ic_wire/contract/
mod.rs

1#[cfg(test)]
2mod tests;
3
4use crate::{Error, Limits, Wire};
5use alloc::vec::Vec;
6use core::marker::PhantomData;
7use postcard::ser_flavors::Flavor;
8
9pub(crate) const HEADER: usize = 11;
10
11/// One consumer-owned endpoint contract. IDs must be unique across incompatible
12/// layouts and methods. A source rename alone must not change its identity.
13pub trait Method {
14    /// Typed request, including any consumer-owned proof/envelope.
15    /// Borrowed fields can use lifetimes on the implementing method marker.
16    type Request: Wire;
17    /// Typed response, typically `Result<Success, ApplicationError>`.
18    type Response: Wire;
19    /// Stable contract identity assigned by the consumer.
20    const ID: u64;
21    /// Exact exported IC method name; used by typed transport adapters.
22    const NAME: &'static str;
23    /// Request admission budget.
24    const REQUEST_LIMITS: Limits;
25    /// Reply admission budget.
26    const RESPONSE_LIMITS: Limits;
27}
28
29macro_rules! retained {
30    ($name:ident) => {
31        /// Validated, immutable bytes bound to a method and direction. Retain
32        /// these for retries; the codec does not decide when retry is safe.
33        pub struct $name<M: Method> {
34            bytes: Vec<u8>,
35            method: PhantomData<fn() -> M>,
36        }
37        impl<M: Method> $name<M> {
38            /// Borrow the exact encoding for transport or hashing.
39            pub fn as_bytes(&self) -> &[u8] {
40                &self.bytes
41            }
42            /// Transfer ownership to a transport or persistence owner.
43            pub fn into_bytes(self) -> Vec<u8> {
44                self.bytes
45            }
46        }
47    };
48}
49retained!(RequestBytes);
50retained!(ResponseBytes);
51
52pub(crate) fn admit<T: Wire>(limits: Limits) -> Result<usize, Error> {
53    let shape = T::SHAPE;
54    if [shape.bytes, shape.heap, shape.nodes, shape.depth].contains(&usize::MAX) {
55        return Err(Error::SchemaLimit);
56    }
57    let size = shape.bytes.checked_add(HEADER).ok_or(Error::SchemaLimit)?;
58    let allocation = shape.heap.checked_add(size).ok_or(Error::SchemaLimit)?;
59    if size > limits.bytes
60        || allocation > limits.allocation
61        || shape.nodes > limits.nodes
62        || shape.depth > limits.depth
63    {
64        return Err(Error::SchemaLimit);
65    }
66    Ok(size)
67}
68
69// Reserve fallibly once, then initialize only emitted bytes. Capacity is not
70// the schema limit: allocators may return more capacity than requested.
71pub(crate) struct Output {
72    pub(crate) bytes: Vec<u8>,
73    pub(crate) limit: usize,
74}
75impl Flavor for Output {
76    type Output = Vec<u8>;
77    fn try_push(&mut self, byte: u8) -> postcard::Result<()> {
78        if self.bytes.len() == self.limit {
79            return Err(postcard::Error::SerializeBufferFull);
80        }
81        self.bytes.push(byte);
82        Ok(())
83    }
84    fn try_extend(&mut self, bytes: &[u8]) -> postcard::Result<()> {
85        if bytes.len() > self.limit - self.bytes.len() {
86            return Err(postcard::Error::SerializeBufferFull);
87        }
88        self.bytes.extend_from_slice(bytes);
89        Ok(())
90    }
91    fn finalize(self) -> postcard::Result<Self::Output> {
92        Ok(self.bytes)
93    }
94}
95
96// Count with the same admitted byte ceiling as encoding, without output storage.
