Add way to look at tx instructions (#11943)

programs/bpf/rust/instruction_introspection/src/lib.rs

@@ -0,0 +1,45 @@
+//! @brief Example Rust-based BPF program that exercises instruction introspection
+
+extern crate solana_sdk;
+use solana_sdk::{
+    account_info::next_account_info, account_info::AccountInfo, entrypoint,
+    entrypoint::ProgramResult, info, program_error::ProgramError, pubkey::Pubkey,
+    sysvar::instructions,
+};
+
+entrypoint!(process_instruction);
+fn process_instruction(
+    _program_id: &Pubkey,
+    accounts: &[AccountInfo],
+    instruction_data: &[u8],
+) -> ProgramResult {
+    if instruction_data.is_empty() {
+        return Err(ProgramError::InvalidAccountData);
+    }
+
+    let secp_instruction_index = instruction_data[0];
+    let account_info_iter = &mut accounts.iter();
+    let instruction_accounts = next_account_info(account_info_iter)?;
+    assert_eq!(*instruction_accounts.key, instructions::id());
+    let data_len = instruction_accounts.try_borrow_data()?.len();
+    if data_len < 2 {
+        return Err(ProgramError::InvalidAccountData);
+    }
+
+    let instruction = instructions::get_instruction(
+        secp_instruction_index as usize,
+        &instruction_accounts.try_borrow_data()?,
+    )
+    .map_err(|_| ProgramError::InvalidAccountData)?;
+
+    let current_instruction =
+        instructions::get_current_instruction(&instruction_accounts.try_borrow_data()?);
+    let my_index = instruction_data[1] as u16;
+    assert_eq!(current_instruction, my_index);
+
+    info!(&format!("id: {}", instruction.program_id));
+
+    info!(&format!("data[0]: {}", instruction.data[0]));
+    info!(&format!("index: {}", current_instruction));
+    Ok(())
+}