Payjoin React Native V2

This project implements Bitcoin PayJoin transactions in TypeScript, supporting both PayJoin V1 (BIP-78) and a preview of PayJoin V2 (BIP-77) using bitcoinjs-lib and axios. PayJoin enhances transaction privacy by allowing the receiver to contribute inputs to a payment.

Features

• PayJoin V1: Direct PSBT exchange with a receiver endpoint.
• PayJoin V2 Preview: Simulated asynchronous flow via a directory, without Oblivious HTTP (OHTTP) due to lack of native JS support.
• Creates, signs, and broadcasts PSBTs using testnet (configurable for mainnet).
• Fetches UTXOs from Blockstream’s API.
• Generates V2-compatible BIP-21 URIs.

Installation

npm install bitcoinjs-lib axios buffer typescript ts-node

Usage

1. Save the code as payjoin.ts.
2. Replace senderWIF and senderAddress with testnet credentials.
3. Run:

   ts-node payjoin.ts

Example

await executePayJoin(
  'cYourTestnetWIF',           // Sender private key (WIF)
  'tb1q...',                  // Sender address
  'tb1q6rz28mcfaxtmd6v789l9rrlrusd9rarc0mh4d0', // Receiver address
  100000,                     // Amount (satoshis)
  'https://example.com/payjoin', // V1 endpoint
  'v1'                        // Version ('v1' or 'v2')
);

PayJoin V2 Preview

• Simulation: Uses plain HTTP to a mock directory (http://localhost:3000) instead of OHTTP.
• Flow: Posts PSBT to directory, polls for response, and broadcasts the result.
• Mock Directory: Run a local server for testing:

  npm install express
  ts-node mockDirectory.ts

  Update PAYJOIN_V2_DIRECTORY to http://localhost:3000.

Limitations

• V2: Lacks OHTTP (not available in JS). Full V2 requires an OHTTP client and real directory (e.g., payjoin.org).
• Directory: Simulated; replace with a real V2 directory URL for production.

Dependencies

• bitcoinjs-lib: Bitcoin transaction handling.
• axios: HTTP requests.
• buffer: Hex encoding/decoding.

Notes

• Tested on testnet; adapt network for mainnet.
• Extend with OHTTP support when a JS library becomes available.

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Warning: This is only preview implementation. It's not live yet.