97struct Size {
98    bytes: usize,
99    limit: usize,
100}
101impl Flavor for Size {
102    type Output = usize;
103    fn try_push(&mut self, _: u8) -> postcard::Result<()> {
104        self.try_extend(&[0])
105    }
106    fn try_extend(&mut self, bytes: &[u8]) -> postcard::Result<()> {
107        if bytes.len() > self.limit - self.bytes {
108            return Err(postcard::Error::SerializeBufferFull);
109        }
110        self.bytes += bytes.len();
111        Ok(())
112    }
113    fn finalize(self) -> postcard::Result<usize> {
114        Ok(self.bytes)
115    }
116}
117
118fn encoded_len<T: Wire>(limits: Limits, value: &T) -> Result<usize, Error> {
119    let limit = admit::<T>(limits)?;
120    postcard::serialize_with_flavor(
121        value,
122        Size {
123            bytes: HEADER,
124            limit,
125        },
126    )
127    .map_err(|_| Error::Malformed)
128}
129
130// Compare canonical serialization directly with the admitted payload. Continue
131// after a mismatch so serializer errors still retain their Malformed mapping.
132pub(crate) struct Compare<'a> {
133    pub(crate) remaining: &'a [u8],
134    pub(crate) allowance: usize,
135    pub(crate) equal: bool,
136}
137impl Flavor for Compare<'_> {
138    type Output = bool;
139    #[inline(always)]
140    fn try_push(&mut self, byte: u8) -> postcard::Result<()> {
141        if self.allowance == 0 {
142            return Err(postcard::Error::SerializeBufferFull);
143        }
144        self.allowance -= 1;
145        if let Some((first, rest)) = self.remaining.split_first() {
146            self.equal &= *first == byte;
147            self.remaining = rest;
148        } else {
149            self.equal = false;
150        }
151        Ok(())
152    }
153    fn try_extend(&mut self, bytes: &[u8]) -> postcard::Result<()> {
154        if let [byte] = bytes {
155            return self.try_push(*byte);
156        }
157        if bytes.len() > self.allowance {
158            return Err(postcard::Error::SerializeBufferFull);
159        }
160        self.allowance -= bytes.len();
161        if let Some((prefix, rest)) = self.remaining.split_at_checked(bytes.len()) {
162            // Wasm's bytewise memcmp is expensive for bulk byte/text payloads.
163            // Exact unaligned word loads preserve canonical equality; no hash or
164            // scratch allocation is involved. Small scalar writes stay simple.
165            self.equal &= if cfg!(any(target_arch = "wasm32", test))
166                && core::ptr::eq(prefix.as_ptr(), bytes.as_ptr())
167            {
168                // Borrowed decoding can serialize the exact input region.
169                // Its length and allowance were checked above; equality needs no scan.
170                true
171            } else if cfg!(any(target_arch = "wasm32", test)) && bytes.len() >= 8 {
172                if bytes.len() >= 64 {
173                    let (left, left_tail) = prefix.as_chunks::<16>();
174                    let (right, right_tail) = bytes.as_chunks::<16>();
175                    left.iter().zip(right).fold(0_u128, |difference, (a, b)| {
176                        difference | (u128::from_ne_bytes(*a) ^ u128::from_ne_bytes(*b))
177                    }) == 0
178                        && left_tail == right_tail
179                } else {
180                    let (left, left_tail) = prefix.as_chunks::<8>();
181                    let (right, right_tail) = bytes.as_chunks::<8>();
182                    left.iter().zip(right).fold(0_u64, |difference, (a, b)| {
183                        difference | (u64::from_ne_bytes(*a) ^ u64::from_ne_bytes(*b))
184                    }) == 0
185                        && left_tail == right_tail
186                }
187            } else {
188                prefix == bytes
189            };
190            self.remaining = rest;
191        } else {
192            self.equal = false;
193            self.remaining = &[];
194        }
195        Ok(())
196    }
