ic_memory/
stable_cell.rs

1use crate::{LedgerCommitStore, constants::WASM_PAGE_SIZE_BYTES};
2use ic_stable_structures::{Memory, Storable, storable::Bound};
3use serde::{Deserialize, Serialize};
4use std::borrow::Cow;
5use thiserror::Error;
6
7/// Stable-cell magic prefix written by `ic-stable-structures::Cell`.
8pub const STABLE_CELL_MAGIC: &[u8; 3] = b"SCL";
9/// Stable-cell layout version supported by this adapter.
10pub const STABLE_CELL_LAYOUT_VERSION: u8 = 1;
11/// Stable-cell header byte length.
12pub const STABLE_CELL_HEADER_SIZE: usize = 8;
13/// Byte offset where the stable-cell value payload starts.
14pub const STABLE_CELL_VALUE_OFFSET: u64 = 8;
15
16///
17/// StableCellLedgerRecord
18///
19/// `ic-stable-structures::Cell` record containing an `ic-memory` allocation
20/// ledger commit store.
21///
22/// This is a substrate adapter DTO. It owns no framework policy and does not
23/// open application allocations.
24///
25
26#[derive(Clone, Debug, Default, Deserialize, Eq, PartialEq, Serialize)]
27#[serde(deny_unknown_fields)]
28pub struct StableCellLedgerRecord {
29    store: LedgerCommitStore,
30}
31
32impl StableCellLedgerRecord {
33    /// Construct a record from a commit store.
34    #[must_use]
35    pub const fn new(store: LedgerCommitStore) -> Self {
36        Self { store }
37    }
38
39    /// Borrow the embedded commit store.
40    #[must_use]
41    pub const fn store(&self) -> &LedgerCommitStore {
42        &self.store
43    }
44
45    /// Mutably borrow the embedded commit store.
46    pub const fn store_mut(&mut self) -> &mut LedgerCommitStore {
47        &mut self.store
48    }
49
50    /// Consume this record and return the embedded commit store.
51    #[must_use]
52    pub fn into_store(self) -> LedgerCommitStore {
53        self.store
54    }
55}
56
57impl Storable for StableCellLedgerRecord {
58    const BOUND: Bound = Bound::Unbounded;
59
60    fn to_bytes(&self) -> Cow<'_, [u8]> {
61        Cow::Owned(serialize_record(self))
62    }
63
64    fn into_bytes(self) -> Vec<u8> {
65        serialize_record(&self)
66    }
67
68    fn from_bytes(bytes: Cow<'_, [u8]>) -> Self {
69        decode_stable_cell_ledger_record(&bytes).unwrap_or_else(|err| {
70            panic!("StableCellLedgerRecord deserialize failed: {err}");
71        })
72    }
73}
74
75///
76/// StableCellPayloadError
77///
78/// Stable-cell payload decode failure.
79#[non_exhaustive]
80#[derive(Clone, Debug, Eq, Error, PartialEq)]
81pub enum StableCellPayloadError {
82    /// Memory contents do not start with the stable-cell marker.
83    #[error("memory is not an ic-stable-structures Cell")]
84    NotStableCell,
85    /// Stable-cell layout version does not match the adapter's current shape.
86    #[error("unexpected stable-cell layout version {version}")]
87    UnexpectedLayoutVersion {
88        /// Observed stable-cell version.
89        version: u8,
90    },
91    /// Stable-cell header length does not fit inside the memory.
92    #[error("stable-cell payload length {value_len} exceeds available bytes {available_bytes}")]
93    InvalidLength {
94        /// Encoded value length.
95        value_len: u64,
96        /// Available payload bytes in memory.
97        available_bytes: u64,
98    },
99    /// Stable-cell length cannot be represented on the current host.
100    #[error("stable-cell payload length {value_len} cannot fit in usize")]
101    LengthOverflow {
102        /// Encoded value length.
103        value_len: u64,
104    },
105}
106
107///
108/// StableCellLedgerError
109///
110/// Stable-cell ledger record validation failure.
