[refactor] do not print traceback for expected errors

Add the ability to declare an exceptions as 'expected'.
This will avoid logging the backtrace on the bitmaskd log.
We will just forward the message in the json that we return to the
caller.

- Resolves: #8506

2 files changed, 15 insertions, 3 deletions

diff --git a/src/leap/bitmask/bonafide/_srp.py b/src/leap/bitmask/bonafide/_srp.py
index 3f69b33b..3939c5ac 100644
--- a/src/leap/bitmask/bonafide/_srp.py
+++ b/src/leap/bitmask/bonafide/_srp.py
@@ -133,7 +133,9 @@ class SRPSignupMechanism(object):
                     msg = 'username ' + msg[0]
                 else:
                     msg = 'unknown signup error'
-            raise SRPRegistrationError(msg)
+            error = SRPRegistrationError(msg)
+            error.expected = True
+            raise error
         else:
             username = signup.get('login')
             return username
diff --git a/src/leap/bitmask/core/dispatcher.py b/src/leap/bitmask/core/dispatcher.py
index 6a5603e6..783094ad 100644
--- a/src/leap/bitmask/core/dispatcher.py
+++ b/src/leap/bitmask/core/dispatcher.py
@@ -465,6 +465,16 @@ def _format_result(result):
 
 
 def _format_error(failure):
-    # TODO --- should check if the failure has the 'expected' attribute set
-    logger.failure('[DISPATCHER] Uncatched error:')
+    """
+    Logs the failure backtrace, and returns a json containing the error
+    message.
+    """
+
+    # If a exception declares the 'expected' attribute as True,
+    # we will not print a full traceback
+    expected = getattr(failure.value, 'expected', False) 
+    if not expected:
+        logger.failure('[DISPATCHER] Unexpected error:')
+
+    # if needed, we could add here the exception type as an extra field
     return json.dumps({'error': failure.value.message, 'result': None})