Creating and Sending a Cross-chain Read Request

To create a cross-chain read request, one needs to call the iSend() function on Router's Gateway contract with the following parameters:

function iSend(
    uint256 version,
    uint256 routeAmount,
    string calldata routeRecipient,
    string calldata destChainId,
    bytes calldata requestMetadata,
    bytes calldata requestPacket
 ) external payable returns (uint256);

Here, the parameter requestMetadata is the metadata that includes abi.encodePacked value of the destination gas limit, destination gas price, acknowledgment type, acknowledgment gas limit, acknowledgment gas price, relayer fees, read call bool, and the ASM address.

function getRequestMetadata(
    uint64 destGasLimit,
    uint64 destGasPrice,
    uint64 ackGasLimit,
    uint64 ackGasPrice,
    uint128 relayerFees,
    uint8 ackType,
    bool isReadCall,
    bytes memory asmAddress
    ) public pure returns (bytes memory) {
    bytes memory requestMetadata = abi.encodePacked(
        destGasLimit,
        destGasPrice,
        ackGasLimit,
        ackGasPrice,
        relayerFees,
        ackType,
        isReadCall,
        asmAddress
    );
    return requestMetadata;
    }

info

The detailed documentation for this function can be found here.

When creating a read request, the isReadCall parameter must be set to true in the requestMetadata parameter. In addition, the payload encoding must be of a specific type.

For example, if a user wants to send a read call to a contract A on the destination chain and wants to query the getA() function, the payload on the source chain should be encoded as follows:

interface A {
   function getA(uint256 a) external returns (uint256);
}

contract Application {
   function createReadQueryPayload(uint256 a) external returns (bytes memory) {
      bytes memory payload = abi.encodeCall(A.getA, (a));
      return payload;
   }
}

An example for sending a cross-chain read query can be found here.