Rust SDK - Binary Canonical Serialization (BCS) Format

Transaction arguments for the Aptos Rust SDK are encoded with Binary Canonical Serialization (BCS). This is the format the Aptos chain recognizes, with specific types such as u64 or u128 instead of a generic integer.

Helpers such as EntryFunction::apt_transfer encode arguments for you. When you build a payload manually, serialize each argument with aptos_bcs:

use aptos_sdk::{
    transaction::{EntryFunction, TransactionPayload},
    types::MoveModuleId,
};

let payload = TransactionPayload::EntryFunction(EntryFunction {
    module: MoveModuleId::from_str_strict("0x1::aptos_account")?,
    function: "transfer".to_string(),
    type_args: vec![],
    args: vec![
        aptos_bcs::to_bytes(&bob.address())?,
        aptos_bcs::to_bytes(&1_000u64)?,
    ],
});
let raw_txn = aptos.build_transaction(&alice, payload).await?;

You can also serialize and deserialize values directly:

let bytes = aptos_bcs::to_bytes(&value)?;
let value: MyType = aptos_bcs::from_bytes(&bytes)?;

Move type tags are available in the SDK:

use aptos_sdk::types::{MoveStructTag, MoveType, TypeTag};

You can learn more about BCS by exploring the BCS GitHub repo.