restructure

crates/concord/src/utils/mod.rs

@@ -0,0 +1,40 @@
+pub mod derive;
+
+use anyhow::{Result, anyhow, bail};
+use data_encoding::HEXLOWER;
+use rand::TryRng as _;
+use rand::rngs::SysRng;
+
+/// Uppercase and other non-canonical spellings are rejected.
+pub(crate) fn decode_hex_32(value: &str) -> Result<[u8; 32]> {
+    decode_hex_lower::<32>(value)
+}
+
+pub(crate) fn decode_hex_lower<const N: usize>(value: &str) -> Result<[u8; N]> {
+    let bytes = HEXLOWER
+        .decode(value.as_bytes())
+        .map_err(|error| anyhow!("invalid hex: {error}"))?;
+
+    let decoded: [u8; N] = bytes
+        .as_slice()
+        .try_into()
+        .map_err(|_| anyhow!("expected {N} bytes, got {}", bytes.len()))?;
+
+    if HEXLOWER.encode(&decoded) != value {
+        bail!("hex must be lowercase and canonical");
+    }
+
+    Ok(decoded)
+}
+
+pub(crate) fn fill_random(bytes: &mut [u8]) -> Result<()> {
+    SysRng
+        .try_fill_bytes(bytes)
+        .map_err(|error| anyhow!("os rng: {error}"))
+}
+
+pub(crate) fn random_32() -> Result<[u8; 32]> {
+    let mut bytes = [0u8; 32];
+    fill_random(&mut bytes)?;
+    Ok(bytes)
+}