Create utility function to parsing json from a file

lib/manifest/index.js

@@ -22,6 +22,7 @@ var async = require('extern/async');
 var sprintf = require('extern/sprintf').sprintf;
 
 var misc = require('util/misc');
+var ufs = require('util/fs');
 var constants = require('manifest/constants');
 var validators = require('manifest/validators');
 
@@ -166,42 +167,25 @@ exports.validate_manifest = function(manifest_path, callback) {
 exports.get_manifest_data_as_object = function(manifest_path, merge_with_defaults, callback) {
   path.exists(manifest_path, function(exists) {
     if (!exists) {
-      return callback(new Error('Invalid path to the manifest file'), null);
+      return callback(new Error('Invalid path to the manifest file: ' + manifest_path), null);
     }
 
-    var return_manifest_object = function() {
+    ufs.json_file(manifest_path, function(err, obj) {
       var default_values, manifest_object;
-      var data = data_buffer.join('');
 
-      try {
-        manifest_object = JSON.parse(data);
-      }
-      catch (error) {
-        return callback(new Error('Manifest file contains invalid JSON'), null);
+      if (err) {
+        callback(err);
+        return;
       }
 
       if (merge_with_defaults) {
         // Merge the manifest file values with the default values for this application type
-        default_values = constants.DEFAULT_VALUES[manifest_object.type];
-        manifest_object = misc.merge(default_values, manifest_object);
+        default_values = constants.DEFAULT_VALUES[obj.type];
+        obj = misc.merge(default_values, obj);
       }
 
-      callback(null, manifest_object);
-    };
-
-    var read_stream = fs.createReadStream(manifest_path);
-    var data_buffer = [];
-
-    read_stream.on('data', function(chunk) {
-      data_buffer.push(chunk);
+      callback(null, obj);
     });
-
-    read_stream.on('error', function(error) {
-      read_stream.removeListener('end', return_manifest_object);
-      callback(error, null);
-    });
-
-    read_stream.on('end', return_manifest_object);
   });
 };
 

lib/util/fs.js

@@ -638,3 +638,41 @@ exports.ensure_directory = function(p, callback) {
     }
   });
 };
+
+/**
+ * Reads a JSON format file off of disk.
+ *
+ * @param {String} path The path to read from.
+ * @param {Function} callback The callback which takes a possible error, second parameter is the json object.
+ */
+exports.json_file = function(path, callback)
+{
+  var read_stream = fs.createReadStream(path);
+  var data_buffer = [];
+
+  function end_callback()
+  {
+    var data = data_buffer.join('');
+    var obj = null;
+    try {
+      obj = JSON.parse(data);
+    }
+    catch (err) {
+      callback(new Error('File ' + path + ' contains invalid JSON: ' + err), null);
+      return;
+    }
+    callback(null, obj);
+    return;
+  }
+
+  read_stream.on('data', function(chunk) {
+    data_buffer.push(chunk);
+  });
+
+  read_stream.on('error', function(error) {
+    read_stream.removeListener('end', end_callback);
+    callback(error, null);
+  });
+
+  read_stream.on('end', end_callback);
+};