Key raises ProtocolBufferDecodeError for some invalid serialized keys

What steps will reproduce the problem?
from google.appengine.ext.ndb import model
model.Key(urlsafe='foo')

What is the expected output?
ValueError?

What do you see instead?
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/ext/ndb/key.py", line 209, in __new__
    self.__reference = _ConstructReference(cls, **kwargs)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/datastore/datastore_rpc.py", line 93, in positional_wrapper
    return wrapped(*args, **kwds)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/ext/ndb/key.py", line 599, in _ConstructReference
    reference = _ReferenceFromSerialized(serialized)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/ext/ndb/key.py", line 731, in _ReferenceFromSerialized
    return entity_pb.Reference(serialized)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/proto1/internal/cpp_message.py", line 555, in Init
    self.MergeFromString(contents)
  File "/base/python27_runtime/python27_lib/versions/1/google/appengine/_internal/proto1/internal/cpp_message.py", line 633, in MergeFromString
    raise ProtocolBufferDecodeError('Unable to merge from string.')
ProtocolBufferDecodeError: Unable to merge from string.

  File "/base/python_runtime/python_lib/versions/1/google/appengine/ext/ndb/key.py", line 209, in __new__
    self.__reference = _ConstructReference(cls, **kwargs)
  File "/base/python_runtime/python_lib/versions/1/google/appengine/datastore/datastore_rpc.py", line 93, in positional_wrapper
    return wrapped(*args, **kwds)
  File "/base/python_runtime/python_lib/versions/1/google/appengine/ext/ndb/key.py", line 599, in _ConstructReference
    reference = _ReferenceFromSerialized(serialized)
  File "/base/python_runtime/python_lib/versions/1/google/appengine/ext/ndb/key.py", line 731, in _ReferenceFromSerialized
    return entity_pb.Reference(serialized)
  File "/base/python_runtime/python_lib/versions/1/google/appengine/datastore/entity_pb.py", line 1774, in __init__
    if contents is not None: self.MergeFromString(contents)
  File "/base/python_runtime/python_lib/versions/1/google/net/proto/ProtocolBuffer.py", line 85, in MergeFromString
    self.MergePartialFromString(s)
  File "/base/python_runtime/python_lib/versions/1/google/net/proto/ProtocolBuffer.py", line 92, in MergePartialFromString
    self._CMergeFromString(s)
  File "/base/python_runtime/python_lib/versions/1/google/appengine/datastore/entity_pb.py", line 1819, in _CMergeFromString
    _net_proto___parse__python.MergeFromString(self, 'storage_onestore_v3.Reference', s)
ProtocolBufferDecodeError: Corrupted message: invalid wire type 6 encountered 
for tag 15

What version of the product are you using?
NDB 0.9.3
App Engine production 1.6.1

Original issue reported on code.google.com by [e-mail] on 22 Jan 2012 at 11:11

[GoogleCodeExporter]

At least to catch it, you can

    try:
        some_key = ndb.Key(urlsafe=123)
    except Exception, e:
        if e.__class__.__name__ == 'ProtocolBufferDecodeError':
            return ...
        else:
            raise

Original comment by [e-mail] on 24 Sep 2013 at 10:36

[salvador-bynd]

Run into this issue while refactoring code.

This bit of code catches this type of exception:

from google.net.proto import ProtocolBuffer

except (TypeError, ProtocolBuffer.ProtocolBufferDecodeError):

Example:

from google.appengine.ext import ndb
from google.net.proto import ProtocolBuffer

def get_entity_by_ident(ident):
    try:
        key = ndb.Key(urlsafe=ident)
    except (TypeError, ProtocolBuffer.ProtocolBufferDecodeError):
        raise endpoints.BadRequestException('Malformed key')

    if not valid_key_namespace(key):
        raise endpoints.BadRequestException('Invalid key namespace')

    # IMPORTANT: Fetch from datastore, to avoid fetching stale entities.
    return key.get(use_cache=False, use_memcache=False)