Add convenience function for programs to get minimum delegation (#24175)

programs/bpf/Cargo.toml

@@ -57,6 +57,7 @@ members = [
     "rust/error_handling",
     "rust/log_data",
     "rust/external_spend",
+    "rust/get_minimum_delegation",
     "rust/finalize",
     "rust/instruction_introspection",
     "rust/invoke",

programs/bpf/build.rs

@@ -70,6 +70,7 @@ fn main() {
             "log_data",
             "external_spend",
             "finalize",
+            "get_minimum_delegation",
             "instruction_introspection",
             "invoke",
             "invoke_and_error",

programs/bpf/rust/get_minimum_delegation/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "solana-bpf-rust-get-minimum-delegation"
+version = "1.11.0"
+description = "Solana BPF test program written in Rust"
+authors = ["Solana Maintainers <[email protected]>"]
+repository = "https://github.com/solana-labs/solana"
+license = "Apache-2.0"
+homepage = "https://solana.com/"
+documentation = "https://docs.rs/solana-bpf-rust-get-minimum-delegation"
+edition = "2021"
+
+[dependencies]
+solana-program = { path = "../../../../sdk/program", version = "=1.11.0" }
+
+[lib]
+crate-type = ["cdylib"]
+
+[package.metadata.docs.rs]
+targets = ["x86_64-unknown-linux-gnu"]

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

@@ -0,0 +1,23 @@
+//! Example/test program to get the minimum stake delegation via the helper function
+
+#![allow(unreachable_code)]
+
+extern crate solana_program;
+use solana_program::{
+    account_info::AccountInfo, entrypoint::ProgramResult, msg, pubkey::Pubkey, stake,
+};
+
+solana_program::entrypoint!(process_instruction);
+#[allow(clippy::unnecessary_wraps)]
+fn process_instruction(
+    _program_id: &Pubkey,
+    _accounts: &[AccountInfo],
+    _instruction_data: &[u8],
+) -> ProgramResult {
+    let minimum_delegation = stake::tools::get_minimum_delegation()?;
+    msg!(
+        "The minimum stake delegation is {} lamports",
+        minimum_delegation
+    );
+    Ok(())
+}

programs/bpf/tests/programs.rs

@@ -56,6 +56,7 @@ use {
         pubkey::Pubkey,
         rent::Rent,
         signature::{keypair_from_seed, Keypair, Signer},
+        stake,
         system_instruction::{self, MAX_PERMITTED_DATA_LENGTH},
         system_program,
         sysvar::{self, clock, rent},
@@ -3522,3 +3523,32 @@ fn test_program_fees() {
     let post_balance = bank_client.get_balance(&mint_keypair.pubkey()).unwrap();
     assert_eq!(pre_balance - post_balance, expected_min_fee);
 }
+
+#[test]
+#[cfg(feature = "bpf_rust")]
+fn test_get_minimum_delegation() {
+    let GenesisConfigInfo {
+        genesis_config,
+        mint_keypair,
+        ..
+    } = create_genesis_config(100_123_456_789);
+    let mut bank = Bank::new_for_tests(&genesis_config);
+    bank.feature_set = Arc::new(FeatureSet::all_enabled());
+
+    let (name, id, entrypoint) = solana_bpf_loader_program!();
+    bank.add_builtin(&name, &id, entrypoint);
+    let bank = Arc::new(bank);
+    let bank_client = BankClient::new_shared(&bank);
+
+    let program_id = load_bpf_program(
+        &bank_client,
+        &bpf_loader::id(),
+        &mint_keypair,
+        "solana_bpf_rust_get_minimum_delegation",
+    );
+
+    let account_metas = vec![AccountMeta::new_readonly(stake::program::id(), false)];
+    let instruction = Instruction::new_with_bytes(program_id, &[], account_metas);
+    let result = bank_client.send_and_confirm_instruction(&mint_keypair, instruction);
+    assert!(result.is_ok());
+}

sdk/program/src/stake/instruction.rs

@@ -228,8 +228,11 @@ pub enum StakeInstruction {
     /// # Account references
     ///   None
     ///
-    /// The minimum delegation will be returned via the transaction context's returndata.
-    /// Use `get_return_data()` to retrieve the result.
+    /// Returns the minimum delegation as a little-endian encoded u64 value.
+    /// Programs can use the [`get_minimum_delegation()`] helper function to invoke and
+    /// retrieve the return value for this instruction.
+    ///
+    /// [`get_minimum_delegation()`]: super::tools::get_minimum_delegation
     GetMinimumDelegation,
 }
 

sdk/program/src/stake/mod.rs

@@ -1,6 +1,7 @@
 pub mod config;
 pub mod instruction;
 pub mod state;
+pub mod tools;
 
 pub mod program {
     crate::declare_id!("Stake11111111111111111111111111111111111111");

sdk/program/src/stake/tools.rs

@@ -0,0 +1,38 @@
+//! Utility functions
+use crate::program_error::ProgramError;
+
+/// Helper function for programs to call [`GetMinimumDelegation`] and then fetch the return data
+///
+/// This fn handles performing the CPI to call the [`GetMinimumDelegation`] function, and then
+/// calls [`get_return_data()`] to fetch the return data.
+///
+/// [`GetMinimumDelegation`]: super::instruction::StakeInstruction::GetMinimumDelegation
+/// [`get_return_data()`]: crate::program::get_return_data
+pub fn get_minimum_delegation() -> Result<u64, ProgramError> {
+    let instruction = super::instruction::get_minimum_delegation();
+    crate::program::invoke_unchecked(&instruction, &[])?;
+    get_minimum_delegation_return_data()
+}
+
+/// Helper function for programs to get the return data after calling [`GetMinimumDelegation`]
+///
+/// This fn handles calling [`get_return_data()`], ensures the result is from the correct
+/// program, and returns the correct type.
+///
+/// [`GetMinimumDelegation`]: super::instruction::StakeInstruction::GetMinimumDelegation
+/// [`get_return_data()`]: crate::program::get_return_data
+fn get_minimum_delegation_return_data() -> Result<u64, ProgramError> {
+    crate::program::get_return_data()
+        .ok_or(ProgramError::InvalidInstructionData)
+        .and_then(|(program_id, return_data)| {
+            (program_id == super::program::id())
+                .then(|| return_data)
+                .ok_or(ProgramError::IncorrectProgramId)
+        })
+        .and_then(|return_data| {
+            return_data
+                .try_into()
+                .or(Err(ProgramError::InvalidInstructionData))
+        })
+        .map(u64::from_le_bytes)
+}