Protobuf packed (de)serialization

Question

Since protobuf does not support the uint16_t datatype, I have a field below describing what I have in place.

uint32_t fingerprints = 1 [packed=true];

To save space, I have a C++ program that packs together two uint16_t values and add them that way, here is an example:

uint16_t value1 = 100; // Arbitrary values
uint16_t value2 = 200;
protoObject.add_fingerprints((uint32_t)value1 << 16) +  value2;

To deserialize them, I do:

uint16_t value1 = protoObject->fingerprints(i) >> 16;
uint16_t value2 = protoObject->fingerprints(i) & 0x0000FFFF;

However, it seems like this does not produce the values I want, and the values after deserialization does not match the values before it. Is there something special protobuf does that prevents me from doing this?

Does your code work if you replace `protoObject->fingerprints(i)` with a pure `uint32_t`? — DazWilkin, Aug 03 '22 at 22:49
Yes, I've tested the combine and split operations using pure uint32_t and uint16_t datatypes, it works just fine. — Baiqing, Aug 03 '22 at 23:05
@for_stack's answer is spot and, and for good measure it's a bad idea to have something like you'd proposed. The .proto file is a contract / interface spec between two separate systems. Your extra packing of 2 uint16's into 1 unint32 is like a hidden clause that no one else knows about, until you tell them! Generally, it's better to just stick with the .proto. — bazza, Aug 05 '22 at 19:26

score 0 · Accepted Answer · answered Aug 04 '22 at 03:52

To save space, I have a C++ program that packs together two uint16_t values and add them that way

No bother to do that. Protobuf uses variable length encoding to serialize uint32_t, which will do 'pack' for you to save space, i.e. for an uint16_t number, protobuf will not encode it to 4 bytes, instead, it might encode it to less than 2 bytes, depends on the number.

Protobuf packed (de)serialization

1 Answers1