port basic config and data structures

core/src/utils/wrapper_opaque.rs

@@ -0,0 +1,243 @@
+// Copyright 2019-2023 Parity Technologies (UK) Ltd.
+// This file is dual-licensed as Apache-2.0 or GPL-3.0.
+// see LICENSE for license details.
+
+use super::PhantomDataSendSync;
+use codec::{Compact, Decode, DecodeAll, Encode};
+use derivative::Derivative;
+use scale_decode::{IntoVisitor, Visitor};
+use scale_encode::EncodeAsType;
+
+/// A wrapper for any type `T` which implement encode/decode in a way compatible with `Vec<u8>`.
+/// [`WrapperKeepOpaque`] stores the type only in its opaque format, aka as a `Vec<u8>`. To
+/// access the real type `T` [`Self::try_decode`] needs to be used.
+// Dev notes:
+//
+// - This is adapted from [here](https://github.com/paritytech/substrate/blob/master/frame/support/src/traits/misc.rs).
+// - The encoded bytes will be a compact encoded length followed by that number of bytes.
+// - However, the TypeInfo describes the type as a composite with first a compact encoded length and next the type itself.
+//  [`Encode`] and [`Decode`] impls will "just work" to take this into a `Vec<u8>`, but we need a custom [`EncodeAsType`]
+//  and [`Visitor`] implementation to encode and decode based on TypeInfo.
+#[derive(Derivative, Encode, Decode)]
+#[derivative(
+    Debug(bound = ""),
+    Clone(bound = ""),
+    PartialEq(bound = ""),
+    Eq(bound = ""),
+    Default(bound = ""),
+    Hash(bound = "")
+)]
+pub struct WrapperKeepOpaque<T> {
+    data: Vec<u8>,
+    _phantom: PhantomDataSendSync<T>,
+}
+
+impl<T> WrapperKeepOpaque<T> {
+    /// Try to decode the wrapped type from the inner `data`.
+    ///
+    /// Returns `None` if the decoding failed.
+    pub fn try_decode(&self) -> Option<T>
+    where
+        T: Decode,
+    {
+        T::decode_all(&mut &self.data[..]).ok()
+    }
+
+    /// Returns the length of the encoded `T`.
+    pub fn encoded_len(&self) -> usize {
+        self.data.len()
+    }
+
+    /// Returns the encoded data.
+    pub fn encoded(&self) -> &[u8] {
+        &self.data
+    }
+
+    /// Create from the given encoded `data`.
+    pub fn from_encoded(data: Vec<u8>) -> Self {
+        Self {
+            data,
+            _phantom: PhantomDataSendSync::new(),
+        }
+    }
+
+    /// Create from some raw value by encoding it.
+    pub fn from_value(value: T) -> Self
+    where
+        T: Encode,
+    {
+        Self {
+            data: value.encode(),
+            _phantom: PhantomDataSendSync::new(),
+        }
+    }
+}
+
+impl<T> EncodeAsType for WrapperKeepOpaque<T> {
+    fn encode_as_type_to(
+        &self,
+        type_id: u32,
+        types: &scale_info::PortableRegistry,
+        out: &mut Vec<u8>,
+    ) -> Result<(), scale_encode::Error> {
+        use scale_encode::error::{Error, ErrorKind, Kind};
+
+        let Some(ty) = types.resolve(type_id) else {
+            return Err(Error::new(ErrorKind::TypeNotFound(type_id)));
+        };
+
+        // Do a basic check that the target shape lines up.
+        let scale_info::TypeDef::Composite(_) = &ty.type_def else {
+            return Err(Error::new(ErrorKind::WrongShape {
+                actual: Kind::Struct,
+                expected: type_id,
+            }));
+        };
+
+        // Check that the name also lines up.
+        if ty.path.ident().as_deref() != Some("WrapperKeepOpaque") {
+            return Err(Error::new(ErrorKind::WrongShape {
+                actual: Kind::Struct,
+                expected: type_id,
+            }));
+        }
+
+        // Just blat the bytes out.
+        self.data.encode_to(out);
+        Ok(())
+    }
+}
+
+pub struct WrapperKeepOpaqueVisitor<T>(std::marker::PhantomData<T>);
+impl<T> Visitor for WrapperKeepOpaqueVisitor<T> {
+    type Value<'scale, 'info> = WrapperKeepOpaque<T>;
+    type Error = scale_decode::Error;
+
+    fn visit_composite<'scale, 'info>(
+        self,
+        value: &mut scale_decode::visitor::types::Composite<'scale, 'info>,
+        _type_id: scale_decode::visitor::TypeId,
+    ) -> Result<Self::Value<'scale, 'info>, Self::Error> {
+        use scale_decode::error::{Error, ErrorKind};
+
+        if value.path().ident().as_deref() != Some("WrapperKeepOpaque") {
+            return Err(Error::custom_str(
+                "Type to decode is not 'WrapperTypeKeepOpaque'",
+            ));
+        }
+        if value.remaining() != 2 {
+            return Err(Error::new(ErrorKind::WrongLength {
+                actual_len: value.remaining(),
+                expected_len: 2,
+            }));
+        }
+
+        // The field to decode is a compact len followed by bytes. Decode the length, then grab the bytes.
