ssb-db

A database of unforgeable append-only feeds, optimized for efficient replication for peer to peer protocols.

What does it do?

ssb-db provides tools for dealing with unforgeable append-only message feeds. You can create a feed, post messages to that feed, verify a feed created by someone else, stream messages to and from feeds, and more (see API).

"Unforgeable" means that only the owner of a feed can modify that feed, as enforced by digital signing (see Security properties). This property makes ssb-db useful for peer-to-peer applications. ssb-db also makes it easy to encrypt messages.

Example

In this example, we create a feed, post a signed message to it, then create a stream that reads from the feed.

/**
 * create an ssb-db instance and add a message to it.
 */

var pull = require('pull-stream')
var fs = require('fs')

// paths:
var pathToDB     = './db'
var pathToSecret = './ssb-identity'
try { fs.mkdirSync(pathToDB) } catch(e) {}

// ways to create keys:
//var keys = require('ssb-keys').generate()
//var keys = require('ssb-keys').loadSync(pathToSecret)
//var keys = require('ssb-keys').createSync(pathToSecret)
var keys = require('ssb-keys').loadOrCreateSync(pathToSecret)

// create the db instance.
//  - uses leveldb.
//  - can only open one instance at a time.

var ssb = require('ssb-db/create')(pathToDB)

// create a feed.
//  - this represents a write access / user.
//  - you must pass in keys.
//  (see options section)

var feed = ssb.createFeed(keys)

// publish a message.
//  - feed.add appends a message to your key's chain.
//  - the `type` attribute is required.

feed.add({ type: 'post', text: 'My First Post!' }, function (err, msg, hash) {
  // the message as it appears in the database:
  console.log(msg)

  // and its hash:
  console.log(hash)
})

// stream all messages for all keypairs.
pull(
  ssb.createFeedStream(),
  pull.collect(function (err, ary) {
    console.log(ary)
  })
)

// stream all messages for a particular keypair.
pull(
  ssb.createHistoryStream({id: feed.id}),
  pull.collect(function (err, ary) {
    console.log(ary)
  })
)

Concepts

Building upon ssb-db requires understanding a few concepts that it uses to ensure the unforgeability of message feeds.

Identities

An identity is simply a public/private key pair.

Even though there is no worldwide store of identities, it's infeasible for anyone to forge your identity. Identities are binary strings, so not particularly human-readable.

Feeds

A feed is an append-only sequence of messages. Each feed is associated 1:1 with an identity. The feed is identified by its public key. This works because public keys are unique.

Since feeds are append-only, replication is simple: request all messages in the feed that are newer than the latest message you know about.

Note that append-only really means append-only: you cannot delete an existing message. If you want to enable entities to be deleted or modified in your data model, that can be implemented in a layer on top of ssb-db using delta encoding.

Messages

Each message contains:

• A message object. This is the thing that the end user cares about. If there is no encryption, this is a {} object. If there is encryption, this is an encrypted string.
• A content-hash of the previous message. This prevents somebody with the private key from changing the feed history after publishing, as a newly-created message wouldn't match the "prev-hash" of later messages which were already replicated.
• The signing public key.
• A signature. This prevents malicious parties from writing fake messages to a stream.
• A sequence number. This prevents a malicious party from making a copy of the feed that omits or reorders messages.

Since each message contains a reference to the previous message, a feed must be replicated in order, starting with the first message. This is the only way that the feed can be verified. A feed can be viewed in any order after it's been replicated.

Object ids

The text inside a message can refer to three types of ssb-db entities: messages, feeds, and blobs (i.e. attachments). Messages and blobs are referred to by their hashes, but a feed is referred to by its signing public key. Thus, a message within a feed can refer to another feed, or to a particular point within a feed.

Object ids begin with a sigil @ % and & for a feedId, msgId
and blobId respectively.

Note that ssb-db does not include facilities for retrieving a blob given the hash.

Replication

It is possible to easily replicate data between two instances of ssb-db. First, they exchange maps of their newest data. Then, each one downloads all data newer than its newest data.

Scuttlebot is a tool that makes it easy to replicate multiple instances of ssb-db using a decentralized network.

Security properties

ssb-db maintains useful security properties even when it is connected to a malicious ssb-db database. This makes it ideal as a store for peer-to-peer applications.

Imagine that we want to read from a feed for which we know the identity, but we're connected to a malicious ssb-db instance. As long as the malicious database does not have the private key:

• The malicious database cannot create a new feed with the same identifier
• The malicious database cannot write new fake messages to the feed
• The malicious database cannot reorder the messages in the feed
• The malicious database cannot send us a new copy of the feed that omits messages from the middle
• The malicious database can refuse to send us the feed, or only send us the first N messages in the feed
• Messages may optionally be encrypted. See test/end-to-end.js.

