Fix/sendtip fee minimum 242

frontend/src/lib/post-conditions.js

@@ -13,9 +13,10 @@
 
 import { PostConditionMode, Pc } from '@stacks/transactions';
 
-// Contract fee parameters — keep in sync with tipstream.clar
+// Contract fee parameters -- keep in sync with tipstream.clar
 export const FEE_BASIS_POINTS = 50;
 export const BASIS_POINTS_DIVISOR = 10000;
+export const MIN_FEE_USTX = 1;
 
 /** Human-readable fee percentage (e.g. 0.5 for 0.5%). */
 export const FEE_PERCENT = FEE_BASIS_POINTS / BASIS_POINTS_DIVISOR * 100;
@@ -37,7 +38,8 @@ export const SAFE_POST_CONDITION_MODE = PostConditionMode.Deny;
  */
 export function maxTransferForTip(amountMicroSTX, feeBps = FEE_BASIS_POINTS) {
     const amt = Number(amountMicroSTX);
-    const fee = Math.ceil(amt * feeBps / BASIS_POINTS_DIVISOR);
+    const rawFee = Math.ceil(amt * feeBps / BASIS_POINTS_DIVISOR);
+    const fee = feeBps > 0 ? Math.max(rawFee, MIN_FEE_USTX) : 0;
     return amt + fee + 1;
 }
 
@@ -57,14 +59,19 @@ export function tipPostCondition(senderAddress, amountMicroSTX, feeBps = FEE_BAS
 
 /**
  * Calculate the platform fee in microSTX for a given tip amount.
- * Uses Math.ceil to match the on-chain rounding behavior.
+ * Uses Math.ceil to match the on-chain rounding behavior and enforces
+ * a minimum of MIN_FEE_USTX when fee basis points are positive.
  *
  * @param {number|string} amountMicroSTX  Tip amount in microSTX (coerced to Number).
  * @param {number} [feeBps=50]  Fee in basis points.
  * @returns {number}
  */
 export function feeForTip(amountMicroSTX, feeBps = FEE_BASIS_POINTS) {
-    return Math.ceil(Number(amountMicroSTX) * feeBps / BASIS_POINTS_DIVISOR);
+    const raw = Math.ceil(Number(amountMicroSTX) * feeBps / BASIS_POINTS_DIVISOR);
+    if (feeBps > 0) {
+        return Math.max(raw, MIN_FEE_USTX);
+    }
+    return 0;
 }
 
 /**
@@ -89,5 +96,7 @@ export function totalDeduction(amountMicroSTX, feeBps = FEE_BASIS_POINTS) {
  */
 export function recipientReceives(amountMicroSTX, feeBps = FEE_BASIS_POINTS) {
     const amt = Number(amountMicroSTX);
-    return amt - Math.floor(amt * feeBps / BASIS_POINTS_DIVISOR);
+    const rawFee = Math.floor(amt * feeBps / BASIS_POINTS_DIVISOR);
+    const fee = feeBps > 0 ? Math.max(rawFee, MIN_FEE_USTX) : 0;
+    return amt - fee;
 }

frontend/src/test/post-conditions.test.js

@@ -3,6 +3,7 @@ import {
     FEE_BASIS_POINTS,
     BASIS_POINTS_DIVISOR,
     FEE_PERCENT,
+    MIN_FEE_USTX,
     SAFE_POST_CONDITION_MODE,
     maxTransferForTip,
     tipPostCondition,
@@ -26,6 +27,10 @@ describe('post-conditions', () => {
             expect(SAFE_POST_CONDITION_MODE).toBeDefined();
         });
 
+        it('defines MIN_FEE_USTX as 1', () => {
+            expect(MIN_FEE_USTX).toBe(1);
+        });
+
         it('exports FEE_PERCENT as a derived percentage', () => {
             expect(FEE_PERCENT).toBe(0.5);
             expect(FEE_PERCENT).toBe(FEE_BASIS_POINTS / BASIS_POINTS_DIVISOR * 100);
@@ -101,6 +106,31 @@ describe('post-conditions', () => {
             // 1000 * 50 / 10000 = 5
             expect(feeForTip(1000)).toBe(5);
         });
+
+        it('enforces minimum fee of 1 uSTX for tiny amounts', () => {
+            // 1 * 50 / 10000 = 0.005, ceil = 1, max(1, 1) = 1
+            expect(feeForTip(1)).toBe(MIN_FEE_USTX);
+        });
+
+        it('returns minimum fee for amounts below the threshold', () => {
+            // 10 * 50 / 10000 = 0.05, ceil = 1, max(1, 1) = 1
+            expect(feeForTip(10)).toBe(1);
+        });
+
+        it('returns minimum fee for 100 uSTX', () => {
+            // 100 * 50 / 10000 = 0.5, ceil = 1, max(1, 1) = 1
+            expect(feeForTip(100)).toBe(1);
+        });
+
+        it('returns minimum fee for 199 uSTX', () => {
+            // 199 * 50 / 10000 = 0.995, ceil = 1, max(1, 1) = 1
+            expect(feeForTip(199)).toBe(1);
+        });
+
+        it('transitions past minimum at 200 uSTX', () => {
+            // 200 * 50 / 10000 = 1.0, ceil = 1, max(1, 1) = 1
+            expect(feeForTip(200)).toBe(1);
+        });
     });
 
     describe('totalDeduction', () => {
@@ -166,5 +196,45 @@ describe('post-conditions', () => {
         it('recipientReceives accepts a string micro-STX value', () => {
             expect(recipientReceives('1000000')).toBe(recipientReceives(1000000));
         });
+
+        it('feeForTip coerces string for sub-threshold amounts', () => {
+            expect(feeForTip('10')).toBe(feeForTip(10));
+        });
+
+        it('totalDeduction coerces string for sub-threshold amounts', () => {
+            expect(totalDeduction('5')).toBe(totalDeduction(5));
+        });
+    });
+
+    describe('minimum fee cross-function consistency', () => {
+        it('totalDeduction equals amount plus feeForTip for sub-threshold tip', () => {
+            expect(totalDeduction(10)).toBe(10 + feeForTip(10));
+        });
+
+        it('maxTransferForTip equals totalDeduction plus 1 at min fee boundary', () => {
+            expect(maxTransferForTip(10)).toBe(totalDeduction(10) + 1);
+        });
+
+        it('fee plus recipient covers full amount at 200 uSTX boundary', () => {
+            const amt = 200;
+            const net = recipientReceives(amt);
+            const fee = feeForTip(amt);
+            expect(net + fee).toBeGreaterThanOrEqual(amt);
+        });
+
+        it('all functions agree when basis points are zero', () => {
+            expect(feeForTip(10, 0)).toBe(0);
+            expect(totalDeduction(10, 0)).toBe(10);
+            expect(recipientReceives(10, 0)).toBe(10);
+            expect(maxTransferForTip(10, 0)).toBe(11);
+        });
+
+        it('consistency holds across a range of sub-threshold amounts', () => {
+            for (const amt of [1, 2, 5, 50, 100, 150, 199, 200]) {
+                const fee = feeForTip(amt);
+                expect(totalDeduction(amt)).toBe(amt + fee);
+                expect(maxTransferForTip(amt)).toBe(amt + fee + 1);
+            }
+        });
     });
 });