Define uint8_t variable in Protocol Buffers message file

Question

I want to define a Point message in Protocol Buffers which represents an RGB Colored Point in 3-dimensional space.

message Point {
    float x   = 1;
    float y   = 2;
    float z   = 3;
    uint8_t r = 4;
    uint8_t g = 5;
    uint8_t b = 6;
}

Here, x, y, z variables defines the position of Point and r, g, b defines the color in RGB space.

Since uint8_t is not defined in Protocol Buffers, I am looking for a workaround to define it. At present, I am using uint32 in place of uint8_t.

Answer 1

There isn't anything in protobuf that represents a single byte - it simply isn't a thing that the wire-format worries about. The options are:

• varint (up to 64 bits input, up to 10 bytes on the wire depending on the highest set bit)
• fixed 32 bit
• fixed 64 bit
• length-prefixed (strings, sub-objects, packed arrays)
• (group tokens; a rare implementation detail)

A single byte isn't a good fit for any of those. Frankly, I'd use a single fixed32 for all 3, and combine/decompose the 3 bytes manually (via shifting etc). The advantage here is that it would only have one field header for the 3 bytes, and wouldn't be artificially stretched via having high bits (I'm not sure that a composed RGB value is a good candidate for varint). You'd also have a spare byte if you want to add something else at a later date (alpha, maybe).

So:

message Point {
    float x     = 1;
    float y     = 2;
    float z     = 3;
    fixed32 rgb = 4;
}