lib: Add convenience function to decode hex strings

lib/src/git_backend.rs

@@ -1506,9 +1506,7 @@ fn tree_value_from_json(json: &serde_json::Value) -> TreeValue {
 
 fn bytes_vec_from_json(value: &serde_json::Value) -> Vec<u8> {
     let s = value.as_str().unwrap();
-    let mut val = vec![0; s.len() / 2];
-    faster_hex::hex_decode(s.as_bytes(), &mut val).unwrap();
-    val
+    crate::hex_util::decode_hex_string(s).unwrap()
 }
 
 #[cfg(test)]

lib/src/hex_util.rs

@@ -51,6 +51,13 @@ pub fn to_reverse_hex(forward_hex: &str) -> Option<String> {
         .collect()
 }
 
+pub fn decode_hex_string(hex: &str) -> Option<Vec<u8>> {
+    let mut dst = vec![0; hex.len() / 2];
+    faster_hex::hex_decode(hex.as_bytes(), &mut dst)
+        .ok()
+        .map(|()| dst)
+}
+
 /// Calculates common prefix length of two byte sequences. The length
 /// to be returned is a number of hexadecimal digits.
 pub fn common_hex_len(bytes_a: &[u8], bytes_b: &[u8]) -> usize {

lib/src/object_id.rs

@@ -105,6 +105,8 @@ macro_rules! impl_id_type {
 pub(crate) use id_type;
 pub(crate) use impl_id_type;
 
+use crate::hex_util::decode_hex_string;
+
 /// An identifier prefix (typically from a type implementing the [`ObjectId`]
 /// trait) with facilities for converting between bytes and a hex string.
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -120,11 +122,10 @@ impl HexPrefix {
     /// hex to bytes.
     pub fn new(prefix: &str) -> Option<HexPrefix> {
         let has_odd_byte = prefix.len() & 1 != 0;
-        let mut min_prefix_bytes = vec![0; prefix.len() / 2 + has_odd_byte as usize];
-        if has_odd_byte {
-            faster_hex::hex_decode(&format!("{prefix}0").as_bytes(), &mut min_prefix_bytes).ok()?;
+        let min_prefix_bytes = if has_odd_byte {
+            decode_hex_string(&format!("{prefix}0"))?
         } else {
-            faster_hex::hex_decode(prefix.as_bytes(), &mut min_prefix_bytes).ok()?;
+            decode_hex_string(prefix)?
         };
         Some(HexPrefix {
             min_prefix_bytes,

lib/src/simple_op_heads_store.rs

@@ -21,6 +21,7 @@ use std::fs;
 use std::path::Path;
 use std::path::PathBuf;
 
+use crate::hex_util::decode_hex_string;
 use crate::lock::FileLock;
 use crate::object_id::ObjectId;
 use crate::op_heads_store::OpHeadsStore;
@@ -97,8 +98,7 @@ impl OpHeadsStore for SimpleOpHeadsStore {
             let op_head_file_name = op_head_entry.unwrap().file_name();
             let op_head_file_name = op_head_file_name.to_str().unwrap();
 
-            let mut op_head = vec![0; op_head_file_name.len() / 2];
-            if faster_hex::hex_decode(op_head_file_name.as_bytes(), &mut op_head).is_ok() {
+            if let Some(op_head) = decode_hex_string(op_head_file_name) {
                 op_heads.push(OperationId::new(op_head));
             }
         }