feat: return buyers to the calling app after Stripe, branded QR endpoint

`_resolve_frontend_root` honours `CreateTicket.frontend_url` when its
origin is one of LNBITS_CORS_ALLOWED_ORIGINS, the LNbits base URL or
LNBITS_CUSTOM_FRONTEND_URL (400 otherwise — a silent fallback would send
the buyer to the wrong app), and falls back to request.base_url as before.
Under that root the fiat path now parameterises the hosted checkout via
`extra["checkout"]` (lnbits StripeCheckoutOptions): success_url
`/events/{id}?checkout=success&tickets=<ids>`, cancel_url
`/events/{id}?checkout=cancelled`, customer_email, an event-named line
item and event_id/quantity/ticket_ids metadata. Ticket ids are minted
before the invoice so the success URL can carry them (the payment_hash
only exists afterwards). ticket_base_url on the rows uses the same root,
so the emailed link lands in the webapp when the webapp was the client.

Purchases are gated on `effective_payment_methods(event)` (checked after
the free-ticket short-circuit, which charges nothing on any rail).

New anonymous `GET /events/api/v1/qr/{ticket_id}` returns a PNG of
`ticket://<id>` — port of upstream v1.6.8's endpoint without ticket-image
compositing — built at error-correction H with the instance QR logo
(`lnbits_qr_logo`) pasted in the centre, matching the client-side QRs.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EYwoAkZZmXMMmaBp4WGUBo

__init__.py

@@ -6,12 +6,13 @@ from loguru import logger
 from .crud import db
 from .tasks import wait_for_paid_invoices
 from .views import events_generic_router
-from .views_api import events_api_router, tickets_api_router
+from .views_api import events_api_router, qr_api_router, tickets_api_router
 
 events_ext: APIRouter = APIRouter(prefix="/events", tags=["Events"])
 events_ext.include_router(events_generic_router)
 events_ext.include_router(events_api_router)
 events_ext.include_router(tickets_api_router)
+events_ext.include_router(qr_api_router)
 
 events_static_files = [
     {

tests/test_frontend_root.py

@@ -0,0 +1,52 @@
+from types import SimpleNamespace
+
+import pytest
+from fastapi import HTTPException
+from lnbits.settings import settings
+
+from ..models import CreateTicket
+from ..views_api import _allowed_frontend_origins, _resolve_frontend_root
+
+
+@pytest.fixture
+def lnbits_settings(monkeypatch):
+    monkeypatch.setattr(settings, "lnbits_baseurl", "https://lnbits.example/")
+    monkeypatch.setattr(
+        settings, "lnbits_cors_allowed_origins", ["https://app.example"], raising=False
+    )
+    monkeypatch.setattr(
+        settings,
+        "lnbits_custom_frontend_url",
+        "https://Front.Example/login",
+        raising=False,
+    )
+
+
+def _request(base_url: str = "https://lnbits.example/"):
+    return SimpleNamespace(base_url=base_url)
+
+
+def test_allowlist_collects_every_configured_origin(lnbits_settings):
+    assert _allowed_frontend_origins() == {
+        "https://lnbits.example",
+        "https://app.example",
+        "https://front.example",
+    }
+
+
+def test_absent_frontend_url_falls_back_to_the_request_host(lnbits_settings):
+    data = CreateTicket(user_id="u1")
+    assert _resolve_frontend_root(data, _request()) == "https://lnbits.example"
+
+
+def test_allowed_origin_is_returned_without_trailing_slash(lnbits_settings):
+    data = CreateTicket(user_id="u1", frontend_url="https://app.example/events/")
+    assert _resolve_frontend_root(data, _request()) == "https://app.example/events"
+
+
+def test_unlisted_origin_is_rejected_loudly(lnbits_settings):
+    data = CreateTicket(user_id="u1", frontend_url="https://evil.example/events")
+    with pytest.raises(HTTPException) as exc:
+        _resolve_frontend_root(data, _request())
+    assert exc.value.status_code == 400
+    assert "frontend_url" in exc.value.detail

tests/test_ticket_qr.py

@@ -0,0 +1,22 @@
+from io import BytesIO
+
+from PIL import Image
+
+from ..views_api import make_qr_png
+
+
+def test_make_qr_png_renders_requested_size():
+    img = make_qr_png("ticket://abc123", size=200)
+    assert img.size == (200, 200)
+
+
+def test_make_qr_png_pastes_a_centred_logo():
+    logo = Image.new("RGBA", (64, 64), (255, 0, 0, 255))
+    img = make_qr_png("ticket://abc123", size=300, logo=logo)
+    assert img.size == (300, 300)
+    # The centre pixel is inside the pasted logo, so it is red — a plain
+    # QR would only ever have black or white there.
+    assert img.getpixel((150, 150))[:3] == (255, 0, 0)
+    out = BytesIO()
+    img.save(out, format="PNG")
+    assert out.getvalue().startswith(b"\x89PNG")

views_api.py

@@ -1,8 +1,13 @@
 import asyncio
 from datetime import datetime, timezone
 from http import HTTPStatus
+from io import BytesIO
+from pathlib import Path
 from typing import Any
+from urllib.parse import urlsplit
 
