feat: PIX codes expire after 30 minutes, with a countdown

A PIX is created with a 30-minute date_of_expiration, and the PIX page
counts down to it. When it runs out the page says the code expired and
offers a new one. The API keeps one open code per quote: the same code
until it expires, then exactly one new attempt (serialised per quote, with
its own idempotency key), the old one marked expired.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/adapters.py

@@ -106,6 +106,11 @@ class FakePayment:
 
     def create(self, quote_id: str, total_cents: int, customer: dict, method: dict | None = None) -> dict:
         kind = (method or {}).get('type', 'pix')
+        if kind == 'pix':
+            from datetime import datetime, timedelta, timezone
+            expires = (datetime.now(timezone.utc) + timedelta(minutes=30)).isoformat(timespec='milliseconds')
+            return {'provider': 'fake', 'id': f"local-{quote_id}-pix-{(method or {}).get('attempt', 1)}",
+                    'status': 'pending', 'total_cents': total_cents, 'expires_at': expires}
         return {'provider': 'fake', 'id': f'local-{quote_id}-{kind}',
                 'status': 'pending', 'total_cents': total_cents}
 

app/api/payments.py

@@ -84,14 +84,25 @@ def intent(body: PaymentIntent, session_id=Depends(owner)):
                           AND created_at < now() - make_interval(mins => %s))))''',
                      (body.quote_id, CHALLENGE_MINUTES)).fetchone():
             raise HTTPException(409, 'A payment for this quote is already approved or in review')
+        method = body.method.model_dump()
         if body.method.type == 'pix':
-            existing = c.execute('''SELECT * FROM dtf_local.payment_intents WHERE quote_id=%s AND method='pix'
+            # One open PIX per quote: the same code until it expires, and a new
+            # one only after that, when the old code can no longer be paid.
+            # Serialised per quote, so two clicks never open two codes.
+            c.execute('SELECT pg_advisory_xact_lock(hashtext(%s))', ('pix:'+str(body.quote_id),))
+            existing = c.execute('''SELECT *, COALESCE((response->>'expires_at')::timestamptz <= now(), false) AS expired
+                FROM dtf_local.payment_intents WHERE quote_id=%s AND method='pix'
                 AND status='pending' ORDER BY created_at DESC LIMIT 1''', (body.quote_id,)).fetchone()
-            if existing:
+            if existing and not existing['expired']:
                 return existing['response']
+            if existing:
+                c.execute("UPDATE dtf_local.payment_intents SET status='expired', updated_at=now() WHERE id=%s",
+                          (existing['id'],))
+            method['attempt'] = c.execute('''SELECT count(*) AS n FROM dtf_local.payment_intents
+                WHERE quote_id=%s AND method='pix' ''', (body.quote_id,)).fetchone()['n'] + 1
         try:
             created = payment.create(str(body.quote_id), quote['approved']['total_cents'],
-                                     quote['approved']['customer'], body.method.model_dump())
+                                     quote['approved']['customer'], method)
         except ValueError as exc:
             raise HTTPException(422, str(exc))
         except Exception:

app/mercadopago.py

@@ -21,6 +21,7 @@ import hmac
 import json
 import os
 import time
+from datetime import datetime, timedelta, timezone
 from decimal import Decimal, InvalidOperation
 from typing import Mapping
 
@@ -35,6 +36,9 @@ MAX_SIGNATURE_AGE = 30 * 60
 STATUSES = {'approved': 'approved', 'pending': 'pending', 'in_process': 'pending',
             'authorized': 'pending', 'in_mediation': 'pending', 'rejected': 'rejected',
             'cancelled': 'cancelled', 'refunded': 'refunded', 'charged_back': 'refunded'}
+# A PIX code stops working after this; Mercado Pago then cancels the payment.
+PIX_MINUTES = 30
+BRASILIA = timezone(timedelta(hours=-3))
 
