(fix) Attempt to improve exception handling of ValueError

Fixes #43

Unfortunatelly it is hard to propagate exceptions from hook files without
propagating hook handler exceptions too. This attempt tries to propagate
everything but json decoding errors which are manifestation of either the
connection being closed or some internal error. If anybody knows a better
solution I am happy to hear about it.

Author: w-vi

dredd_hooks/dredd.py

@@ -109,12 +109,18 @@ def handle(self):
                     self.wfile.write(msg.encode('utf-8'))
                 else:
                     self.wfile.write(msg)
-        except ValueError:
-            print("\nConnection closed\n", file=sys.stderr)
-        except Exception:
-            traceback.print_exc(file=sys.stderr)
-            sys.stderr.flush()
-            raise
+
+        except Exception as e:
+            if sys.version_info[0] > 2 and isinstance(e, json.JSONDecodeError):
+                print('Connection closed, could not parse JSON',
+                      file=sys.stderr)
+            elif str(e) == "No JSON object could be decoded":
+                print('Connection closed, could not parse JSON',
+                      file=sys.stderr)
+            else:
+                traceback.print_exc(file=sys.stderr)
+                sys.stderr.flush()
+                raise
 
 
 def add_named_hook(obj, hook, name):

test/test_excepts_hook.py

@@ -0,0 +1,136 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+from __future__ import print_function
+import unittest
+import sys
+import socket
+import os
+import json
+import threading
+import time
+import dredd_hooks as hooks
+if sys.version_info[0] > 2:
+    import io
+else:
+    import StringIO as io
+
+hooks_thr = None
+
+
+class Connection(object):
+
+    def __init__(self):
+        self.connection = socket.create_connection((hooks.HOST, hooks.PORT))
+        self.rfile = self.connection.makefile('rb', -1)  # buffered input
+        self.wfile = self.connection.makefile('wb', 0)  # unbuffered output
+
+    def writeline(self, msg):
+        msg = msg + hooks.MESSAGE_DELIMITER
+        if sys.version_info[0] > 2:
+            self.wfile.write(msg.encode('utf-8'))
+        else:
+            self.wfile.write(msg)
+
+    def readline(self):
+        if sys.version_info[0] > 2:
+            return self.rfile.readline().decode('utf-8').strip()
+        else:
+            return self.rfile.readline().strip()
+
+    def close(self):
+        self.rfile.close()
+        self.wfile.close()
+        self.connection.close()
+
+
+class TestValueError(unittest.TestCase):
+    """
+    Tests exception handling.
+    """
+    @classmethod
+    def setUpClass(cls):
+        cls.output = io.StringIO()
+        cls.saved_stderr = sys.stderr
+        sys.stderr = cls.output
+        cls.hooks_thr = threading.Thread(target=hooks.main,
+                                         args=([os.path.abspath(__file__)],))
+        cls.hooks_thr.start()
+        time.sleep(1)
+        cls.conn = Connection()
+
+    @classmethod
+    def tearDownClass(cls):
+        cls.output.close()
+        sys.stderr = cls.saved_stderr
+        cls.conn.close()
+        hooks.shutdown()
+        cls.hooks_thr.join()
+
+    def setUp(self):
+        self.conn.writeline(json.dumps({"event": "beforeAll", "data": [{}]}))
+        try:
+            json.loads(self.conn.readline())
+        except Exception:
+            pass
+
+    def tearDown(self):
+        pass
+
+    def test_output(self):
+        out = self.output.getvalue()
+        self.assertNotEqual(out.find('ValueErrorRaised'), -1)
+
+
+class TestGenericException(unittest.TestCase):
+    """
+    Tests exception handling.
+    """
+    @classmethod
+    def setUpClass(cls):
+        cls.output = io.StringIO()
+        cls.saved_stderr = sys.stderr
+        sys.stderr = cls.output
+        cls.hooks_thr = threading.Thread(target=hooks.main,
+                                         args=([os.path.abspath(__file__)],))
+        cls.hooks_thr.start()
+        time.sleep(1)
+        cls.conn = Connection()
+
+    @classmethod
+    def tearDownClass(cls):
+        cls.output.close()
+        sys.stderr = cls.saved_stderr
+        cls.conn.close()
+        hooks.shutdown()
+        cls.hooks_thr.join()
+
+    def setUp(self):
+        self.conn.writeline(json.dumps({"event": "afterAll", "data": [{}]}))
+        try:
+            json.loads(self.conn.readline())
+        except Exception:
+            pass
+
+    def tearDown(self):
+        pass
+
+    def test_output(self):
+        out = self.output.getvalue()
+        self.assertNotEqual(out.find("ExceptionRaised"), -1)
+
+
+@hooks.before_all
+def before_all_test(transactions):
+    raise ValueError("ValueErrorRaised")
+
+
+@hooks.after_all
+def after_all_test(transactions):
+    raise Exception("ExceptionRaised")
+
+
+if __name__ == '__main__':
+    try:
+        unittest.main()
+    except Exception as e:
+        exit(-1)