111#[non_exhaustive]
112#[derive(Debug, Error)]
113pub enum StableCellLedgerError {
114    /// Stable-cell envelope is corrupt or unexpected.
115    #[error(transparent)]
116    Payload(#[from] StableCellPayloadError),
117    /// Stable-cell value bytes are not a valid ledger record.
118    #[error("stable-cell ledger record decode failed")]
119    Record(#[source] serde_cbor::Error),
120}
121
122/// Decode the raw value payload from an `ic-stable-structures::Cell` memory.
123///
124/// This helper is intentionally narrow: it recognizes the physical stable-cell
125/// envelope and returns the value bytes. It does not deserialize those bytes or
126/// decide whether they represent a valid allocation ledger.
127pub fn decode_stable_cell_payload<M: Memory>(
128    memory: &M,
129) -> Result<Vec<u8>, StableCellPayloadError> {
130    if memory.size() == 0 {
131        return Err(StableCellPayloadError::NotStableCell);
132    }
133
134    let mut header = [0; STABLE_CELL_HEADER_SIZE];
135    memory.read(0, &mut header);
136    if &header[0..3] != STABLE_CELL_MAGIC {
137        return Err(StableCellPayloadError::NotStableCell);
138    }
139    if header[3] != STABLE_CELL_LAYOUT_VERSION {
140        return Err(StableCellPayloadError::UnexpectedLayoutVersion { version: header[3] });
141    }
142
143    let value_len = u64::from(u32::from_le_bytes([
144        header[4], header[5], header[6], header[7],
145    ]));
146    let available_bytes = memory.size().saturating_mul(WASM_PAGE_SIZE_BYTES);
147    let payload_capacity = available_bytes.saturating_sub(STABLE_CELL_VALUE_OFFSET);
148    if value_len > payload_capacity {
149        return Err(StableCellPayloadError::InvalidLength {
150            value_len,
151            available_bytes: payload_capacity,
152        });
153    }
154    let value_len = usize::try_from(value_len)
155        .map_err(|_| StableCellPayloadError::LengthOverflow { value_len })?;
156
157    let mut bytes = vec![0; value_len];
158    memory.read(STABLE_CELL_VALUE_OFFSET, &mut bytes);
159    Ok(bytes)
160}
161
162/// Decode a `StableCellLedgerRecord` from stable-cell value bytes.
163///
164/// This decodes only the cell value payload, not the enclosing stable-cell
165/// header. Use [`decode_stable_cell_payload`] first when inspecting raw stable
166/// memory.
167///
168/// The returned record is decoded DTO state, not authority. Recover through the
169/// embedded [`LedgerCommitStore`] before trusting any ledger payload.
170pub fn decode_stable_cell_ledger_record(
171    bytes: &[u8],
172) -> Result<StableCellLedgerRecord, serde_cbor::Error> {
173    serde_cbor::from_slice(bytes)
174}
175
176pub fn decode_stable_cell_ledger_record_from_memory<M: Memory>(
177    memory: &M,
178) -> Result<StableCellLedgerRecord, StableCellLedgerError> {
179    if memory.size() == 0 {
180        return Ok(StableCellLedgerRecord::default());
181    }
182
183    let payload = decode_stable_cell_payload(memory)?;
184    decode_stable_cell_ledger_record(&payload).map_err(StableCellLedgerError::Record)
185}
186
187/// Validate an existing stable-cell ledger record before opening it with
188/// `ic-stable-structures::Cell`.
189///
190/// `Cell::init` decodes the existing value through [`Storable::from_bytes`].
191/// That trait is panic-based, so the runtime preflights the raw memory with
192/// this fallible helper first. Empty memory is treated as uninitialized and is
193/// safe for `Cell::init` to create.
