some refactoring:

- new module for messages
 - new module for helper functions

www/helpers.js

@@ -0,0 +1,195 @@
+var pluginId = module.id.slice(0, module.id.lastIndexOf('.'));
+var cookieHandler = require(pluginId + '.cookie-handler');
+var messages = require(pluginId + '.messages');
+
+var validSerializers = ['urlencoded', 'json', 'utf8' ];
+
+module.exports = {
+  b64EncodeUnicode: b64EncodeUnicode,
+  checkHeaders: checkHeaders,
+  onInvalidHeader: onInvalidHeader,
+  checkSerializer: checkSerializer,
+  injectCookieHandler: injectCookieHandler,
+  injectFileEntryHandler: injectFileEntryHandler,
+  getMergedHeaders: getMergedHeaders,
+  getProcessedData: getProcessedData,
+  handleMissingCallbacks: handleMissingCallbacks
+};
+
+// Thanks Mozilla: https://developer.mozilla.org/en-US/docs/Web/API/WindowBase64/Base64_encoding_and_decoding#The_.22Unicode_Problem.22
+function b64EncodeUnicode(str) {
+  return btoa(encodeURIComponent(str).replace(/%([0-9A-F]{2})/g, function (match, p1) {
+    return String.fromCharCode('0x' + p1);
+  }));
+}
+
+function mergeHeaders(globalHeaders, localHeaders) {
+  var globalKeys = Object.keys(globalHeaders);
+  var key;
+
+  for (var i = 0; i < globalKeys.length; i++) {
+    key = globalKeys[i];
+
+    if (!localHeaders.hasOwnProperty(key)) {
+      localHeaders[key] = globalHeaders[key];
+    }
+  }
+
+  return localHeaders;
+}
+
+function checkHeaders(headers) {
+  var keys = Object.keys(headers);
+  var key;
+
+  for (var i = 0; i < keys.length; i++) {
+    key = keys[i];
+
+    if (typeof headers[key] !== 'string') {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+function onInvalidHeader(handler) {
+  handler({
+    status: 0,
+    error: messages.HEADER_VALUE_MUST_BE_STRING,
+    headers: {}
+  });
+}
+
+function checkSerializer(serializer) {
+  serializer = serializer || '';
+  serializer = serializer.trim().toLowerCase();
+
+  if (validSerializers.indexOf(serializer) > -1) {
+    return serializer;
+  }
+
+  return serializer[0];
+}
+
+function resolveCookieString(headers) {
+  var keys = Object.keys(headers || {});
+
+  for (var i = 0; i < keys.length; ++i) {
+    if (keys[i].match(/^set-cookie$/i)) {
+      return headers[keys[i]];
+    }
+  }
+
+  return null;
+}
+
+function createFileEntry(rawEntry) {
+  var entry = new (require('cordova-plugin-file.FileEntry'))();
+
+  entry.isDirectory = rawEntry.isDirectory;
+  entry.isFile = rawEntry.isFile;
+  entry.name = rawEntry.name;
+  entry.fullPath = rawEntry.fullPath;
+  entry.filesystem = new FileSystem(rawEntry.filesystemName || (rawEntry.filesystem == window.PERSISTENT ? 'persistent' : 'temporary'));
+  entry.nativeURL = rawEntry.nativeURL;
+
+  return entry;
+}
+
+function injectCookieHandler(url, cb) {
+  return function(response) {
+    cookieHandler.setCookieFromString(url, resolveCookieString(response.headers));
+    cb(response);
+  }
+}
+
+function injectFileEntryHandler(cb) {
+  return function(response) {
+    cb(createFileEntry(response.file));
+  }
+}
+
+function getCookieHeader(url) {
+  return { Cookie: cookieHandler.getCookieString(url) };
+}
+
+function getMatchingHostHeaders(url, headersList) {
+  var matches = url.match(/^https?\:\/\/([^\/?#]+)(?:[\/?#]|$)/i);
+  var domain = matches && matches[1];
+
+  return headersList[domain] || null;
+}
+
+function getMergedHeaders(url, requestHeaders, predefinedHeaders) {
+  var globalHeaders = predefinedHeaders['*'] || {};
+  var hostHeaders = getMatchingHostHeaders(url, predefinedHeaders) || {};
+  var mergedHeaders = mergeHeaders(globalHeaders, hostHeaders);
+
+  mergedHeaders = mergeHeaders(mergedHeaders, requestHeaders);
+  mergedHeaders = mergeHeaders(mergedHeaders, getCookieHeader(url));
+
+  return mergedHeaders;
+}
+
+// typeof is not working reliably in JS
+function getTypeOf(object) {
+  switch (Object.prototype.toString.call(object)) {
+    case '[object Array]':
+      return 'Array';
+    case '[object Boolean]':
+      return 'Boolean';
+    case '[object Function]':
+      return 'Function';
+    case '[object Null]':
+      return 'Null';
+    case '[object Number]':
+      return 'Number';
+    case '[object Object]':
+      return 'Object';
+    case '[object String]':
+      return 'String';
+    case '[object Undefined]':
+      return 'Undefined';
+    default:
+      return 'Unknown';
+  }
+}
+
+function getAllowedDataTypes(dataSerializer) {
+  switch (dataSerializer) {
+    case 'utf8':
+      return ['String'];
+    case 'urlencoded':
+      return ['Object'];
+    default:
+      return ['Array', 'Object'];
+  }
+}
+
+function getProcessedData(data, dataSerializer) {
+  data = data || {};
+
+  var currentDataType = getTypeOf(data);
+  var allowedDataTypes = getAllowedDataTypes(dataSerializer);
+
+  if (allowedDataTypes.indexOf(currentDataType) === -1) {
+    throw new Error(messages.DATA_TYPE_MISMATCH + ' ' + allowedDataTypes.join(', '));
+  }
+
+  if (dataSerializer === 'utf8') {
+    data = { text: data };
+  }
+
+  return data;
+}
+
+function handleMissingCallbacks(successFn, failFn) {
+  if (getTypeOf(successFn) !== 'Function') {
+    throw new Error(messages.MANDATORY_SUCCESS);
+  }
+
+  if (getTypeOf(failFn) !== 'Function') {
+    throw new Error(messages.MANDATORY_FAIL);
+  }
+}