fix(fees): avoid floating point error when converting sats/vbyte to sats/kvbyte

src/components/send/collaborativeSend.test.ts

@@ -81,6 +81,18 @@ describe('buildCollaborativeSendRequest', () => {
     expect(request.txfee).toBe(1_334)
   })
 
+  it('passes txfee in sats/kvbyte without floating point rounding errors', () => {
+    const request = buildCollaborativeSendRequest({
+      ...baseValues(),
+      txFee: {
+        txFeeUnit: TX_FEE_UNITS.SATS_PER_VBYTE,
+        txFeeInSatsPerVbyte: 4.03,
+      },
+    })
+
+    expect(request.txfee).toBe(4_030)
+  })
+
   it('throws for invalid destination address', () => {
     expect(() =>
       buildCollaborativeSendRequest({

src/components/send/collaborativeSend.ts

@@ -1,5 +1,5 @@
 import type { DirectSendRequest, DoCoinjoinRequest } from '@joinmarket-webui/joinmarket-api-ts/jm'
-import { TX_FEE_UNITS } from '@/lib/feeConfig'
+import { satsPerVbyteToSatsPerKvbyte, TX_FEE_UNITS } from '@/lib/feeConfig'
 import { isValidAddress, normalizeBitcoinAddress } from '@/lib/formValidation'
 import { isValidInteger, isValidNumber } from '@/lib/utils'
 import type { SendFormValues } from './types'
@@ -15,7 +15,7 @@ const txFeeValueForRequest = (data: SendFormValues): number | undefined => {
   if (data.txFee.txFeeUnit === TX_FEE_UNITS.BLOCKS && data.txFee.txFeeInBlocks !== undefined) {
     return data.txFee.txFeeInBlocks
   } else if (data.txFee.txFeeUnit === TX_FEE_UNITS.SATS_PER_VBYTE && data.txFee.txFeeInSatsPerVbyte !== undefined) {
-    return Math.ceil(data.txFee.txFeeInSatsPerVbyte * 1_000)
+    return satsPerVbyteToSatsPerKvbyte(data.txFee.txFeeInSatsPerVbyte)
   }
   return undefined
 }

src/components/settings/fees/FeeConfigDialog.test.tsx

@@ -245,6 +245,37 @@ describe('FeeConfigDialog', () => {
     })
   })
 
+  it('saves the sats per vbyte value unchanged', async () => {
+    h.mutateAsync = vi.fn().mockResolvedValue({})
+    const refetchAll = vi.fn().mockResolvedValue(undefined)
+    renderDialog(
+      makeValidValidation({
+        refetchAll,
+        feeConfigValues: {
+          txFeeFactor: 0.1,
+          maxSweepFeeChangeFactor: 0.8,
+          maxCjAbsoluteFee: 100,
+          maxCjRelativeFee: 0.001,
+          txFee: {
+            txFeeUnit: 'sats/vbyte',
+            txFeeInBlocks: undefined,
+            txFeeInSatsPerVbyte: 4.03,
+          },
+        },
+      }),
+    )
+
+    fireEvent.click(screen.getByText('settings.fees.text_button_submit'))
+
+    await waitFor(() => {
+      expect(h.toastSuccess).toHaveBeenCalled()
+    })
+    expect(h.mutateAsync).toHaveBeenCalledWith({
+      path: { walletname: 'test.jmdat' },
+      body: { section: 'POLICY', field: 'tx_fees', value: '4030' },
+    })
+  })
+
   it('skips validation when form validation is disabled in developer mode', async () => {
     h.developerModeEnabled = true
     h.mutateAsync = vi.fn().mockResolvedValue({})

src/components/settings/fees/FeeConfigDialog.tsx

@@ -25,7 +25,7 @@ import { FEE_CONFIG_KEYS, type FeeConfigName } from '@/constants/jm'
 import { useApiClient } from '@/hooks/useApiClient'
 import { useFeeConfigValidation } from '@/hooks/useFeeConfigValidation'
 import { getErrorReason } from '@/lib/errorReason'
-import { TX_FEE_UNITS } from '@/lib/feeConfig'
+import { satsPerVbyteToSatsPerKvbyte, TX_FEE_UNITS } from '@/lib/feeConfig'
 import { cn, factorToPercentage, isValidInteger, isValidNumber, percentageToFactorString } from '@/lib/utils'
 import type { WalletFileName } from '@/lib/utils'
 import { useDeveloperMode } from '@/store/jamSettingsStore'
@@ -136,7 +136,7 @@ export const FeeConfigDialog = ({
 
