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

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)
+}