1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
//! configuration for network rent
use crate::clock::DEFAULT_SLOTS_PER_EPOCH;

#[repr(C)]
#[derive(Serialize, Deserialize, PartialEq, Clone, Copy, Debug, AbiExample)]
pub struct Rent {
    /// Rental rate
    pub lamports_per_byte_year: u64,

    /// exemption threshold, in years
    pub exemption_threshold: f64,

    // What portion of collected rent are to be destroyed, percentage-wise
    pub burn_percent: u8,
}

/// default rental rate in lamports/byte-year, based on:
///  10^9 lamports per SOL
///  $1 per SOL
///  $0.01 per megabyte day
///  $3.65 per megabyte year
pub const DEFAULT_LAMPORTS_PER_BYTE_YEAR: u64 = 1_000_000_000 / 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;

/// default percentage of rent to burn (Valid values are 0 to 100)
pub const DEFAULT_BURN_PERCENT: u8 = 50;

/// account storage overhead for calculation of base rent
pub const ACCOUNT_STORAGE_OVERHEAD: u64 = 128;

impl Default for Rent {
    fn default() -> Self {
        Self {
            lamports_per_byte_year: DEFAULT_LAMPORTS_PER_BYTE_YEAR,
            exemption_threshold: DEFAULT_EXEMPTION_THRESHOLD,
            burn_percent: DEFAULT_BURN_PERCENT,
        }
    }
}

impl Rent {
    /// calculate how much rent to burn from the collected rent
    pub fn calculate_burn(&self, rent_collected: u64) -> (u64, u64) {
        let burned_portion = (rent_collected * u64::from(self.burn_percent)) / 100;
        (burned_portion, rent_collected - burned_portion)
    }
    /// minimum balance due for a given size Account::data.len()
    ///
    /// Note: a stripped-down version of this calculation is used in
    /// calculate_split_rent_exempt_reserve in the stake program. When this function is updated, --
    /// eg. when making rent variable -- the stake program will need to be refactored
    pub fn minimum_balance(&self, data_len: usize) -> u64 {
        let bytes = data_len as u64;
        (((ACCOUNT_STORAGE_OVERHEAD + bytes) * self.lamports_per_byte_year) as f64
            * self.exemption_threshold) 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, bool) {
        if self.is_exempt(balance, data_len) {
            (0, true)
        } else {
            (
                ((self.lamports_per_byte_year * (data_len as u64 + ACCOUNT_STORAGE_OVERHEAD))
                    as f64
                    * years_elapsed) as u64,
                false,
            )
        }
    }

    pub fn free() -> Self {
        Self {
            lamports_per_byte_year: 0,
            ..Rent::default()
        }
    }

    pub fn with_slots_per_epoch(slots_per_epoch: u64) -> Self {
        let ratio = slots_per_epoch as f64 / DEFAULT_SLOTS_PER_EPOCH as f64;
        let exemption_threshold = DEFAULT_EXEMPTION_THRESHOLD as f64 * ratio;
        let lamports_per_byte_year = (DEFAULT_LAMPORTS_PER_BYTE_YEAR as f64 / ratio) as u64;
        Self {
            lamports_per_byte_year,
            exemption_threshold,
            ..Self::default()
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_due() {
        let default_rent = Rent::default();

        assert_eq!(
            default_rent.due(0, 2, 1.2),
            (
                (((2 + ACCOUNT_STORAGE_OVERHEAD) * DEFAULT_LAMPORTS_PER_BYTE_YEAR) as f64 * 1.2)
                    as u64,
                DEFAULT_LAMPORTS_PER_BYTE_YEAR == 0
            )
        );
        assert_eq!(
            default_rent.due(
                (((2 + ACCOUNT_STORAGE_OVERHEAD) * DEFAULT_LAMPORTS_PER_BYTE_YEAR) as f64
                    * DEFAULT_EXEMPTION_THRESHOLD) as u64,
                2,
                1.2
            ),
            (0, true)
        );

        let custom_rent = Rent {
            lamports_per_byte_year: 5,
            exemption_threshold: 2.5,
            ..Rent::default()
        };

        assert_eq!(
            custom_rent.due(0, 2, 1.2),
            (
                (((2 + ACCOUNT_STORAGE_OVERHEAD) * custom_rent.lamports_per_byte_year) as f64 * 1.2)
                    as u64,
                false
            )
        );

        assert_eq!(
            custom_rent.due(
                (((2 + ACCOUNT_STORAGE_OVERHEAD) * custom_rent.lamports_per_byte_year) as f64
                    * custom_rent.exemption_threshold) as u64,
                2,
                1.2
            ),
            (0, true)
        );
    }

    #[ignore]
    #[test]
    #[should_panic]
    fn show_rent_model() {
        use crate::{clock::*, sysvar::Sysvar};

        const SECONDS_PER_YEAR: f64 = 365.242_199 * 24.0 * 60.0 * 60.0;
        const SLOTS_PER_YEAR: f64 = SECONDS_PER_YEAR / DEFAULT_S_PER_SLOT;

        let rent = Rent::default();
        panic!(
            "\n\n\
             ==================================================\n\
             empty account, no data:\n\
             \t{} lamports per epoch, {} lamports to be rent_exempt\n\n\
             stake_history, which is {}kB of data:\n\
             \t{} lamports per epoch, {} lamports to be rent_exempt\n\
             ==================================================\n\n",
            rent.due(
                0,
                0,
                (1.0 / SLOTS_PER_YEAR) * DEFAULT_SLOTS_PER_EPOCH as f64,
            )
            .0,
            rent.minimum_balance(0),
            crate::sysvar::stake_history::StakeHistory::size_of() / 1024,
            rent.due(
                0,
                crate::sysvar::stake_history::StakeHistory::size_of(),
                (1.0 / SLOTS_PER_YEAR) * DEFAULT_SLOTS_PER_EPOCH as f64,
            )
            .0,
            rent.minimum_balance(crate::sysvar::stake_history::StakeHistory::size_of()),
        );
    }
}