logoot-crdt

Replicate text or sequences over networks without conflicts.

Allows an unlimited number of authors to seamlessly collaborate on text. Has much better memory performance than woot-crdt.

Uses an optimized version of the Logoot CRDT algorithm: https://hal.inria.fr/inria-00432368/document

Also adds some improvements:

• An execution readiness check for deletions.
• LSEQ base doubling to reduce identifier integer size.
• A hybrid of the LSEQ random and boundary allocation strategys that should work for most editing behaviours.
• Support for a 2-step initial state transfer.
• Implemented as a tree for fast character position lookups.

TODO:

• Implement the Split optimization.
• Implement some way of preventing Logoot's interleaving anomaly.
• Performance benchmarks between different strategys.

example

var l1 = new Logoot('site1')
var l2 = new Logoot('site1')

// send sync messages between peers
l1.on('operation', (op) => {
  // send through your network (just need at-least-once, in-order delivery)
  l2.receive(op)
})
l2.on('operation', (op) => {
  l1.receive(op)
})

// make concurrent changes
l1.insert('abc', 0)
l2.insert('123', 0)

// the values eventually converge!
l1.value() // 'abc123'
l2.value() // 'abc123'

install

<script src="dist/logoot.js>"></script>

or

npm install --save logoot-crdt

api

var doc = new Logoot(site, [state], [bias])

Create a new synchronized sequence.

• site is a globally unique identifer.
• state allows you to initialize from an existing sequence state.
• bias is the bias for the probability distribution used to allocate identifiers. It defaults to 15, which is a good value for most left-to-right editing usecases. If your sequence is randomly edited, use 1.

doc.insert(value, index)

Insert a new string.

• value is the string value to insert.
• index is the position to insert.

doc.delete(index, [length])

Delete characters.

• index starting position of deletion.
• length number of characters to delete (default is 1).

doc.replaceRange(value, index, length)

Replace a range of elements with a new string.

• value is the string value to insert.
• index is the position to insert/delete.
• length number of characters to delete before inserting (default is 0).

doc.setValue(value)

Replaces all text with the given value.

• value is the string value to set the text to.

doc.getState()

Returns the current state of the CRDT. Can be passed into the constructor of another sequence to transfer state or into setState().

doc.setState(state)

Sets the current state of the CRDT. Equivalent to constructing a new instance with the given state.

Changing the state is unsafe; edits may have been made while you are transfering state that will need to be integrated. The best way to handle this is a two-step sync:

var state = l1.getState()
var missedOperations = []
network.on('operation', (op) => {
  l1.receive(op)
  missedOperations.push(op) // save this to send to l2 later
})

// send state to l2 (l2 is not receiving any operations until now)
l2.setState(state)
network.on('operation', op => { // l2 can now receive operations
  l2.receive(op)
})

// then send all the operations l2 missed during sync (don't worry about duplicates)
missedOperations.forEach(op => l2.receive(op))

// both peers are now safely synced

doc.on('operation', (op) => {})

This event fires when an operation object needs to be sent to all other synchronized sequences.

doc.receive(op)

Receive an operation object from another sequence.

doc.value()

Get the full string content of the sequence. Useful for initializing the view.

doc.on('insert', (event) => {})

This event fires when a remote insertion has been integrated. Useful for updating the view. Event object looks like:

{
  value: 'a', // The character inserted
  index: 0  // The index in the sequence
}

doc.on('delete', (event) => {})

This event fires when a remote insertion has been integrated. Useful for updating the view. Event object looks like:

{
  value: 'a', // The character deleted
  index: 0  // The index in the sequence where the element was
}

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