ssb-db

secret-stack plugin which provides storing of valid secure-scuttlebutt messages in an append-only log.

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. Note: ssb-server includes the ssb-db dependency already, so the example here uses this as a plugin for secret-stack.

/**
 * create an ssb-db instance and add a message to it.
 */
var pull = require('pull-stream')

//create a secret-stack instance and add ssb-db, for persistence.
var createApp = require('secret-stack')({})
  .use(require('ssb-db'))


// create the db instance.
// Only one instance may be created at a time due to os locks on port and database files.

var app = createApp(require('ssb-config'))

//your public key, the default key of this instance.

app.id

//or, called remotely

app.whoami(function (err, data) {
  console.log(data.id) //your id
})

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

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

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

// collect all the messages into an array, calls back, and then ends
// https://github.com/pull-stream/pull-stream/blob/master/docs/sinks/collect.md
pull(
  app.createLogStream(),
  pull.collect(function (err, messagesArray) {
    console.log(messagesArray)
  })
)

// collect all messages for a particular keypair into an array, calls back, and then ends
// https://github.com/pull-stream/pull-stream/blob/master/docs/sinks/collect.md
pull(
  app.createHistoryStream({id: app.id}),
  pull.collect(function (err, messagesArray) {
    console.log(messagesArray)
  })
)

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.

ssb-server 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

require('ssb-db')

SecretStack.use(require('ssb-db')) => SecretStackApp

The design pattern of ssb-db is for it to act as a plugin within the SecretStack plugin framework. The main export provides the plugin, which extends the SecretStack app with this plugins functionality, and API. ssb-db adds persistence to a SecretStack setup. Without other plugins, this instance will not have replication or querying. Loading ssb-db directly is useful for testing, but it's recommended to instead start from a plugin bundle like ssb-server

Because of legacy reasons, all the ssb-db methods are mounted on the top level object, so it's app.get instead of app.db.get as it would be with all the other ssb-* plugins.

In the API docs below, we'll just call it db

db.get: async

db.get(id | seq | opts, cb) // cb(error, message)

Get a message by its hash-id.

If id is a message id, the message is returned.
If seq is provided, the message at that offset in the underlying flumelog is returned.
If opts is passed, the message id is taken from either opts.id or opts.key.
If opts.private = true the message will be decrypted if possible.
If opts.meta = true is set, or seq is used, the message will be in {key, value: msg, timestamp} format. Otherwise the raw message (without key and timestamp) are returned. This is for backwards compatibility reasons.

Given that most other apis (such as createLogStream) by default return {key, value, timestamp} it's recommended to use db.get({id: key, meta: true}, cb)

Note that the cb callback is called with 3 arguments: cb(err, msg, offset), where the 3rd argument is the offset position of that message in the log (flumelog-offset).

db.add: async

db.add(msg, cb) // cb(error, data)

Append a raw message to the local log. msg must be a valid, signed message. ssb-validate is used internally to validate messages.

db.publish: async

db.publish(content, cb) // cb(error, data)

Create a valid message with content with the default identity and append it to the local log. ssb-validate is used to construct a valid message.

This is the recommended method for publishing new messages, as it handles the tasks of correctly setting the message's timestamp, sequence number, previous-hash, and signature.

content (object): The content of the message.
- .type (string): The object's type.

db.del: async

⚠ This could break your feed. Please don't run this unless you understand it.

Delete a message by its message key or a whole feed by its key. This only deletes the message from your local database, not the network, and could have unintended consequences if you try to delete a single message in the middle of a feed.

The intended use-case is to delete all messages from a given feed or deleting a single message from the tip of your feed if you're completely confident that the message hasn't left your device.