       const txFeesSatsPerKvByteValue =
         miningData.txFee.txFeeInSatsPerVbyte !== undefined && isValidNumber(miningData.txFee.txFeeInSatsPerVbyte)
-          ? String(Math.ceil(miningData.txFee.txFeeInSatsPerVbyte * 1_000))
+          ? String(satsPerVbyteToSatsPerKvbyte(miningData.txFee.txFeeInSatsPerVbyte))
           : ''
       const txFeesValue =
         miningData.txFee.txFeeUnit === TX_FEE_UNITS.BLOCKS ? txFeesBlocksValue : txFeesSatsPerKvByteValue

src/lib/feeConfig.test.ts

@@ -1,6 +1,6 @@
 import { describe, it, expect } from 'vitest'
 import { MAX_TX_FEE_IN_BLOCKS, MIN_TX_FEE_IN_SATS_PER_VBYTE } from '@/components/send/TxFeeForm.schema'
-import { isMaxFeesConfigMissing, toJamFeeConfigValues, TX_FEE_UNITS } from './feeConfig'
+import { isMaxFeesConfigMissing, satsPerVbyteToSatsPerKvbyte, toJamFeeConfigValues, TX_FEE_UNITS } from './feeConfig'
 
 describe('toJamFeeConfigValues', () => {
   it('should parse raw values successfully', () => {
@@ -202,3 +202,33 @@ describe('isMaxFeesConfigMissing', () => {
     expect(isMaxFeesConfigMissing(values)).toBe(false)
   })
 })
+
+describe('satsPerVbyteToSatsPerKvbyte', () => {
+  it('should convert sats/vbyte to sats/kvbyte', () => {
+    expect(satsPerVbyteToSatsPerKvbyte(1.001)).toBe(1_001)
+    expect(satsPerVbyteToSatsPerKvbyte(5)).toBe(5_000)
+    expect(satsPerVbyteToSatsPerKvbyte(350)).toBe(350_000)
+  })
+
+  it('should not round up because of floating point noise', () => {
+    // e.g. 4.03 * 1_000 === 4030.0000000000005
+    expect(satsPerVbyteToSatsPerKvbyte(2.007)).toBe(2_007)
+    expect(satsPerVbyteToSatsPerKvbyte(4.03)).toBe(4_030)
+    expect(satsPerVbyteToSatsPerKvbyte(4.001)).toBe(4_001)
+  })
+
+  it('should round up fractions of a sat/kvbyte', () => {
+    expect(satsPerVbyteToSatsPerKvbyte(1 + 1 / 3)).toBe(1_334)
+    expect(satsPerVbyteToSatsPerKvbyte(4.0301)).toBe(4_031)
+  })
+
+  it('should return the value of "tx_fees" it was parsed from', () => {
+    const mismatches: string[] = []
+    for (let txFees = 1_001; txFees <= 350_000; txFees++) {
+      const { txFee } = toJamFeeConfigValues({ tx_fees: String(txFees) })
+      const result = satsPerVbyteToSatsPerKvbyte(txFee.txFeeInSatsPerVbyte!)
+      if (result !== txFees) mismatches.push(`${txFees} -> ${result}`)
+    }
+    expect(mismatches).toStrictEqual([])
+  })
+})

src/lib/feeConfig.ts

@@ -28,6 +28,14 @@ export interface JamFeeConfigValues {
   }
 }
 
+/**
+ * Converts a fee rate in sats/vbyte to the integer sats/kvbyte value used for `tx_fees`.
+ *
+ * The product is rounded to 3 decimals before rounding up, so floating point noise
+ * (e.g. `4.03 * 1_000 === 4030.0000000000005`) doesn't bump the result by 1 sat/kvbyte.
+ */
+export const satsPerVbyteToSatsPerKvbyte = (value: number): number => Math.ceil(Number((value * 1_000).toFixed(3)))
+
 export const isMaxFeesConfigMissing = (values: JamFeeConfigValues | undefined): boolean => {
   return !!values && (values.maxCjAbsoluteFee === undefined || values.maxCjRelativeFee === undefined)
 }