Money Makes Your App Go Round

Your customers have money, and you’d like them to give it to you. Payment gateways, such as Stripe, Braintree, and Paypal, make it easy to start charging credit cards and get the money flowing. But charging cards is only the beginning. You need to worry that your app responds gracefully to service failures, since charging a customer for a failed transaction is bad. You need to guard against fraud and security breaches. You need administrative tools that are flexible but secure. You want to test against external services. And you’ll run up against the law. Learn from some of my mistakes and build a robust financial application.

Transcript

1. We Are Experiencing An Introduction Please Stand By Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
2. I've made some mistakes Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
3. Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
4. Once upon a time... Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
5. I got a new client Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
6. They wanted to add complex payment logic to an existing payment gateway connection Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
7. The API call already existed I thought the hard part was done Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
8. (Spoiler Alert) The API call isn't the hard part Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
9. Money Makes Your App Go Round Noel Rappin, Table XI (@noelrap) Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
10. Some context Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
11. token = params[:stripeToken] begin charge = Stripe::Charge.create( amount: 1000, currency: "usd", source: token, description: "Example charge") rescue Stripe::CardError => e # The card has been declined end Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
12. The resulting transaction involves at least ! institutions Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
13. As many as 1,000,000 per minute Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
14. But then there's this: Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
15. validates :last_4, format: {with: /X{12}\d{4}/} Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
16. There's a really common pattern Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
17. Save some data Charge the card Save the response Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
18. Charge Fails Save Succeeds Angry Manager! Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
19. Charge Succeeds Save Fails Angry Customer! Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
20. Back to validates :last_4, format: {with: /X{12}\d{4}/} Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
21. Every line of code after the card processes is a potential angry customer Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
22. Is this validation really necessary? Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
23. PragDave: "screw up in favor of the customer" Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
24. Mitigating failure Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
25. Test failure conditions Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
26. Testing for credit card failures is actually pretty easy Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
27. Testing for local failures is trickier Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
28. Foreign key constraints are useful, but irritating Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
29. Small background jobs are great Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
30. Idempotence is your friend Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
31. It is often easier to see the result of bugs than to find the cause Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
32. An ounce of mitigation can be worth a pound of bug fixing Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
33. Money is precise Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
34. Money is so precise that it breaks math Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
35. Okay, it just breaks floating point numbers Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
36. Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
37. Use the Money gem to store money as BigDecimal Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
38. Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
39. Money requires records Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
40. Handling Fee: $2.00 Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
41. It's a constant HANDLING_FEE: 200 Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
42. Later... Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
43. Change the constant HANDLING_FEE: 250 Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
44. And we're done... Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
45. Except for the past Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
46. Store all your partial results Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
47. You should be able to recreate the entire purchase even if the logic has changed Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
48. If there is failure, keep a record of the failure Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
49. Audit changes Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
50. Check your data Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
51. Money has legal obligations Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
52. Take your administrative users seriously Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
53. Pragmatic's admin code is 2x the size of the main app Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
54. Admins can change rules which makes them complicated Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
55. Example: Refunds Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
56. Refunds are a one-line API call Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
57. But: 4 Who can authorize one? 4 Full or partial? 4 How to manage response? 4 How to track inventory 4 How to track changes to revenue? 4 Etc.. Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
58. Take Reporting Seriously (I didn't) Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
59. Reporting is how you make business decisions Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
60. Taxes security requirements financial system compliance Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
61. Money is Private Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
62. Don't store personal information that you don't need Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
63. Don't store credit card info Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
64. Even seemingly boring information can be harmful Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
65. Takeaways Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
66. The API is the easy part Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
67. Run in small steps to manage potential failure points Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
68. Store all your work Store as little personal info as you can Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
69. Administration is important Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap
70. Noel Rappin (@noelrap) Table XI http://pragprog.com/book/ nrwebpay http://www.noelrappin.com/trdd http://pragprog.com/book/ Noel Rappin, Money Makes Your App Go Round, WindyCityRails 2016. http://www.noelrappin.com | http://www.tablexi.com | @noelrap