Estimate fee

assets/rpc.proto

@@ -191,6 +191,16 @@ service Lightning {
         };
     }
 
+    /** lncli: `estimatefee`
+    EstimateFee asks the chain backend to estimate the fee rate and total fees
+    for a transaction that pays to multiple specified outputs.
+    */
+    rpc EstimateFee (EstimateFeeRequest) returns (EstimateFeeResponse) {
+        option (google.api.http) = {
+            get: "/v1/transactions/fee"
+        };
+    }
+
     /** lncli: `sendcoins`
     SendCoins executes a request to send coins to a particular address. Unlike
     SendMany, this RPC call only allows creating a single output at a time. If
@@ -654,6 +664,27 @@ message LightningAddress {
     string host = 2 [json_name = "host"];
 }
 
+message FeeEstimate {
+    /// The total fee in satoshis.
+    int64 fee_sat = 1;
+
+    /// The fee rate in satoshi/byte.
+    int64 feerate_sat_per_byte = 2;
+}
+
+message EstimateFeeRequest {
+    /// The map from addresses to amounts for the transaction.
+    map<string, int64> AddrToAmount = 1;
+
+    /// The target number of blocks that this transaction should be confirmed by.
+    int32 target_conf = 2;
+}
+
+message EstimateFeeResponse {
+    /// A fee estimate for the specified confirmation target.
+    FeeEstimate estimate = 1;
+}
+
 message SendManyRequest {
     /// The map from addresses to amounts
     map<string, int64> AddrToAmount = 1;

src/action/payment.js

@@ -53,6 +53,20 @@ class PaymentAction {
     }
   }
 
+  async estimateFee() {
+    try {
+      const { payment, settings } = this._store;
+      const AddrToAmount = {};
+      AddrToAmount[payment.address] = toSatoshis(payment.amount, settings.unit);
+      const { estimate } = await this._grpc.sendCommand('estimateFee', {
+        AddrToAmount,
+      });
+      payment.fee = toAmount(parseSat(estimate.fee_sat), settings.unit);
+    } catch (err) {
+      this._notification.display({ msg: 'Estimating fee failed!', err });
+    }
+  }
+
   async payBitcoin() {
     try {
       const { payment, settings } = this._store;

test/integration/action/action-integration.spec.js

@@ -245,9 +245,14 @@ describe('Action Integration Tests', function() {
       transactions2.subscribeTransactions();
     });
 
-    it('should send some on-chain funds to node2', async () => {
+    it('should estimate on-chain fees', async () => {
       store1.payment.address = store2.walletAddress;
       store1.payment.amount = '10';
+      await payments1.estimateFee();
+      expect(store1.payment.fee, 'to be ok');
+    });
+
+    it('should send some on-chain funds to node2', async () => {
       await payments1.payBitcoin();
     });
 

test/unit/action/payment.spec.js

@@ -39,6 +39,7 @@ describe('Action Payments Unit Tests', () => {
       payment.init();
       expect(store.payment.address, 'to equal', '');
       expect(store.payment.amount, 'to equal', '');
+      expect(store.payment.fee, 'to equal', '');
       expect(store.payment.note, 'to equal', '');
       expect(nav.goPay, 'was called once');
     });
@@ -80,6 +81,31 @@ describe('Action Payments Unit Tests', () => {
     });
   });
 
+  describe('estimateFee()', () => {
+    it('should get fee estimate to display', async () => {
+      store.payment.amount = '0.00001';
+      store.payment.address = 'some-address';
+      grpc.sendCommand.withArgs('estimateFee').resolves({
+        estimate: {
+          fee_sat: '8250',
+          feerate_sat_per_byte: '50',
+        },
+      });
+      await payment.estimateFee();
+      expect(grpc.sendCommand, 'was called with', 'estimateFee', {
+        AddrToAmount: { 'some-address': 1000 },
+      });
+      expect(store.payment.fee, 'to equal', '0.0000825');
+    });
+
+    it('should display notification on error', async () => {
+      grpc.sendCommand.withArgs('estimateFee').rejects();
+      await payment.estimateFee();
+      expect(notification.display, 'was called once');
+      expect(store.payment.fee, 'to equal', '');
+    });
+  });
+
   describe('payBitcoin()', () => {
     it('should send on-chain transaction', async () => {
       store.payment.amount = '0.00001';