rent (#5205)

programs/vote_api/src/vote_instruction.rs

@@ -35,6 +35,12 @@ fn initialize_account(vote_pubkey: &Pubkey, node_pubkey: &Pubkey, commission: u8
     )
 }
 
+pub fn minimum_balance() -> u64 {
+    let rent = solana_sdk::rent::Rent::default();
+
+    rent.minimum_balance(VoteState::size_of())
+}
+
 pub fn create_account(
     from_pubkey: &Pubkey,
     vote_pubkey: &Pubkey,
@@ -222,4 +228,12 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_minimum_balance() {
+        let rent = solana_sdk::rent::Rent::default();
+        let minimum_balance = rent.minimum_balance(VoteState::size_of());
+        // vote state cheaper than "my $0.02" ;)
+        assert!(minimum_balance as f64 / 2f64.powf(34.0) < 0.02)
+    }
+
 }

sdk/src/genesis_block.rs

@@ -6,6 +6,7 @@ use crate::hash::{hash, Hash};
 use crate::inflation::Inflation;
 use crate::poh_config::PohConfig;
 use crate::pubkey::Pubkey;
+use crate::rent::Rent;
 use crate::signature::{Keypair, KeypairUtil};
 use crate::system_program;
 use crate::timing::{DEFAULT_SLOTS_PER_EPOCH, DEFAULT_SLOTS_PER_SEGMENT, DEFAULT_TICKS_PER_SLOT};
@@ -28,6 +29,7 @@ pub struct GenesisBlock {
     pub poh_config: PohConfig,
     pub fee_calculator: FeeCalculator,
     pub inflation: Inflation,
+    pub rent: Rent,
 }
 
 // useful for basic tests
@@ -59,6 +61,7 @@ impl Default for GenesisBlock {
             poh_config: PohConfig::default(),
             inflation: Inflation::default(),
             fee_calculator: FeeCalculator::default(),
+            rent: Rent::default(),
         }
     }
 }

sdk/src/lib.rs

@@ -14,6 +14,7 @@ pub mod native_loader;
 pub mod packet;
 pub mod poh_config;
 pub mod pubkey;
+pub mod rent;
 pub mod rpc_port;
 pub mod short_vec;
 pub mod signature;

sdk/src/rent.rs

@@ -0,0 +1,72 @@
+//! configuration for network rent
+
+#[derive(Serialize, Deserialize, PartialEq, Clone, Debug)]
+pub struct Rent {
+    /// Rental rate
+    pub lamports_per_byte_year: u64,
+
+    /// exemption threshold, in years
+    pub exemption_threshold: f64,
+}
+
+/// default rental rate in lamports/byte-year, based on:
+///  2^^34 lamports per Sol
+///  $1 per Sol
+///  $0.01 per megabyte day
+///  $3.65 per megabyte year
+pub const DEFAULT_LAMPORTS_PER_BYTE_YEAR: u64 = 17_179_869_184 / 100 * 365 / (1024 * 1024);
+
+/// default amount of time (in years) the balance has to include rent for
+pub const DEFAULT_EXEMPTION_THRESHOLD: f64 = 2.0;
+
+impl Default for Rent {
+    fn default() -> Self {
+        Self {
+            lamports_per_byte_year: DEFAULT_LAMPORTS_PER_BYTE_YEAR,
+            exemption_threshold: DEFAULT_EXEMPTION_THRESHOLD,
+        }
+    }
+}
+
+impl Rent {
+    /// minimum balance due for a given size Account::data.len()
+    pub fn minimum_balance(&self, data_len: usize) -> u64 {
+        let bytes = data_len as u64;
+        bytes * (self.exemption_threshold * self.lamports_per_byte_year as f64) as u64
+    }
+
+    /// whether a given balance and data_len would be exempt
+    pub fn is_exempt(&self, balance: u64, data_len: usize) -> bool {
+        balance >= self.minimum_balance(data_len)
+    }
+
+    /// rent due on account's data_len with balance
+    pub fn due(&self, balance: u64, data_len: usize, years_elapsed: f64) -> u64 {
+        if self.is_exempt(balance, data_len) {
+            0
+        } else {
+            let bytes = data_len as u64;
+            ((self.lamports_per_byte_year * bytes) as f64 * years_elapsed) as u64
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_due() {
+        let rent = Rent::default();
+
+        assert_eq!(rent.due(0, 1, 1.0), DEFAULT_LAMPORTS_PER_BYTE_YEAR);
+        assert_eq!(
+            rent.due(
+                DEFAULT_LAMPORTS_PER_BYTE_YEAR * DEFAULT_EXEMPTION_THRESHOLD as u64,
+                1,
+                1.0
+            ),
+            0
+        );
+    }
+}