static decoding of signed extensions

subxt/src/blocks/extrinsic_types.rs

@@ -19,6 +19,8 @@ use codec::{Compact, Decode};
 use derivative::Derivative;
 use scale_decode::{DecodeAsFields, DecodeAsType};
 
+use crate::config::signed_extensions::{ChargeAssetTxPayment, ChargeTransactionPayment};
+use crate::config::SignedExtension;
 use std::sync::Arc;
 
 /// Trait to uniquely identify the extrinsic's identity from the runtime metadata.
@@ -371,12 +373,13 @@ where
     }
 
     /// Returns `None` if the extrinsic is not signed.
-    pub fn signed_extensions(&self) -> Option<ExtrinsicSignedExtensions> {
+    pub fn signed_extensions(&self) -> Option<ExtrinsicSignedExtensions<'_, T>> {
         let signed = self.signed_details.as_ref()?;
         let extra_bytes = &self.bytes[signed.signature_end_idx..signed.extra_end_idx];
         Some(ExtrinsicSignedExtensions {
             bytes: extra_bytes,
             metadata: self.metadata.clone(),
+            _marker: std::marker::PhantomData,
         })
     }
 
@@ -610,24 +613,26 @@ impl<T: Config> ExtrinsicEvents<T> {
 
 /// The signed extensions of an extrinsic.
 #[derive(Debug, Clone)]
-pub struct ExtrinsicSignedExtensions<'a> {
+pub struct ExtrinsicSignedExtensions<'a, T: Config> {
     bytes: &'a [u8],
     metadata: Metadata,
+    _marker: std::marker::PhantomData<T>,
 }
 
 /// A single signed extension
 #[derive(Debug, Clone)]
-pub struct ExtrinsicSignedExtension<'a> {
+pub struct ExtrinsicSignedExtension<'a, T: Config> {
     bytes: &'a [u8],
     ty_id: u32,
     identifier: &'a str,
     metadata: Metadata,
+    _marker: std::marker::PhantomData<T>,
 }
 
-impl<'a> ExtrinsicSignedExtensions<'a> {
+impl<'a, T: Config> ExtrinsicSignedExtensions<'a, T> {
     /// Returns an iterator ove all signed extensions, allowing access to their names, bytes and types.
     /// If the decoding of any signed extension fails, an error item is yielded and the iterator stops.
-    pub fn iter(&'a self) -> impl Iterator<Item = Result<ExtrinsicSignedExtension<'a>, Error>> {
+    pub fn iter(&'a self) -> impl Iterator<Item = Result<ExtrinsicSignedExtension<'a, T>, Error>> {
         let signed_extension_types = self.metadata.extrinsic().signed_extensions();
         let num_signed_extensions = signed_extension_types.len();
         let mut index = 0;
@@ -661,17 +666,29 @@ impl<'a> ExtrinsicSignedExtensions<'a> {
                 ty_id,
                 identifier: extension.identifier(),
                 metadata: self.metadata.clone(),
+                _marker: std::marker::PhantomData,
             }))
         })
     }
 
+    fn find_by_name(&self, name: impl AsRef<str>) -> Option<ExtrinsicSignedExtension<'_, T>> {
+        let signed_extension = self
+            .iter()
+            .find_map(|e| e.ok().filter(|e| e.name() == name.as_ref()))?;
+        Some(signed_extension)
+    }
+
+    pub fn find<S: SignedExtension<T>>(&self) -> Option<Result<S::Extra, Error>> {
+        let signed_extension = self.find_by_name(S::NAME)?;
+        Some(signed_extension.as_type().map_err(Into::into))
+    }
+
     /// The tip of an extrinsic, extracted from the ChargeTransactionPayment or ChargeAssetTxPayment signed extension, depending on which is present.
     pub fn tip(&self) -> Option<u128> {
-        let tip = self.iter().find_map(|e| {
-            e.ok().filter(|e| {
-                e.name() == "ChargeTransactionPayment" || e.name() == "ChargeAssetTxPayment"
-            })
-        })?;
+        // Note: the overhead of iterating twice should be negligible.
+        let tip = self
+            .find_by_name(<ChargeTransactionPayment as SignedExtension<T>>::NAME)
+            .or_else(|| self.find_by_name(<ChargeAssetTxPayment as SignedExtension<T>>::NAME))?;
         // Note: ChargeAssetTxPayment might have addition information in it (asset_id).
         //       But both should start with a compact encoded u128, so this decoding is fine.
         let tip = Compact::<u128>::decode(&mut tip.bytes()).ok()?.0;
@@ -688,7 +705,7 @@ impl<'a> ExtrinsicSignedExtensions<'a> {
     }
 }
 