//Delete message
db.del(msg.key, (err, key) => {
  if (err) throw err
})

//Delete all author messages
db.del(msg.value.author, (err, key) => {
  if (err) throw err
})

db.whoami: async

db.whoami(cb) // cb(error, {"id": FeedID })

Get information about the current ssb-server user.

db.createLogStream: source

db.createLogStream({ live, old, gt, gte, lt, lte, reverse, keys, values, limit, fillCache, keyEncoding, 
valueEncoding, raw }): 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.

live (boolean) Keep the stream open and emit new messages as they are received. Defaults to false.
old (boolean) If false the output will not include the old data. If live and old are both false, an error is thrown. Defaults to true.
gt (greater than), gte (greater than or equal) (timestamp) Define the lower bound of the range to be streamed. Only records where the key is greater than (or equal to) this option will be included in the range. When reverse=true the order will be reversed, but the records streamed will be the same.
lt (less than), lte (less than or equal) (timestamp) Define the higher bound of the range to be streamed. Only key/value pairs where the key is less than (or equal to) this option will be included in the range. When reverse=true the order will be reversed, but the records streamed will be the same.
reverse (boolean) Set true and the stream output will be reversed. Beware that due to the way LevelDB works, a reverse seek will be slower than a forward seek. Defaults to false.
keys (boolean) Whether the data event should contain keys. If set to true and values set to false then data events will simply be keys, rather than objects with a key property. Defaults to true.
values (boolean) Whether the data event should contain values. If set to true and keys set to false then data events will simply be values, rather than objects with a value property. Defaults to true.
limit (number) Limit the number of results collected by this stream. This number represents a maximum number of results and may not be reached if you get to the end of the data first. A value of -1 means there is no limit. When reverse=true the highest keys will be returned instead of the lowest keys. Defaults to false.
keyEncoding / valueEncoding (string) The encoding applied to each read piece of data.
raw (boolean) Provides access to the raw flumedb log. Defaults to false.

The objects in this stream will be of the form:

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

timestamp * is the time which the message was received. It is generated by monotonic-timestamp. The range queries (gt, gte, lt, lte) filter against this receive timestap.

If raw option is provided, then instead createRawLogStream is called, messages are returned in the form:

{
  "seq": offset,
  "value": {
    "key": Hash,
    "value": Message,
    "timestamp": timestamp
  }
}

All options supported by flumelog-offset are supported.

db.createHistoryStream: source

db.createHistoryStream(id, seq, live) -> PullSource
//or
db.createHistoryStream({ id, seq, live, limit, keys, values, reverse }) -> 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

createHistoryStream and createUserStream serve the same purpose.

createHistoryStream exists as a separate call because it provides fewer range parameters, which makes it safer for RPC between untrusted peers.

Note: since createHistoryStream is provided over the network to anonymous peers, not all options are supported. createHistoryStream does not decrypt private messages.

id (FeedID) The id of the feed to fetch.
seq (number) If seq > 0, then only stream messages with sequence numbers greater than or equal to seq. Defaults to 0.
live (boolean): Keep the stream open and emit new messages as they are received. Defaults to false
keys (boolean): Whether the data event should contain keys. If set to true and values set to false then data events will simply be keys, rather than objects with a key property. Defaults to true
values (boolean) Whether the data event should contain values. If set to true and keys set to false then data events will simply be values, rather than objects with a value property. Defaults to true.
limit (number) Limit the number of results collected by this stream. This number represents a maximum number of results and may not be reached if you get to the end of the data first. A value of -1 means there is no limit. When reverse=true the highest keys will be returned instead of the lowest keys. Defaults to false.
reverse (boolean) Set true and the stream output will be reversed. Beware that due to the way LevelDB works, a reverse seek will be slower than a forward seek. Defaults to false.

db.messagesByType: source

db.messagesByType({type: string, live,old,reverse: bool?, gt,gte,lt,lte: timestamp, limit: number }) -> PullSource

Retrieve messages with a given type, ordered by receive-time. All messages must have a type, so this is a good way to select messages that an application might use. This function returns a source pull-stream.

As with createLogStream messagesByType takes all the options from pull-level#read (gt, lt, gte, lte, limit, reverse, live, old)

db.createFeedStream: source

db.createFeedStream({ live, old, gt, gte, lt, lte, reverse, keys, value,, limit, fillCache, keyEncoding, 
valueEncoding, raw }))

Like createLogStream, but messages are in order of the claimed time, instead of the received time.

