feat(codec): add utility for untyped CBOR fragments (#327)

pallas-codec/src/utils.rs

@@ -649,6 +649,86 @@ impl<C, T> minicbor::Encode<C> for KeepRaw<'_, T> {
     }
 }
 
+/// Struct to hold arbitrary CBOR to be processed independently
+///
+/// # Examples
+///
+/// ```
+/// use pallas_codec::utils::AnyCbor;
+///
+/// let a = (123u16, (456u16, 789u16), 123u16);
+/// let data = minicbor::to_vec(a).unwrap();
+///
+/// let (_, any, _): (u16, AnyCbor, u16) = minicbor::decode(&data).unwrap();
+/// let confirm: (u16, u16) = any.into_decode().unwrap();
+/// assert_eq!(confirm, (456u16, 789u16));
+/// ```
+#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Clone)]
+pub struct AnyCbor {
+    inner: Vec<u8>,
+}
+
+impl AnyCbor {
+    pub fn raw_bytes(&self) -> &[u8] {
+        &self.inner
+    }
+
+    pub fn unwrap(self) -> Vec<u8> {
+        self.inner
+    }
+
+    pub fn from_encode<T>(other: T) -> Self
+    where
+        T: Encode<()>,
+    {
+        let inner = minicbor::to_vec(other).unwrap();
+        Self { inner }
+    }
+
+    pub fn into_decode<T>(self) -> Result<T, minicbor::decode::Error>
+    where
+        for<'b> T: Decode<'b, ()>,
+    {
+        minicbor::decode(&self.inner)
+    }
+}
+
+impl Deref for AnyCbor {
+    type Target = Vec<u8>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.inner
+    }
+}
+
+impl<'b, C> minicbor::Decode<'b, C> for AnyCbor {
+    fn decode(
+        d: &mut minicbor::Decoder<'b>,
+        _ctx: &mut C,
+    ) -> Result<Self, minicbor::decode::Error> {
+        let all = d.input();
+        let start = d.position();
+        d.skip()?;
+        let end = d.position();
+
+        Ok(Self {
+            inner: Vec::from(&all[start..end]),
+        })
+    }
+}
+
+impl<C> minicbor::Encode<C> for AnyCbor {
+    fn encode<W: minicbor::encode::Write>(
+        &self,
+        e: &mut minicbor::Encoder<W>,
+        _ctx: &mut C,
+    ) -> Result<(), minicbor::encode::Error<W::Error>> {
+        e.writer_mut()
+            .write_all(self.raw_bytes())
+            .map_err(minicbor::encode::Error::write)
+    }
+}
+
 #[derive(Serialize, Deserialize, Clone, Debug)]
 #[serde(from = "Option::<T>", into = "Option::<T>")]
 pub enum Nullable<T>