Verify payment on chain before generating image

src/app/api/flux/route.ts

@@ -1,6 +1,8 @@
 import { NextRequest, NextResponse } from 'next/server'
 import { fal } from "@fal-ai/client"
 
+import { verifyPayment } from '../../../services/paymentService'
+
 if (!process.env.FAL_AI_KEY) {
   throw new Error('FAL_AI_KEY is not configured in environment variables')
 }
@@ -16,15 +18,28 @@ const IMAGE_HEIGHT: number = 1024
 
 export async function POST(req: NextRequest): Promise<NextResponse> {
   try {
-    const { prompt, modelId } = await req.json()
+    const { prompt, modelId, transactionSignature, expectedAmount } = await req.json()
 
     if (!prompt || !modelId) {
       return NextResponse.json(
-        { error: 'Prompt and modelId are required' },
-        { status: 400 }
+      { error: 'Prompt and modelId are required' },
+      { status: 400 }
       )
     }
 
+    if (!transactionSignature || !expectedAmount) {
+      return NextResponse.json(
+      { error: 'Transaction signature and expected amount are required' },
+      { status: 400 }
+      )
+    }
+
+    const isPaymentVerified = await verifyPayment(transactionSignature, expectedAmount);
+    console.log({isPaymentVerified});
+    if (!isPaymentVerified) {
+      throw new Error('Payment verification failed');
+    }
+
     console.log('Generating with Flux model:', modelId)
     console.log('Prompt:', prompt)
 

src/app/page.tsx

@@ -49,8 +49,10 @@ const Page: React.FC = (): React.ReactElement => {
         return { error: paymentResult.error }
       }
 
+      const transactionSignature = paymentResult.signature;
+
       // Then generate image with specified model
-      return generateWithFlux(prompt, modelId)
+      return generateWithFlux(prompt, modelId, transactionSignature, cost)
     }
   }
 

src/services/fluxService.ts

@@ -34,7 +34,9 @@ export const FLUX_MODELS: FluxModelConfig[] = [
 
 export async function generateWithFlux(
   prompt: string,
-  modelId: string
+  modelId: string,
+  transactionSignature: string,
+  expectedAmount: number,
 ): Promise<FluxGenerationResult> {
   try {
     const response = await fetch('/api/flux', {
@@ -44,7 +46,9 @@ export async function generateWithFlux(
       },
       body: JSON.stringify({
         prompt,
-        modelId
+        modelId,
+        transactionSignature,
+        expectedAmount
       }),
     })
 

src/services/paymentService.ts

@@ -1,4 +1,4 @@
-import { Connection, PublicKey, Transaction, SystemProgram } from '@solana/web3.js'
+import { Connection, PublicKey, Transaction } from '@solana/web3.js'
 import {
   TOKEN_PROGRAM_ID,
   createTransferInstruction,
@@ -48,7 +48,7 @@ export async function processMTMPayment(
   walletPublicKey: string,
   tokenAmount: number,
   walletType: WalletType
-): Promise<PaymentResult> {
+): Promise<PaymentResult & { signature?: string }> {
   try {
     let wallet: WalletAdapter | null = null;
 
@@ -146,7 +146,7 @@ export async function processMTMPayment(
       throw new Error(`Transaction failed: ${JSON.stringify(confirmation.value.err)}`)
     }
 
-    return { success: true }
+    return { success: true, signature };
   } catch (error) {
     console.error('Payment error:', error)
     return {
@@ -155,3 +155,38 @@ export async function processMTMPayment(
     }
   }
 }
+
+export async function verifyPayment(
+  transactionSignature: string,
+  expectedAmount: number,
+): Promise<boolean> {
+  try {
+    console.log('Verifying payment:');
+
+    const transaction = await connection.getParsedTransaction(transactionSignature, 'confirmed');
+    if (!transaction) {
+      throw new Error('Transaction not found');
+    }
+
+    const transferInstruction = transaction.transaction.message.instructions.find(
+      (instr) => 'parsed' in instr && instr.programId.equals(TOKEN_PROGRAM_ID)
+    );
+
+    if (!transferInstruction || !('parsed' in transferInstruction)) {
+      throw new Error('Transfer instruction not found');
+    }
+
+    const { parsed } = transferInstruction;
+    const { info } = parsed;
+    const { amount } = info;
+
+    if (BigInt(amount) === BigInt(expectedAmount * (10 ** 6))) {
+      return true;
+    }
+
+    return false;
+  } catch (error) {
+    console.error('Verification error:', error);
+    return false;
+  }
+}