CODEWITHSUNDEEP
client-serverprotobuf-netprotobuf-c
Ayush Ranjan
Ayush Ranjan

Reputation: 59

How to know size of protobuf message incoming from server?

I have a server-client application. The server is in C++ while the client is in C#. The server might be running on a Linux instance while the client is in Windows. Hence we cannot make any assumptions about the architecture and hence endianness. I am using protobuf to send data structures back and forth. Currently have adopted a strategy of sending a message as a header which will contain the size of the next message which is a large data structure. It looks like:

message message_size {
    required fixed64  size = 1;
}

Is there a way I can know how many bytes protobuf will be sending on both ends, which is how many bytes will the above structure be serialized into?

Upvotes: 1

Views: 1538

Answers (1)

Marc Gravell
Marc Gravell

Reputation: 1062820

The ultimate problem here is that root protobuf messages are not length prefixed (by design). There is no explicit agreed-upon API for dealing with multiple messages over an open stream, so basically: any length prefix that you care to encode and handle would work. A common pattern is to treat it using protobuf rules with a dummy field-number; in the case of protobuf-net, that is what SerializeWithLengthPrefix and DeserializeWithLengthPrefix does; but: that may not be easily available from C++. It might be easier just to encode the length manually using fixed-width/endianness rules, then dump the raw payload right after.

Upvotes: 3

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