fix(backend): update minSendAmount in local and ILP payments

packages/backend/src/payment-method/ilp/service.test.ts

@@ -1,4 +1,8 @@
-import { IlpPaymentService, retryableIlpErrors } from './service'
+import {
+  IlpPaymentService,
+  calculateMinSendAmount,
+  retryableIlpErrors
+} from './service'
 import { initIocContainer } from '../../'
 import { createTestApp, TestContainer } from '../../tests/app'
 import { IAppConfig, Config } from '../../config/app'
@@ -972,4 +976,32 @@ describe('IlpPaymentService', (): void => {
       }
     })
   })
+
+  describe('calculateMinSendAmount', (): void => {
+    test('returns reciprocal of highEstimatedExchangeRate', async (): Promise<void> => {
+      expect(
+        calculateMinSendAmount({
+          highEstimatedExchangeRate: Pay.Ratio.from(0.05)
+        } as Pay.Quote)
+      ).toBe(20n)
+      expect(
+        calculateMinSendAmount({
+          highEstimatedExchangeRate: Pay.Ratio.from(0.01)
+        } as Pay.Quote)
+      ).toBe(100n)
+    })
+
+    test('returns at least 2 even if highEstimatedExchangeRate reciprocal under 2', async (): Promise<void> => {
+      expect(
+        calculateMinSendAmount({
+          highEstimatedExchangeRate: Pay.Ratio.from(1)
+        } as Pay.Quote)
+      ).toBe(2n)
+      expect(
+        calculateMinSendAmount({
+          highEstimatedExchangeRate: Pay.Ratio.from(20)
+        } as Pay.Quote)
+      ).toBe(2n)
+    })
+  })
 })

packages/backend/src/payment-method/ilp/service.ts

@@ -126,9 +126,7 @@ async function getQuote(
         retryable: false,
         code: PaymentMethodHandlerErrorCode.QuoteNonPositiveReceiveAmount,
         details: {
-          minSendAmount: BigInt(
-            Math.ceil(ilpQuote.highEstimatedExchangeRate.reciprocal().valueOf())
-          )
+          minSendAmount: calculateMinSendAmount(ilpQuote)
         }
       })
     }
@@ -172,9 +170,7 @@ async function getQuote(
         retryable: false,
         code: PaymentMethodHandlerErrorCode.QuoteNonPositiveReceiveAmount,
         details: {
-          minSendAmount: BigInt(
-            Math.ceil(ilpQuote.highEstimatedExchangeRate.reciprocal().valueOf())
-          )
+          minSendAmount: calculateMinSendAmount(ilpQuote)
         }
       })
     }
@@ -205,9 +201,7 @@ async function getQuote(
         retryable: false,
         code: PaymentMethodHandlerErrorCode.QuoteNonPositiveReceiveAmount,
         details: {
-          minSendAmount: BigInt(
-            Math.ceil(ilpQuote.highEstimatedExchangeRate.reciprocal().valueOf())
-          )
+          minSendAmount: calculateMinSendAmount(ilpQuote)
         }
       })
     }
@@ -392,6 +386,14 @@ async function pay(
   }
 }
 
+export function calculateMinSendAmount(quote: Pay.Quote): bigint {
+  const minSendAmount = Math.ceil(
+    quote.highEstimatedExchangeRate.reciprocal().valueOf()
+  )
+
+  return BigInt(Math.max(minSendAmount, 2)) // because of rounding in ILP pay, you must always send at least 2 units of an asset
+}
+
 export function canRetryError(err: Error | Pay.PaymentError): boolean {
   return err instanceof Error || !!retryableIlpErrors[err]
 }

packages/backend/src/payment-method/local/service.test.ts

@@ -185,7 +185,14 @@ describe('LocalPaymentService', (): void => {
     })
 
     test('fails if debit amount is non-positive', async (): Promise<void> => {
-      expect.assertions(4)
+      jest
+        .spyOn(await deps.use('ratesService'), 'convertDestination')
+        .mockImplementation(() =>
+          Promise.resolve({ amount: 0n, scaledExchangeRate: 1 })
+        )
+
+      expect.assertions(5)
+
       try {
         await localPaymentService.getQuote({
           walletAddress: walletAddressMap['USD'],
@@ -205,6 +212,9 @@ describe('LocalPaymentService', (): void => {
           'debit amount of local quote is non-positive'
         )
         expect((err as PaymentMethodHandlerError).retryable).toBe(false)
+        expect((err as PaymentMethodHandlerError).details).toEqual({
+          minSendAmount: 1n
+        })
       }
     })
     test('fails if receive amount is non-positive', async (): Promise<void> => {
@@ -214,7 +224,7 @@ describe('LocalPaymentService', (): void => {
         .mockImplementation(() =>
           Promise.resolve({ amount: 100n, scaledExchangeRate: 1 })
         )
-      expect.assertions(4)
+      expect.assertions(5)
       try {
         await localPaymentService.getQuote({
           walletAddress: walletAddressMap['USD'],
@@ -234,6 +244,9 @@ describe('LocalPaymentService', (): void => {
           'receive amount of local quote is non-positive'
         )
         expect((err as PaymentMethodHandlerError).retryable).toBe(false)
+        expect((err as PaymentMethodHandlerError).details).toEqual({
+          minSendAmount: 1n
+        })
       }
     })
 

packages/backend/src/payment-method/local/service.ts

@@ -173,7 +173,11 @@ async function getQuote(
   if (debitAmountValue <= BigInt(0)) {
     throw new PaymentMethodHandlerError('Received error during local quoting', {
       description: 'debit amount of local quote is non-positive',
-      retryable: false
+      retryable: false,
+      code: PaymentMethodHandlerErrorCode.QuoteNonPositiveReceiveAmount,
+      details: {
+        minSendAmount: BigInt(Math.ceil(1 / exchangeRate))
+      }
     })
   }