added amp linker utils

utils/linker/index.js

@@ -0,0 +1,140 @@
+/**
+ * @description AMP Linker Parser (works for Rudder, GA or any other linker created by following Google's linker standard.)
+ * @version v1.0.0
+ * @author Parth Mahajan, Ayush Mehra
+ */
+
+import crc32 from "./utils/crc32";
+import USER_INTERFACE from "./utils/userLib";
+import decode from "./utils/base64decoder";
+
+const KEY_VALIDATOR = /^[a-zA-Z0-9\-_.]+$/;
+const CHECKSUM_OFFSET_MAX_MIN = 1;
+const VALID_VERSION = 1;
+const DELIMITER = "*";
+
+/**
+ * Return the key value pairs
+ * @param {string} value
+ * @return {?Object<string, string>}
+ */
+function parseLinker(value) {
+  const linkerObj = parseLinkerParamValue(value);
+  if (!linkerObj) {
+    return null;
+  }
+  const { checksum, serializedIds } = linkerObj;
+  if (!isCheckSumValid(serializedIds, checksum)) {
+    return null;
+  }
+  return deserialize(serializedIds);
+}
+
+/**
+ * Parse the linker param value to version checksum and serializedParams
+ * @param {string} value
+ * @return {?Object}
+ */
+function parseLinkerParamValue(value) {
+  const parts = value.split(DELIMITER);
+  const isEven = parts.length % 2 == 0;
+
+  if (parts.length < 4 || !isEven) {
+    // Format <version>*<checksum>*<key1>*<value1>
+    // Note: linker makes sure there's at least one pair of non empty key value
+    // Make sure there is at least three delimiters.
+    return null;
+  }
+
+  const version = Number(parts.shift());
+  if (version !== VALID_VERSION) {
+    return null;
+  }
+
+  const checksum = parts.shift();
+  const serializedIds = parts.join(DELIMITER);
+  return {
+    checksum,
+    serializedIds,
+  };
+}
+
+/**
+ * Check if the checksum is valid with time offset tolerance.
+ * @param {string} serializedIds
+ * @param {string} checksum
+ * @return {boolean}
+ */
+function isCheckSumValid(serializedIds, checksum) {
+  const userAgent = USER_INTERFACE.getUserAgent();
+  const language = USER_INTERFACE.getUserLanguage();
+  for (let i = 0; i <= CHECKSUM_OFFSET_MAX_MIN; i++) {
+    const calculateCheckSum = getCheckSum(
+      serializedIds,
+      i,
+      userAgent,
+      language
+    );
+    if (calculateCheckSum == checksum) {
+      return true;
+    }
+  }
+  return false;
+}
+
+/**
+ * Deserialize the serializedIds and return keyValue pairs.
+ * @param {string} serializedIds
+ * @return {!Object<string, string>}
+ */
+function deserialize(serializedIds) {
+  const keyValuePairs = {};
+  const params = serializedIds.split(DELIMITER);
+  for (let i = 0; i < params.length; i += 2) {
+    const key = params[i];
+    const valid = KEY_VALIDATOR.test(key);
+    if (!valid) {
+      continue;
+    }
+    const value = decode(params[i + 1]);
+    //const value = params[i + 1];
+    keyValuePairs[key] = value;
+  }
+  return keyValuePairs;
+}
+
+/**
+ * Create a unique checksum hashing the fingerprint and a few other values.
+ * @param {string} serializedIds
+ * @param {number=} opt_offsetMin
+ * @return {string}
+ */
+function getCheckSum(serializedIds, opt_offsetMin, userAgent, language) {
+  const fingerprint = getFingerprint(userAgent, language);
+  const offset = opt_offsetMin || 0;
+  const timestamp = getMinSinceEpoch() - offset;
+  const crc = crc32([fingerprint, timestamp, serializedIds].join(DELIMITER));
+  // Encoded to base36 for less bytes.
+  return crc.toString(36);
+}
+
+/**
+ * Generates a semi-unique value for page visitor.
+ * @return {string}
+ */
+function getFingerprint(userAgent, language) {
+  const date = new Date();
+  const timezone = date.getTimezoneOffset();
+  return [userAgent, timezone, language].join(DELIMITER);
+}
+
+/**
+ * Rounded time used to check if t2 - t1 is within our time tolerance.
+ * @return {number}
+ */
+function getMinSinceEpoch() {
+  // Timestamp in minutes, floored.
+  return Math.floor(Date.now() / 60000);
+}
+
+export default parseLinker;