feat: first cut on M0 - base structure of project

crates/bds-core/src/util/checksum.rs

@@ -0,0 +1,48 @@
+use sha2::{Digest, Sha256};
+
+/// Compute a hex-encoded SHA-256 hash of the given content.
+pub fn content_hash(content: &[u8]) -> String {
+    let mut hasher = Sha256::new();
+    hasher.update(content);
+    let result = hasher.finalize();
+    hex::encode(result)
+}
+
+// sha2 doesn't include hex encoding, so we use a tiny inline helper.
+mod hex {
+    const HEX_CHARS: &[u8; 16] = b"0123456789abcdef";
+
+    pub fn encode(bytes: impl AsRef<[u8]>) -> String {
+        let bytes = bytes.as_ref();
+        let mut s = String::with_capacity(bytes.len() * 2);
+        for &b in bytes {
+            s.push(HEX_CHARS[(b >> 4) as usize] as char);
+            s.push(HEX_CHARS[(b & 0xf) as usize] as char);
+        }
+        s
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn known_hash() {
+        // SHA-256 of "hello"
+        let hash = content_hash(b"hello");
+        assert_eq!(
+            hash,
+            "2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824"
+        );
+    }
+
+    #[test]
+    fn empty_hash() {
+        let hash = content_hash(b"");
+        assert_eq!(
+            hash,
+            "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
+        );
+    }
+}