Update EventSource to support chunked data

This code doesn't work when a line comes in but it hasn't been terminated with a new line (chunked data). In that case, the split('\n') call will give you some junk data which the rest of the logic can't handle.

There might be another edge case where the XHR request finishes before the full line comes in but that's outside the scope of this change

Author: jlkalberer

EventSource.js

@@ -10,7 +10,7 @@ var EventSource = function(url, options) {
   var eventsource = this,
     interval = 500, // polling interval
     lastEventId = null,
-    cache = '',
+    lastIndexProcessed = 0,
     eventType;
 
   if (!url || typeof url != 'string') {
@@ -50,7 +50,7 @@ var EventSource = function(url, options) {
 
       if (lastEventId != null)
         xhr.setRequestHeader('Last-Event-ID', lastEventId);
-      cache = '';
+      lastIndexProcessed = 0;
 
       xhr.timeout =
         this.OPTIONS && this.OPTIONS.timeout !== undefined
@@ -74,13 +74,12 @@ var EventSource = function(url, options) {
           } catch (e) {}
 
           // process this.responseText
-          var parts = responseText.substr(cache.length).split('\n'),
+          var parts = responseText.substr(lastIndexProcessed).split('\n'),
             data = [],
             i = 0,
             retry = 0,
             line = '';
-
-          cache = responseText;
+          lastIndexProcessed = responseText.lastIndexOf('\n\n') + 2;
 
           // TODO handle 'event' (for buffer name), retry
           for (; i < parts.length; i++) {