Tutorials > Polkadot SDK > Parachains > Build Custom Pallet > Build t…

…he Pallet (#232)

* wip: build-pallet

* Page ready

* Improvements

* Extract code snippets

* Description and grammarly

* fix: typo

* Add suggestions

* Update tutorials/polkadot-sdk/parachains/build-custom-pallet/build-pallet.md

Co-authored-by: Nicolás Hussein <[email protected]>

* Add root origin reference

* Apply suggestions from code review

Co-authored-by: Erin Shaben <[email protected]>

* Apply fmt

* Apply suggestions from code review

Co-authored-by: Erin Shaben <[email protected]>

* Apply suggestions from code review

Co-authored-by: Nicolás Hussein <[email protected]>

* Apply fixes

---------

Co-authored-by: nhussein11 <[email protected]>
Co-authored-by: Nicolás Hussein <[email protected]>
Co-authored-by: Erin Shaben <[email protected]>

.snippets/code/tutorials/polkadot-sdk/parachains/build-custom-pallet/build-pallet/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "custom-pallet"
+version = "0.1.0"
+license.workspace = true
+authors.workspace = true
+homepage.workspace = true
+repository.workspace = true
+edition.workspace = true
+
+[dependencies]
+codec = { features = ["derive"], workspace = true }
+scale-info = { features = ["derive"], workspace = true }
+frame-support.workspace = true
+frame-system.workspace = true
+
+[features]
+default = ["std"]
+std = ["codec/std", "frame-support/std", "frame-system/std", "scale-info/std"]

.snippets/code/tutorials/polkadot-sdk/parachains/build-custom-pallet/build-pallet/call_structure.rs

@@ -0,0 +1,14 @@
+#[pallet::call]
+impl<T: Config> Pallet<T> {
+    #[pallet::call_index(0)]
+    #[pallet::weight(0)]
+    pub fn set_counter_value(origin: OriginFor<T>, new_value: u32) -> DispatchResult {}
+
+    #[pallet::call_index(1)]
+    #[pallet::weight(0)]
+    pub fn increment(origin: OriginFor<T>, amount_to_increment: u32) -> DispatchResult {}
+
+    #[pallet::call_index(2)]
+    #[pallet::weight(0)]
+    pub fn decrement(origin: OriginFor<T>, amount_to_decrement: u32) -> DispatchResult {}
+}

.snippets/code/tutorials/polkadot-sdk/parachains/build-custom-pallet/build-pallet/compilation-output.html

@@ -0,0 +1,5 @@
+<div id="termynal" data-termynal>
+  <span data-ty="input"><span class="file-path"></span>cargo build --release</span>
+  <span data-ty>Compiling solochain-template-node</span>
+  <span data-ty>Finished `release` profile [optimized] target(s) in 27.12s</span>
+</div>

.snippets/code/tutorials/polkadot-sdk/parachains/build-custom-pallet/build-pallet/lib.rs

