drive.promises.rmdir('/dir')

// copy a file using read/write streams
drive.createReadStream('/hello.txt').pipe(drive.createWriteStream('/copy.txt'))

await drive.promises.unlink('/copy.txt') // delete the copy

Run this step (full code):

node step-2.js

Downloading files

Files will be downloaded and cached automatically when they're read via readFile or createReadStream. If you want to pre-download a set of files, you can use the download function.

For instance, this will download all of the files in a subdirectory:

await drive.promises.download('/subdir')

Step 3: Versioning and version tags

All drives have a .version number which increments each time a change is made. You can "checkout" previous versions of a drive to read the state at that time, if it's available.

// see the files after the first write
await drive.checkout(1).promises.readdir('/')

You can diff between two versions to quickly see what has been modified:

// create an example drive
const ram = require('random-access-memory')
const drive = new Hyperdrive(ram, null)

// write a file and capture a checkout at this time
await drive.promises.writeFile('/hello.txt', 'world')
const frozen = drive.checkout(drive.version)

// now delete the file
await drive.promises.unlink('/hello.txt')

// output the difference
for await (let change of drive.createDiffStream(frozen)) {
console.log(change) // => { type: 'del', name: 'hello.txt', previous: { seq: 1 } }
}

The .version value is just a "sequence number" and not very helpful to look at, so hyperdrive has "version tags" which allow you to label specific versions under human-readable strings. Here's how they work:

// tag the current version as "tag1"
await drive.promises.createTag('tag1', drive.version)

// write a new file
await drive.promises.writeFile('/new.txt', 'This is new')

// fetch the tagged version's seq number
const tag1Version = await drive.promises.getTaggedVersion('tag1')
console.log(tag1Version) // => 3

// output the diff
for await (let change of drive.createDiffStream(tag1Version)) {
console.log(change) /* => {
type: 'put',
name: 'new.txt',
seq: 4,
value: Stat { ... }
}*/

}

Run this step (full code):

node step-3.js

Next steps

Learn more at the Hyperdrive module page.