cow_settlement_interface/pda/
buffer.rs

1//! Buffer PDA seed and address derivation.
2//!
3//! Each buffer is a per-token SPL token account that holds funds controlled
4//! by the settlement state PDA. It lives at a PDA keyed by the token mint, so
5//! there is exactly one buffer address per token.
6//!
7//! The token account stored at this address is initialized by the
8//! `CreateBuffer` instruction; its SPL `owner` (token authority) is the
9//! settlement state PDA (see [`crate::pda::state`]), the single authority
10//! controlling every buffer.
11//!
12//! The seeds start with [`SETTLEMENT_SEED`], which carries
13//! the cargo package major and minor version, so a version bump moves every buffer.
14//! Since only the state PDA can spend a buffer and that address moves too,
15//! buffers must be drained under the old version before a bump ships, or their
16//! contents are stranded.
17//!
18//! Unlike the order PDA, which stores its own bump (see
19//! [`crate::data::order::OrderAccount`]), a buffer's layout belongs entirely to
20//! the token program, leaving no room for one.
21
22use solana_address::Address;
23use solana_program_error::ProgramError;
24use solana_pubkey::Pubkey;
25
26use crate::pda::{is_pda_with_signer_seeds, SETTLEMENT_SEED};
27use crate::SettlementError;
28
29/// Trailing seed identifying the buffer PDAs.
30pub const BUFFER_SEED: &[u8] = b"buffer";
31
32/// Canonical seed components for the buffer PDA holding the specified `mint`
33/// token.
34///
35/// `mint` is the raw 32-byte token mint address, so the same helper serves
36/// both the off-chain builder and the on-chain handler (which holds the mint
37/// as an `Address`).
38pub fn buffer_pda_seeds(mint: &[u8; 32]) -> [&[u8]; 3] {
39    [SETTLEMENT_SEED, mint, BUFFER_SEED]
40}
41
42/// Canonical seeds for re-deriving the buffer PDA for `mint` with `bump`.
43pub fn buffer_pda_signer_seeds<'a>(mint: &'a [u8; 32], bump: &'a [u8; 1]) -> [&'a [u8]; 4] {
44    let [s0, s1, s2] = buffer_pda_seeds(mint);
45    [s0, s1, s2, bump]
46}
47
48/// Derive the canonical buffer PDA address (and bump) for the token `mint`.
49pub fn find_buffer_pda(program_id: &Pubkey, mint: &Pubkey) -> (Pubkey, u8) {
50    Pubkey::find_program_address(&buffer_pda_seeds(mint.as_array()), program_id)
51}
52
53/// Confirm `buffer` matches the derived buffer PDA for `mint` and `bump`.
54#[must_use = "ignoring the output means ignoring the validation result"]
55pub fn validate_buffer_pda(
56    program_id: &Address,
57    buffer: &Address,
58    mint: &Address,
59    bump: u8,
60) -> Result<(), ProgramError> {
61    is_pda_with_signer_seeds(
62        buffer,
63        program_id,
64        buffer_pda_signer_seeds(&mint.to_bytes(), &[bump]),
65    )
66    .then_some(())
67    .ok_or(SettlementError::PushSourceNotBuffer.into())
68}
69
70#[cfg(test)]
71mod tests {
72    use super::*;
73    use crate::pda::tests::assert_distinct_versions_yield_distinct_pdas;
74
75    #[test]
76    fn find_buffer_pda_uses_canonical_seeds() {
77        let token = Pubkey::new_unique();
78
79        crate::pda::tests::assert_canonical_bump(
80            |program_id| find_buffer_pda(program_id, &token),
81            buffer_pda_seeds(token.as_array()),
82        );
83    }
84
85    #[test]
86    fn distinct_versions_yield_distinct_buffer_pdas() {
87        let mint = Pubkey::new_unique();
88        let (pda, _) = find_buffer_pda(&crate::ID, &mint);
89
90        assert_distinct_versions_yield_distinct_pdas(&pda, &[mint.as_array(), BUFFER_SEED]);
91    }
92
93    #[test]
94    fn accepts_a_valid_address() {
95        let program_id = Pubkey::new_unique();
96        let mint = Pubkey::new_unique();
97        let (pda, bump) = find_buffer_pda(&program_id, &mint);
98
99        let buffer = crate::instruction::fixtures::fake_account(pda);
100        validate_buffer_pda(&program_id, buffer.address(), &mint, bump)
101            .expect("the canonical buffer PDA must be accepted");
102    }
103
104    #[test]
105    fn rejects_an_invalid_address() {
106        let program_id = Pubkey::new_unique();
107        let mint = Pubkey::new_unique();
108        let (_, bump) = find_buffer_pda(&program_id, &mint);
109
110        // An account sitting at some other address is not the buffer.
111        let buffer = crate::instruction::fixtures::fake_account(Pubkey::new_unique());
112        let err = validate_buffer_pda(&program_id, buffer.address(), &mint, bump)
113            .expect_err("a non-canonical address must be rejected");
114        assert_eq!(err, SettlementError::PushSourceNotBuffer.into());
115    }
116
117    #[test]
118    fn rejects_a_wrong_bump() {
119        let program_id = Pubkey::new_unique();
120        let mint = Pubkey::new_unique();
121        let (pda, bump) = find_buffer_pda(&program_id, &mint);
122
123        // The address is canonical but the carried bump doesn't derive it.
124        let buffer = crate::instruction::fixtures::fake_account(pda);
125        let err = validate_buffer_pda(&program_id, buffer.address(), &mint, bump ^ 1)
126            .expect_err("a wrong bump must be rejected");
127        assert_eq!(err, SettlementError::PushSourceNotBuffer.into());
128    }
129
130    mod proptest {
131        use ::proptest::prelude::*;
132
133        use super::*;
134
135        proptest! {
136            #[test]
137            fn distinct_tokens_yield_distinct_pdas(
138                program_id in any::<[u8; 32]>(),
139                token1 in any::<[u8; 32]>(),
140                token2 in any::<[u8; 32]>(),
141            ) {
142                prop_assume!(token1 != token2);
143                let program_id = Pubkey::new_from_array(program_id);
144                let (pda1, _) = find_buffer_pda(&program_id, &Pubkey::new_from_array(token1));
145                let (pda2, _) = find_buffer_pda(&program_id, &Pubkey::new_from_array(token2));
146                prop_assert_ne!(pda1, pda2);
147            }
148        }
149    }
150}
cow_settlement_interface/pda/buffer.rs

cow_settlement_interface/pda/
buffer.rs
