Mercury: Stripping the start and end sentinels on card-present track …

…data for max-length track1 requests

Closes #2026

CHANGELOG

@@ -43,6 +43,7 @@
 * Clearhaus: Make request signing more transparent & robust [sdball]
 * Cashnet: Default custcode option and proper redirect handling [hoenth]
 * SagePay: Properly detect Electron brand [sdball]
+* Mercury: Fix for max-length track 1 [ryanbalsdon]
 
 
 == Version 1.56.0 (December 1, 2015)

lib/active_merchant/billing/gateways/mercury.rb

@@ -197,12 +197,20 @@ def add_credit_card(xml, credit_card, action)
           if credit_card.track_data.present?
             # Track 1 has a start sentinel (STX) of '%' and track 2 is ';'
             # Track 1 and 2 have identical end sentinels (ETX) of '?'
+            # Tracks may or may not have checksum (LRC) after the ETX
             # If the track has no STX or is corrupt, we send it as track 1, to let Mercury
             #handle with the validation error as it sees fit.
-            # Track 2 requires having the start and end sentinels stripped. Track 1 does not.
-            if credit_card.track_data[0] == ';' # track 2 start sentinel (STX)
-              xml.tag! 'Track2', credit_card.track_data[1..-2]
-            else # track 1 or a corrupt track
+            # Track 2 requires having the STX and ETX stripped. Track 1 does not.
+            # Max-length track 1s require having the STX and ETX stripped. Max is 79 bytes including LRC.
+            is_track_2 = credit_card.track_data[0] == ';'
+            etx_index = credit_card.track_data.rindex('?') || credit_card.track_data.length
+            is_max_track1 = etx_index >= 77
+
+            if is_track_2
+              xml.tag! 'Track2', credit_card.track_data[1...etx_index]
+            elsif is_max_track1
+              xml.tag! 'Track1', credit_card.track_data[1...etx_index]
+            else
               xml.tag! 'Track1', credit_card.track_data
             end
           else

test/unit/gateways/mercury_test.rb

@@ -90,6 +90,20 @@ def test_card_present_with_track_2_data
     assert_success response
   end
 
+  def test_card_present_with_max_length_track_1_data
+    track_data    = "%B373953192351004^CARDUSER/JOHN^200910100000019301000000877000000930001234567?"
+    stripped_data =  "B373953192351004^CARDUSER/JOHN^200910100000019301000000877000000930001234567"
+    @credit_card.track_data = track_data
+    response = stub_comms do
+      @gateway.purchase(@amount, @credit_card, @options)
+    end.check_request do |endpoint, data, headers|
+      assert_match(/<Track1>#{Regexp.escape(stripped_data)}<\/Track1>/, data)
+    end.respond_with(successful_purchase_response)
+
+    assert_instance_of Response, response
+    assert_success response
+  end
+
   def test_card_present_with_invalid_data
     track_data = "this is not valid track data"
     @credit_card.track_data = track_data