subxt_core/utils/
wrapper_opaque.rs

1// Copyright 2019-2024 Parity Technologies (UK) Ltd.
2// This file is dual-licensed as Apache-2.0 or GPL-3.0.
3// see LICENSE for license details.
4
5use super::PhantomDataSendSync;
6use codec::{Compact, Decode, DecodeAll, Encode};
7use derive_where::derive_where;
8use scale_decode::{ext::scale_type_resolver::visitor, IntoVisitor, TypeResolver, Visitor};
9use scale_encode::EncodeAsType;
10
11use alloc::format;
12use alloc::vec::Vec;
13
14/// A wrapper for any type `T` which implement encode/decode in a way compatible with `Vec<u8>`.
15/// [`WrapperKeepOpaque`] stores the type only in its opaque format, aka as a `Vec<u8>`. To
16/// access the real type `T` [`Self::try_decode`] needs to be used.
17// Dev notes:
18//
19// - This is adapted from [here](https://github.com/paritytech/substrate/blob/master/frame/support/src/traits/misc.rs).
20// - The encoded bytes will be a compact encoded length followed by that number of bytes.
21// - However, the TypeInfo describes the type as a composite with first a compact encoded length and next the type itself.
22//  [`Encode`] and [`Decode`] impls will "just work" to take this into a `Vec<u8>`, but we need a custom [`EncodeAsType`]
23//  and [`Visitor`] implementation to encode and decode based on TypeInfo.
24#[derive(Encode, Decode)]
25#[derive_where(Debug, Clone, PartialEq, Eq, Default, Hash)]
26pub struct WrapperKeepOpaque<T> {
27    data: Vec<u8>,
28    _phantom: PhantomDataSendSync<T>,
29}
30
31impl<T> WrapperKeepOpaque<T> {
32    /// Try to decode the wrapped type from the inner `data`.
33    ///
34    /// Returns `None` if the decoding failed.
35    pub fn try_decode(&self) -> Option<T>
36    where
37        T: Decode,
38    {
39        T::decode_all(&mut &self.data[..]).ok()
40    }
41
42    /// Returns the length of the encoded `T`.
43    pub fn encoded_len(&self) -> usize {
44        self.data.len()
45    }
46
47    /// Returns the encoded data.
48    pub fn encoded(&self) -> &[u8] {
49        &self.data
50    }
51
52    /// Create from the given encoded `data`.
53    pub fn from_encoded(data: Vec<u8>) -> Self {
54        Self {
55            data,
56            _phantom: PhantomDataSendSync::new(),
57        }
58    }
59
60    /// Create from some raw value by encoding it.
61    pub fn from_value(value: T) -> Self
62    where
63        T: Encode,
64    {
65        Self {
66            data: value.encode(),
67            _phantom: PhantomDataSendSync::new(),
68        }
69    }
70}
71
72impl<T> EncodeAsType for WrapperKeepOpaque<T> {
73    fn encode_as_type_to<R: TypeResolver>(
74        &self,
75        type_id: R::TypeId,
76        types: &R,
77        out: &mut Vec<u8>,
78    ) -> Result<(), scale_encode::Error> {
79        use scale_encode::error::{Error, ErrorKind, Kind};
80
81        let ctx = (type_id.clone(), out);
82        let visitor = visitor::new(ctx, |(type_id, _out), _| {
83            // Check that the target shape lines up: any other shape but composite is wrong.
84            Err(Error::new(ErrorKind::WrongShape {
85                actual: Kind::Struct,
86                expected_id: format!("{type_id:?}"),
87            }))
88        })
89        .visit_composite(|(_type_id, out), _path, _fields| {
90            self.data.encode_to(out);
91            Ok(())
92        });
93
94        types
95            .resolve_type(type_id.clone(), visitor)
96            .map_err(|_| Error::new(ErrorKind::TypeNotFound(format!("{:?}", type_id))))?
97    }
98}
99
100pub struct WrapperKeepOpaqueVisitor<T, R>(core::marker::PhantomData<(T, R)>);
101impl<T, R: TypeResolver> Visitor for WrapperKeepOpaqueVisitor<T, R> {
102    type Value<'scale, 'info> = WrapperKeepOpaque<T>;
103    type Error = scale_decode::Error;
104    type TypeResolver = R;
105
106    fn visit_composite<'scale, 'info>(
107        self,
108        value: &mut scale_decode::visitor::types::Composite<'scale, 'info, R>,
109        _type_id: R::TypeId,
110    ) -> Result<Self::Value<'scale, 'info>, Self::Error> {
111        use scale_decode::error::{Error, ErrorKind};
112        use scale_decode::visitor::DecodeError;
113
114        if value.name() != Some("WrapperKeepOpaque") {
115            return Err(Error::new(ErrorKind::VisitorDecodeError(
116                DecodeError::TypeResolvingError(format!(
117                    "Expected a type named 'WrapperKeepOpaque', got: {:?}",
118                    value.name()
119                )),
120            )));
121        }
122
123        if value.remaining() != 2 {
124            return Err(Error::new(ErrorKind::WrongLength {
125                actual_len: value.remaining(),
126                expected_len: 2,
127            }));
128        }
129
130        // The field to decode is a compact len followed by bytes. Decode the length, then grab the bytes.
