stripe: Move error handling into stripe.py too.

This completes the separation of our logic for managing Stripe
customers from the view code for the billing page.

As we add more features to our Customer model and to our Stripe
integration, we might further separate those two things; but for now
they're nearly synonymous and there's no problem in them being mixed
together.

zilencer/lib/stripe.py

@@ -1,12 +1,13 @@
-
+from functools import wraps
 import logging
 import os
+from typing import Any, Callable, TypeVar
 
 from django.conf import settings
+from django.utils.translation import ugettext as _
 import stripe
-from stripe.error import CardError, RateLimitError, InvalidRequestError, \
-    AuthenticationError, APIConnectionError, StripeError
 
+from zerver.lib.exceptions import JsonableError
 from zerver.lib.logging_util import log_to_file
 from zerver.models import Realm, UserProfile
 from zilencer.models import Customer
@@ -24,6 +25,35 @@ billing_logger = logging.getLogger('zilencer.stripe')
 log_to_file(billing_logger, BILLING_LOG_PATH)
 log_to_file(logging.getLogger('stripe'), BILLING_LOG_PATH)
 
+CallableT = TypeVar('CallableT', bound=Callable[..., Any])
+
+class StripeError(JsonableError):
+    pass
+
+def catch_stripe_errors(func: CallableT) -> CallableT:
+    @wraps(func)
+    def wrapped(*args: Any, **kwargs: Any) -> Any:
+        if STRIPE_PUBLISHABLE_KEY is None:
+            # Dev-only message; no translation needed.
+            raise StripeError(
+                "Missing Stripe config. In dev, add to zproject/dev-secrets.conf .")
+        try:
+            return func(*args, **kwargs)
+        except stripe.error.StripeError as e:
+            billing_logger.error("Stripe error: %d %s",
+                                 e.http_status, e.__class__.__name__)
+            if isinstance(e, stripe.error.CardError):
+                raise StripeError(e.json_body.get('error', {}).get('message'))
+            else:
+                raise StripeError(
+                    _("Something went wrong. Please try again or email us at %s.")
+                    % (settings.ZULIP_ADMINISTRATOR,))
+        except Exception as e:
+            billing_logger.exception("Uncaught error in Stripe integration")
+            raise
+    return wrapped  # type: ignore # https://github.com/python/mypy/issues/1927
+
+@catch_stripe_errors
 def count_stripe_cards(realm: Realm) -> int:
     try:
         customer_obj = Customer.objects.get(realm=realm)
@@ -32,6 +62,7 @@ def count_stripe_cards(realm: Realm) -> int:
     except Customer.DoesNotExist:
         return 0
 
+@catch_stripe_errors
 def save_stripe_token(user: UserProfile, token: str) -> int:
     """Returns total number of cards."""
     # The card metadata doesn't show up in Dashboard but can be accessed