Skip to main content

Cross-Program Invocation

Cross-Program Invocation (CPI) is the core of the "composability" of BBAChain, allowing programs to "call" each other.

Overview​

Cross-Program Invocation allows one program to invoke instructions on another program, enabling programs to build on top of each other and create complex applications.

How CPI Works​

When a program invokes another program:

  1. The calling program creates an instruction for the target program
  2. The instruction is executed in the context of the calling program
  3. The target program processes the instruction
  4. Control returns to the calling program

CPI Example​

use bbachain_program::{
    account_info::{next_account_info, AccountInfo},
    entrypoint::ProgramResult,
    program::invoke,
    pubkey::Pubkey,
};

pub fn transfer_tokens(
    accounts: &[AccountInfo],
    amount: u64,
) -> ProgramResult {
    let account_info_iter = &mut accounts.iter();
    let source = next_account_info(account_info_iter)?;
    let destination = next_account_info(account_info_iter)?;
    let authority = next_account_info(account_info_iter)?;
    let token_program = next_account_info(account_info_iter)?;

    let instruction = bbachain_token::instruction::transfer(
        &bbachain_token::id(),
        source.key,
        destination.key,
        authority.key,
        &[],
        amount,
    )?;

    invoke(
        &instruction,
        &[
            source.clone(),
            destination.clone(),
            authority.clone(),
            token_program.clone(),
        ],
    )
}

CPI Benefits​

  • Composability: Programs can build on top of each other
  • Reusability: Common functionality can be shared across programs
  • Modularity: Complex applications can be broken down into smaller programs

CPI Security​

When a program invokes another program via CPI:

  • The calling program's privileges are passed to the invoked program
  • The invoked program can only modify accounts that the calling program has permission to modify
  • The invoked program cannot access accounts that weren't passed to it

Next Steps​