Compute size of serialized message?

[npow]

Hi, is there a ByteSize() equivalent in ProtoBuf.js? Did a quick search and wasn't able to find anything.

https://developers.google.com/protocol-buffers/docs/reference/cpp/google.protobuf.message_lite#MessageLite.ByteSize.details

[dcodeIO]

Currently. there is no equivalent to ByteSize. You may, of course, encode a message and evaluate its size. Let's say using a static eval buffer:

var evalBuffer = new ByteBuffer();

function calculateLength(msg) {
    msg.encode(evalBuffer.reset());
    return evalBuffer.offset; // corrected
}

var byteSize = calculateLength(myMessage);

[npow]

Hmm ok, was hoping I could avoid the encoding.
Also, I guess you meant to return the offset instead of limit?

return evalBuffer.offset;

[dcodeIO]

Yes, sorry, it's the offset.

What is your specific use case that you require the byte size but not the actual encoded message?

[npow]

I need to calculate the partial size of a message, which will be included in the main message itself. Basically I have some other services that only depend on the partial message, so I'm just extracting the serialized sub-message and forwarding it to them without having to go through the whole deserialize/serialize process again. In the code below, the "data" field will be encoded twice (once in calculateLength(), and then again in toArrayBuffer()).

        var msg = new Message();
        msg.setData(v);
        msg.setDataLen(calculateLength(msg));

        // set some more fields on msg here

        if (ws.readyState === WebSocket.OPEN) ws.send(msg.toArrayBuffer());

[dcodeIO]

This is kind of a larger addition and I've added an additional assertion to lots of test cases to assure that it actually works. If it however does produce unexpected results, please let me know. It's also a good thing to consider that calculation is of course faster than encoding, but still has its cost (like when there are UTF8 strings to calculate, or just calculating the byte size of varints assembled from bitwise operations).

Usage: Call MyMessage#calculate() on a populated message instance.

[GeorgePap-719]

Hello @dcodeIO , i stumbled upon this issue and i'm wondering how did you implement calculate without serializing the message itself first? I'm looking through the commit but i'm having hard time to underrtand the implementation details.

Thanks in advance for any answer!

[dcodeIO]

Iirc there are calculate functions for the basic ingredients like varints and strings, which are used by the calculate methods of fields, which again are iterated and summed by the calculate methods of messages.