Added base64decode to Tracker (snowplow#36)

Author: alexanderdean

CHANGELOG

@@ -5,7 +5,7 @@ Added retrospective tags back in (#22)
 Restructured folders (#21)
 Added setPlatform support, thanks @rcs! (#25)
 Added currency field to ecommerce transactions (#34)
-Added base64decode to Tracker (#36)                          - TODO
+Added base64decode to Tracker (#36)
 Added `value !== null` check to requestStringBuilder() (#40)
 Added custom unstructured contexts (#49)                     - TODO
 Added array helpers (#41)                                    - TODO

src/js/lib/base64.js

@@ -65,3 +65,45 @@ SnowPlow.base64urlencode = function(data) {
             .replace(/\+/g, '-')
             .replace(/\//g, '_');
 };
+
+/*
+ * Base64 decode data
+ */
+SnowPlow.base64decode = function(data) {
+  var keyStr = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
+  var output = "";
+  var chr1, chr2, chr3 = "";
+  var enc1, enc2, enc3, enc4 = "";
+  var i = 0;
+
+  // remove all characters that are not A-Z, a-z, 0-9, +, /, or =
+  var base64test = /[^A-Za-z0-9\+\/\=]/g;
+
+  data = data.replace(/[^A-Za-z0-9\+\/\=]/g, "");
+
+  do {
+    enc1 = keyStr.indexOf(data.charAt(i++));
+    enc2 = keyStr.indexOf(data.charAt(i++));
+    enc3 = keyStr.indexOf(data.charAt(i++));
+    enc4 = keyStr.indexOf(data.charAt(i++));
+
+    chr1 = (enc1 << 2) | (enc2 >> 4);
+    chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);
+    chr3 = ((enc3 & 3) << 6) | enc4;
+
+    output = output + String.fromCharCode(chr1);
+
+    if (enc3 != 64) {
+      output = output + String.fromCharCode(chr2);
+    }
+
+    if (enc4 != 64) {
+      output = output + String.fromCharCode(chr3);
+    }
+
+    chr1 = chr2 = chr3 = "";
+    enc1 = enc2 = enc3 = enc4 = "";
+  } while (i < data.length);
+
+  return unescape(output);
+};