"ParseFromString()" and "JsonStringToMessage()" have inconsistent behavior when parsing an unrecognized enum value.

[Qian Zhang]

Hi,

I am using protobuf-3.3.0, and I found when parsing an unrecognized enum value for an optional enum field, the behaviors of "ParseFromString()" and "JsonStringToMessage()" are different. "ParseFromString()" will succeed and the field's getter method will return the default enum value, but "JsonStringToMessage" will fail with an error:

invalid value "xxx" for type TYPE_ENUM

Is this a bug of protobuf-3.3.0? IMHO, "ParseFromString()" and "JsonStringToMessage()" should have consistent behavior.

Thanks,

Qian

[Feng Xiao]

This is the expected behavior. The issue at core is that protobuf message is only able to hold unknown binary data. It's designed that way with its UnknownFieldSet data structure and you can not achieve the same with other formats.

 

Thanks,

Qian

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[Feng Xiao]

Note that you can use the always_print_enums_as_ints option to work around this problem:

https://github.com/google/protobuf/blob/master/src/google/protobuf/util/json_util.h#L73

With this option enum value will printed as integers and will be accepted by JsonStringToMessage.

[Qian Zhang]

Note that you can use the always_print_enums_as_ints option to work around this problem:

https://github.com/google/protobuf/blob/master/src/google/protobuf/util/json_util.h#L73

 

With this option enum value will printed as integers and will be accepted by JsonStringToMessage.

"always_print_enums_as_ints" is an option for the method "MessageToJsonString()", but the issue that I am talking about is the method "JsonStringToMessage()", the only option that "JsonStringToMessage()" accepts is "JsonParseOptions.ignore_unknown_fields", but I do not think it can help here.

This is the expected behavior. The issue at core is that protobuf message is only able to hold unknown binary data. It's designed that way with its UnknownFieldSet data structure and you can not achieve the same with other formats.

But that behavior is not desired for us :-( We are implementing a server which can accept both protobuf serialized string and JSON string from clients, and then the server will call "ParseFromString()" and "JsonStringToMessage" to get the protobuf message from the serialized string and JSON string respectively. But now these two methods have different behaviors, "ParseFromString()" can successfully parse a serialized string which contains unrecognized enum value, but "JsonStringToMessage()" will fail to do that. This makes our server can not behave consistently for protobuf serialized string and JSON string.

Any suggestions? Thanks!

Regards,

Qian Zhang

[Qian Zhang]

Feng, any comments? :-)

[Feng Xiao]

On Tue, Oct 10, 2017 at 8:15 PM, Qian Zhang <zhq5...@gmail.com> wrote:

Note that you can use the always_print_enums_as_ints option to work around this problem:

https://github.com/google/protobuf/blob/master/src/google/protobuf/util/json_util.h#L73

 

With this option enum value will printed as integers and will be accepted by JsonStringToMessage.

"always_print_enums_as_ints" is an option for the method "MessageToJsonString()", but the issue that I am talking about is the method "JsonStringToMessage()", the only option that "JsonStringToMessage()" accepts is "JsonParseOptions.ignore_unknown_fields", but I do not think it can help here.

This is the expected behavior. The issue at core is that protobuf message is only able to hold unknown binary data. It's designed that way with its UnknownFieldSet data structure and you can not achieve the same with other formats.

But that behavior is not desired for us :-( We are implementing a server which can accept both protobuf serialized string and JSON string from clients, and then the server will call "ParseFromString()" and "JsonStringToMessage" to get the protobuf message from the serialized string and JSON string respectively. But now these two methods have different behaviors, "ParseFromString()" can successfully parse a serialized string which contains unrecognized enum value, but "JsonStringToMessage()" will fail to do that. This makes our server can not behave consistently for protobuf serialized string and JSON string.

Any suggestions? Thanks!

There really isn't a good way to solve this. The server has to know the enum definition to be able to accept it in JSON format. You will either need to make sure the server is updated with the new definition before sending it JSON data using the new enum names, or use integer instead of enum names in the request.