在Google App Engine中，如何检查URLSAFE创建的密钥的输入有效性

Question

假设我从用户输入WebSAFE URL

创建一个键

key = ndb.Key(urlsafe=some_user_input)

如何检查some_user_input是否有效？

我当前的实验表明，如果some_user_input无效，上面的语句将抛出ProtocolBufferDecodeError (Unable to merge from string.)异常，但从API中找不到任何内容。有人可以确认这一点，并为我指出一些更好的方法来检查用户输入有效性检查而不是捕获异常吗？

非常感谢！

Answer 1

如果您尝试使用无效的URLSAFE参数构造键

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

您会遇到一个错误

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

有趣的是

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

这是在key.py模块中执行的最后一个代码：

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这是解码的URLSAFE字符串，您可以在指向源代码的链接中阅读有关它的更多信息。

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模块中，看起来像

  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)

这是将"将输入合并到键中"的实际尝试。

---

您可以在源代码中看到，在从URLSAFE参数构建密钥的过程中，很多情况可能会出错。首先，它检查输入是否为a string ，如果不是，则升高了TypeError，如果是，则是"有效的"，实际上是 ProtocolBufferDecodeError。

---

我当前的实验表明，上面的语句将抛出协议BufferDecodeError（无法从字符串中合并。）例外，如果Some_user_input无效，但从API中找不到任何有关此内容的信息。有人可以确认这个

已被确认 - 我们现在知道也可以提高类型。

并指向用户输入有效性检查而不是捕获异常的更好方法？

这是检查有效性的绝佳方法！如果附录已经完成，为什么要检查一下它们？代码段看起来像这样（不工作代码，只是一个示例）

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'