如果您尝试使用无效的 urlsafe 参数构造 Key
key = ndb.Key(urlsafe='bogus123')
你会得到一个类似的错误
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)
这是最后执行的代码key.py模块:
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
in the 实体_pb.py模块看起来像这样
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“将输入合并到键中”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TypeError被提出，如果是但它不是“有效”，确实是ProtocolBufferDecodeError被提出。
我当前的实验表明，如果 some_user_input 无效，但无法从 API 中找到任何相关信息，则上面的语句将抛出 ProtocolBufferDecodeError (Unable to merge from string.) 异常。有人可以确认一下吗
有点确认了——我们现在知道也可以引发 TypeError。
并向我指出一些更好的方法来检查用户输入的有效性，而不是捕获异常？
这是检查有效性的好方法！如果应用程序引擎已经完成了这些检查，为什么还要自己检查呢？代码片段可能如下所示（不是工作代码，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'
