This package introduces a purposed library on Solidity for declaring and serializing deBridge's ExternalInstruction data struct, giving the ability to construct valid authentic calls to arbitrary Solana smart contracts on supported EVM chains (Ethereum, etc), so they can be further bridged to Solana through the deBridge generic messaging and cross-chain interoperability protocol.
In the world of Ethereum Virtual Machine (EVM), the call of a function of an arbitrary smart contract may be encoded into a hexadecimal string. This string is known as the call data and consists of a four bytes selector (representing the target function signature) and encoded argument values. For example, encoding a call to the balanceOf(address) function with the 0xd8dA6BF26964aF9D7eEd9e03E53415D37aA96045 address as the first argument value would results the following string:
0x70a08231000000000000000000000000d8da6bf26964af9d7eed9e03e53415d37aa96045
| |-- encoded argument values ------------------------------------
|
\
four-byte selector
To facilitate cross-chain communication, deBridge's deBridgeGate.sendMessage() accepts the address of a smart contract to call, and the call data to use for such call:
deBridgeGate.sendMessage{value: _executionFee}(
56, // BNB Chain ID
contractAddress, // contract to call on BNB Chain upon message arrival
callData // call data to use for the call
);However, smart contracts on the Solana blockchain are organized differently. That's why the deBridgeGate smart contract residing on Solana expects a call data that represents a custom complex data struct serialized in a specific way (serde+bincode, if you are interested). The name of this custom data struct is ExternalInstruction:
pub struct ExternalInstruction {
pub reward: Amount,
pub expense: Option<Amount>,
pub execute_policy: ExecutePolicy,
pub pubkey_substitutions: Option<Vec<(u64, PubkeySubstitution)>>,
pub data_substitutions: Option<Vec<DataSubstitution>>,
pub instruction: Instruction,
}Its complete definition in Rust can be found in ExternalInstruction.rs. The example of declaring the ExternalInstruction data struct with values in Rust can be found in the example.rs.
The given library your are looking at provides a full featured implementation of the ExternalInstruction data struct and its serializer on Solidity, giving the ability to construct valid authentic calls to arbitrary Solana smart contracts on supported EVM chains (Ethereum, etc), so they can be further bridged to Solana through the deBridge generic messaging and cross-chain interoperability protocol.
Start with inspecting the definition of the ExternalInstruction struct inside the DeBridgeSolana library.
Next, look at the BasicExample smart contract which is straightforward PoC example of preparing the ExternalInstruction struct with the given values on-chain.
Finally, inspect the DlnBuilder library which is the example of a production-grade library used in the wild by DLN.trade, a high performance cross-chain exchange, for cross-chain communication. The DlnBuilder library uses DeBridgeSolana library under the hood to construct a set of two serialized ExternalInstructions to be sent to Solana blockchain.
This library takes responsibility for the correct packaging of the data struct for transmission. It is a developers' responsibility to prepare values to be included in the data struct, and ensure these values are correct.
All smart contracts are released under LGPL-3.0 by deBridge.