Dealing with payments

When things go right and our product starts making money everyone is happy, but sometimes this means the start of the nightmare for people working with payments.

Let's not sugar coat it. In this talk you'll learn about some where thing went terribly wrong, some of them involved loosing money. Stories of stuff that can easily get overlooked, about the most common mistakes when working with payments and things you probably won't consider until shit hits the fan. All of this so that you don't run into the same problems and don't have to learn those lessons the hard way.

Presented at: Rails Pacific 2016

Transcript

1. Dealing with Payments WHEN MAKING MONEY BECOMES A HEADACHE
2. My name is Sebastián Sogamoso Tweet me @sebasoga
4. This talk is about
5. Trust This talk is about
6. Colleagues
7. Company
8. Users
9. Trust
10. Trust Information is safe
11. Information is safe App works as expected Trust
12. Information is safe App works as expected Trust
13. Trust
14. Trust
15. Trust
16. Geolocation Chat service
17. Weather updates Traffic updates Reminders Trust
18. Payments Trust
19. Payments Trust
20. Common pitfalls
21. Payment gateway
22. 2XX status code doesn’t necessarily mean the transaction was successful
23. class Transfer def create(user, trip) @response = PaymentGatewayClient.create_transfer( amount: trip.price, currency: user.currency, destination: user.account, description: trip.to_s ) end def successful? @response.status_code == "201" end end
24. class Transfer def create(user, trip) @response = PaymentGatewayClient.create_transfer( amount: trip.price, currency: user.currency, destination: user.account, description: trip.to_s ) end def successful? @response.status_code == "201" end end
25. class Transfer def create(user, trip) @response = PaymentGatewayClient.create_transfer( amount: trip.price, currency: user.currency, destination: user.account, description: trip.to_s ) end def successful? @response.status_code == "201" end end
26. class Transfer def create(user, trip) @response = PaymentGatewayClient.create_transfer( amount: trip.price, currency: user.currency, destination: user.account, description: trip.to_s ) end def successful? @response.status_code == "201" end end user = User.last trip = User.trips.last transfer = Transfer.new.create(user, trip)
27. class Transfer def create(user, trip) @response = PaymentGatewayClient.create_transfer( amount: trip.price, currency: user.currency, destination: user.account, description: trip.to_s ) end def successful? @response.status_code == "201" end end user = User.last trip = User.trips.last transfer = Transfer.new.create(user, trip) transfer.successful? # Not correct
28. Payment gateway Your system Create transfer
29. Payment gateway Your system Ok (200) Create transfer
30. Payment gateway Your system Ok (200) Transfer result Create transfer
31. Payment gateway Your system Ok (200) Transfer result Ok Create transfer
32. Operations should be idempotent
33. # Not idempotent def charge_not_idempotent(invoice) Stripe::Charge.create( amount: invoice.total, currency: invoice.currency, source: invoice.user.credit_card, description: invoice.to_s ) end # Idempotent def charge_idempotent(invoice) if invoice.charged? Stripe::Charge.retrieve(invoice.charge_id) else Stripe::Charge.create( amount: invoice.total, currency: invoice.currency, source: invoice.user.credit_card, description: invoice.to_s ) end end
34. # Not idempotent def charge_not_idempotent(invoice) Stripe::Charge.create( amount: invoice.total, currency: invoice.currency, source: invoice.user.credit_card, description: invoice.to_s ) end # Idempotent def charge_idempotent(invoice) if invoice.charged? Stripe::Charge.retrieve(invoice.charge_id) else Stripe::Charge.create( amount: invoice.total, currency: invoice.currency, source: invoice.user.credit_card, description: invoice.to_s ) end end
35. # Not idempotent def charge_not_idempotent(invoice) Stripe::Charge.create( amount: invoice.total, currency: invoice.currency, source: invoice.user.credit_card, description: invoice.to_s ) end # Idempotent def charge_idempotent(invoice) if invoice.charged? Stripe::Charge.retrieve(invoice.charge_id) else Stripe::Charge.create( amount: invoice.total, currency: invoice.currency, source: invoice.user.credit_card, description: invoice.to_s ) end end
36. invoice = Invoice.last # It will charge the invoice 10 times 10.times do charge_not_idempotent(invoice) end # It will charge the invoice 1 time 10.times do charge_idempotent(invoice) end
37. Tracking history
38. How did this record get in its current state?
39. What was this record’s state at some point in the past?
40. • Hard to know which code led a state change • Previous data might be overwritten • Relevant code might not exist
41. Record events every time state changes
42. Never update them
43. gem 'paper_trail'
44. class Charge < ActiveRecord::Base belongs_to :user has_many :events, class_name: "ChargeEvent" end
45. class Charge < ActiveRecord::Base belongs_to :user has_many :events, class_name: "ChargeEvent" end
46. class Charge < ActiveRecord::Base belongs_to :user has_many :events, class_name: "ChargeEvent" end class ChargeEvent < ActiveRecord::Base EVENT_TYPES = %w(creation success failure refund) belongs_to :charge validates :charge, :data, presence: true validates :event_type, inclusion: { in: EVENT_TYPES} end
