Add fees syscall to expose cluster fees into programs (#4472)

sdk/src/syscall/fees.rs

@@ -0,0 +1,71 @@
+//! This account contains the current cluster fees
+//!
+use crate::account::Account;
+use crate::account_utils::State;
+use crate::fee_calculator::FeeCalculator;
+use crate::pubkey::Pubkey;
+use crate::syscall;
+use bincode::serialized_size;
+
+/// "Sysca11Fees11111111111111111111111111"
+///  fees account pubkey
+const ID: [u8; 32] = [
+    6, 167, 211, 138, 69, 218, 104, 33, 3, 92, 89, 173, 16, 89, 109, 253, 49, 97, 98, 165, 87, 222,
+    119, 112, 253, 90, 76, 184, 0, 0, 0, 0,
+];
+
+pub fn id() -> Pubkey {
+    Pubkey::new(&ID)
+}
+
+pub fn check_id(pubkey: &Pubkey) -> bool {
+    pubkey.as_ref() == ID
+}
+
+#[repr(C)]
+#[derive(Serialize, Deserialize, Debug, Default)]
+pub struct Fees {
+    pub fee_calculator: FeeCalculator,
+}
+
+impl Fees {
+    pub fn from(account: &Account) -> Option<Self> {
+        account.state().ok()
+    }
+    pub fn to(&self, account: &mut Account) -> Option<()> {
+        account.set_state(self).ok()
+    }
+
+    pub fn size_of() -> usize {
+        serialized_size(&Fees::default()).unwrap() as usize
+    }
+}
+
+pub fn create_account(lamports: u64) -> Account {
+    Account::new(lamports, Fees::size_of(), &syscall::id())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_fees_id() {
+        let name = "Sysca11Fees11111111111111111111111111111111";
+        // To get the bytes above:
+        // dbg!((name, bs58::decode(name).into_vec().unwrap()));
+        assert_eq!(name, id().to_string());
+        assert!(check_id(&id()));
+    }
+
+    #[test]
+    fn test_fees_create_account() {
+        let lamports = 42;
+        let account = create_account(lamports);
+        let fees = Fees::from(&account).unwrap();
+        assert_eq!(
+            fees.fee_calculator.lamports_per_signature,
+            FeeCalculator::default().lamports_per_signature
+        );
+    }
+}

sdk/src/syscall/mod.rs

@@ -2,6 +2,7 @@
 //!
 use crate::pubkey::Pubkey;
 
+pub mod fees;
 pub mod slot_hashes;
 
 /// "Sysca11111111111111111111111111111111111111"