ChargeAssetTxPayment: support providing u32 or MultiLocation in default impl (#1227)

* Asset Id in Config trait

* add example configuring the config

* fmt

* fix Default trait bound

* merge examples, fix default again

* adjust config in examples

* Update subxt/src/config/mod.rs

Co-authored-by: James Wilson <james@jsdw.me>

---------

Co-authored-by: James Wilson <james@jsdw.me>

subxt/src/config/default_extrinsic_params.rs

@@ -15,7 +15,7 @@ pub type DefaultExtrinsicParams<T> = signed_extensions::AnyOf<
         signed_extensions::CheckNonce,
         signed_extensions::CheckGenesis<T>,
         signed_extensions::CheckMortality<T>,
-        signed_extensions::ChargeAssetTxPayment,
+        signed_extensions::ChargeAssetTxPayment<T>,
         signed_extensions::ChargeTransactionPayment,
     ),
 >;
@@ -27,7 +27,7 @@ pub struct DefaultExtrinsicParamsBuilder<T: Config> {
     /// `None` means the tx will be immortal.
     mortality: Option<Mortality<T::Hash>>,
     /// `None` means we'll use the native token.
-    tip_of_asset_id: Option<u32>,
+    tip_of_asset_id: Option<T::AssetId>,
     tip: u128,
     tip_of: u128,
 }
@@ -103,7 +103,7 @@ impl<T: Config> DefaultExtrinsicParamsBuilder<T> {
     /// Provide a tip to the block auther using the token denominated by the `asset_id` provided. This
     /// is not applicable on chains which don't use the `ChargeAssetTxPayment` signed extension; in this
     /// case, no tip will be given.
-    pub fn tip_of(mut self, tip: u128, asset_id: u32) -> Self {
+    pub fn tip_of(mut self, tip: u128, asset_id: T::AssetId) -> Self {
         self.tip = 0;
         self.tip_of = tip;
         self.tip_of_asset_id = Some(asset_id);

subxt/src/config/mod.rs

@@ -51,6 +51,9 @@ pub trait Config: Sized + Send + Sync + 'static {
 
     /// This type defines the extrinsic extra and additional parameters.
     type ExtrinsicParams: ExtrinsicParams<Self>;
+
+    /// This is used to identify an asset in the `ChargeAssetTxPayment` signed extension.
+    type AssetId: Debug + Encode;
 }
 
 /// given some [`Config`], this return the other params needed for its `ExtrinsicParams`.

subxt/src/config/polkadot.rs

@@ -21,6 +21,7 @@ impl Config for PolkadotConfig {
     type Hasher = <SubstrateConfig as Config>::Hasher;
     type Header = <SubstrateConfig as Config>::Header;
     type ExtrinsicParams = PolkadotExtrinsicParams<Self>;
+    type AssetId = u32;
 }
 
 /// A struct representing the signed extra and additional parameters required

subxt/src/config/signed_extensions.rs

@@ -217,19 +217,27 @@ impl<T: Config> SignedExtension<T> for CheckMortality<T> {
 
 /// The [`ChargeAssetTxPayment`] signed extension.
 #[derive(Debug)]
-pub struct ChargeAssetTxPayment {
+pub struct ChargeAssetTxPayment<T: Config> {
     tip: Compact<u128>,
-    asset_id: Option<u32>,
+    asset_id: Option<T::AssetId>,
 }
 
 /// Parameters to configure the [`ChargeAssetTxPayment`] signed extension.
-#[derive(Default)]
-pub struct ChargeAssetTxPaymentParams {
+pub struct ChargeAssetTxPaymentParams<T: Config> {
     tip: u128,
-    asset_id: Option<u32>,
+    asset_id: Option<T::AssetId>,
 }
 
-impl ChargeAssetTxPaymentParams {
+impl<T: Config> Default for ChargeAssetTxPaymentParams<T> {
+    fn default() -> Self {
+        ChargeAssetTxPaymentParams {
+            tip: Default::default(),
+            asset_id: Default::default(),
+        }
+    }
+}
+
+impl<T: Config> ChargeAssetTxPaymentParams<T> {
     /// Don't provide a tip to the extrinsic author.
     pub fn no_tip() -> Self {
         ChargeAssetTxPaymentParams {
@@ -245,7 +253,7 @@ impl ChargeAssetTxPaymentParams {
         }
     }
     /// Tip the extrinsic author using the asset ID given.
-    pub fn tip_of(tip: u128, asset_id: u32) -> Self {
+    pub fn tip_of(tip: u128, asset_id: T::AssetId) -> Self {
         ChargeAssetTxPaymentParams {
             tip,
             asset_id: Some(asset_id),
@@ -253,8 +261,8 @@ impl ChargeAssetTxPaymentParams {
     }
 }
 
-impl<T: Config> ExtrinsicParams<T> for ChargeAssetTxPayment {
-    type OtherParams = ChargeAssetTxPaymentParams;
+impl<T: Config> ExtrinsicParams<T> for ChargeAssetTxPayment<T> {
+    type OtherParams = ChargeAssetTxPaymentParams<T>;
     type Error = std::convert::Infallible;
 
     fn new<Client: OfflineClientT<T>>(
@@ -269,13 +277,13 @@ impl<T: Config> ExtrinsicParams<T> for ChargeAssetTxPayment {
     }
 }
 
-impl ExtrinsicParamsEncoder for ChargeAssetTxPayment {
+impl<T: Config> ExtrinsicParamsEncoder for ChargeAssetTxPayment<T> {
     fn encode_extra_to(&self, v: &mut Vec<u8>) {
-        (self.tip, self.asset_id).encode_to(v);
+        (self.tip, &self.asset_id).encode_to(v);
     }
 }
 
-impl<T: Config> SignedExtension<T> for ChargeAssetTxPayment {
+impl<T: Config> SignedExtension<T> for ChargeAssetTxPayment<T> {
     const NAME: &'static str = "ChargeAssetTxPayment";
 }
 

subxt/src/config/substrate.rs

@@ -24,6 +24,7 @@ impl Config for SubstrateConfig {
     type Hasher = BlakeTwo256;
     type Header = SubstrateHeader<u32, BlakeTwo256>;
     type ExtrinsicParams = SubstrateExtrinsicParams<Self>;
+    type AssetId = u32;
 }
 
 /// A struct representing the signed extra and additional parameters required