This may sound like a much better idea, but has surprising effects with live messages (you may receive a old message in real time) but for old messages, it makes sense.

The range queries (gt, gte, lt, lte) filter against this claimed timestap.

As with createLogStream createFeedStream takes all the options from pull-level#read (gt, lt, gte, lte, limit, reverse, live, old)

db.createUserStream: source

db.createUserStream({id: feed_id, lt, lte ,gt ,gte: sequence, reverse, old, live, raw: boolean, limit: number, private: boolean})

createUserStream is like createHistoryStream, except all options are supported. Local access is allowed, but not remote anonymous access. createUserStream can decrypt private messages if you pass the option { private: true }.

db.links: source

db.links({ source, dest: feedId|msgId|blobId, rel, meta, keys, values, live, reverse }) -> 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) An id or filter, specifying where the link should originate from. To filter, just use the sigil of the type you want: @ for feeds, % for messages, and & for blobs. Optional.
dest (string) 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. Optional.
rel (string) Filters the links by the relation string. Optional.
live (boolean): Keep the stream open and emit new messages as they are received. Defaults to `false.
values (boolean) Whether the data event should contain values. If set to true and keys set to false then data events will simply be values, rather than objects with a value property. Defaults to false.
keys (boolean) Whether the data event should contain keys. If set to true and values set to false then data events will simply be keys, rather than objects with a key property. Defaults to true.
reverse (boolean): Set true and the stream output will be reversed. Beware that due to the way LevelDB works, a reverse seek will be slower than a forward seek. Defaults to false.
meta If is unset source, hash, rel will be left off. Defaults to true.

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.

db.addMap: sync

db.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.

db.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

db.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)
})

db._flumeUse: view

db._flumeUse(name, flumeview) => View

Add a flumeview to the current instance. This method was intended to be a temporary solution, but is now used by many plugins, which is why it starts with _.

See creating a secret-stack plugin for more details.

db.getAtSequence: async

db.getAtSequence([id, seq], cb) //cb(err, msg)

Get a message for a given feed id with given sequence. Calls back a message or an error, takes a two element array with a feed id as the first element, and sequence as second element.

Needed for ssb-ebt replication

db.getVectorClock: async

db.getVectorClock(cb) //cb(error, clock)

Load a map of id to latest sequence ({<id>: <seq>,...}) for every feed in the database.

Needed for ssb-ebt replication

db.progress: sync

db.progress()

Return the current status of various parts of the scuttlebut system that indicate progress. This api is hooked by a number of plugins, but ssb-db adds an indexes section (which represents how fully built the indexes are).

The output might look like:

{
  "indexes": {
    "start": 607551054,
    "current": 607551054,
    "target": 607551054
  }
}

Progress is represented linearly from start to target. Once current is equal to target the progress is complete. start shows how far it's come. The numbers could be anything, but start <= current <= target if all three numbers are equal that should be considered 100%

db.status: sync

db.status()

Returns metadata about the status of various ssb plugins. ssb-db adds an sync section, that shows where each index is up to. The purpose is to provide an overview of how ssb is working.

Output might took like this:

{
  "sync": {
    "since": 607560288,
    "plugins": {
      "last": 607560288,
      "keys": 607560288,
      "clock": 607560288,
      "time": 607560288,
      "feed": 607560288,
      "contacts2": 607560288,
      "query": 607560288,
      ...
    },
    "sync": true
  }
}

sync.since is where the main log is up to, and since.plugins.<name> is where each plugin's indexes are up to.

db.version: sync

db.version()

Return the version of ssb-db. currently, this returns only the ssb-db version and not the ssb-server version, or the version of any other plugins. We should fix this soon

db.queue: async

db.queue(msg, cb) //cb(error, msg)

Add a message to be validated and written, but don't worry about actually writing it. The callback is called when the database is ready for more writes to be queued. Usually that means it's called back immediately. This method is not exposed over RPC.

db.flush: async

db.flush(cb) //cb()

Callback when all queued writes are actually definitely written to the disk.