 
 class MercadoPagoPayment:
@@ -70,8 +74,11 @@ class MercadoPagoPayment:
                           'identification': {'type': 'CNPJ', 'number': customer['cnpj']}}}
         if self.notification_url:
             body['notification_url'] = self.notification_url
+        expires_at = None
         if method['type'] == 'pix':
             body['payment_method_id'] = 'pix'
+            expires_at = (datetime.now(BRASILIA) + timedelta(minutes=PIX_MINUTES)).isoformat(timespec='milliseconds')
+            body['date_of_expiration'] = expires_at
         elif method['type'] == 'card':
             # The issuer decides whether the cardholder must confirm in the
             # bank's app or page (3-D Secure); debit cards usually must.
@@ -82,10 +89,11 @@ class MercadoPagoPayment:
                 body['issuer_id'] = method['issuer_id']
         else:
             raise ValueError('Unsupported payment method')
-        # A PIX retry must return the same code. A card retry after a decline
+        # A PIX retry must return the same code; a new one, after the last
-        # is a new attempt with a new token, so the token is part of the key;
+        # expired, is the next attempt. A card retry after a decline is a new
-        # the intent route refuses new attempts once one is approved or in review.
+        # attempt with a new token, so the token is part of the key; the intent
-        key = f'dtf-quote-{quote_id}-pix' if method['type'] == 'pix' else \
+        # route refuses new attempts once one is approved or in review.
+        key = f"dtf-quote-{quote_id}-pix-{int(method.get('attempt', 1))}" if method['type'] == 'pix' else \
             f"dtf-quote-{quote_id}-card-{hashlib.sha256(method['token'].encode()).hexdigest()[:24]}"
         response = self.http.post('/v1/payments', json=body, headers={'X-Idempotency-Key': key})
         response.raise_for_status()
@@ -104,6 +112,7 @@ class MercadoPagoPayment:
                 'pix_qr_code': transaction.get('qr_code'),
                 'pix_qr_code_base64': transaction.get('qr_code_base64'),
                 'ticket_url': transaction.get('ticket_url'),
+                'expires_at': payment.get('date_of_expiration') or expires_at,
                 'challenge': challenge}
 
     def lookup(self, payment_id: str) -> dict:

tests/payment_test.py

@@ -12,6 +12,7 @@ from urllib.error import HTTPError
 from urllib.request import Request, urlopen
 from uuid import uuid4
 
+from app.core import db
 from tests.smoke_test import BASE, Client, approved_quote, upload_bytes, item_spec, with_host
 
 SECRET = os.environ.get('PAYMENT_WEBHOOK_SECRET', 'local-webhook-secret').encode()
@@ -60,7 +61,22 @@ def run():
     # Starting a PIX twice returns the same one. A card in review blocks every
     # further attempt, so one quote can never be charged twice.
     pix = customer.call('/payments/intent', {'quote_id': quote_id, 'method': {'type': 'pix'}})
+    assert pix['expires_at']
     assert customer.call('/payments/intent', {'quote_id': quote_id, 'method': {'type': 'pix'}})['id'] == pix['id']
+    # Once the code has expired, asking again opens a new one, and only one.
+    with db.connect() as c:
+        c.execute('''UPDATE dtf_local.payment_intents
+            SET response=jsonb_set(response,'{expires_at}',to_jsonb((now()-interval '1 minute')::text))
+            WHERE provider_payment_id=%s''', (pix['id'],))
+    renewed = customer.call('/payments/intent', {'quote_id': quote_id, 'method': {'type': 'pix'}})
+    assert renewed['id'] != pix['id'], 'an expired PIX was offered again'
+    assert customer.call('/payments/intent', {'quote_id': quote_id, 'method': {'type': 'pix'}})['id'] == renewed['id']
+    with db.connect() as c:
+        statuses = {r['provider_payment_id']: r['status'] for r in c.execute(
+            "SELECT provider_payment_id,status FROM dtf_local.payment_intents WHERE quote_id=%s AND method='pix'",
+            (quote_id,)).fetchall()}
+    assert statuses == {pix['id']: 'expired', renewed['id']: 'pending'}, statuses
+    print('PASS: a PIX code expires after 30 minutes and is replaced by exactly one new code')
     customer.call('/payments/intent', {'quote_id': quote_id, 'method': {'type': 'card'}}, expected=422)
     card = {'type': 'card', 'token': 'tok-1', 'payment_method_id': 'visa', 'installments': 1}
     customer.call('/payments/intent', {'quote_id': quote_id, 'method': card})

tests/test_mercadopago.py

@@ -8,6 +8,7 @@ import hashlib
 import hmac
 import json
 import unittest
+from datetime import datetime, timezone
 
