feat(rust/hermes-ipfs): Doc Sync .new and .diff payloads (#681)

Author: no30bit

.config/dictionaries/project.dic

@@ -27,6 +27,7 @@ blockdiag
 blockfetch
 blosc
 bmac
+bytemuck
 Bogale
 bootstrapper
 BROTLI

rust/hermes-ipfs/Cargo.toml

@@ -17,7 +17,8 @@ doc-sync = ["minicbor", "ed25519-dalek", "catalyst-types"]
 
 [dependencies]
 anyhow = "1.0.100"
-derive_more = {version = "2.0.1", features = ["from","into","display"] }
+bytemuck = { version = "1.23.2", features = ["derive", "extern_crate_alloc"] }
+derive_more = {version = "2.0.1", features = ["from", "into", "display", "try_from", "deref"] }
 ipld-core = { version = "0.4.1", features = ["serde"]}
 # A fork of crates-io version with updated dependencies (`libp2p` and `ring` in particular).
 # rev-26b99cb as at July 30, 2025

rust/hermes-ipfs/src/doc_sync/envelope.rs

@@ -128,6 +128,12 @@ impl EnvelopePayload {
         &self.payload
     }
 
+    /// Returns the decoded payload body.
+    #[must_use]
+    pub fn payload<T: for<'a> Decode<'a, ()>>(&self) -> Result<(), minicbor::decode::Error> {
+        minicbor::decode(self.payload_bytes())
+    }
+
     /// Returns CBOR bytes for `[peer, seq, ver, payload]`.
     ///
     /// These are the bytes the spec signs over.

rust/hermes-ipfs/src/doc_sync/mod.rs

@@ -2,7 +2,29 @@
 
 mod envelope;
 
+pub mod payload;
+
 pub use envelope::{Envelope, EnvelopePayload};
 
 /// Current document synchronization protocol version.
 const PROTOCOL_VERSION: u64 = 1;
+
+/// `CID` version that Doc Sync supports.
+const CID_VERSION: u8 = 1;
+
+/// `CID` codec that Doc Sync supports (CBOR).
+const CID_CODEC: u8 = 0x51;
+
+/// `CID` multihash code that Doc Sync supports (SHA256).
+const CID_MULTIHASH_CODE: u8 = 0x12;
+
+/// `CID` multihash digest size that Doc Sync supports.
+const CID_DIGEST_SIZE: u8 = 32;
+
+/// Validates CID according to Doc Sync specification constraints.
+fn validate_cid(cid: &crate::Cid) -> bool {
+    cid.version() as u8 == CID_VERSION
+        && cid.codec() == u64::from(CID_CODEC)
+        && cid.hash().code() == u64::from(CID_MULTIHASH_CODE)
+        && cid.hash().digest().len() == usize::from(CID_DIGEST_SIZE)
+}