API

ssb = require('ssb-db/create')(path)

Create an ssb-db database at the given path, returns an instance.

require('ssb-db')(db, opts)

Pass in a levelup instance (it must have sublevel installed), and an options object. The options object provides the crypto and encoding functions, that are not directly tied into how ssb-db works.

The following methods all apply to a ssb-db instance

SSBdb#createFeed (keys?)

Create a Feed object. A feed is a chain of messages signed by a single key (the identity of the feed). This handles the state needed to append valid messages to a feed. If keys are not provided, then a new key pair will be generated.

The following methods apply to the Feed type.

Feed#add (message, cb)

Adds a message of a given type to a feed. This is the recommended way to append messages. message is a javascript object. It must be a {} object with a type
property that is a string between 3 and 32 chars long.

If message has recps property which is an array of feed ids, then the message content will be encrypted using private-box to those recipients. Any invalid recipients will cause an error, instead of accidentially posting a message publically or without a recipient.

Feed#id

the id of the feed (which is the feed's public key)

Feed#keys

the key pair for this feed.

ssbDb#createFeedStream (opts) -> PullSource

Create a pull-stream
of all the feeds in the database, ordered by timestamps. All pull-level options are allowed (start, end, reverse, tail)

ssbDb#createLogStream({gt: ts, tail: boolean}) -> PullSource

create a stream of the messages that have been written to this instance in the order they arrived. This is mainly intended for building views. The objects in this stream will be of the form:

{
  key: Hash, value: Message, timestamp: timestamp
}

timestamp is generated by monotonic-timestamp

ssbDb#createHistoryStream ({id: feedId, seq: int?, live: bool?, limit: int?, keys: bool?, values: bool?}) -> PullSource

Create a stream of the history of id. If seq > 0, then only stream messages with sequence numbers greater than seq. if live is true, the stream will be a live mode

ssbDb#messagesByType ({type: string, live: bool?}) -> PullSource

retrieve messages with a given type. All messages must have a type, so this is a good way to select messages that an application might use. Returns a source pull-stream. This function takes all the options from pull-level#read
(gt, lt, gte, lte, limit, reverse, live)

ssbDb#links ({source: feedId?, dest: feedId|msgId|blobId?, rel: string?, meta: true?, keys: true?, values: false?, live:false?, reverse: false?}) -> PullSource

Get a stream of links from a feed to a blob/msg/feed id.

The objects in this stream will be of the form:

{ source: feedId, rel: String, dest: Id, key: MsgId, value: Object? }

• source (string, optional): feed id..
• dest (string, optional): An id or filter, specifying where the link should point to. To filter, just use the sigil of the type you want: @ for feeds, % for messages, and & for blobs.
• rel (string, optional): Filters the links by the relation string.

If opts.values is set (default: false) value will be the message the link occurs in. If opts.keys is set (default: true) key will be the message id. If opts.meta is unset (default: true) source, hash, rel will be left off.

Note: if source, and dest is provided, but not rel, ssb will have to scan all the links from source, and then filter by dest. your query will be more efficient if you also provide rel.

ssbDb#addMap (fn)

Add a map function to be applied to all messages on read. The fn function is should expect (msg, cb), and must eventually call cb(err, msg) to finish.

These modifications only change the value being read, but the underlying data is never modified. If multiple map functions are added, they are called serially and the msg output by one map function is passed as the input msg to the next.

Additional properties may only be added to msg.value.meta, and modifications may only be made after the original value is saved in msg.value.meta.original.

ssbDb.addMap(function (msg, cb) {
  if (!msg.value.meta) {
    msg.value.meta = {}
  }

  if (msg.value.timestamp % 3 === 0)
    msg.value.meta.fizz = true
  if (msg.timestamp % 5 === 0)
    msg.value.meta.buzz = true
  cb(null, msg)
})

const metaBackup = require('ssb-db/util').metaBackup

ssbDb.addMap(function (msg, cb) {
  // This could instead go in the first map function, but it's added as a second
  // function for demonstration purposes to show that `msg` is passed serially.
  if (msg.value.meta.fizz && msg.value.meta.buzz) {
    msg.meta = metaBackup(msg.value, 'content')

    msg.value.content = {
      type: 'post',
      text: 'fizzBuzz!'
    }
  }
  cb(null, msg)
})

Stability

Stable: Expect patches, possible features additions.

License

MIT