Looks very much like a format that should just have been gzipped JSON. Don't use binary formats when it isn't absolutely needed.
> Don't use binary formats when it isn't absolutely needed. JSON in particular isn't very good [0] but I'd also argue that text formats in general aren't great. Isn't it a lot better that an int32_t always takes exactly 4 bytes instead of anywhere between one and eleven bytes (-2147483648)? [0] https://news.ycombinator.com/item?id=40555431
I would agree that binary formats can be much better. Sometimes you can use fixed fields, but there are also structured formats such as DER (which is generally better than JSON in my opinion). JSON has many problems, including that it does not have a non-Unicode type (so you must use base64 encoding or hex encoding instead and that isn't very good), and other problems. Parsing it will also mean that you must handle escaping.