Update readme, further error handling

Author: mterwill

README.md

@@ -47,3 +47,25 @@ There are several additional functions available to simplify frequent calls:
                        '/Meetings?startDate=05-01-2015&endDate=05-03-2015';
 
         api.call(options, callback);
+
+## Caching
+
+Caching is turned on by default. Queries are cached for a period of 12 hours.
+The cache can be turned off by invoking the following function:
+
+    api.useCache(false);
+
+or individually, for each query by specifying an optional parameter in the 
+options object (defaults to the global useCache, which is set above, or true by
+default):
+
+    options.useCache = false;
+
+Additionally, we fall back on old cached data (even if it's older than 12 hours)
+if the API is unavailable or returns an error for any reason. Otherwise, you
+will get back from the server a response code 500, with an error object and
+message like so:
+
+    {
+        "error": "Error getting access token: UNABLE_TO_VERIFY_LEAF_SIGNATURE"
+    }

api.js

@@ -74,6 +74,22 @@ module.exports.call = function(options, callback) {
             }
         },
         getCallback = function(response) {
+            // non-standard response
+            if(response.statusCode !== 200) {
+                if(options.useCache && cache.isCached(options) >= 0) {
+                    // the object is cached, even if it's old,
+                    // let's return that object.
+                    cache.getCachedResponse(options, callback);
+                    return;
+                } else {
+                    // the server is unavailable, and the object isn't
+                    // cached at all, or the cache is off.
+                    // we return an error:
+                    callback({ error: 'UM API returned non-200 status code' });
+                    return;
+                }
+            }
+
             var responseData = '';
 
             response.on('data', function (chunk) {

cache.js

@@ -19,8 +19,7 @@ module.exports.isCached = function(options) {
         var timeDiff = Date.now() - cache[searchQuery].timestamp;
 
         // (now - time saved) < 12 hours
-        if(timeDiff < 15000) {
-        // if(timeDiff < 43200000) {
+        if(timeDiff < 43200000) {
             return 1;
         } else {
             return 0;

token.js

@@ -52,6 +52,13 @@ var getAccessToken = function(callback) {
             }
         },
         postCallback = function(response) {
+            // non-standard response
+            if(response.statusCode !== 200) {
+                callback({ error: 'UM access token request returned non-200' + 
+                    'status code' });
+                return;
+            }
+
             var tokenData = '';
             response.on('data', function (chunk) {
                 tokenData += chunk;