有关Google协议缓冲区的查询

Question

message Person {
    required string name = 1;
    required int32 id = 2;
    optional string email = 3; 
}

The above is a snippet from addrbook.proto file mentioned in Google Protocol Buffer tutorials. The requirement is that, the application that is being developed will need to decode binary data received from a socket.For example,name, id and e-mail represented as binary data. Now, id can be read as an integer. But I am really not sure how to read name and email considering that these two can be of variable lengths. (And unfortunately, I do not get lengths prefixed before these two fields) Application is expected to read these kind of data from a variety of sources. Our objective is to make a decoder/adapter for the different types of data originating from these sources. Then there could be different types of messages from same source too. Thanks in advance

Answer 1

But I am really not sure how to read name and email considering that these two can be of variable lengths.

The entire point of a serializer such as protobuf is that you don't need to worry about that . Specifically, in the case of protobuf strings are always prefixed by their length in bytes (using UTF-8 encoding, and varint encoding of the length).

And unfortunately, I do not get lengths prefixed before these two fields

Then you aren't processing protobuf data. Protobuf is a specific data format, in the same way that xml or json is a data format. Any conversation involving "protocol buffers" only makes sense if you are actually discussing the protobuf format, or data serialized using that format.

Protocol buffers is not an arbitrary data handling API. It will not allow you to process data in any format other than protobuf.

Answer 2

It sounds like you might be trying to re-implement Protocol Buffers by hand; you don't need to do that (though I'm sure it would be fun). Google provides C, Java, and Python implementations to serialize and de-serialize content in protobuf format as part of the Protocol Buffers project.