Add support for idempotency keys

lib/mollie/client.rb

@@ -72,6 +72,7 @@ def perform_http_call(http_method, api_method, id = nil, http_body = {}, query =
 
       api_key      = http_body.delete(:api_key) || query.delete(:api_key) || @api_key
       api_endpoint = http_body.delete(:api_endpoint) || query.delete(:api_endpoint) || @api_endpoint
+      idempotency_key = http_body.delete(:idempotency_key) || query.delete(:idempotency_key)
 
       unless query.empty?
         camelized_query = Util.camelize_keys(query)
@@ -110,6 +111,10 @@ def perform_http_call(http_method, api_method, id = nil, http_body = {}, query =
       request['Authorization'] = "Bearer #{api_key}"
       request['User-Agent']    = @version_strings.join(' ')
 
+      if http_method == 'POST' && idempotency_key
+        request['Idempotency-Key'] = idempotency_key
+      end
+
       begin
         response = client.request(request)
       rescue Timeout::Error, Errno::EINVAL, Errno::ECONNRESET, EOFError,

test/mollie/client_test.rb

@@ -53,6 +53,18 @@ def test_perform_http_call_with_api_key_block
       assert_equal 'test_dHar4XY7LxsDOtmnkVtjNVWXLSlXsM', Mollie::Client.instance.api_key
     end
 
+    def test_post_with_idempotency_key
+      stub_request(:post, 'https://api.mollie.com/v2/payments')
+        .with(headers: { "Idempotency-Key" => '91d42bd5-e47f-4f4a-b38e-99333b264e78' })
+        .to_return(status: 200, body: '{}', headers: {})
+
+      payment = Mollie::Payment.create(
+        amount: { value: '10.00', currency: 'EUR' },
+        redirect_url: 'https://webshop.example.org/order/12345/',
+        idempotency_key: '91d42bd5-e47f-4f4a-b38e-99333b264e78'
+      )
+    end
+
     def test_get_request_convert_to_camel_case
       stub_request(:get, 'https://api.mollie.com/v2/my-method?myParam=ok')
         .to_return(status: 200, body: '{}', headers: {})