Synchronized Network Accounting Protocol (SNAP)

NPM package: snap-checker

An implementation of the Synchronized Network Accounting Protocol (SNAP).

Usage: see example

The most basic unit is the Transaction:

type Transaction = {
  amount: number;
  condition?: string; // 32-byte hex sha256
  expiresAt?: Date;
};

Transactions go through state transitions:

type StateTransition = {
  transId: number;
  newState: SnapTransactionState;
  amount?: number;
  condition?: string;
  preimage?: string;
  expiresAt?: Date;
};

Valid combinations:

• Proposer -> Decider: transId, newState=Proposing, amount, unit.

• Proposer -> Decider: transId, newState=Proposing, amount, unit, condition.

• Proposer -> Decider: transId, newState=Proposing, amount, unit, expiresAt.

• Proposer -> Decider: transId, newState=Proposing, amount, unit, condition, expiresAt.

• Proposer <- Decider: transId, newState=Proposed.

• Proposer <- Decider: transId, newState=Accepting (if the Propose did not have a condition).

• Proposer <- Decider: transId, newState=Accepting, preimage (if the Propose did have a condition).

• Proposer -> Decider: transId, newState=Accepted.

• Proposer <- Decider: transId, newState=Rejecting.

• Proposer -> Decider: transId, newState=Rejected.

A SimplexWatcher will watch the transactions from one specific proposer to one specific decider in one specific currency. It can report the sum of all transactions, including/excluding all committed, pending, and rejected transactions, respectively. It will throw an error if:

• a transaction will make the sum of committed + pending transactions go over the max,
• a transaction is accepted after it has expired, or
• a transaction is accepted without satisfying its condition.

A ChannelWatcher combines two SimplexWatchers into a duplex channel. It takes two trust levels and adaptively sets the max of each SimplexWatcher as transactions go back and forth. It can report on current, payable, and receivable balance.

A SnapChecker combines an append-only message log with one ChannelWatcher per combination of (sender, receiver, unit). It has one public method, processMessage, which takes a log entry of the following type:

type SnapMessageLogEntry = {
  stateTransition: StateTransition;
  time: Date;
  from: string;
  to: string;
  unit: string;
};

You can replay a historical message log through a SnapChecker and it will arrive at the same combination of balances for each combination of (sender, receiver, unit).