47. class Charge < ActiveRecord::Base belongs_to :user has_many :events, class_name: "ChargeEvent" end class ChargeEvent < ActiveRecord::Base EVENT_TYPES = %w(creation success failure refund) belongs_to :charge validates :charge, :data, presence: true validates :event_type, inclusion: { in: EVENT_TYPES} end
48. class Order < ActiveRecord::Base attr_reader :user, :items, :total def charge ActiveRecord.transation do charge = Charge.create!(user: user, total: total) charge.events.create!(data: data, event_type: "creation") self.update!(charge: charge) end end private def data {items: items.inspect, total: total, user: user} end end
49. class Order < ActiveRecord::Base attr_reader :user, :items, :total def charge ActiveRecord.transation do charge = Charge.create!(user: user, total: total) charge.events.create!(data: data, event_type: "creation") self.update!(charge: charge) end end private def data {items: items.inspect, total: total, user: user} end end
50. class Order < ActiveRecord::Base attr_reader :user, :items, :total def charge ActiveRecord.transation do charge = Charge.create!(user: user, total: total) charge.events.create!(data: data, event_type: "creation") self.update!(charge: charge) end end private def data {items: items.inspect, total: total, user: user} end end
51. class PaymentGateway def initialize(client) @client = client end def charge(order) charge = order.charge response = @client.create_charge(order.charge) transaction_id = response.transaction_id if response.successful? charge.update!(transaction_id: response.transaction_id) charge.events.create!(data: transaction_id, event_type: "success") else charge.update!(transaction_id: response.transaction_id) charge.events.create!(data: transaction_id, event_type: "failure") end end end
52. class PaymentGateway def initialize(client) @client = client end def charge(order) charge = order.charge response = @client.create_charge(order.charge) transaction_id = response.transaction_id if response.successful? charge.update!(transaction_id: response.transaction_id) charge.events.create!(data: transaction_id, event_type: "success") else charge.update!(transaction_id: response.transaction_id) charge.events.create!(data: transaction_id, event_type: "failure") end end end
53. class PaymentGateway def initialize(client) @client = client end def charge(order) charge = order.charge response = @client.create_charge(order.charge) transaction_id = response.transaction_id if response.successful? charge.update!(transaction_id: response.transaction_id) charge.events.create!(data: transaction_id, event_type: "success") else charge.update!(transaction_id: response.transaction_id) charge.events.create!(data: transaction_id, event_type: "failure") end end end
54. Idempotent operations Payment gateway Tracking history
55. Great news!
57. ActionPayment
58. ActionPayment ⚡TurboPayments⚡
59. Trust
60. Payments are a huge part of the User Experience
61. 5 things to provide a good payments UX
62. Async transactions
63. Payment status visibility
64. Deleting payment information
65. Prepare to ship big changes
66. Dealing with bugs
67. Async transactions
68. class ChargesController < ApplicationController def create @charge = current_user.charges.build.new(charge_params) if charge_user(@charge) redirect_to :charge_sucess else render :cart end end ...
69. class ChargesController < ApplicationController def create @charge = current_user.charges.build.new(charge_params) if charge_user(@charge) redirect_to :charge_sucess else render :cart end end ...
70. def charge_user(charge) result = Stripe::Charge.create( amount: charge.amount, currency: charge.currency, source: charge.credit_card_token, description: charge.product_name ) charge.status = result.status charge.save result.status == "succeeded" end
71. def charge_user(charge) result = Stripe::Charge.create( amount: charge.amount, currency: charge.currency, source: charge.credit_card_token, description: charge.product_name ) charge.status = result.status charge.save result.status == "succeeded" end
72. def charge_user(charge) result = Stripe::Charge.create( amount: charge.amount, currency: charge.currency, source: charge.credit_card_token, description: charge.product_name ) charge.status = result.status charge.save result.status == "succeeded" end
73. What seems to be happening
74. Your system User
75. Your system Payment gateway User
76. Your system User Payment gateway
77. What really happens
78. Your system User Payment gateway
79. Payment Processor Your system User Payment gateway
80. Payment Processor Card’s Brand Your system User Payment gateway
81. Payment Processor Card Issuing Bank Card’s Brand Your system User Payment gateway
82. Payment Processor Card Issuing Bank Marchant’s Bank Card’s Brand Your system User Payment gateway
83. Asynchronous implementation
84. class ChargesController < ApplicationController def create @charge = Charge.create(charge_params) ChargeWorker.perform_async(@charge.id) redirect_to :charge_in_process end end
