I'm not working with binary protocols that often, so I cannot point to an existing protocol. However, if I had to implement a serialization format that doesn't need to be human-readable, I would never use number literals. I would write numbers as one byte whose value means e.g. "the next 4 bytes are an uint32 in little-endian", followed by just these 4 bytes.

Then you also don't have to worry about whitespace, because there is none. The next field can follow directly afterwards, because the type header byte defines how long exactly the current field is. (For variable-length strings, use something like netstrings.)

The only problem that I can see with this is that Son wants to ensure deterministic encoding, but in my example, 0 could be encoded as an integer of any size or signedness. You could add a rule like "encode every integer as the smallest possible type", but that may have practical implications elsewhere.

I wouldn't be too worried about it, seeing how half-baked Son appears to be. For example:

> Object members must be sorted by ascending lexicographic order of their keys.

Yeah right, because there is only one lexicographic order in the world.