feat: add community ui (#52)

Reviewed-on: #52

crates/concord/src/utils/mod.rs

@@ -1,12 +1,18 @@
+pub mod base64url;
 pub mod derive;
 
 use anyhow::{Result, anyhow, bail};
 use data_encoding::HEXLOWER;
 use rand::TryRng as _;
 use rand::rngs::SysRng;
+use serde::Serialize;
 
+use crate::Extra;
+
+/// Decode a 64-character lowercase-hex string into 32 bytes.
+///
 /// Uppercase and other non-canonical spellings are rejected.
-pub(crate) fn decode_hex_32(value: &str) -> Result<[u8; 32]> {
+pub fn decode_hex_32(value: &str) -> Result<[u8; 32]> {
     decode_hex_lower::<32>(value)
 }
 
@@ -38,3 +44,34 @@ pub(crate) fn random_32() -> Result<[u8; 32]> {
     fill_random(&mut bytes)?;
     Ok(bytes)
 }
+
+/// Hex to unpadded base64url for one 32-byte §8 value.
+pub(crate) fn hex32_to_base64(value: &str) -> Result<String> {
+    Ok(base64url::encode(&decode_hex_32(value)?))
+}
+
+/// Unpadded base64url to lowercase hex for one 32-byte §8 value.
+pub(crate) fn base64_to_hex32(value: &str) -> Result<String> {
+    Ok(HEXLOWER.encode(&base64url::decode_32(value)?))
+}
+
+/// Canonical JSON bytes: the total-order tie-break every content merge uses.
+pub(crate) fn canonical<T: Serialize>(value: &T) -> String {
+    serde_json::to_string(value).unwrap_or_default()
+}
+
+/// Unions an unknown-field map. Where both sides carry a key, the
+/// lexicographically lowest canonical bytes win, so two devices converge
+/// instead of flapping.
+pub(crate) fn union(into: &mut Extra, other: Extra) {
+    for (key, value) in other {
+        let replace = match into.get(&key) {
+            Some(existing) => canonical(&value) < canonical(existing),
+            None => true,
+        };
+
+        if replace {
+            into.insert(key, value);
+        }
+    }
+}