Add callback functionality to log.fail

This enables the common pattern of being able to log a failure and
then do something.

lbrynet/core/log_support.py

@@ -332,7 +332,7 @@ class LogUploader(object):
 
 class Logger(logging.Logger):
     """A logger that has an extra `fail` method useful for handling twisted failures."""
-    def fail(self):
+    def fail(self, callback=None, *args):
         """Returns a function to log a failure from an errback.
 
         The returned function appends the error message and extracts
@@ -346,23 +346,29 @@ class Logger(logging.Logger):
         reported values are from inside twisted's deferred handling
         code.
 
-        Args (for the returned function):
+        Args:
+            callback: callable to call after making the log. The first argument
+                will be the `err` from the deferred
+            args: extra arguments to pass into `callback`
+
+        Returns: a function that takes the following arguments:
             err: twisted.python.failure.Failure
             msg: the message to log, using normal logging string iterpolation.
-            args: the values to subtitute into `msg`
+            msg_args: the values to subtitute into `msg`
             kwargs: set `level` to change from the default ERROR severity. Other
                 keywoards are treated as normal log kwargs.
-
         """
         fn, lno, func = findCaller()
-        def _fail(err, msg, *args, **kwargs):
+        def _fail(err, msg, *msg_args, **kwargs):
             level = kwargs.pop('level', logging.ERROR)
             msg += ": %s"
-            args += (err.getErrorMessage(),)
+            msg_args += (err.getErrorMessage(),)
             exc_info = (err.type, err.value, err.getTracebackObject())
             record = self.makeRecord(
-                self.name, level, fn, lno, msg, args, exc_info, func, kwargs)
+                self.name, level, fn, lno, msg, msg_args, exc_info, func, kwargs)
             self.handle(record)
+            if callback:
+                callback(err, *args)
         return _fail
 
 

tests/unit/core/test_log_support.py

@@ -1,6 +1,7 @@
 import StringIO
 import logging
 
+import mock
 from twisted.internet import defer
 from twisted.trial import unittest
 
@@ -11,30 +12,37 @@ class TestLogger(unittest.TestCase):
     def raiseError(self):
         raise Exception('terrible things happened')
 
-    def triggerErrback(self, log):
+    def triggerErrback(self, callback=None):
         d = defer.Deferred()
         d.addCallback(lambda _: self.raiseError())
-        d.addErrback(log.fail(), 'My message')
+        d.addErrback(self.log.fail(callback), 'My message')
         d.callback(None)
         return d
 
+    def setUp(self):
+        self.log = log_support.Logger('test')
+        self.stream = StringIO.StringIO()
+        handler = logging.StreamHandler(self.stream)
+        handler.setFormatter(logging.Formatter("%(filename)s:%(lineno)d - %(message)s"))
+        self.log.addHandler(handler)
+
     def test_can_log_failure(self):
         def output_lines():
-            return stream.getvalue().split('\n')
-
-        log = log_support.Logger('test')
-        stream = StringIO.StringIO()
-        handler = logging.StreamHandler(stream)
-        handler.setFormatter(logging.Formatter("%(filename)s:%(lineno)d - %(message)s"))
-        log.addHandler(handler)
+            return self.stream.getvalue().split('\n')
 
         # the line number could change if this file gets refactored
-        expected_first_line = 'test_log_support.py:17 - My message: terrible things happened'
+        expected_first_line = 'test_log_support.py:18 - My message: terrible things happened'
 
         # testing the entirety of the message is futile as the
         # traceback will depend on the system the test is being run on
         # but hopefully these two tests are good enough
-        d = self.triggerErrback(log)
+        d = self.triggerErrback()
         d.addCallback(lambda _: self.assertEquals(expected_first_line, output_lines()[0]))
         d.addCallback(lambda _: self.assertEqual(10, len(output_lines())))
         return d
+
+    def test_can_log_failure_with_callback(self):
+        callback = mock.Mock()
+        d = self.triggerErrback(callback)
+        d.addCallback(lambda _: callback.assert_called_once_with(mock.ANY))
+        return d