-impl<'a> ExtrinsicSignedExtension<'a> {
+impl<'a, T: Config> ExtrinsicSignedExtension<'a, T> {
     /// The bytes representing this signed extension.
     pub fn bytes(&self) -> &[u8] {
         self.bytes
@@ -719,8 +736,8 @@ impl<'a> ExtrinsicSignedExtension<'a> {
         self.decoded()?.to_value()
     }
 
-    pub fn as_type<T: DecodeAsType>(&self) -> Result<T, Error> {
-        self.decoded()?.as_type::<T>().map_err(Into::into)
+    pub fn as_type<E: DecodeAsType>(&self) -> Result<E, Error> {
+        self.decoded()?.as_type::<E>().map_err(Into::into)
     }
 }
 

subxt/src/config/signed_extensions.rs

@@ -10,19 +10,45 @@
 use super::extrinsic_params::{ExtrinsicParams, ExtrinsicParamsEncoder, ExtrinsicParamsError};
 use crate::utils::Era;
 use crate::{client::OfflineClientT, Config};
-use codec::{Compact, Encode};
+use codec::{Compact, Decode, Encode};
 use core::fmt::Debug;
+use scale_decode::DecodeAsType;
 use std::collections::HashMap;
 
 /// A single [`SignedExtension`] has a unique name, but is otherwise the
 /// same as [`ExtrinsicParams`] in describing how to encode the extra and
 /// additional data.
-pub trait SignedExtension<T: Config>: ExtrinsicParams<T> {
+pub trait SignedExtension<T: Config>: ExtrinsicParams<T> + SignedExtensionDecoder {
     /// The name of the signed extension. This is used to associate it
     /// with the signed extensions that the node is making use of.
     const NAME: &'static str;
 }
 
+/// Specifies the Extra and Additional data types of the signed extension.
+/// `ExtrinsicParamsEncoder` is implemented for all `SignedExtensionDecoder`s.
+pub trait SignedExtensionDecoder {
+    /// Signed Extra parameter of a Signed Extension.
+    /// Included in a signed extension behind the signature.
+    type Extra: Encode + DecodeAsType;
+    /// Additional Signed parameter of a Signed Extension.
+    /// Used as part of the payload for signing an extrinsic.
+    type Additional: Encode;
+    /// Retrieves the signed extra parameter.
+    fn extra(&self) -> &Self::Extra;
+    /// Retrieves the additional signed parameter.
+    fn additional(&self) -> &Self::Additional;
+}
+
+impl<S: SignedExtensionDecoder + 'static> ExtrinsicParamsEncoder for S {
+    fn encode_extra_to(&self, v: &mut Vec<u8>) {
+        self.extra().encode_to(v);
+    }
+
+    fn encode_additional_to(&self, v: &mut Vec<u8>) {
+        self.additional().encode_to(v);
+    }
+}
+
 /// The [`CheckSpecVersion`] signed extension.
 #[derive(Debug)]
 pub struct CheckSpecVersion(u32);
@@ -40,9 +66,16 @@ impl<T: Config> ExtrinsicParams<T> for CheckSpecVersion {
     }
 }
 
-impl ExtrinsicParamsEncoder for CheckSpecVersion {
-    fn encode_additional_to(&self, v: &mut Vec<u8>) {
-        self.0.encode_to(v);
+impl SignedExtensionDecoder for CheckSpecVersion {
+    type Extra = ();
+    type Additional = u32;
+
+    fn extra(&self) -> &Self::Extra {
+        &()
+    }
+
+    fn additional(&self) -> &Self::Additional {
+        &self.0
     }
 }
 
@@ -67,9 +100,16 @@ impl<T: Config> ExtrinsicParams<T> for CheckNonce {
     }
 }
 
-impl ExtrinsicParamsEncoder for CheckNonce {
-    fn encode_extra_to(&self, v: &mut Vec<u8>) {
-        self.0.encode_to(v);
+impl SignedExtensionDecoder for CheckNonce {
+    type Extra = Compact<u64>;
+    type Additional = ();
+
+    fn extra(&self) -> &Self::Extra {
+        &self.0
+    }
+
+    fn additional(&self) -> &Self::Additional {
+        &()
     }
 }
 
@@ -94,9 +134,16 @@ impl<T: Config> ExtrinsicParams<T> for CheckTxVersion {
     }
 }
 
