Added check for existence of file in api path '/disseminate'

Author: StephanU

lib/danrw.js

@@ -101,8 +101,13 @@ function dawebAuthenticate(params) {
 function getDip(params) {
   var filePath = path.join(config.userArea, config.daweb.user, 'outgoing', params.identifier + '.tgz');
   // TODO error handling if file does not exist
-
-  params.success(filePath);
+  fs.exists(filePath, function (exists) {
+    if (exists) {
+      params.success(filePath);
+    } else {
+      params.error(404, "File not found");
+    }
+  });
 }