Not only are the standards fairly brief, but they contain errors. I’ve not managed to find an official errata, so here’s my starter for 10.

1.3.1 Variable Length Unsigned 29-bit Integer Encoding (U29)

The standard states that the largest unsigned integer permitted is pow(2,29)-1, which would be 0x1FFFFFFF, but then goes on to state that the range of a 4 byte value goes up to 0x3FFFFFFF. This looks like a typo, unless I am missing something critical!

The AMF standard is supposed to be platform independent [ish], so it doesn’t talk about Flash [much]; but it’s worth noting that the Flash Player uses U29 for serializing signed integers, making its useful range -0x10000000 -> 0x0FFFFFFF. Flash serializes all integers outside this range as a doubles, even when the AS type is uint; because the AMF protocol does not support an unsigned data type.

I find this data type a bit pointless. It is designed cut down on redundancy, but surely this could be achieved with different integer markers, 8-bit, 16-bit, etc.. The range of the integer wouldn’t have to be restricted and it would probably deserialize faster too.

1.3.2 Strings and UTF-8

There appears to be a typo in the third paragraph which contradicts the grammar notation below. It states that a zero flag indicates a string literal, although it says below that a zero value indicates a reference. The latter seems correct and is the same convention used in other parts of the standard.

More to come …