db.getFeedState: async

db.getFeedState(feedId, (err, state))

Calls back with state, { id, sequence } - the most recent message ID and sequence number according to SSB-Validate:

NOTE

this may contain messages that have been queued and not yet persisted to the database
- this is required for e.g. boxers which depend on knowing previous message state
this is the current locally known state of the feed, it is possible if it's a foreign feed that the state has progressed beyond whay you know but you haven't got a copy yet, so use this carefully.
"no known state" is represented by { id: null, sequence: 0 }

db.post: Observable

db.post(fn({key, value: msg, timestamp})) => Ovb

Observable that calls fn whenever a message is appended (with that message). This method is not exposed over RPC.

db.since: Observable

db.since(fn(seq)) => Obv

An observable of the current log sequence. This is always a positive integer that usually increases, except in the exceptional circumstance that the log is deleted or corrupted.

db.addBoxer: sync

db.addBoxer({ value: boxer, init: initUnboxer })

Add a boxer, which will be added to the list of boxers which will try to automatically box (encrypt) the message content if the appropriate content.recps is provided.

Where:

boxer (msg.value.content, feedState) => ciphertext which is expected to either:
- successfully box the content (based on content.recps), returning a ciphertext String
- not know how to box this content (because recps are outside it's understanding), and undefined (or null)
- break (because it should know how to handle recps, but can't), and so throw an Error
- The feedState object contains id and sequence properties that describe the most recent message ID and sequence number for the feed. This is the same data exposed by db.getFeedState().
initUnboxer (done) => null (optional)
- is a functional which allows you set up your unboxer
- you're expected to call done() once all your initialisation is complete

db.addUnboxer: sync

db.addUnboxer({ key: unboxKey, value: unboxValue, init: initBoxer })

Add an unboxer object, any encrypted message is passed to the unboxer object to test if it can be unboxed (decrypted)

Where:

unboxKey(msg.value.content, msg.value) => readKey
- Is a function which tries to extract the message key from the encrypted content (ciphertext).
- Is expected to return readKey which is the read capability for the message
unboxValue(msg.value.content, msg.value, readKey) => plainContent
- Is a function which takes a readKey and uses it to try to extract the plainContent from the `ciphertext
initBoxer (done) => null (optional)
- is a functional which allows you set up your boxer
- you're expected to call done() once all your initialisation is complete

db.box(content, recps, cb)

attempt to encrypt some content to recps (an Array of keys/ identifiers). callback has signature cb(err, ciphertext)

db.unbox: sync

db.unbox(data, key)

Attempt to decrypt data using key. Key is a symmetric key, that is passed to the unboxer objects.

db.rebuild: async

db.rebuild(cb)

Rebuilds the indexes. This takes a while to run and using SSB features before it is completed may lead to confusing experiences as the indexes will be out of sync.

db.Deprecated apis

db.getLatest: async

db.getLatest(feed, cb) //cb(err, {key, value: msg})

Get the latest message for the given feed, with {key, value: msg} style. Maybe used by some front ends, and by ssb-feed.

db.latestSequene: async

db.latestSequence(feed, cb) //cb(err, sequence)

Call back the sequence number of the latest message for the given feed.

db.latest: source

db.latest() => PullSource

Returns a stream of {author, sequence, ts} tuples. ts is the time claimed by the author, not the received time.

db.createWriteStream: source

db.createWriteStream() => PullSink`

Create a pull-stream sink that expects a stream of messages and calls db.add on each item, appending every valid message to the log.

db.createFeed: sync

db.createFeed(keys?)

db.createSequenceStream() => PullSource

Create a pull-stream source that provides the latest sequence number from the database. Each time a message is appended the sequence number should increase and a new event should be sent through the stream.

Note: In the future this stream may be debounced. The number of events passed through this stream may be less than the number of messages appended.

db.createFeed(keys?) => Feed (deprecated)

Use ssb-identities instead.

Create and return 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.

May only be called locally, not from a ssb-client connection.

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.

Stability

Stable Expect patches, possible features additions.

License

MIT

ssbc/ssb-db

ssbc

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