google-app-engine - 在 Google App Engine 中，如何检查 urlsafe 创建的 key 的输入有效性？

Question

假设我从用户输入的网络安全 url 创建一个 key

key = ndb.Key(urlsafe=some_user_input)

如何检查 some_user_input 是否有效？

我目前的实验表明，如果 some_user_input 无效，上面的语句将抛出 ProtocolBufferDecodeError (Unable to merge from string.) 异常，但无法从API。有人可以确认这一点，并指出一些更好的用户输入有效性检查方法，而不是捕获异常吗？

非常感谢!

Answer 1

如果您尝试使用无效的 urlsafe 参数构造 Key

key = ndb.Key(urlsafe='bogus123')

你会得到类似这样的错误

Traceback (most recent call last):
  File "/opt/google/google_appengine/google/appengine/runtime/wsgi.py", line 240, in Handle
    handler = _config_handle.add_wsgi_middleware(self._LoadHandler())
  File "/opt/google/google_appengine/google/appengine/runtime/wsgi.py", line 299, in _LoadHandler
    handler, path, err = LoadObject(self._handler)
  File "/opt/google/google_appengine/google/appengine/runtime/wsgi.py", line 85, in LoadObject
    obj = __import__(path[0])
  File "/home/tim/git/project/main.py", line 10, in <module>
    from src.tim import handlers as handlers_
  File "/home/tim/git/project/src/tim/handlers.py", line 42, in <module>
    class ResetHandler(BaseHandler):
  File "/home/tim/git/project/src/tim/handlers.py", line 47, in ResetHandler
    key = ndb.Key(urlsafe='bogus123')
  File "/opt/google/google_appengine/google/appengine/ext/ndb/key.py", line 212, in __new__
    self.__reference = _ConstructReference(cls, **kwargs)
  File "/opt/google/google_appengine/google/appengine/ext/ndb/utils.py", line 142, in positional_wrapper
    return wrapped(*args, **kwds)
  File "/opt/google/google_appengine/google/appengine/ext/ndb/key.py", line 642, in _ConstructReference
    reference = _ReferenceFromSerialized(serialized)
  File "/opt/google/google_appengine/google/appengine/ext/ndb/key.py", line 773, in _ReferenceFromSerialized
    return entity_pb.Reference(serialized)
  File "/opt/google/google_appengine/google/appengine/datastore/entity_pb.py", line 1710, in __init__
    if contents is not None: self.MergeFromString(contents)
  File "/opt/google/google_appengine/google/net/proto/ProtocolBuffer.py", line 152, in MergeFromString
    self.MergePartialFromString(s)
  File "/opt/google/google_appengine/google/net/proto/ProtocolBuffer.py", line 168, in MergePartialFromString
    self.TryMerge(d)
  File "/opt/google/google_appengine/google/appengine/datastore/entity_pb.py", line 1839, in TryMerge
    d.skipData(tt)
  File "/opt/google/google_appengine/google/net/proto/ProtocolBuffer.py", line 677, in skipData
    raise ProtocolBufferDecodeError, "corrupted"
ProtocolBufferDecodeError: corrupted

这里有趣的是

File "/opt/google/google_appengine/google/appengine/ext/ndb/key.py", line 773, in _ReferenceFromSerialized
  return entity_pb.Reference(serialized)

这是 key.py module 中最后执行的代码:

def _ReferenceFromSerialized(serialized):
  """Construct a Reference from a serialized Reference."""
  if not isinstance(serialized, basestring):
    raise TypeError('serialized must be a string; received %r' % serialized)
  elif isinstance(serialized, unicode):
    serialized = serialized.encode('utf8')
  return entity_pb.Reference(serialized)

serialized 这里是解码后的 urlsafe 字符串，您可以在源代码链接中阅读更多相关信息。

另一个有趣的是最后一个:

File "/opt/google/google_appengine/google/appengine/datastore/entity_pb.py",   line 1839, in TryMerge

在entity_pb.py module看起来像这样

  def TryMerge(self, d):
    while d.avail() > 0:
      tt = d.getVarInt32()
      if tt == 106:
        self.set_app(d.getPrefixedString())
        continue
      if tt == 114:
        length = d.getVarInt32()
        tmp = ProtocolBuffer.Decoder(d.buffer(), d.pos(), d.pos() + length)
        d.skip(length)
        self.mutable_path().TryMerge(tmp)
        continue
      if tt == 162:
        self.set_name_space(d.getPrefixedString())
        continue


      if (tt == 0): raise ProtocolBuffer.ProtocolBufferDecodeError
      d.skipData(tt)

这是实际尝试“将输入合并到 key 中”的地方。

---

您可以在源代码中看到，在从 urlsafe 参数构造 Key 的过程中，不会出现很多错误。首先它检查输入是否是 string，如果不是，则引发 TypeError，如果是但不是“有效”，实际上是 ProtocolBufferDecodeError 被提出。

---

My current experiment shows that statement above will throw ProtocolBufferDecodeError (Unable to merge from string.) exception if the some_user_input is invalid, but could not find anything about this from the API. Could someone kindly confirm this

有点确认 - 我们现在知道也可以引发 TypeError。

and point me some better way for user input validity checking instead of catching the exception?

这是检查有效性的好方法!如果应用引擎已经完成检查，为什么还要自己检查？代码片段可能看起来像这样(不是工作代码，只是一个例子)

def get(self):
  # first, fetch the user_input from somewhere

  try:
    key = ndb.Key(urlsafe=user_input)
  except TypeError:
    return 'Sorry, only string is allowed as urlsafe input'
  except ProtocolBufferDecodeError:
    return 'Sorry, the urlsafe string seems to be invalid'