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IBC Smart Contracts Overview

This project demonstrates how to implement and configure IBC Smart Contracts and a Relayer that will transfer the IBC Packets between them.

For greater detail into the IBC Protocol, check out the developer resources

Project layout

In order to test out the IBC protocol with smart contracts, we need two chains running. We will call them local chain and remote chain. Each of these chains will host a contract that is designed specifically for it. These contracts are local contract and remote contract respectively.

In this scenario, a relayer with correct configuration is required in order for IBC messages to be transmitted between the two chains.

There are several scripts in each contract and relayer projects that will do the heavy lifting of configuring and running the host chains, storing and instantiating the contracts, configuring and running the relayer, and executing IBC messages and querying the local contract.

Workflow

Follow these steps to run the end-to-end IBC smart contract example. It is easiest to use 5 terminals.

1. start the local chain (terminal 1)

2. store and initialize the local contract (terminal 2)

3. start the remote chain (terminal 3)

4. store and initialize the remote contract (terminal 4)

We are now ready to start the relayer. It may seem odd at first, but the contracts must be instantiated before the relayer is started. This is so that the relayer will have the required contract specific ports to bind to. The relayer script will:

5. init and start relayer (terminal 5)

At this point, the local contract is ready to receive execute commands that will in turn create an IBC message to be relayed to the remote contract. The remote contract will create a response that will then be relayed back to the local contract. This response will contain example data such as:

  • the remote contract's address
  • current time and block of the remote chain
  • the remote chain's chain-id

6. execute the local contract (terminal 2)

This script will invoke the WhoAmI executable function of the local contract. This function will create a message requesting the aforementioned data from the remote contract. Then, the script will continuously query the local contract showing the state data. This state data will update once the response is received from the remote contract. Depending on the relayer configuration and system performance, it may take 10-30 seconds for the entire process to finish.

IBC Message Flow

sequenceDiagram
    Local Chain->>Local Chain: Local Contract requests WhoAmI
    Local Chain->>Relayer: Relayer detects IBC request message created on Local Chain
    Relayer->>Remote Chain: IBC request message is commited to Remote Chain
    Remote Chain->>Remote Chain: Remote Contract receives request and creates response on Remote Chain
    Remote Chain->>Relayer: Relayer detects IBC response message created on Remote Chain
    Relayer->>Local Chain: IBC response message is commited to Local Chain
    Local Chain->>Local Chain: Local Contract receives response and commits it to state data
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