@@ -0,0 +1,184 @@
+#![cfg_attr(not(feature = "std"), no_std)]
+
+pub use pallet::*;
+
+#[frame_support::pallet(dev_mode)]
+pub mod pallet {
+    use super::*;
+    use frame_support::pallet_prelude::*;
+    use frame_system::pallet_prelude::*;
+
+    #[pallet::pallet]
+    pub struct Pallet<T>(_);
+
+    // Configuration trait for the pallet
+    #[pallet::config]
+    pub trait Config: frame_system::Config {
+        // Defines the event type for the pallet
+        type RuntimeEvent: From<Event<Self>> + IsType<<Self as frame_system::Config>::RuntimeEvent>;
+
+        // Defines the maximum value the counter can hold
+        #[pallet::constant]
+        type CounterMaxValue: Get<u32>;
+    }
+
+    #[pallet::event]
+    #[pallet::generate_deposit(pub(super) fn deposit_event)]
+    pub enum Event<T: Config> {
+        /// The counter value has been set to a new value by Root.
+        CounterValueSet {
+            /// The new value set.
+            counter_value: u32,
+        },
+        /// A user has successfully incremented the counter.
+        CounterIncremented {
+            /// The new value set.
+            counter_value: u32,
+            /// The account who incremented the counter.
+            who: T::AccountId,
+            /// The amount by which the counter was incremented.
+            incremented_amount: u32,
+        },
+        /// A user has successfully decremented the counter.
+        CounterDecremented {
+            /// The new value set.
+            counter_value: u32,
+            /// The account who decremented the counter.
+            who: T::AccountId,
+            /// The amount by which the counter was decremented.
+            decremented_amount: u32,
+        },
+    }
+
+    /// Storage for the current value of the counter.
+    #[pallet::storage]
+    pub type CounterValue<T> = StorageValue<_, u32>;
+
+    /// Storage map to track the number of interactions performed by each account.
+    #[pallet::storage]
+    pub type UserInteractions<T: Config> = StorageMap<_, Twox64Concat, T::AccountId, u32>;
+
+    #[pallet::error]
+    pub enum Error<T> {
+        /// The counter value exceeds the maximum allowed value.
+        CounterValueExceedsMax,
+        /// The counter value cannot be decremented below zero.
+        CounterValueBelowZero,
+        /// Overflow occurred in the counter.
+        CounterOverflow,
+        /// Overflow occurred in user interactions.
+        UserInteractionOverflow,
+    }
+
+    #[pallet::call]
+    impl<T: Config> Pallet<T> {
+        /// Set the value of the counter.
+        ///
+        /// The dispatch origin of this call must be _Root_.
+        ///
+        /// - `new_value`: The new value to set for the counter.
+        ///
+        /// Emits `CounterValueSet` event when successful.
+        #[pallet::call_index(0)]
+        #[pallet::weight(0)]
+        pub fn set_counter_value(origin: OriginFor<T>, new_value: u32) -> DispatchResult {
+            ensure_root(origin)?;
+
+            ensure!(
+                new_value <= T::CounterMaxValue::get(),
+                Error::<T>::CounterValueExceedsMax
+            );
+
+            CounterValue::<T>::put(new_value);
+
+            Self::deposit_event(Event::<T>::CounterValueSet {
+                counter_value: new_value,
+            });
+
+            Ok(())
+        }
+
+        /// Increment the counter by a specified amount.
+        ///
+        /// This function can be called by any signed account.
+        ///
+        /// - `amount_to_increment`: The amount by which to increment the counter.
+        ///
+        /// Emits `CounterIncremented` event when successful.
+        #[pallet::call_index(1)]
+        #[pallet::weight(0)]
+        pub fn increment(origin: OriginFor<T>, amount_to_increment: u32) -> DispatchResult {
+            let who = ensure_signed(origin)?;
+
+            let current_value = CounterValue::<T>::get().unwrap_or(0);
+
+            let new_value = current_value
+                .checked_add(amount_to_increment)
+                .ok_or(Error::<T>::CounterOverflow)?;
+
+            ensure!(
+                new_value <= T::CounterMaxValue::get(),
+                Error::<T>::CounterValueExceedsMax
+            );
+
+            CounterValue::<T>::put(new_value);
+
+            UserInteractions::<T>::try_mutate(&who, |interactions| -> Result<_, Error<T>> {
+                let new_interactions = interactions
+                    .unwrap_or(0)
+                    .checked_add(1)
+                    .ok_or(Error::<T>::UserInteractionOverflow)?;
+                *interactions = Some(new_interactions); // Store the new value
+
+                Ok(())
+            })?;
+
+            Self::deposit_event(Event::<T>::CounterIncremented {
+                counter_value: new_value,
+                who,
+                incremented_amount: amount_to_increment,
+            });
+
+            Ok(())
+        }
+
+        /// Decrement the counter by a specified amount.
+        ///
+        /// This function can be called by any signed account.
+        ///
+        /// - `amount_to_decrement`: The amount by which to decrement the counter.
+        ///
+        /// Emits `CounterDecremented` event when successful.
+        #[pallet::call_index(2)]
+        #[pallet::weight(0)]
+        pub fn decrement(origin: OriginFor<T>, amount_to_decrement: u32) -> DispatchResult {
+            let who = ensure_signed(origin)?;
+
+            let current_value = CounterValue::<T>::get().unwrap_or(0);
+
+            let new_value = current_value
+                .checked_sub(amount_to_decrement)
+                .ok_or(Error::<T>::CounterValueBelowZero)?;
+
+            CounterValue::<T>::put(new_value);
+
+            UserInteractions::<T>::try_mutate(&who, |interactions| -> Result<_, Error<T>> {
+                let new_interactions = interactions
+                    .unwrap_or(0)
+                    .checked_add(1)
+                    .ok_or(Error::<T>::UserInteractionOverflow)?;
+                *interactions = Some(new_interactions); // Store the new value
+
+                Ok(())
+            })?;
+
+            Self::deposit_event(Event::<T>::CounterDecremented {
+                counter_value: new_value,
+                who,
+                decremented_amount: amount_to_decrement,
+            });
+
+            Ok(())
+        }
+    }
+}

