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
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
//! The `budget_expr` module provides a domain-specific language for payment plans. Users create BudgetExpr objects that
//! are given to an interpreter. The interpreter listens for `Witness` transactions,
//! which it uses to reduce the payment plan. When the budget is reduced to a
//! `Payment`, the payment is executed.

use chrono::prelude::*;
use serde_derive::{Deserialize, Serialize};
use solana_sdk::hash::Hash;
use solana_sdk::pubkey::Pubkey;

/// The types of events a payment plan can process.
#[derive(Serialize, Deserialize, Debug, PartialEq, Eq, Clone)]
pub enum Witness {
    /// The current time.
    Timestamp(DateTime<Utc>),

    /// A signature from Pubkey.
    Signature,

    /// Account snapshot.
    AccountData(Hash, Pubkey),
}

/// Some amount of lamports that should be sent to the `to` `Pubkey`.
#[derive(Serialize, Deserialize, Debug, PartialEq, Eq, Clone)]
pub struct Payment {
    /// Amount to be paid.
    pub lamports: u64,

    /// The `Pubkey` that `lamports` should be paid to.
    pub to: Pubkey,
}

/// The account constraints a Condition would wait on.
/// Note: ideally this would be function that accepts an Account and returns
/// a bool, but we don't have a way to pass functions over the wire. To simulate
/// higher order programming, create your own program that includes an instruction
/// that sets account data to a boolean. Pass that account key and program_id here.
#[derive(Serialize, Deserialize, Debug, PartialEq, Eq, Clone)]
pub struct AccountConstraints {
    /// The account holder.
    pub key: Pubkey,

    /// The program id that must own the account at `key`.
    pub program_id: Pubkey,

    /// The hash of the data in the account at `key`.
    pub data_hash: Hash,
}

/// A data type representing a `Witness` that the payment plan is waiting on.
#[derive(Serialize, Deserialize, Debug, PartialEq, Eq, Clone)]
pub enum Condition {
    /// Wait for a `Timestamp` `Witness` at or after the given `DateTime`.
    Timestamp(DateTime<Utc>, Pubkey),

    /// Wait for a `Signature` `Witness` from `Pubkey`.
    Signature(Pubkey),

    /// Wait for the account with the given constraints.
    AccountData(AccountConstraints),
}

impl Condition {
    /// Return true if the given Witness satisfies this Condition.
    pub fn is_satisfied(&self, witness: &Witness, from: &Pubkey) -> bool {
        match (self, witness) {
            (Condition::Signature(pubkey), Witness::Signature) => pubkey == from,
            (Condition::Timestamp(dt, pubkey), Witness::Timestamp(last_time)) => {
                pubkey == from && dt <= last_time
            }
            (
                Condition::AccountData(constraints),
                Witness::AccountData(actual_hash, program_id),
            ) => {
                constraints.program_id == *program_id
                    && constraints.key == *from
                    && constraints.data_hash == *actual_hash
            }
            _ => false,
        }
    }
}

/// A data type representing a payment plan.
#[repr(C)]
#[derive(Serialize, Deserialize, Debug, PartialEq, Eq, Clone)]
pub enum BudgetExpr {
    /// Make a payment.
    Pay(Payment),

    /// Make a payment after some condition.
    After(Condition, Box<BudgetExpr>),

    /// Either make a payment after one condition or a different payment after another
    /// condition, which ever condition is satisfied first.
    Or((Condition, Box<BudgetExpr>), (Condition, Box<BudgetExpr>)),

    /// Make a payment after both of two conditions are satisfied
    And(Condition, Condition, Box<BudgetExpr>),
}

impl BudgetExpr {
    /// Create the simplest budget - one that pays `lamports` to Pubkey.
    pub fn new_payment(lamports: u64, to: &Pubkey) -> Self {
        BudgetExpr::Pay(Payment { lamports, to: *to })
    }

    /// Create a budget that pays `lamports` to `to` after being witnessed by `from`.
    pub fn new_authorized_payment(from: &Pubkey, lamports: u64, to: &Pubkey) -> Self {
        BudgetExpr::After(
            Condition::Signature(*from),
            Box::new(Self::new_payment(lamports, to)),
        )
    }

    /// Create a budget that pays `lamports` to `to` after witnessing account data in `account_pubkey` with the given hash.
    pub fn new_payment_when_account_data(
        account_pubkey: &Pubkey,
        account_program_id: &Pubkey,
        account_hash: Hash,
        lamports: u64,
        to: &Pubkey,
    ) -> Self {
        BudgetExpr::After(
            Condition::AccountData(AccountConstraints {
                key: *account_pubkey,
                program_id: *account_program_id,
                data_hash: account_hash,
            }),
            Box::new(Self::new_payment(lamports, to)),
        )
    }