+import httpx
+import pyqrcode  # type: ignore[import-untyped]
 from fastapi import (
     APIRouter,
     Depends,
@@ -12,18 +17,19 @@ from fastapi import (
     WebSocket,
     WebSocketDisconnect,
 )
+from fastapi.responses import StreamingResponse
 from lnbits.core.crud import get_user
 from lnbits.core.crud.wallets import get_wallet
 from lnbits.core.models import Account, User, WalletTypeInfo
 from lnbits.core.models.payments import CreateInvoice
 from lnbits.core.services import create_payment_request
-from lnbits.helpers import urlsafe_short_hash
 from lnbits.decorators import (
     check_admin,
     check_user_exists,
     require_admin_key,
     require_invoice_key,
 )
+from lnbits.helpers import urlsafe_short_hash
 from lnbits.settings import settings
 from lnbits.utils.exchange_rates import (
     fiat_amount_as_satoshis,
@@ -31,6 +37,8 @@ from lnbits.utils.exchange_rates import (
     satoshis_amount_as_fiat,
 )
 from lnbits.utils.nostr import normalize_public_key
+from loguru import logger
+from PIL import Image, ImageDraw
 
 from .crud import (
     create_event,
@@ -64,6 +72,8 @@ from .models import (
     PublicTicket,
     Ticket,
     TicketPaymentRequest,
+    TicketResendResult,
+    effective_payment_methods,
 )
 from .nostr_hooks import publish_or_delete_nostr_event
 from .services import (
@@ -76,6 +86,7 @@ from .tasks import deregister_payment_listener, register_payment_listener
 
 events_api_router = APIRouter(prefix="/api/v1/events")
 tickets_api_router = APIRouter(prefix="/api/v1/tickets")
+qr_api_router = APIRouter(prefix="/api/v1")
 
 
 def _is_fiat_currency(currency: str | None) -> bool:
@@ -513,6 +524,136 @@ async def api_get_ticket(ticket_id: str) -> Ticket:
     return ticket
 
