How to decode `solana_sdk::instruction::CompiledInstruction` (rust solana sdk)?

Question

I want to extract some user readable data from CompiledInstruction. Specifically, I want to understand if CompiledInstruction is native token transfer (SOL), and print sender, recipient, and amount. I looked at sdk docs, and didn't found methods which can extract such high level information from it. Probably, convert CompiledInstruction to Instruction can help, but I didn't find functions for this as well.

Answer 1

CompiledInstruction requires the account_keys from the overall Message. Given that, you can decompile the instruction yourself:

fn decompile(ix: &CompiledInstruction, keys: &[Pubkey]) -> Instruction {
    Instruction {
        program_id: keys[ix.program_id_index],
        accounts: ix.accounts.map(|index| AccountMeta::new(keys[index], false)).collect::<Vec<_>>()
        data: ix.data,
    }
}

Important note: this simplified function doesn't take into account the role of each account in the instruction (ie signer, writable, read-only signer, writable signer). But it should be a good start!

With the instruction, you can use the SDK that goes along with the program to investigate further. In the case of a SOL transfer, you want to see if the program id is 11111111111111111111111111111111 and the instruction data starts with [2, 0, 0, 0]. The following 8 bytes are the transfer amount, encoded as a little-endian u64.

Reference is at https://github.com/anza-xyz/agave/blob/164d37c526ba46cffed765416344013e2c1807c7/sdk/program/src/system_instruction.rs#L885