feat: gas service

contracts/axelar-gas-service/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "axelar-gas-service"
+version = "0.1.0"
+edition = { workspace = true }
+
+[lib]
+crate-type = ["cdylib"]
+
+[dependencies]
+soroban-sdk = { workspace = true, features = ["alloc"] }
+
+[dev_dependencies]
+soroban-sdk = { workspace = true, features = ["testutils", "alloc"] }
+secp256k1 = { version = "0.28.2", features = ["recovery", "rand"] }
+
+[features]
+testutils = ["soroban-sdk/testutils"]

contracts/axelar-gas-service/src/contract.rs

@@ -0,0 +1,109 @@
+use soroban_sdk::{contract, contractimpl, token, Address, Bytes, BytesN, Env, String, U256};
+
+use crate::interface::AxelarGasServiceInterface;
+use crate::storage_types::DataKey;
+use crate::{error::Error, event};
+
+#[contract]
+pub struct AxelarGasService;
+
+#[contractimpl]
+impl AxelarGasService {
+    pub fn initialize(env: Env, gas_collector: Address) {
+        if env
+            .storage()
+            .instance()
+            .get(&DataKey::Initialized)
+            .unwrap_or(false)
+        {
+            panic!("Already initialized");
+        }
+
+        env.storage().instance().set(&DataKey::Initialized, &true);
+
+        env.storage()
+            .instance()
+            .set(&DataKey::GasCollector, &gas_collector);
+    }
+}
+
+#[contractimpl]
+impl AxelarGasServiceInterface for AxelarGasService {
+    fn pay_native_gas_for_contract_call(
+        env: Env,
+        sender: Address,
+        destination_chain: String,
+        destination_address: String,
+        payload: Bytes,
+        refund_address: Address,
+    ) {
+        event::native_gas_paid_for_contract_call(
+            &env,
+            sender,
+            destination_chain,
+            destination_address,
+            payload,
+            refund_address,
+        )
+    }
+
+    fn collect_fees(
+        env: Env,
+        receiver: Address,
+        token_address: Address,
+        amount: i128,
+    ) -> Result<(), Error> {
+        let gas_collector: Address = env
+            .storage()
+            .instance()
+            .get(&DataKey::GasCollector)
+            .unwrap();
+
+        gas_collector.require_auth();
+
+        //TODO: sanity check address zero
+
+        if amount == 0 {
+            return Err(Error::InvalidAmounts);
+        }
+
+        let token_client = token::Client::new(&env, &token_address);
+
+        let contract_token_balance = token_client.balance(&env.current_contract_address());
+
+        if contract_token_balance >= amount {
+            token_client.transfer(&env.current_contract_address(), &receiver, &amount)
+        } else {
+            return Err(Error::InsufficientBalance);
+        }
+
+        event::fee_collected(&env, &gas_collector, &token_address, amount);
+
+        Ok(())
+    }
+
+    fn refund(
+        env: Env,
+        tx_hash: BytesN<32>,
+        log_index: U256,
+        receiver: Address,
+        token_addr: Address,
+        amount: i128,
+    ) {
+        let gas_collector: Address = env
+            .storage()
+            .instance()
+            .get(&DataKey::GasCollector)
+            .unwrap();
+
+        gas_collector.require_auth();
+
+        event::refunded(&env, tx_hash, log_index, &receiver, &token_addr, amount);
+
+        token::Client::new(&env, &token_addr).transfer(
+            &env.current_contract_address(),
+            &receiver,
+            &amount,
+        );
+    }
+}

contracts/axelar-gas-service/src/error.rs

@@ -0,0 +1,10 @@
+use soroban_sdk::contracterror;
+
+#[contracterror]
+#[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord)]
+#[repr(u32)]
+pub enum Error {
+    InvalidAddress = 1,
+    InvalidAmounts = 2,
+    InsufficientBalance = 3,
+}

contracts/axelar-gas-service/src/event.rs

@@ -0,0 +1,40 @@
+use soroban_sdk::{symbol_short, Address, Bytes, BytesN, Env, String, U256};
+
+pub(crate) fn native_gas_paid_for_contract_call(
+    env: &Env,
+    sender: Address,
+    destination_chain: String,
+    destination_address: String,
+    payload: Bytes,
+    refund_address: Address,
+) {
+    let topics = (symbol_short!("cc_g_paid"), env.crypto().keccak256(&payload));
+    env.events().publish(
+        topics,
+        (
+            sender,
+            destination_chain,
+            destination_address,
+            payload,
+            refund_address,
+        ),
+    );
+}
+
+pub(crate) fn refunded(
+    env: &Env,
+    tx_hash: BytesN<32>,
+    log_index: U256,
+    receiver: &Address,
+    token: &Address,
+    amount: i128,
+) {
+    let topics = (symbol_short!("refunded"), tx_hash, log_index);
+    env.events().publish(topics, (receiver, token, amount));
+}
+
+pub(crate) fn fee_collected(env: &Env, receiver: &Address, token_address: &Address, amount: i128) {
+    let topics = (symbol_short!("coll_fees"),);
+    env.events()
+        .publish(topics, (receiver, token_address, amount));
+}

contracts/axelar-gas-service/src/interface.rs

@@ -0,0 +1,33 @@
+use crate::error::Error;
+use soroban_sdk::{Address, Bytes, BytesN, Env, String, U256};
+/// Interface for the Axelar Gas Service.
+// #[contractclient(crate_path = "crate", name = "AxelarGasService")]
+pub trait AxelarGasServiceInterface {
+    /// Pay for gas using native currency for a contract call on a destination chain. This function is called on the source chain before calling the gateway to execute a remote contract.
+    fn pay_native_gas_for_contract_call(
+        env: Env,
+        sender: Address,
+        destination_chain: String,
+        destination_address: String,
+        payload: Bytes,
+        refund_address: Address,
+    );
+
+    /// Allows the gasCollector to collect accumulated fees from the contract.
+    fn collect_fees(
+        env: Env,
+        receiver: Address,
+        token_addr: Address,
+        amounts: i128,
+    ) -> Result<(), Error>;
+
+    /// Refunds gas payment to the receiver in relation to a specific cross-chain transaction. Only callable by the gasCollector.
+    fn refund(
+        env: Env,
+        tx_hash: BytesN<32>,
+        log_index: U256,
+        receiver: Address,
+        token: Address,
+        amount: i128,
+    );
+}

contracts/axelar-gas-service/src/lib.rs

@@ -0,0 +1,13 @@
+#![no_std]
+
+pub mod contract;
+mod error;
+mod event;
+pub mod interface;
+mod storage_types;
+mod types;
+
+#[cfg(test)]
+mod test;
+
+pub use contract::AxelarGasService;

contracts/axelar-gas-service/src/storage_types.rs

@@ -0,0 +1,8 @@
+use soroban_sdk::contracttype;
+
+#[contracttype]
+#[derive(Clone, Debug)]
+pub enum DataKey {
+    Initialized,
+    GasCollector,
+}