How to encode arguments in AssemblyScript when calling Aurora contract from Near blockchain? - nearprotocol

Question

I'm trying to call a contract located in Aurora from a contract located in Near. I'm using AssemblyScript and I'm struggling with passing arguments to the Aurora contract itself. I receive ERR_BORSH_DESERIALIZE panic from the Aurora contract. Can anybody help me with figuring out how I would encode arguments? Here is sample code:
import { BorshSerializer } from '#serial-as/borsh'
#serializable
class FunctionCallArgs {
contract: Uint8Array;
input: Uint8Array;
}
export function myFunction(): void {
const args: FunctionCallArgs = {
contract: util.stringToBytes(contractAddress),
input: util.stringToBytes(abiEncodedFn),
};
const argsBorsh = BorshSerializer.encode(args);
ContractPromise.create("aurora", "call", argsBorsh, 100);
}

Answer 1

I managed to find a solution. The flow of calling the contract was right, however I had two errors in implementation.
Wrong conversion of the contract address to 20 byte array. My custom implementation of the function a bit verbose, so here is a single line JS script that does the same:
Buffer.from(contractAddress.substring(2), 'hex') // removing 0x prefix is mandatory
"#serial-as/borsh" doesn't deserialize fixed length arrays. So I had to convert contractAddress (which is Uint8Array after converting it to bytes in 1st point) to StaticArray(20), like this:
const contract = hexToBytes(tokenAddress).reduce((memo, v, i) => {
memo[i] = <u8>v;
return memo;
}, new StaticArray<u8>(20);
And finally monkey-patched "encode_static_array" method in the library to not allocate space before adding bytes to buffer. So removed:
encode_static_array<T>(value: StaticArray<T>): void {
...
this.buffer.store<u32>(value.length); // remove this line
...
}