Move hash into its own module

src/hash.rs

@@ -0,0 +1,19 @@
+use generic_array::GenericArray;
+use generic_array::typenum::U32;
+use sha2::{Digest, Sha256};
+
+pub type Sha256Hash = GenericArray<u8, U32>;
+
+/// Return a Sha256 hash for the given data.
+pub fn hash(val: &[u8]) -> Sha256Hash {
+    let mut hasher = Sha256::default();
+    hasher.input(val);
+    hasher.result()
+}
+
+/// Return the hash of the given hash extended with the given value.
+pub fn extend_and_hash(id: &Sha256Hash, val: &[u8]) -> Sha256Hash {
+    let mut hash_data = id.to_vec();
+    hash_data.extend_from_slice(val);
+    hash(&hash_data)
+}