State Transfer

Overview

Polygon validators continuously monitor a contract on Ethereum chain called StateSender. Each time a registered contract on Ethereum chain calls this contract, it emits an event. Using this event Polygon validators relay the data to another contract on Polygon chain. This StateSync mechanism is used to send data from Ethereum to Polygon.

Polygon validators also periodically submit a hash of all transactions on Polygon chain to Ethereum chain. This Checkpoint can be used to verify any transaction that happened on Polygon. Once a transaction is verified to have happened on Polygon chain, action can be taked accordingly on Ethereum.

These 2 mechanisms can be used together to enable two way data(state) transfer between Ethereum and Polygon. To abstract out all these interactions, you can directly inherit our FxBaseRootTunnel (on Ethereum) and FxBaseChildTunnel (on Polygon) contracts.

Fx-Portal

Overview

The usual mechanism to natively read Ethereum data from Polygon is using State Sync. This enables the transfer of arbitrary data from Ethereum to Polygon. However, this approach also requires mapping of the root and child contracts if the default interface cannot be used. FxPortal offers an alternative where ERC standardized tokens can be deployed without any mapping involved, simply using the deployed base FxPortal contracts.

What is Fx-Portal?

It is a powerful yet simple implementation Polygon state sync mechanism. The Polygon PoS bridge is built on the same architecture. The code in the examples folder are some examples of usage. You can easily use these examples to build your own implementations or own custom bridge which allows any state-syncs without mapping.

How does it work?

FxChild (FxChild.sol) and FxRoot (FxRoot.sol) are the main contracts on which FxPortal works. It calls and passes data to user-defined methods on another chain without any mapping using the state sync mechanism. To use the deployed main contracts, you can implement FxPortal's base contracts in the smart contracts you deploy - FxBaseRootTunnel and FxBaseChildTunnel. By building on these contracts, your deployed contracts will be able to communicate with each other using the data tunnel mechanism.