    /// Create a budget that pays `lamports` to `to` after being witnessed by `witness` unless
    /// canceled with a signature from `from`.
    pub fn new_cancelable_authorized_payment(
        witness: &Pubkey,
        lamports: u64,
        to: &Pubkey,
        from: Option<Pubkey>,
    ) -> Self {
        if from.is_none() {
            return Self::new_authorized_payment(witness, lamports, to);
        }
        let from = from.unwrap();
        BudgetExpr::Or(
            (
                Condition::Signature(*witness),
                Box::new(BudgetExpr::new_payment(lamports, to)),
            ),
            (
                Condition::Signature(from),
                Box::new(BudgetExpr::new_payment(lamports, &from)),
            ),
        )
    }

    /// Create a budget that pays lamports` to `to` after being witnessed by 2x `from`s
    pub fn new_2_2_multisig_payment(
        from0: &Pubkey,
        from1: &Pubkey,
        lamports: u64,
        to: &Pubkey,
    ) -> Self {
        BudgetExpr::And(
            Condition::Signature(*from0),
            Condition::Signature(*from1),
            Box::new(Self::new_payment(lamports, to)),
        )
    }

    /// Create a budget that pays `lamports` to `to` after the given DateTime signed
    /// by `dt_pubkey`.
    pub fn new_future_payment(
        dt: DateTime<Utc>,
        dt_pubkey: &Pubkey,
        lamports: u64,
        to: &Pubkey,
    ) -> Self {
        BudgetExpr::After(
            Condition::Timestamp(dt, *dt_pubkey),
            Box::new(Self::new_payment(lamports, to)),
        )
    }

    /// Create a budget that pays `lamports` to `to` after the given DateTime
    /// signed by `dt_pubkey` unless canceled by `from`.
    pub fn new_cancelable_future_payment(
        dt: DateTime<Utc>,
        dt_pubkey: &Pubkey,
        lamports: u64,
        to: &Pubkey,
        from: Option<Pubkey>,
    ) -> Self {
        if from.is_none() {
            return Self::new_future_payment(dt, dt_pubkey, lamports, to);
        }
        let from = from.unwrap();
        BudgetExpr::Or(
            (
                Condition::Timestamp(dt, *dt_pubkey),
                Box::new(Self::new_payment(lamports, to)),
            ),
            (
                Condition::Signature(from),
                Box::new(Self::new_payment(lamports, &from)),
            ),
        )
    }

    /// Return Payment if the budget requires no additional Witnesses.
    pub fn final_payment(&self) -> Option<Payment> {
        match self {
            BudgetExpr::Pay(payment) => Some(payment.clone()),
            _ => None,
        }
    }

    /// Return true if the budget spends exactly `spendable_lamports`.
    pub fn verify(&self, spendable_lamports: u64) -> bool {
        match self {
            BudgetExpr::Pay(payment) => payment.lamports == spendable_lamports,
            BudgetExpr::After(_, sub_expr) | BudgetExpr::And(_, _, sub_expr) => {
                sub_expr.verify(spendable_lamports)
            }
            BudgetExpr::Or(a, b) => {
                a.1.verify(spendable_lamports) && b.1.verify(spendable_lamports)
            }
        }
    }

    /// Apply a witness to the budget to see if the budget can be reduced.
    /// If so, modify the budget in-place.
    pub fn apply_witness(&mut self, witness: &Witness, from: &Pubkey) {
        let new_expr = match self {
            BudgetExpr::After(cond, sub_expr) if cond.is_satisfied(witness, from) => {
                Some(sub_expr.clone())
            }
            BudgetExpr::Or((cond, sub_expr), _) if cond.is_satisfied(witness, from) => {
                Some(sub_expr.clone())
            }
            BudgetExpr::Or(_, (cond, sub_expr)) if cond.is_satisfied(witness, from) => {
                Some(sub_expr.clone())
            }
            BudgetExpr::And(cond0, cond1, sub_expr) => {
                if cond0.is_satisfied(witness, from) {
                    Some(Box::new(BudgetExpr::After(cond1.clone(), sub_expr.clone())))
                } else if cond1.is_satisfied(witness, from) {
                    Some(Box::new(BudgetExpr::After(cond0.clone(), sub_expr.clone())))
                } else {
                    None
                }
            }
            _ => None,
        };
        if let Some(expr) = new_expr {
            *self = *expr;
        }
    }
}

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

    #[test]
    fn test_signature_satisfied() {
        let from = Pubkey::default();
        assert!(Condition::Signature(from).is_satisfied(&Witness::Signature, &from));
    }

    #[test]
    fn test_timestamp_satisfied() {
        let dt1 = Utc.ymd(2014, 11, 14).and_hms(8, 9, 10);
        let dt2 = Utc.ymd(2014, 11, 14).and_hms(10, 9, 8);
        let from = Pubkey::default();
        assert!(Condition::Timestamp(dt1, from).is_satisfied(&Witness::Timestamp(dt1), &from));
        assert!(Condition::Timestamp(dt1, from).is_satisfied(&Witness::Timestamp(dt2), &from));
        assert!(!Condition::Timestamp(dt2, from).is_satisfied(&Witness::Timestamp(dt1), &from));
    }