197    fn finalize(self) -> postcard::Result<Self::Output> {
198        Ok(self.equal && self.remaining.is_empty())
199    }
200}
201
202fn encode<T: Wire>(id: u64, direction: u8, limits: Limits, value: &T) -> Result<Vec<u8>, Error> {
203    let size = admit::<T>(limits)?;
204    let mut bytes = Vec::new();
205    bytes
206        .try_reserve_exact(size)
207        .map_err(|_| Error::Allocation)?;
208    bytes.extend_from_slice(&header(id, direction));
209    postcard::serialize_with_flavor(value, Output { bytes, limit: size })
210        .map_err(|_| Error::Malformed)
211}
212
213fn decode<'de, T: Wire + serde::Deserialize<'de>>(
214    id: u64,
215    direction: u8,
216    limits: Limits,
217    bytes: &'de [u8],
218) -> Result<T, Error> {
219    let size = admit::<T>(limits)?;
220    if bytes.len() > size || bytes.len() > limits.bytes {
221        return Err(Error::Limit);
222    }
223    let payload = payload(id, direction, bytes)?;
224    let (value, rest) = postcard::take_from_bytes::<T>(payload).map_err(|_| Error::Malformed)?;
225    if !rest.is_empty() {
226        return Err(Error::Trailing);
227    }
228    let equal = postcard::serialize_with_flavor(
229        &value,
230        Compare {
231            remaining: payload,
232            allowance: size - HEADER,
233            equal: true,
234        },
235    )
236    .map_err(|_| Error::Malformed)?;
237    if !equal {
238        return Err(Error::Noncanonical);
239    }
240    Ok(value)
241}
242
243/// Encode once, retaining exact request bytes bound to `M`.
244pub fn encode_request<M: Method>(value: &M::Request) -> Result<RequestBytes<M>, Error> {
245    Ok(RequestBytes {
246        bytes: encode(M::ID, 0, M::REQUEST_LIMITS, value)?,
247        method: PhantomData,
248    })
249}
250/// Measure the complete request envelope without allocating an output buffer.
251/// Uses the same schema admission as encoding. Custom serializers must be
252/// deterministic; sizing does not retain bytes for retries.
253pub fn encoded_request_len<M: Method>(value: &M::Request) -> Result<usize, Error> {
254    encoded_len(M::REQUEST_LIMITS, value)
255}
256/// Measure the complete response envelope without allocating an output buffer.
257/// Consumers can compare this with a delivery allowance before encoding. Schema
258/// admission still applies to the entire type, not just this value.
259pub fn encoded_response_len<M: Method>(value: &M::Response) -> Result<usize, Error> {
260    encoded_len(M::RESPONSE_LIMITS, value)
261}
262/// Decode a request only after method, direction, canonical and resource checks.
263pub fn decode_request<'de, M: Method>(bytes: &'de [u8]) -> Result<M::Request, Error>
264where
265    M::Request: serde::Deserialize<'de>,
266{
267    decode(M::ID, 0, M::REQUEST_LIMITS, bytes)
268}
269/// Encode a reply. Application errors belong inside `M::Response`.
270pub fn encode_response<M: Method>(value: &M::Response) -> Result<ResponseBytes<M>, Error> {
271    Ok(ResponseBytes {
272        bytes: encode(M::ID, 1, M::RESPONSE_LIMITS, value)?,
273        method: PhantomData,
274    })
275}
276/// Decode a reply under the selected method's response contract.
277pub fn decode_response<'de, M: Method>(bytes: &'de [u8]) -> Result<M::Response, Error>
278where
279    M::Response: serde::Deserialize<'de>,
280{
281    decode(M::ID, 1, M::RESPONSE_LIMITS, bytes)
282}
283
284pub(crate) fn header(id: u64, direction: u8) -> [u8; HEADER] {
285    let mut header = [0; HEADER];
286    header[..2].copy_from_slice(b"IW");
287    header[2..10].copy_from_slice(&id.to_le_bytes());
288    header[10] = direction;
289    header
290}
291pub(crate) fn payload(id: u64, direction: u8, bytes: &[u8]) -> Result<&[u8], Error> {
292    if bytes.len() < HEADER {
293        return Err(Error::Malformed);
294    }
295    if &bytes[..2] != b"IW" || bytes[2..10] != id.to_le_bytes() || bytes[10] != direction {
296        return Err(Error::Identity);
297    }
298    Ok(&bytes[HEADER..])
299}
ic_wire/contract/mod.rs

ic_wire/contract/
mod.rs
