oid: Make `Oid::SHA1_LEN` public

The length of a SHA-1 object identifier is defined in various locations.
Instead of this redundancy, make the definition in `radicle-oid` public, and
use it in `radicle{-{core,protocol},}`.

crates/radicle-core/src/repo.rs

@@ -14,8 +14,8 @@ pub const RAD_PREFIX: &str = "rad:";
 pub enum IdError {
     #[error(transparent)]
     Multibase(#[from] multibase::Error),
-    #[error("invalid length: expected {expected} bytes, got {actual} bytes")]
+    #[error("invalid length: expected {} bytes, got {actual} bytes", Oid::LEN_SHA1)]
-    Length { expected: usize, actual: usize },
+    Length { actual: usize },
     #[error(fmt = fmt_mismatched_base_encoding)]
     MismatchedBaseEncoding {
         input: String,
@@ -106,12 +106,10 @@ impl RepoId {
     ///
     /// [multibase]: https://github.com/multiformats/multibase?tab=readme-ov-file#multibase-table
     pub fn from_canonical(input: &str) -> Result<Self, IdError> {
-        const EXPECTED_LEN: usize = 20;
         let (base, bytes) = multibase::decode(input)?;
         Self::guard_base_encoding(input, base)?;
-        let bytes: [u8; EXPECTED_LEN] =
+        let bytes: [u8; Oid::LEN_SHA1] =
             bytes.try_into().map_err(|bytes: Vec<u8>| IdError::Length {
-                expected: EXPECTED_LEN,
                 actual: bytes.len(),
             })?;
         Ok(Self(Oid::from_sha1(bytes)))

crates/radicle-oid/src/lib.rs

@@ -86,7 +86,7 @@ pub enum Oid {
 // length becomes popular?
 impl Oid {
     /// The length of a SHA-1 object identifier in bytes.
-    const SHA1_LEN: usize = 20;
+    pub const LEN_SHA1: usize = 20;
 
     /// A SHA-1 object identifier with all digest bytes set to zero.
     /// This is sometimes used as a sentinel value to indicate the absence of

crates/radicle-protocol/src/wire.rs

@@ -7,7 +7,6 @@ pub use message::{AddressType, MessageType};
 
 use std::convert::TryFrom;
 use std::fmt::Debug;
-use std::mem;
 use std::ops::Deref;
 use std::str::FromStr;
 use std::string::FromUtf8Error;
@@ -45,8 +44,11 @@ pub type Size = u16;
 
 #[derive(thiserror::Error, Debug)]
 pub enum Invalid {
-    #[error("invalid Git object identifier size: expected {expected}, got {actual}")]
+    #[error(
-    Oid { expected: usize, actual: usize },
+        "invalid Git object identifier size: expected {}, got {actual}",
+        git::Oid::LEN_SHA1
+    )]
+    Oid { actual: usize },
     #[error(transparent)]
     Bounded(#[from] crate::bounded::Error),
     #[error("invalid filter size: {actual}")]
@@ -382,19 +384,13 @@ where
 
 impl Decode for git::Oid {
     fn decode(buf: &mut impl Buf) -> Result<Self, Error> {
-        const LEN_EXPECTED: usize = mem::size_of::<raw::Oid>();
-
         let len = Size::decode(buf)? as usize;
 
-        if len != LEN_EXPECTED {
+        if len != git::Oid::LEN_SHA1 {
-            return Err(Invalid::Oid {
+            return Err(Invalid::Oid { actual: len }.into());
-                expected: LEN_EXPECTED,
-                actual: len,
-            }
-            .into());
         }
 
-        let buf: [u8; LEN_EXPECTED] = Decode::decode(buf)?;
+        let buf: [u8; git::Oid::SHA1_LEN] = Decode::decode(buf)?;
         let oid = raw::Oid::from_bytes(&buf).expect("the buffer is exactly the right size");
         let oid = git::Oid::from(oid);
 
@@ -633,7 +629,7 @@ mod tests {
     }
 
     #[quickcheck]
-    fn prop_oid(input: [u8; 20]) {
+    fn prop_oid(input: [u8; git::Oid::SHA1_LEN]) {
         roundtrip(git::Oid::from_sha1(input));
     }