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).