This Ruby gem implements the LiqPAY billing system.

As of now it only covers the Liq&Buy 1.2 API, which is used to accept credit card payments on your site.

Include the liqpay gem in your app.

The recommended way is setting the Liqpay.default_options hash somewhere in your initializers.

You MUST supply the merchant_id and merchant_signature options, that are provided by LiqPAY when you sign up, on the merchant details page.

1. User initiates the payment process; you redirect him to LiqPAY via POST, providing necessary parameters to set up the payment's amount and description

2. Users completes payment through LiqPAY.

3. LiqPAY redirects the user to the URL you specified.

4. You validate the response against your secret signature.

5. If the payment was successful: You process the payment on your side.

6. If the payment was cancelled: You cancel the operation.

So, LiqPAY is pretty simple, it does no server-to-server validation, just a browser-driven flow.

0. Configure Liqpay:

    # config/initializers/liqpay.rb
    Liqpay.default_options[:merchant_id] = 'MY_MERCHANT_ID'
    Liqpay.default_options[:merchant_signature] = 'MY_MERCHANT_SIGNATURE'
   

1. Create a Liqpay::Request object

   The required options are: the amount and currency of the payment, and an "order ID".

   The "order ID" is just a random string that you will use to identify the payment after it has been completed. If you have an Order model (I suggest that you should), pass its ID. If not, it can be a random string stored in the session, or whatever, but it must be unique.

    @liqpay_request = Liqpay::Request.new(
      :amount => '999.99', 
      :currency => 'UAH', 
      :order_id => '123', 
      :description => 'Some Product',
      :result_url => liqpay_payment_url
    )
   

   Note that this does not do anything permanent. No saves to the database, no requests to LiqPAY.

2. Put a payment button somewhere

   As you need to make a POST request, there is definitely going to be a form somewhere.

   To output a form consisting of a single "Pay with LiqPAY" button, do

    <%=liqpay_button @liqpay_request %>
   

   Or:

    <%=liqpay_button @liqpay_request, :title => "Pay now!" %>
   

   Or:

    <%=liqpay_button @liqpay_request do %>
      <%=link_to 'Pay now!', '#', :onclick => 'document.forms[0].submit();' %>
    <% end %>
   

3. Set up a receiving endpoint.

    # config/routes.rb
    post '/liqpay_payment' => 'payments#liqpay_payment'
   
    # app/controllers/payments_controller.rb
    class PaymentsController < ApplicationController
      # Skipping forgery protection here is important
      protect_from_forgery :except => :liqpay_payment
   
      def liqpay_payment
        @liqpay_response = Liqpay::Response.new(params)
   
        if @liqpay_response.success?
          # check that order_id is valid
          # check that amount matches
          # handle success
        else
          # handle error
        end
      rescue Liqpay::InvalidResponse
        # handle error
      end
    end
   

That's about it.

• Check that amount from response matches the expected amount;
• check that the order id is valid;
• check that the order isn't completed yet (to avoid replay attacks);

2012 Leonid Shevtsov