    #[test]
    fn test_verify() {
        let dt = Utc.ymd(2014, 11, 14).and_hms(8, 9, 10);
        let from = Pubkey::default();
        let to = Pubkey::default();
        assert!(BudgetExpr::new_payment(42, &to).verify(42));
        assert!(BudgetExpr::new_authorized_payment(&from, 42, &to).verify(42));
        assert!(BudgetExpr::new_future_payment(dt, &from, 42, &to).verify(42));
        assert!(
            BudgetExpr::new_cancelable_future_payment(dt, &from, 42, &to, Some(from)).verify(42)
        );
    }

    #[test]
    fn test_authorized_payment() {
        let from = Pubkey::default();
        let to = Pubkey::default();

        let mut expr = BudgetExpr::new_authorized_payment(&from, 42, &to);
        expr.apply_witness(&Witness::Signature, &from);
        assert_eq!(expr, BudgetExpr::new_payment(42, &to));
    }

    #[test]
    fn test_future_payment() {
        let dt = Utc.ymd(2014, 11, 14).and_hms(8, 9, 10);
        let from = solana_sdk::pubkey::new_rand();
        let to = solana_sdk::pubkey::new_rand();

        let mut expr = BudgetExpr::new_future_payment(dt, &from, 42, &to);
        expr.apply_witness(&Witness::Timestamp(dt), &from);
        assert_eq!(expr, BudgetExpr::new_payment(42, &to));
    }

    #[test]
    fn test_unauthorized_future_payment() {
        // Ensure timestamp will only be acknowledged if it came from the
        // whitelisted public key.
        let dt = Utc.ymd(2014, 11, 14).and_hms(8, 9, 10);
        let from = solana_sdk::pubkey::new_rand();
        let to = solana_sdk::pubkey::new_rand();

        let mut expr = BudgetExpr::new_future_payment(dt, &from, 42, &to);
        let orig_expr = expr.clone();
        expr.apply_witness(&Witness::Timestamp(dt), &to); // <-- Attack!
        assert_eq!(expr, orig_expr);
    }

    #[test]
    fn test_cancelable_future_payment() {
        let dt = Utc.ymd(2014, 11, 14).and_hms(8, 9, 10);
        let from = Pubkey::default();
        let to = Pubkey::default();

        let mut expr = BudgetExpr::new_cancelable_future_payment(dt, &from, 42, &to, Some(from));
        expr.apply_witness(&Witness::Timestamp(dt), &from);
        assert_eq!(expr, BudgetExpr::new_payment(42, &to));

        let mut expr = BudgetExpr::new_cancelable_future_payment(dt, &from, 42, &to, Some(from));
        expr.apply_witness(&Witness::Signature, &from);
        assert_eq!(expr, BudgetExpr::new_payment(42, &from));
    }
    #[test]
    fn test_2_2_multisig_payment() {
        let from0 = solana_sdk::pubkey::new_rand();
        let from1 = solana_sdk::pubkey::new_rand();
        let to = Pubkey::default();

        let mut expr = BudgetExpr::new_2_2_multisig_payment(&from0, &from1, 42, &to);
        expr.apply_witness(&Witness::Signature, &from0);
        assert_eq!(expr, BudgetExpr::new_authorized_payment(&from1, 42, &to));
    }

    #[test]
    fn test_multisig_after_sig() {
        let from0 = solana_sdk::pubkey::new_rand();
        let from1 = solana_sdk::pubkey::new_rand();
        let from2 = solana_sdk::pubkey::new_rand();
        let to = Pubkey::default();

        let expr = BudgetExpr::new_2_2_multisig_payment(&from0, &from1, 42, &to);
        let mut expr = BudgetExpr::After(Condition::Signature(from2), Box::new(expr));

        expr.apply_witness(&Witness::Signature, &from2);
        expr.apply_witness(&Witness::Signature, &from0);
        assert_eq!(expr, BudgetExpr::new_authorized_payment(&from1, 42, &to));
    }

    #[test]
    fn test_multisig_after_ts() {
        let from0 = solana_sdk::pubkey::new_rand();
        let from1 = solana_sdk::pubkey::new_rand();
        let dt = Utc.ymd(2014, 11, 11).and_hms(7, 7, 7);
        let to = Pubkey::default();

        let expr = BudgetExpr::new_2_2_multisig_payment(&from0, &from1, 42, &to);
        let mut expr = BudgetExpr::After(Condition::Timestamp(dt, from0), Box::new(expr));

        expr.apply_witness(&Witness::Timestamp(dt), &from0);
        assert_eq!(
            expr,
            BudgetExpr::new_2_2_multisig_payment(&from0, &from1, 42, &to)
        );

        expr.apply_witness(&Witness::Signature, &from0);
        assert_eq!(expr, BudgetExpr::new_authorized_payment(&from1, 42, &to));
    }
}