[bin] Fixed binary standard output + added test

bin/netjsonconfig

@@ -1,6 +1,7 @@
 #!/usr/bin/env python
 
 import sys
+import six
 import argparse
 
 import netjsonconfig
@@ -121,6 +122,24 @@ def recognize_method_argument(arg_string):
         return False
     return arg_string
 
+
+def print_output(output):
+    """
+    prints result to standard output
+    """
+    # if file object, get bytes
+    if hasattr(output, 'getvalue'):
+        output = output.getvalue()
+    # python2: always print
+    # python3: if string, just print
+    if isinstance(output, six.string_types):
+        print(output)
+    # python2: never enters this block
+    # python3: writes binary data to standard output
+    else:
+        sys.stdout.buffer.write(output)
+
+
 args = parser.parse_args()
 config = _load(args.config)
 templates = [_load(template) for template in args.templates]
@@ -142,7 +161,7 @@ except TypeError as e:
 try:
     output = getattr(instance, method)(**method_arguments)
     if output:
-        print(output)
+        print_output(output)
 except netjsonconfig.exceptions.ValidationError as e:
     message = 'netjsonconfig: JSON Schema violation\n'
     if not args.verbose:

tests/test_bin.py

@@ -1,6 +1,8 @@
+import os
 import json
 import unittest
 import subprocess
+import tarfile
 
 from netjsonconfig.utils import _TabsMixin
 
@@ -9,6 +11,10 @@ class TestBin(unittest.TestCase, _TabsMixin):
     """
     tests for netjsonconfig command line tool
     """
+    @classmethod
+    def tearDownClass(self):
+        os.remove('test.tar.gz')
+
     def test_file_not_found(self):
         with self.assertRaises(subprocess.CalledProcessError):
             output = subprocess.check_output("netjsonconfig -c WRONG -b openwrt -m generate", shell=True)
@@ -107,3 +113,10 @@ def test_valid_arg(self):
         output = subprocess.check_output(command, shell=True).decode()
         self.assertNotIn('test.txt', output)
         self.assertNotIn('test_valid_arg', output)
+
+    def test_generate_redirection(self):
+        command = """netjsonconfig -c '{"general": { "hostname": "example" }}' -b openwrt -m generate > test.tar.gz"""
+        subprocess.check_output(command, shell=True)
+        tar = tarfile.open('test.tar.gz', 'r')
+        self.assertEqual(len(tar.getmembers()), 1)
+        tar.close()