131        let Compact(len) = value
132            .decode_item(Compact::<u32>::into_visitor())
133            .expect("length checked")?;
134        let field = value.next().expect("length checked")?;
135
136        // Sanity check that the compact length we decoded lines up with the number of bytes encoded in the next field.
137        if field.bytes().len() != len as usize {
138            return Err(Error::custom_str("WrapperTypeKeepOpaque compact encoded length doesn't line up with encoded byte len"));
139        }
140
141        Ok(WrapperKeepOpaque {
142            data: field.bytes().to_vec(),
143            _phantom: PhantomDataSendSync::new(),
144        })
145    }
146}
147
148impl<T> IntoVisitor for WrapperKeepOpaque<T> {
149    type AnyVisitor<R: TypeResolver> = WrapperKeepOpaqueVisitor<T, R>;
150    fn into_visitor<R: TypeResolver>() -> WrapperKeepOpaqueVisitor<T, R> {
151        WrapperKeepOpaqueVisitor(core::marker::PhantomData)
152    }
153}
154
155#[cfg(test)]
156mod test {
157    use scale_decode::DecodeAsType;
158
159    use alloc::vec;
160
161    use super::*;
162
163    // Copied from https://github.com/paritytech/substrate/blob/master/frame/support/src/traits/misc.rs
164    // and used for tests to check that we can work with the expected TypeInfo without needing to import
165    // the frame_support crate, which has quite a lot of dependencies.
166    impl<T: scale_info::TypeInfo + 'static> scale_info::TypeInfo for WrapperKeepOpaque<T> {
167        type Identity = Self;
168        fn type_info() -> scale_info::Type {
169            use scale_info::{build::Fields, meta_type, Path, Type, TypeParameter};
170
171            Type::builder()
172                .path(Path::new("WrapperKeepOpaque", module_path!()))
173                .type_params(vec![TypeParameter::new("T", Some(meta_type::<T>()))])
174                .composite(
175                    Fields::unnamed()
176                        .field(|f| f.compact::<u32>())
177                        .field(|f| f.ty::<T>().type_name("T")),
178                )
179        }
180    }
181
182    /// Given a type definition, return type ID and registry representing it.
183    fn make_type<T: scale_info::TypeInfo + 'static>() -> (u32, scale_info::PortableRegistry) {
184        let m = scale_info::MetaType::new::<T>();
185        let mut types = scale_info::Registry::new();
186        let id = types.register_type(&m);
187        let portable_registry: scale_info::PortableRegistry = types.into();
188        (id.id, portable_registry)
189    }
190
191    fn roundtrips_like_scale_codec<T>(t: T)
192    where
193        T: EncodeAsType
194            + DecodeAsType
195            + Encode
196            + Decode
197            + PartialEq
198            + core::fmt::Debug
199            + scale_info::TypeInfo
200            + 'static,
201    {
202        let (type_id, types) = make_type::<T>();
203
204        let scale_codec_encoded = t.encode();
205        let encode_as_type_encoded = t.encode_as_type(type_id, &types).unwrap();
206
207        assert_eq!(
208            scale_codec_encoded, encode_as_type_encoded,
209            "encoded bytes should match"
210        );
211
212        let decode_as_type_bytes = &mut &*scale_codec_encoded;
213        let decoded_as_type = T::decode_as_type(decode_as_type_bytes, type_id, &types)
214            .expect("decode-as-type decodes");
215
216        let decode_scale_codec_bytes = &mut &*scale_codec_encoded;
217        let decoded_scale_codec = T::decode(decode_scale_codec_bytes).expect("scale-codec decodes");
218
219        assert!(
220            decode_as_type_bytes.is_empty(),
221            "no bytes should remain in decode-as-type impl"
222        );
223        assert!(
224            decode_scale_codec_bytes.is_empty(),
225            "no bytes should remain in codec-decode impl"
226        );
227
228        assert_eq!(
229            decoded_as_type, decoded_scale_codec,
230            "decoded values should match"
231        );
232    }
233
234    #[test]
235    fn wrapper_keep_opaque_roundtrips_ok() {
236        roundtrips_like_scale_codec(WrapperKeepOpaque::from_value(123u64));
237        roundtrips_like_scale_codec(WrapperKeepOpaque::from_value(true));
238        roundtrips_like_scale_codec(WrapperKeepOpaque::from_value(vec![1u8, 2, 3, 4]));
239    }
240}
subxt_core/utils/wrapper_opaque.rs

subxt_core/utils/
wrapper_opaque.rs
