Simple native Solana Rust program that echoes back whatever message you send it.

lib.rs

use solana_program::{
    account_info::{AccountInfo},
    entrypoint,
    entrypoint::ProgramResult,
    msg,
    pubkey::Pubkey,
};

entrypoint!(process_instruction);

fn process_instruction(
    _program_id: &Pubkey,
    _accounts: &[AccountInfo],
    instruction_data: &[u8]
) -> ProgramResult {

    // Log the received data
    msg!("Received data: {:?}", instruction_data);

    // Echo back the instruction data
    if let Ok(instruction_str) = std::str::from_utf8(instruction_data) {
        msg!("Echo: {}", instruction_str);
    }

    Ok(())
}