fix(UTXO): improve tx fee calculation and min relay fee handling

mm2src/coins/qrc20.rs

@@ -493,7 +493,7 @@ impl Qrc20Coin {
     /// `gas_fee` should be calculated by: gas_limit * gas_price * (count of contract calls),
     /// or should be sum of gas fee of all contract calls.
     pub async fn get_qrc20_tx_fee(&self, gas_fee: u64) -> Result<u64, String> {
-        match try_s!(self.get_tx_fee().await) {
+        match try_s!(self.get_fee_per_kb().await) {
             ActualTxFee::Dynamic(amount) | ActualTxFee::FixedPerKb(amount) => Ok(amount + gas_fee),
         }
     }
@@ -613,7 +613,7 @@ impl UtxoTxBroadcastOps for Qrc20Coin {
 #[cfg_attr(test, mockable)]
 impl UtxoTxGenerationOps for Qrc20Coin {
     /// Get only QTUM transaction fee.
-    async fn get_tx_fee(&self) -> UtxoRpcResult<ActualTxFee> { utxo_common::get_tx_fee(&self.utxo).await }
+    async fn get_fee_per_kb(&self) -> UtxoRpcResult<ActualTxFee> { utxo_common::get_fee_per_kb(&self.utxo).await }
 
     async fn calc_interest_if_required(
         &self,

mm2src/coins/qrc20/qrc20_tests.rs

@@ -59,7 +59,7 @@ pub fn qrc20_coin_for_test(priv_key: [u8; 32], fallback_swap: Option<&str>) -> (
 }
 
 fn check_tx_fee(coin: &Qrc20Coin, expected_tx_fee: ActualTxFee) {
-    let actual_tx_fee = block_on(coin.get_tx_fee()).unwrap();
+    let actual_tx_fee = block_on(coin.get_fee_per_kb()).unwrap();
     assert_eq!(actual_tx_fee, expected_tx_fee);
 }
 

mm2src/coins/rpc_command/lightning/open_channel.rs

@@ -174,7 +174,7 @@ pub async fn open_channel(ctx: MmArc, req: OpenChannelRequest) -> OpenChannelRes
         .with_fee_policy(fee_policy);
 
     let fee = platform_coin
-        .get_tx_fee()
+        .get_fee_per_kb()
         .await
         .map_err(|e| OpenChannelError::RpcError(e.to_string()))?;
     tx_builder = tx_builder.with_fee(fee);

mm2src/coins/utxo.rs

@@ -279,11 +279,43 @@ pub enum TxFee {
 pub enum ActualTxFee {
     /// fee amount per Kbyte received from coin RPC
     Dynamic(u64),
-    /// Use specified amount per each 1 kb of transaction and also per each output less than amount.
+    /// Use specified fee amount per each 1 kb of transaction and also per each output less than the fee amount.
     /// Used by DOGE, but more coins might support it too.
     FixedPerKb(u64),
 }
 
+impl ActualTxFee {
+    fn get_tx_fee(&self, tx_size: u64) -> u64 {
+        match self {
+            ActualTxFee::Dynamic(fee_per_kb) => (fee_per_kb * tx_size) / KILO_BYTE,
+            // return fee_per_kb here as swap spend transaction size is always less than 1 kb
+            ActualTxFee::FixedPerKb(fee_per_kb) => {
+                let tx_size_kb = if tx_size % KILO_BYTE == 0 {
+                    tx_size / KILO_BYTE
+                } else {
+                    tx_size / KILO_BYTE + 1
+                };
+                fee_per_kb * tx_size_kb
+            },
+        }
+    }
+
+    /// Return extra tx fee for the change output as p2pkh
+    fn get_tx_fee_for_change(&self, tx_size: Option<u64>) -> u64 {
+        match self {
+            ActualTxFee::Dynamic(fee_per_kb) => (*fee_per_kb * P2PKH_OUTPUT_LEN) / KILO_BYTE,
+            ActualTxFee::FixedPerKb(fee_per_kb) => {
+                // take into account the change output if tx_size_kb(tx with change) > tx_size_kb(tx without change)
+                if tx_size.unwrap_or_default() % KILO_BYTE + P2PKH_OUTPUT_LEN > KILO_BYTE {
+                    *fee_per_kb
+                } else {
+                    0
+                }
+            },
+        }
+    }
+}
+
 /// Fee policy applied on transaction creation
 pub enum FeePolicy {
     /// Send the exact amount specified in output(s), fee is added to spent input amount
@@ -840,7 +872,7 @@ pub trait UtxoTxBroadcastOps {
 #[async_trait]
 #[cfg_attr(test, mockable)]
 pub trait UtxoTxGenerationOps {
-    async fn get_tx_fee(&self) -> UtxoRpcResult<ActualTxFee>;
+    async fn get_fee_per_kb(&self) -> UtxoRpcResult<ActualTxFee>;
 
     /// Calculates interest if the coin is KMD
     /// Adds the value to existing output to my_script_pub or creates additional interest output
@@ -1741,7 +1773,6 @@ where
 {
     let my_address = try_tx_s!(coin.as_ref().derivation_method.single_addr_or_err().await);
     let key_pair = try_tx_s!(coin.as_ref().priv_key_policy.activated_key_or_err());
-
     let mut builder = UtxoTxBuilder::new(coin)
         .await
         .add_available_inputs(unspents)

mm2src/coins/utxo/bch.rs

@@ -697,7 +697,7 @@ impl UtxoTxBroadcastOps for BchCoin {
 #[async_trait]
 #[cfg_attr(test, mockable)]
 impl UtxoTxGenerationOps for BchCoin {
-    async fn get_tx_fee(&self) -> UtxoRpcResult<ActualTxFee> { utxo_common::get_tx_fee(&self.utxo_arc).await }
+    async fn get_fee_per_kb(&self) -> UtxoRpcResult<ActualTxFee> { utxo_common::get_fee_per_kb(&self.utxo_arc).await }
 
     async fn calc_interest_if_required(
         &self,

mm2src/coins/utxo/qtum.rs

@@ -315,7 +315,7 @@ impl UtxoTxBroadcastOps for QtumCoin {
 #[async_trait]
 #[cfg_attr(test, mockable)]
 impl UtxoTxGenerationOps for QtumCoin {
-    async fn get_tx_fee(&self) -> UtxoRpcResult<ActualTxFee> { utxo_common::get_tx_fee(&self.utxo_arc).await }
+    async fn get_fee_per_kb(&self) -> UtxoRpcResult<ActualTxFee> { utxo_common::get_fee_per_kb(&self.utxo_arc).await }
 
     async fn calc_interest_if_required(
         &self,

mm2src/coins/utxo/slp.rs

@@ -1078,7 +1078,7 @@ impl UtxoTxBroadcastOps for SlpToken {
 
 #[async_trait]
 impl UtxoTxGenerationOps for SlpToken {
-    async fn get_tx_fee(&self) -> UtxoRpcResult<ActualTxFee> { self.platform_coin.get_tx_fee().await }
+    async fn get_fee_per_kb(&self) -> UtxoRpcResult<ActualTxFee> { self.platform_coin.get_fee_per_kb().await }
 
     async fn calc_interest_if_required(
         &self,