194pub fn validate_stable_cell_ledger_memory<M: Memory>(
195    memory: &M,
196) -> Result<(), StableCellLedgerError> {
197    decode_stable_cell_ledger_record_from_memory(memory)?;
198    Ok(())
199}
200
201fn serialize_record(record: &StableCellLedgerRecord) -> Vec<u8> {
202    serde_cbor::to_vec(record).unwrap_or_else(|err| {
203        panic!("StableCellLedgerRecord serialize failed: {err}");
204    })
205}
206
207#[cfg(test)]
208mod tests {
209    use super::*;
210    use ic_stable_structures::{Cell, VectorMemory};
211
212    fn hex_fixture(contents: &str) -> Vec<u8> {
213        let hex = contents
214            .chars()
215            .filter(|char| !char.is_whitespace())
216            .collect::<String>();
217        assert_eq!(hex.len() % 2, 0, "fixture hex must have byte pairs");
218        hex.as_bytes()
219            .chunks_exact(2)
220            .map(|pair| {
221                let pair = std::str::from_utf8(pair).expect("fixture hex is utf8");
222                u8::from_str_radix(pair, 16).expect("fixture hex byte")
223            })
224            .collect()
225    }
226
227    #[test]
228    fn stable_cell_ledger_record_round_trips_through_cell() {
229        let memory = VectorMemory::default();
230        let record = StableCellLedgerRecord::default();
231        let cell = Cell::init(memory.clone(), record.clone());
232
233        assert_eq!(cell.get(), &record);
234        let payload = decode_stable_cell_payload(&memory).expect("decode stable cell payload");
235        let decoded = StableCellLedgerRecord::from_bytes(Cow::Owned(payload));
236        assert_eq!(decoded, record);
237    }
238
239    #[test]
240    fn current_stable_cell_record_fixture_recovers() {
241        let bytes = hex_fixture(include_str!(
242            "../fixtures/current/stable_cell_record.cbor.hex"
243        ));
244        let record = decode_stable_cell_ledger_record(&bytes).expect("stable-cell fixture");
245
246        assert_eq!(
247            bytes,
248            serde_cbor::to_vec(&record).expect("re-encoded stable-cell fixture")
249        );
250        assert_eq!(
251            record
252                .store()
253                .recover()
254                .expect("fixture store recovers")
255                .current_generation(),
256            1
257        );
258    }
259
260    #[test]
261    fn stable_cell_ledger_record_rejects_unknown_top_level_fields() {
262        use serde_cbor::Value;
263        use std::collections::BTreeMap;
264
265        let mut map = BTreeMap::new();
266        map.insert(
267            Value::Text("store".to_string()),
268            serde_cbor::value::to_value(LedgerCommitStore::default()).expect("store value"),
269        );
270        map.insert(Value::Text("future_field".to_string()), Value::Bool(true));
271        let bytes = serde_cbor::to_vec(&Value::Map(map)).expect("unknown-field stable cell");
272
273        let err = decode_stable_cell_ledger_record(&bytes)
274            .expect_err("unknown stable-cell record field must fail closed");
275
276        assert!(err.to_string().contains("future_field"));
277    }
278
279    #[test]
280    fn stable_cell_payload_rejects_non_cell_memory() {
281        let memory = VectorMemory::default();
282        memory.grow(1);
283        memory.write(0, b"BAD");
284
285        assert_eq!(
286            decode_stable_cell_payload(&memory),
287            Err(StableCellPayloadError::NotStableCell)
288        );
289    }
290
291    #[test]
292    fn stable_cell_payload_rejects_empty_memory_without_panic() {
293        let memory = VectorMemory::default();
294
295        assert_eq!(
296            decode_stable_cell_payload(&memory),
297            Err(StableCellPayloadError::NotStableCell)
298        );
299    }
300
301    #[test]
302    fn stable_cell_ledger_preflight_classifies_bad_record_without_panic() {
303        let memory = VectorMemory::default();
304        memory.grow(1);
305        memory.write(0, STABLE_CELL_MAGIC);
306        memory.write(3, &[STABLE_CELL_LAYOUT_VERSION]);
307        memory.write(4, &1_u32.to_le_bytes());
308        memory.write(STABLE_CELL_VALUE_OFFSET, &[0xff]);
309
310        let err =
311            validate_stable_cell_ledger_memory(&memory).expect_err("bad record must be classified");
312
313        assert!(matches!(err, StableCellLedgerError::Record(_)));
314    }
315}
ic_memory/stable_cell.rs

ic_memory/
stable_cell.rs
