1 files changed, 124 insertions, 0 deletions
diff --git a/src/value/canonical.rs b/src/value/canonical.rs
new file mode 100644
index 0000000..f1196f4
--- /dev/null
+++ b/src/value/canonical.rs
@@ -0,0 +1,124 @@
+// SPDX-License-Identifier: Apache-2.0
+
+use crate::value::Value;
+use alloc::vec::Vec;
+use core::cmp::Ordering;
+use serde::{de, ser};
+
+/// Manually serialize values to compare them.
+fn serialized_canonical_cmp(v1: &Value, v2: &Value) -> Ordering {
+    // There is an optimization to be done here, but it would take a lot more code
+    // and using mixing keys, Arrays or Maps as CanonicalValue is probably not the
+    // best use of this type as it is meant mainly to be used as keys.
+
+    let mut bytes1 = Vec::new();
+    let _ = crate::ser::into_writer(v1, &mut bytes1);
+    let mut bytes2 = Vec::new();
+    let _ = crate::ser::into_writer(v2, &mut bytes2);
+
+    match bytes1.len().cmp(&bytes2.len()) {
+        Ordering::Equal => bytes1.cmp(&bytes2),
+        x => x,
+    }
+}
+
+/// Compares two values uses canonical comparison, as defined in both
+/// RFC 7049 Section 3.9 (regarding key sorting) and RFC 8949 4.2.3 (as errata).
+///
+/// In short, the comparison follow the following rules:
+///   - If two keys have different lengths, the shorter one sorts earlier;
+///   - If two keys have the same length, the one with the lower value in
+///     (byte-wise) lexical order sorts earlier.
+///
+/// This specific comparison allows Maps and sorting that respect these two rules.
+pub fn cmp_value(v1: &Value, v2: &Value) -> Ordering {
+    use Value::*;
+
+    match (v1, v2) {
+        (Integer(i), Integer(o)) => {
+            // Because of the first rule above, two numbers might be in a different
+            // order than regular i128 comparison. For example, 10 < -1 in
+            // canonical ordering, since 10 serializes to `0x0a` and -1 to `0x20`,
+            // and -1 < -1000 because of their lengths.
+            i.canonical_cmp(o)
+        }
+        (Text(s), Text(o)) => match s.len().cmp(&o.len()) {
+            Ordering::Equal => s.cmp(o),
+            x => x,
+        },
+        (Bool(s), Bool(o)) => s.cmp(o),
+        (Null, Null) => Ordering::Equal,
+        (Tag(t, v), Tag(ot, ov)) => match Value::from(*t).partial_cmp(&Value::from(*ot)) {
+            Some(Ordering::Equal) | None => match v.partial_cmp(ov) {
+                Some(x) => x,
+                None => serialized_canonical_cmp(v1, v2),
+            },
+            Some(x) => x,
+        },
+        (_, _) => serialized_canonical_cmp(v1, v2),
+    }
+}
+
+/// A CBOR Value that impl Ord and Eq to allow sorting of values as defined in both
+/// RFC 7049 Section 3.9 (regarding key sorting) and RFC 8949 4.2.3 (as errata).
+///
+/// Since a regular [Value] can be
+#[derive(Clone, Debug)]
+pub struct CanonicalValue(Value);
+
+impl PartialEq for CanonicalValue {
+    fn eq(&self, other: &Self) -> bool {
+        self.cmp(other) == Ordering::Equal
+    }
+}
+
+impl Eq for CanonicalValue {}
+
+impl From<Value> for CanonicalValue {
+    fn from(v: Value) -> Self {
+        Self(v)
+    }
+}
+
+impl From<CanonicalValue> for Value {
+    fn from(v: CanonicalValue) -> Self {
+        v.0
+    }
+}
+
+impl ser::Serialize for CanonicalValue {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: ser::Serializer,
+    {
+        self.0.serialize(serializer)
+    }
+}
+
+impl<'de> de::Deserialize<'de> for CanonicalValue {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: de::Deserializer<'de>,
+    {
+        Value::deserialize(deserializer).map(Into::into)
+    }
+
+    fn deserialize_in_place<D>(deserializer: D, place: &mut Self) -> Result<(), D::Error>
+    where
+        D: de::Deserializer<'de>,
+    {
+        Value::deserialize_in_place(deserializer, &mut place.0)
+    }
+}
+
+impl Ord for CanonicalValue {
+    fn cmp(&self, other: &Self) -> Ordering {
+        cmp_value(&self.0, &other.0)
+    }
+}
+
+impl PartialOrd for CanonicalValue {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(cmp_value(&self.0, &other.0))
+    }
+}