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Celer Inter-Chain Messaging (IM)

Celer Inter-Chain Messaging (IM) is a message passing protocol that facilitates the seamless transfer of any type of generic message, including function calls, across multiple blockchains via a single source-chain transaction. Celer IM currently supports message passing between Oasis Sapphire and all other IM-supported chains. The message-passing support enables developers to build entirely new privacy-centric dApps or add confidentiality to existing dApps on popular EVM networks using Sapphire as a privacy layer.

Celer IM offers two design patterns:

  • Cross-chain logic execution without fund transfer
  • Cross-chain logic execution with accompanying fund transfer

This documentation focuses on cross-chain logic execution without fund transfer. For information on using Celer IM with fund transfer, please refer to the Celer IM documentation.

Architecture​

Celer IM Architecture Architecture diagram for Celer IM1

Celer IM’s architecture is composed of several core components that work together to facilitate secure and reliable cross-chain messaging:

  • MessageBus: The primary component managing message transmission between source and destination blockchains. It ensures proper formatting and routing of messages through the Celer network.
  • State Guardian Network (SGN): A decentralized network of validators that manage the state of cross-chain messages. SGN validators sign off on messages and coordinate their secure delivery, providing security and availability for cross-chain interactions.
  • Executor: An off-chain component that listens to the SGN for validated messages ready for execution on the destination chain. Once a message is verified, the Executor sends transactions to the MessageBus on the destination chain, triggering the execution of the specified logic.

Executor​

The Executor is a crucial part of the Celer IM framework. It performs two main functions:

  • Monitors the Celer State Guardian Network (SGN) for messages ready to be submitted (with sufficient validator signatures).
  • Submits message execution transactions to the MessageBus contract on the destination chain.

It is necessary a Message Executor runs for you dapp. To set up an executor, you have two options:

  • Follow the documentation to set up your own executor.
  • Fill out this form for Celer to set up a hosted executor service for you.

For Hackathon or Grant participants, we recommend filling out the relay request form to use the shared Message Executor.

In most cases, Celer advises dApp developers to use the shared executor services provided by the Celer Network team to avoid server configuration and operation concerns.

info

Oasis is running an executor for the Sapphire Testnet, which is okay to rely on for a test, for a faster execution it's recommended to run your own or use the hosted service.

Fees​

The cross-chain messaging process involves fees paid to two parties:

  • SGN Fee: Paid as msg.value to the MessageBus contract by the entity calling sendMessge.
  • Executor Fee: Charged by the Executor for submitting execute message transactions.

Monitoring​

The Celer IM Scan API can be used to retrieve status and message details by providing the globally unique transaction ID from the chain which originated the message.

https://api.celerscan.com/scan/searchByTxHash?tx=0x...

For details of the response format, see the Query IM Tx Status page of the Celer-IM documentation. Using this API lets you to check if messages have been delivered.

Footnotes​

  1. The Celer IM architecture diagram is courtesy of Celer documentation. ↩