-impl ExtrinsicParamsEncoder for CheckTxVersion {
-    fn encode_additional_to(&self, v: &mut Vec<u8>) {
-        self.0.encode_to(v);
+impl SignedExtensionDecoder for CheckTxVersion {
+    type Extra = ();
+    type Additional = u32;
+
+    fn extra(&self) -> &Self::Extra {
+        &()
+    }
+
+    fn additional(&self) -> &Self::Additional {
+        &self.0
     }
 }
 
@@ -126,9 +173,16 @@ impl<T: Config> ExtrinsicParams<T> for CheckGenesis<T> {
     }
 }
 
-impl<T: Config> ExtrinsicParamsEncoder for CheckGenesis<T> {
-    fn encode_additional_to(&self, v: &mut Vec<u8>) {
-        self.0.encode_to(v);
+impl<T: Config> SignedExtensionDecoder for CheckGenesis<T> {
+    type Extra = ();
+    type Additional = T::Hash;
+
+    fn extra(&self) -> &Self::Extra {
+        &()
+    }
+
+    fn additional(&self) -> &Self::Additional {
+        &self.0
     }
 }
 
@@ -202,12 +256,16 @@ impl<T: Config> ExtrinsicParams<T> for CheckMortality<T> {
     }
 }
 
-impl<T: Config> ExtrinsicParamsEncoder for CheckMortality<T> {
-    fn encode_extra_to(&self, v: &mut Vec<u8>) {
-        self.era.encode_to(v);
+impl<T: Config> SignedExtensionDecoder for CheckMortality<T> {
+    type Extra = Era;
+    type Additional = T::Hash;
+
+    fn extra(&self) -> &Self::Extra {
+        &self.era
     }
-    fn encode_additional_to(&self, v: &mut Vec<u8>) {
-        self.checkpoint.encode_to(v)
+
+    fn additional(&self) -> &Self::Additional {
+        &self.checkpoint
     }
 }
 
@@ -216,7 +274,7 @@ impl<T: Config> SignedExtension<T> for CheckMortality<T> {
 }
 
 /// The [`ChargeAssetTxPayment`] signed extension.
-#[derive(Debug)]
+#[derive(Debug, Encode, Decode, DecodeAsType)]
 pub struct ChargeAssetTxPayment {
     tip: Compact<u128>,
     asset_id: Option<u32>,
@@ -269,9 +327,16 @@ impl<T: Config> ExtrinsicParams<T> for ChargeAssetTxPayment {
     }
 }
 
-impl ExtrinsicParamsEncoder for ChargeAssetTxPayment {
-    fn encode_extra_to(&self, v: &mut Vec<u8>) {
-        (self.tip, self.asset_id).encode_to(v);
+impl SignedExtensionDecoder for ChargeAssetTxPayment {
+    type Extra = Self;
+    type Additional = ();
+
+    fn extra(&self) -> &Self::Extra {
+        &self
+    }
+
+    fn additional(&self) -> &Self::Additional {
+        &()
     }
 }
 
@@ -280,7 +345,7 @@ impl<T: Config> SignedExtension<T> for ChargeAssetTxPayment {
 }
 
 /// The [`ChargeTransactionPayment`] signed extension.
-#[derive(Debug)]
+#[derive(Debug, Encode, Decode, DecodeAsType)]
 pub struct ChargeTransactionPayment {
     tip: Compact<u128>,
 }
@@ -317,9 +382,16 @@ impl<T: Config> ExtrinsicParams<T> for ChargeTransactionPayment {
     }
 }
 
-impl ExtrinsicParamsEncoder for ChargeTransactionPayment {
-    fn encode_extra_to(&self, v: &mut Vec<u8>) {
-        self.tip.encode_to(v);
+impl SignedExtensionDecoder for ChargeTransactionPayment {
+    type Extra = Self;
+    type Additional = ();
+
+    fn extra(&self) -> &Self::Extra {
+        &self
+    }
+
+    fn additional(&self) -> &Self::Additional {
+        &()
     }
 }
 

subxt/src/utils/era.rs

@@ -4,7 +4,17 @@
 
 // Dev note: This and related bits taken from `sp_runtime::generic::Era`
 /// An era to describe the longevity of a transaction.
-#[derive(PartialEq, Default, Eq, Clone, Copy, Debug, serde::Serialize, serde::Deserialize)]
+#[derive(
+    PartialEq,
+    Default,
+    Eq,
+    Clone,
+    Copy,
+    Debug,
+    serde::Serialize,
+    serde::Deserialize,
+    scale_decode::DecodeAsType,
+)]
 pub enum Era {
     /// The transaction is valid forever. The genesis hash must be present in the signed content.
     #[default]