https://github.com/faremeter/solana-payment-program-example

https://github.com/faremeter/solana-payment-program-example

Last synced: 5 months ago
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• Host: GitHub
• URL: https://github.com/faremeter/solana-payment-program-example
• Owner: faremeter
• License: gpl-3.0
• Created: 2025-05-28T20:23:06.000Z (about 1 year ago)
• Default Branch: main
• Last Pushed: 2025-07-03T13:38:32.000Z (12 months ago)
• Last Synced: 2025-07-03T14:47:00.253Z (12 months ago)
• Language: Rust
• Size: 142 KB
• Stars: 0
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.MD
  • License: LICENSE

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README

          
# Solana Payment-Gated API System

## Concept

This system creates a **Solana program** that manages micropayments for API access. Here's how it works:

1. **Payment Creation**: When a user wants to access a protected endpoint, they create a payment transaction that:

   - Transfers SOL to the API provider

   - Creates a **Payment account** (PDA) that stores payment metadata

   - Uses a unique nonce to prevent duplicate payments

2. **Settlement with Race Condition Protection**: When the server processes the payment, it immediately settles it using an admin transaction that:

   - **Uses a unique settle nonce** - this is crucial for preventing race conditions

   - Multiple settlement attempts will fail because only one can successfully close the account

   - **Returns the rent** from the Payment account back to the original payer

   - Ensures each payment can only be settled once

3. **Rent Recovery**: The Payment account requires rent (~0.002 SOL) to exist on-chain. When settled, this rent is automatically returned to the original payer, so they only pay the actual service fee.

## 🔒 Race Condition Prevention

The **settle nonce** is key to preventing race conditions:

```rust

// Each settlement transaction uses a unique nonce

pub fn settle_payment(

    ctx: Context,

    original_payer: Pubkey,

    payment_nonce: [u8; 32],  // Original payment nonce

    settle_nonce: [u8; 32],   // UNIQUE settle nonce - prevents race

) -> Result<()>

```

Example createPayment tx: https://solscan.io/tx/4F1kPoz3L6JqWcUM53cGMZjvYb41TuzqZbAXrXDYQmF6HWNQB2M9WFBbXzdE56GFCNudieAKH5tfJzk6u51EMUF?cluster=devnet

Example settlePayment tx: https://solscan.io/tx/3UZNTyG7QsceTCBmJmTHE8Fiah6TeJpzopKzCcLNciXHrtTKUrZQub9322AWBuuxba2q1zsN4NXp6Pja6podNfrH?cluster=devnet