 
+def _origin(url: str | None) -> str | None:
+    if not url:
+        return None
+    parts = urlsplit(url.strip())
+    if not parts.scheme or not parts.netloc:
+        return None
+    return f"{parts.scheme.lower()}://{parts.netloc.lower()}"
+
+
+def _allowed_frontend_origins() -> set[str]:
+    """Origins a buyer-side client may name in `CreateTicket.frontend_url`.
+
+    The CORS allow-list is literally "which web apps may talk to this
+    LNbits", so it is the natural allow-list for "which web apps may be
+    linked from a ticket email". The LNbits host itself and the configured
+    custom frontend are always fine.
+    """
+    origins: set[str] = set()
+    for candidate in [
+        *getattr(settings, "lnbits_cors_allowed_origins", []),
+        settings.lnbits_baseurl,
+        getattr(settings, "lnbits_custom_frontend_url", None),
+    ]:
+        origin = _origin(candidate)
+        if origin:
+            origins.add(origin)
+    return origins
+
+
+def _resolve_frontend_root(data: CreateTicket, request: Request) -> str:
+    """Root under which `/events/{event_id}` and `/events/ticket/{ticket_id}`
+    resolve for the buyer — the calling app when it says so, else the LNbits
+    host (the extension's own Quasar pages)."""
+    if not data.frontend_url:
+        return str(request.base_url).rstrip("/")
+    origin = _origin(data.frontend_url)
+    if not origin or origin not in _allowed_frontend_origins():
+        # Fail loud rather than silently falling back: a wrong root means
+        # the buyer is returned to (and emailed a link into) the wrong app.
+        raise HTTPException(
+            status_code=HTTPStatus.BAD_REQUEST,
+            detail="frontend_url origin is not allowed.",
+        )
+    return data.frontend_url.rstrip("/")
+
+
+_qr_logo_cache: dict[str, Image.Image | None] = {}
+
+
+async def _load_qr_logo() -> Image.Image | None:
+    """LNbits' "QR Code/Favicon Logo" setting, as a Pillow image (cached).
+
+    Local `/static/...` values resolve inside the LNbits package; absolute
+    URLs are fetched once. Any failure just yields a plain QR.
+    """
+    source = (settings.lnbits_qr_logo or "").strip()
+    if not source:
+        return None
+    if source in _qr_logo_cache:
+        return _qr_logo_cache[source]
+    logo: Image.Image | None = None
+    try:
+        if source.startswith(("http://", "https://")):
+            async with httpx.AsyncClient(timeout=5) as client:
+                resp = await client.get(source)
+                resp.raise_for_status()
+                logo = Image.open(BytesIO(resp.content)).convert("RGBA")
+        else:
+            local = Path(settings.lnbits_path) / source.lstrip("/")
+            if local.is_file():
+                logo = Image.open(local).convert("RGBA")
+    except Exception as exc:
+        logger.warning(f"QR logo '{source}' unavailable: {exc}")
+        logo = None
+    _qr_logo_cache[source] = logo
+    return logo
+
+
+def make_qr_png(
+    data: str,
+    size: int = 235,
+    border: int = 4,
+    logo: Image.Image | None = None,
+) -> Image.Image:
+    """Render `data` as a QR image (upstream v1.6.8 shape). With `logo`, the
+    code is built at error-correction level H and the logo is pasted in the
+    centre on a white pad at ≤ 20 % of the width — the same look LNbits'
+    client-side `lnbits-qrcode` component produces."""
+    qr = pyqrcode.create(data, error="H" if logo is not None else "M")
+    matrix = qr.code
+    modules = len(matrix)
+
+    total_modules = modules + border * 2
+    box_size = max(1, size // total_modules)
+    img_size = total_modules * box_size
+
+    img = Image.new("RGBA", (img_size, img_size), "white")
+    draw = ImageDraw.Draw(img)
+
+    for y, row in enumerate(matrix):
+        for x, cell in enumerate(row):
+            if cell:
+                x0 = (x + border) * box_size
+                y0 = (y + border) * box_size
+                draw.rectangle(
+                    [x0, y0, x0 + box_size - 1, y0 + box_size - 1],
+                    fill="black",
+                )
+
+    if img_size != size:
+        img = img.resize((size, size), Image.Resampling.NEAREST)
+
+    if logo is not None:
+        logo_size = max(8, int(size * 0.2))
+        pad = max(2, logo_size // 8)
+        scaled = logo.copy()
+        scaled.thumbnail((logo_size, logo_size), Image.Resampling.LANCZOS)
+        plate = Image.new(
+            "RGBA", (scaled.width + 2 * pad, scaled.height + 2 * pad), "white"
+        )
+        plate.paste(scaled, (pad, pad), scaled)
+        img.paste(
+            plate,
+            ((size - plate.width) // 2, (size - plate.height) // 2),
+            plate,
+        )
+
+    return img
+
+
 async def _issue_free_tickets(
     *,
     event: Event,
@@ -522,7 +663,7 @@ async def _issue_free_tickets(
     user_id: str | None,
     promo_code: str | None,
     nostr_identifier: str | None,
-    request: Request,
+    frontend_root: str,
 ) -> TicketPaymentRequest:
     """Issue `quantity` free tickets without minting an invoice.
 
@@ -552,7 +693,7 @@ async def _issue_free_tickets(
             extra={
                 "applied_promo_code": promo_code,
                 "nostr_identifier": nostr_identifier,
-                "ticket_base_url": str(request.base_url).rstrip("/"),
+                "ticket_base_url": frontend_root,
                 "sats_paid": 0,
             },
         )
@@ -588,7 +729,9 @@ async def api_ticket_create(
     quantity = data.quantity
     if event.amount_tickets > 0:
         if event.sold >= event.amount_tickets:
-            raise HTTPException(status_code=HTTPStatus.GONE, detail="Event is sold out.")
+            raise HTTPException(
+                status_code=HTTPStatus.GONE, detail="Event is sold out."
+            )
         remaining = event.amount_tickets - event.sold
         if quantity > remaining:
             raise HTTPException(
@@ -618,6 +761,7 @@ async def api_ticket_create(
             ) from exc
     unit_price = event.price_per_ticket
     extra: dict[str, Any] = {"tag": "events", "name": name, "email": email}
+    frontend_root = _resolve_frontend_root(data, request)
 
     if promo_code:
         # check if promo_code exists in event.extra.promo_codes
@@ -645,13 +789,16 @@ async def api_ticket_create(
             user_id=user_id,
             promo_code=promo_code,
             nostr_identifier=nostr_identifier,
-            request=request,
+            frontend_root=frontend_root,
         )
 
-    if payment_method == "fiat" and not event.allow_fiat:
+    # Organizer-controlled rails (extra.payment_methods; legacy events fall
+    # back to Lightning + fiat-if-allow_fiat). Checked after the free path
+    # because a free claim charges nothing on any rail.
+    if payment_method not in effective_payment_methods(event):
         raise HTTPException(
             status_code=HTTPStatus.BAD_REQUEST,
-            detail="Fiat payments are not enabled for this event.",
+            detail="Payment method not enabled for this event.",
         )
 
     if _is_fiat_currency(event.currency):
@@ -692,6 +839,36 @@ async def api_ticket_create(
     else:
         invoice_unit = "sat"
 