+        let Compact(len) = value
+            .decode_item(Compact::<u32>::into_visitor())
+            .expect("length checked")?;
+        let field = value.next().expect("length checked")?;
+
+        // Sanity check that the compact length we decoded lines up with the number of bytes encoded in the next field.
+        if field.bytes().len() != len as usize {
+            return Err(Error::custom_str("WrapperTypeKeepOpaque compact encoded length doesn't line up with encoded byte len"));
+        }
+
+        Ok(WrapperKeepOpaque {
+            data: field.bytes().to_vec(),
+            _phantom: PhantomDataSendSync::new(),
+        })
+    }
+}
+
+impl<T> IntoVisitor for WrapperKeepOpaque<T> {
+    type Visitor = WrapperKeepOpaqueVisitor<T>;
+    fn into_visitor() -> Self::Visitor {
+        WrapperKeepOpaqueVisitor(std::marker::PhantomData)
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use scale_decode::DecodeAsType;
+
+    use super::*;
+
+    // Copied from https://github.com/paritytech/substrate/blob/master/frame/support/src/traits/misc.rs
+    // and used for tests to check that we can work with the expected TypeInfo without needing to import
+    // the frame_support crate, which has quite a lot of dependencies.
+    impl<T: scale_info::TypeInfo + 'static> scale_info::TypeInfo for WrapperKeepOpaque<T> {
+        type Identity = Self;
+        fn type_info() -> scale_info::Type {
+            use scale_info::{build::Fields, meta_type, Path, Type, TypeParameter};
+
+            Type::builder()
+                .path(Path::new("WrapperKeepOpaque", module_path!()))
+                .type_params(vec![TypeParameter::new("T", Some(meta_type::<T>()))])
+                .composite(
+                    Fields::unnamed()
+                        .field(|f| f.compact::<u32>())
+                        .field(|f| f.ty::<T>().type_name("T")),
+                )
+        }
+    }
+
+    /// Given a type definition, return type ID and registry representing it.
+    fn make_type<T: scale_info::TypeInfo + 'static>() -> (u32, scale_info::PortableRegistry) {
+        let m = scale_info::MetaType::new::<T>();
+        let mut types = scale_info::Registry::new();
+        let id = types.register_type(&m);
+        let portable_registry: scale_info::PortableRegistry = types.into();
+        (id.id, portable_registry)
+    }
+
+    fn roundtrips_like_scale_codec<T>(t: T)
+    where
+        T: EncodeAsType
+            + DecodeAsType
+            + Encode
+            + Decode
+            + PartialEq
+            + std::fmt::Debug
+            + scale_info::TypeInfo
+            + 'static,
+    {
+        let (type_id, types) = make_type::<T>();
+
+        let scale_codec_encoded = t.encode();
+        let encode_as_type_encoded = t.encode_as_type(type_id, &types).unwrap();
+
+        assert_eq!(
+            scale_codec_encoded, encode_as_type_encoded,
+            "encoded bytes should match"
+        );
+
+        let decode_as_type_bytes = &mut &*scale_codec_encoded;
+        let decoded_as_type = T::decode_as_type(decode_as_type_bytes, type_id, &types)
+            .expect("decode-as-type decodes");
+
+        let decode_scale_codec_bytes = &mut &*scale_codec_encoded;
+        let decoded_scale_codec = T::decode(decode_scale_codec_bytes).expect("scale-codec decodes");
+
+        assert!(
+            decode_as_type_bytes.is_empty(),
+            "no bytes should remain in decode-as-type impl"
+        );
+        assert!(
+            decode_scale_codec_bytes.is_empty(),
+            "no bytes should remain in codec-decode impl"
+        );
+
+        assert_eq!(
+            decoded_as_type, decoded_scale_codec,
+            "decoded values should match"
+        );
+    }
+
+    #[test]
+    fn wrapper_keep_opaque_roundtrips_ok() {
+        roundtrips_like_scale_codec(WrapperKeepOpaque::from_value(123u64));
+        roundtrips_like_scale_codec(WrapperKeepOpaque::from_value(true));
+        roundtrips_like_scale_codec(WrapperKeepOpaque::from_value(vec![1u8, 2, 3, 4]));
+    }
+}