Express cashu middleware

Express middleware for cashu payments using NUT-24

Installation

npm install -s express-cashu

Usage

Add middleware function to express http routes

import express from 'express';
import { cashu } from 'express-cashu';

const app = express();

app.use('/', cashu({
    paymentCallback: async (token: string, _req: express.Request) => {
        console.log('Received payment', token);
    },
    trustedMints: ['https://mint.lnserver.com'],
    amount: 10,
    unit: 'sat',
    debug: true
}));

app.get('/', (_req, res) => {
    res.send('Payment received!');
});

Server responds with http 402 status code and X-Cashu header, containing the payment request creqA...

X-Cashu: creqAo2FhBWF1Y3NhdGFt...

The client sends a cashu token with the requested amount to pay for the service

X-Cashu: cashuBo2FteBlodHRwczovL...

Payment Example:

import { decodePaymentRequest, getEncodedTokenV4, Proof, Token, Wallet, } from '@cashu/cashu-ts';

payToServer();

async function payToServer() {
    const protectedApiUrl = 'http://localhost:3000';

    // try access the API resource
    const req = await fetch(protectedApiUrl);

    // decode the received payment request from the API resource
    const paymentRequest = req.headers.get('x-cashu');
    const decodedPaymentRequest = decodePaymentRequest(paymentRequest);
    const mintUrl = decodedPaymentRequest.mints[0];

    // Internal stored proofs
    let proofs: Proof[];
    let sentProofs: Proof[];

    // Init wallet
    const wallet = new Wallet(mintUrl);
    await wallet.loadMint();

    // Example: get proofs from cashu token
    const storedToken = 'cashuBo2FteBlo....';
    const decodedToken = wallet.decodeToken(storedToken);
    proofs = decodedToken.proofs;

    // now use your proofs and send the requested amount back to the resource
    const { keep, send } = await wallet.send(decodedPaymentRequest.amount, proofs);

    // update remaining proof list
    proofs = keep;

    // store sent proofs to redeem them back later, if the receiver does not claim them
    sentProofs = send;

    // create a token with proof list
    const token: Token = {
        mint: mintUrl,
        proofs: send
    };

    // encode the token as a cashu string
    const cashuString = getEncodedTokenV4(token);

    // finally pay the requested amount with encoded token
    await fetch(protectedApiUrl, {
        headers: {
            'x-cashu': cashuString
        }
    });
};

Test

Run test suite

npm test