85. class ChargesController < ApplicationController def create @charge = Charge.create(charge_params) ChargeWorker.perform_async(@charge.id) redirect_to :charge_in_process end end
86. Retries
87. class ChargeWorker def perform(charge_id) charge = ::Charge.find(charge_id) Stripe::Charge.create( amount: charge.amount, currency: charge.currency, source: charge.credit_card_token, description: charge.product_name ) end end
88. class ChargeWorker include Sidekiq::Worker def perform(charge_id) charge = ::Charge.find(charge_id) Stripe::Charge.create( amount: charge.amount, currency: charge.currency, source: charge.credit_card_token, description: charge.product_name ) end end
89. class ChargeWorker include Sidekiq::Worker def perform(charge_id) charge = ::Charge.find(charge_id) Stripe::Charge.create( amount: charge.amount, currency: charge.currency, source: charge.credit_card_token, description: charge.product_name ) end end
90. class ChargeWorker include Sidekiq::Worker sidekiq_options retry: 3 def perform(charge_id) charge = ::Charge.find(charge_id) Stripe::Charge.create( amount: charge.amount, currency: charge.currency, source: charge.credit_card_token, description: charge.product_name ) end end
91. Payment status visibility
92. Why don’t I see the refund in my card statement?
93. When am I getting payed out?
94. Why was I charged X amount?
96. Deleting payment information
97. Give users full control of their payment information
99. class CreditCardsController < ApplicationController def destroy @credit_card = current_user.credit_cards.find(params[:id]) @credit_card.destroy redirect_to credit_cards_url, notice: "Credit card deleted" end end end
100. class CreditCardsController < ApplicationController def destroy @credit_card = current_user.credit_cards.find(params[:id]) @credit_card.destroy redirect_to credit_cards_url, notice: "Credit card deleted" end end end
101. Settle payments first
102. class CreditCardsController < ApplicationController def destroy @credit_card = current_user.credit_cards.find(params[:id]) if current_user.charge_pending_trips @credit_card.destroy redirect_to credit_cards_url, notice: "Credit card deleted" else redirect_to @credit_card, notice: “Settlement failed" end end end
103. class CreditCardsController < ApplicationController def destroy @credit_card = current_user.credit_cards.find(params[:id]) if current_user.charge_pending_trips @credit_card.destroy redirect_to credit_cards_url, notice: "Credit card deleted" else redirect_to @credit_card, notice: "Settlement failed" end end end
104. class CreditCardsController < ApplicationController def destroy @credit_card = current_user.credit_cards.find(params[:id]) if current_user.charge_pending_trips @credit_card.destroy redirect_to credit_cards_url, notice: "Credit card deleted" else redirect_to @credit_card, notice: "Settlement failed" end end end
105. Prepare to ship big changes
106. Discuss big changes
107. RFCs
109. Make changing stuff easy
110. Business logic Payment gateway
111. Payment gateway Business logic
112. Business logic Payment gateway
113. Business logic Payment gateway two Payment gateway one
114. This is how it looks in code
115. class Charge def initialize(payment_gateway) @payment_gateway = payment_gateway end def create(user:, amount:) @payment_gateway.new(user) @payment_gateway.charge(amount) end end
116. class PaymentGatewayOne def initialize(customer) @customer = customer end def charge ... end end class PaymentGatewayTwo def initialize(user) @user = user end def charge ... end end
117. > Charge.new(PaymentGatewayOne).charge(User.find(1), 100) => true
118. > Charge.new(PaymentGatewayOne).charge(User.find(1), 100) => true > Charge.new(PaymentGatewayTwo).charge(User.find(1), 100) => true
119. > Charge.new(PaymentGatewayOne).charge(User.find(1), 100) => true > Charge.new(PaymentGatewayTwo).charge(User.find(1), 100) => true
120. Simulate
121. class SimulationPaymentGateway def initialize(user) @user = user end def charge Rails.logger.debug(“Charging $#{amount} to user ##{@user.id}”) end end
122. class SimulationPaymentGateway def initialize(user) @user = user end def charge Rails.logger.debug(“Charging $#{amount} to user ##{@user.id}”) end end
123. > Charge.new(SimulationPaymentGateway).charge(User.find(1), 100)
124. > Charge.new(SimulationPaymentGateway).charge(User.find(1), 100) Charging $100 to user #1 => nil
125. Payment gateway Business logic
126. Business logic Simulation gateway Payment gateway
127. Simulation gateway Business logic
128. Dealing with bugs
129. Yes, you will introduce bugs
130. Catch them quick
131. How?
132. Monitoring & alterting
133. if: charge_amount_greater_than_1000_dollars then: send_pager_duty_alert
134. if: user_charged_more_than_once_for_same_trip then: send_pager_duty_alert
135. Have a damage control plan
136. 1. Communication
137. Be proactive. Reach out to affected users External communication
138. Write a postmortem Internal communication
140. 2. Handbook to deal with
141. Anyone can deal with payment bugs
142. • Refunds • Reversals • Recalculating accounts balance
143. 3. Write documentation
144. • Structure • Business rules
145. Async transactions Payment status visibility Deleting payment information Prepare to ship big changes Dealing with bugs
146. The whole purpose is to…
147. Trust ✔
148. 拽拽 @sebasoga