1.3 Wiretypes

The wire-stream consists of six primitive payload types, two of which have been deprecated. A primitive in the wire-stream is a multi-byte string that provides three pieces of information: a wire-type, a user-specified tag, and the raw payload. Except for the tag and its wire-type, protobuf payloads are not instantaneously recognizable because the wire-stream contains no payload type information. The interpreter uses the tag to associate the raw payload with a local host type specified by the template. Hence, the message can only be properly decoded using the template that was used to encode it. Note also that the primitive is interpreted according to the needs of a local host. Local word-size and endianness are dealt with at this level.

The following table shows the association between various "host types" used by several peer languages, and the primitives used in the wire-stream:

Prolog	Wirestream	C++	Java	Notes
double	fixed64	double	double
integer64	fixed64	int64	long
float	fixed32	float	float
integer32	fixed32	int32	int
integer	varint	int32/64	int/long	1, 2
unsigned	varint	uint32/64	int/long	2, 3
boolean	varint	bool	boolean	2
enum	varint	int	int	2
atom	length delimited	string	String	4
codes	length delimited	string	ByteString
utf8_codes	length delimited	string	ByteString	4
string	length delimited	string	String	4

Notes:

1. Encoded using a compression technique known as zig-zagging.
2. Encoded as a modulo 128 string. Its length is proprotional to its magnitude. The intrinsic word length is decoupled between parties.
3. Prolog's unbounded integer may be expressed as unsigned. This is not portable across languages.
4. Encoded as UTF8 in the wire-stream.