+    # Each row gets a fresh urlsafe_short_hash id so single- and
+    # multi-ticket purchases stay shape-consistent — every scannable
+    # ticket id is a short hash, never the long bolt11 payment_hash.
+    # The shared `payment_hash` column is the join key for invoice
+    # lookup (poll endpoint, ws notifier, set_ticket_paid loop). Ids are
+    # minted BEFORE the invoice so the fiat success URL can carry them
+    # (the payment_hash only exists after `create_payment_request`).
+    ticket_ids: list[str] = [urlsafe_short_hash() for _ in range(quantity)]
+
+    if payment_method == "fiat":
+        # Parameterise the provider's hosted checkout (consumed by
+        # lnbits/fiat/stripe.py `StripeCheckoutOptions`): bring the buyer
+        # back to the app they came from, lock the email they gave us, and
+        # label the line item with the event rather than the raw memo.
+        ticket_label = "ticket" if quantity == 1 else "tickets"
+        extra["checkout"] = {
+            "success_url": (
+                f"{frontend_root}/events/{event.id}"
+                f"?checkout=success&tickets={','.join(ticket_ids)}"
+            ),
+            "cancel_url": f"{frontend_root}/events/{event.id}?checkout=cancelled",
+            "customer_email": email,
+            "line_item_name": f"{event.name} — {quantity} {ticket_label}",
+            "metadata": {
+                "event_id": event.id,
+                "quantity": str(quantity),
+                "ticket_ids": ",".join(ticket_ids),
+            },
+        }
+
     payment = await create_payment_request(
         wallet_id=event.wallet,
         invoice_data=CreateInvoice(
@@ -703,15 +880,8 @@ async def api_ticket_create(
             extra=extra,
         ),
     )
-    # Each row gets a fresh urlsafe_short_hash id so single- and
-    # multi-ticket purchases stay shape-consistent — every scannable
-    # ticket id is a short hash, never the long bolt11 payment_hash.
-    # The shared `payment_hash` column is the join key for invoice
-    # lookup (poll endpoint, ws notifier, set_ticket_paid loop).
-    ticket_ids: list[str] = []
     sats_per_ticket = payment.sat // quantity if quantity else payment.sat
-    for _ in range(quantity):
+    for row_id in ticket_ids:
-        row_id = urlsafe_short_hash()
         await create_ticket(
             payment_hash=payment.payment_hash,
             wallet=event.wallet,
@@ -724,11 +894,10 @@ async def api_ticket_create(
                 "applied_promo_code": promo_code,
                 "refund_address": refund_address,
                 "nostr_identifier": nostr_identifier,
-                "ticket_base_url": str(request.base_url).rstrip("/"),
+                "ticket_base_url": frontend_root,
                 "sats_paid": sats_per_ticket,
             },
         )
-        ticket_ids.append(row_id)
 
     return TicketPaymentRequest(
         payment_hash=payment.payment_hash,
@@ -824,10 +993,10 @@ async def api_ticket_delete(
     await delete_ticket(ticket_id)
 
 
-@tickets_api_router.post("/{ticket_id}/resend-email")
+@tickets_api_router.post("/{ticket_id}/resend-email", response_model=TicketResendResult)
 async def api_ticket_resend_email(
     ticket_id: str, wallet: WalletTypeInfo = Depends(require_admin_key)
-) -> Ticket:
+) -> TicketResendResult:
     ticket = await get_ticket(ticket_id)
     if not ticket:
         raise HTTPException(
@@ -959,3 +1128,31 @@ async def api_event_ticket_stats(
             for t in paid_tickets
         ],
     }
+
+
+@qr_api_router.get("/qr/{ticket_id}", response_class=StreamingResponse)
+async def api_ticket_qr(ticket_id: str):
+    """PNG of the ticket's scan payload (`ticket://<id>`), branded with the
+    instance QR logo. Anonymous by design — it is what the ticket email
+    embeds — and the id is the same bearer token the ticket page exposes.
+    Port of upstream v1.6.8 without ticket-image compositing."""
+    ticket = await get_ticket(ticket_id)
+    if not ticket:
+        raise HTTPException(
+            status_code=HTTPStatus.NOT_FOUND, detail="Ticket does not exist."
+        )
+
+    logo = await _load_qr_logo()
+    image = make_qr_png(f"ticket://{ticket_id}", size=300, logo=logo)
+    output = BytesIO()
+    image.save(output, format="PNG")
+    output.seek(0)
+    return StreamingResponse(
+        output,
+        media_type="image/png",
+        headers={
+            "Cache-Control": "no-cache, no-store, must-revalidate",
+            "Pragma": "no-cache",
+            "Expires": "0",
+        },
+    )