max / everycycle

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1	//! Deterministic JSON encoding for the payload-signing contract.
2	//!
3	//! Rule: serialize a payload into `serde_json::Value`, then write that
4	//! value to a string. The default `serde_json::Map` is `BTreeMap` (the
5	//! `preserve_order` feature is not enabled here), so `to_value`
6	//! produces sorted keys at every level. `to_string` emits compact JSON
7	//! with no insignificant whitespace and no trailing newline.
8	//!
9	//! The writer and the verifier both call `canonical_json`. Two
10	//! `serde_json` invocations are not free, but the payloads are small
11	//! (single-KB), and using `serde_json` directly keeps the canonical
12	//! rule a function of a widely-audited dependency rather than a
13	//! hand-rolled encoder.
14	//!
15	//! `serde_json::Value` represents numbers via its own `Number` type,
16	//! preserving the input formatting (integers stay integral, floats stay
17	//! float). Floats are written by Rust's `f64::to_string`, which is
18	//! bit-stable across Rust versions in stable releases.
19
20	use serde::Serialize;
21
22	#[derive(Debug)]
23	pub enum CanonicalError {
24	Serde(serde_json::Error),
25	}
26
27	impl core::fmt::Display for CanonicalError {
28	fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
29	match self {
30	Self::Serde(e) => write!(f, "canonical encoding failed: {e}"),
31	}
32	}
33	}
34
35	impl std::error::Error for CanonicalError {
36	fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
37	match self {
38	Self::Serde(e) => Some(e),
39	}
40	}
41	}
42
43	impl From<serde_json::Error> for CanonicalError {
44	fn from(e: serde_json::Error) -> Self {
45	Self::Serde(e)
46	}
47	}
48
49	/// Encode `payload` as canonical JSON suitable for signing.
50	///
51	/// See the module doc for the encoding rule. The output is the exact
52	/// byte string a verifier will re-derive from the same `payload`.
53	pub fn canonical_json<T: Serialize>(payload: &T) -> Result<String, CanonicalError> {
54	let value = serde_json::to_value(payload)?;
55	Ok(serde_json::to_string(&value)?)
56	}
57