.snippets/code/tutorials/polkadot-sdk/parachains/build-custom-pallet/build-pallet/scaffold.rs

@@ -0,0 +1,16 @@
+#![cfg_attr(not(feature = "std"), no_std)]
+
+pub use pallet::*;
+
+#[frame_support::pallet(dev_mode)]
+pub mod pallet {
+    use super::*;
+    use frame_support::pallet_prelude::*;
+    use frame_system::pallet_prelude::*;
+
+    #[pallet::pallet]
+    pub struct Pallet<T>(_);
+
+    #[pallet::config]
+    pub trait Config: frame_system::Config {}
+}

tutorials/interoperability/xcm-transfers/from-relaychain-to-parachain.md

@@ -46,7 +46,6 @@ b. Click **Switch** to connect to the respective network
 
 ![](/images/tutorials/interoperability/xcm-transfers/from-relaychain-to-parachain/from-relaychain-to-parachain-01.webp)
 
-
 This reserve-backed transfer method facilitates asset transfers from a local chain to a destination chain by trusting a third party called a reserve to store the real assets. Fees on the destination chain are deducted from the asset specified in the assets vector at the `fee_asset_item` index, covering up to the specified `weight_limit.` The operation fails if the required weight exceeds this limit, potentially putting the transferred assets at risk.
 
 The following steps outline how to execute a reserve-backed transfer from the Polkadot relay chain to the Astar parachain.
@@ -76,6 +75,7 @@ The following steps outline how to execute a reserve-backed transfer from the Po
 
     3. **beneficiary** - defines the recipient of the assets within the destination context, typically represented as an `AccountId32` value. This example uses the following account present in the destination chain:
 
+
         ```bash
         X2mE9hCGX771c3zzV6tPa8U2cDz4U4zkqUdmBrQn83M3cm7
         ```
@@ -102,6 +102,7 @@ After submitting the transaction from the relay chain, confirm its success by ch
 To programmatically execute the reserve-backed asset transfer between the relay chain and the parachain, you can use [Polkadot API (PAPI)](/develop/toolkit/api-libraries/papi.md){target=\_blank}. PAPI is a robust toolkit that simplifies interactions with Polkadot-based chains. For this project, you'll first need to set up your environment, install necessary dependencies, and create a script to handle the transfer process.
 
 1. Start by creating a folder for your project:
+
    ```bash
    mkdir reserve-backed-asset-transfer
    cd reserve-backed-asset

tutorials/polkadot-sdk/parachains/.pages

@@ -2,4 +2,5 @@ title: Parachains
 nav:
   - index.md
   - local-chain
-  - connect-to-relay-chain
+  - connect-to-relay-chain
+  - build-custom-pallet

tutorials/polkadot-sdk/parachains/build-custom-pallet/.pages

@@ -0,0 +1,4 @@
+title: Build Custom Pallet
+nav:
+  - index.md
+  - 'Build Pallet': build-pallet.md