 import httpx
 
@@ -110,11 +111,20 @@ class MercadoPagoTests(unittest.TestCase):
         request = self.requests[-1]
         body = json.loads(request.content)
         self.assertEqual(request.headers['x-idempotency-key'],
-                         'dtf-quote-11111111-2222-3333-4444-555555555555-pix')
+                         'dtf-quote-11111111-2222-3333-4444-555555555555-pix-1')
         self.assertEqual((body['payment_method_id'], body['transaction_amount']), ('pix', 123.45))
         self.assertEqual(body['external_reference'], '11111111-2222-3333-4444-555555555555')
         self.assertEqual(body['notification_url'], 'https://dtf.example/api/payments/webhook')
         self.assertEqual((created['pix_qr_code'], created['status']), ('000201PIX', 'pending'))
+        # The code expires in 30 minutes, in the format Mercado Pago documents.
+        expires = datetime.fromisoformat(body['date_of_expiration'])
+        self.assertRegex(body['date_of_expiration'], r'^\d{4}-\d\d-\d\dT\d\d:\d\d:\d\d\.\d{3}-03:00$')
+        self.assertAlmostEqual((expires - datetime.now(timezone.utc)).total_seconds(), 1800, delta=60)
+        self.assertEqual(created['expires_at'], body['date_of_expiration'])
+        # A new code after the last expired is the next attempt, not the same payment.
+        self.mp.create('11111111-2222-3333-4444-555555555555', 12345,
+                       {'mail': 'a@example.test', 'cnpj': '11222333000181'}, {'type': 'pix', 'attempt': 2})
+        self.assertTrue(self.requests[-1].headers['x-idempotency-key'].endswith('-pix-2'))
 
     def test_card_payment_uses_the_browser_token_only(self):
         self.mp.create('q', 1000, {'mail': 'a@example.test', 'cnpj': '11222333000181'},

web/checkout.js

@@ -7,6 +7,7 @@
   const naPagina = () => ['pagamento','pix'].includes(document.documentElement.dataset.rota);
   const naPix = () => document.documentElement.dataset.rota === 'pix';
   let shownCart = null;
+  let pixClock = null;
   let busy = false;
   let draftId = localStorage.getItem('dtf-quote');
   let requestKey = localStorage.getItem('dtf-request-key');
@@ -162,6 +163,7 @@
       if(version!==refreshVersion || draftId!==shownId) return;
       if (!naPagina()) { message(''); vaiPara(PAGAMENTO); return; }
       shownCart=cartSnapshot();
+      clearInterval(pixClock);
       unmountCard();
       actions.replaceChildren();
       message('');
@@ -319,9 +321,26 @@
       try{ await navigator.clipboard.writeText(intent.pix_qr_code); copiar.textContent='Código copiado'; }
       catch(_){ code.select(); }
     },linha);
-    box.append(linha,node('p','Aguardando a confirmação do pagamento…','aguarda'));
+    const prazo=node('p',null,'prazo');
+    box.append(linha,prazo,node('p','Aguardando a confirmação do pagamento…','aguarda'));
     actions.append(box);
     waitForOrder();
+    // The code stops working when it expires; a new one is a click away.
+    const fim=Date.parse(intent.expires_at);
+    if (!Number.isFinite(fim)) { prazo.remove(); return; }
+    const tick=()=>{
+      const s=Math.max(0,Math.ceil((fim-Date.now())/1000));
+      prazo.textContent='Pague em '+String(Math.floor(s/60)).padStart(2,'0')+':'+String(s%60).padStart(2,'0');
+      if (s>0) return;
+      clearInterval(pixClock);
+      const fimBox=node('div',null,'pixBox');
+      fimBox.append(node('h4','O código PIX expirou'),
+        node('p','Gere um novo código para pagar. O anterior não pode mais ser pago.','pagNota'));
+      button('Gerar novo PIX',()=>refresh(),fimBox);
+      actions.replaceChildren(fimBox);
+    };
+    tick();
+    pixClock=setInterval(tick,1000);
   }
 
   // Card: Mercado Pago's own form (Card Payment Brick). The card is typed into
@@ -399,7 +418,7 @@
   // The cart page keeps only the sending progress and errors, never a payment.
   window.addEventListener('dtf-page-changed',()=>{
     if (naPagina()) refresh();
-    else if (!busy) { refreshVersion++; message(''); actions.replaceChildren(); pintaResumo(null); }
+    else if (!busy) { refreshVersion++; clearInterval(pixClock); message(''); actions.replaceChildren(); pintaResumo(null); }
   });
   refresh();
 })();

web/site-v2.css

@@ -254,6 +254,7 @@ html:is([data-rota="pagamento"],[data-rota="pix"]) .pagGrid{display:grid;grid-te
 .pixBox .codigo{display:flex;gap:10px;width:100%}
 .pixBox .codigo input{flex:1;min-width:0;font-size:13px}
 .pixBox .aguarda{font-size:14px;color:var(--texto2)}
+.pixBox .prazo{font-family:"Inter",sans-serif;font-weight:800;font-size:18px;font-variant-numeric:tabular-nums}
 .confirmado{border:1px solid #BFE6CE;background:var(--verde-fundo);border-radius:16px;padding:24px}
 .confirmado h4{font-size:22px;color:#14532D;margin-bottom:8px}
 .confirmado p{font-size:15px;color:#14532D;margin-bottom:18px;line-height:1.5}