ProtoBuf

Protocol Buffers

This module parses and formats the raw wire encoding.

• https://wikipedia.org/wiki/Protocol_Buffers
• https://protobuf.dev/programming-guides/encoding
• https://protobuf.dev/programming-guides/proto3

Embedded message wire type

Currently Protocol Buffers is an inherently flawed protocol, in that it is not self describing. This is evidenced by the fact that "type 2" wire type, can be any of these values:

1. string
2. byte slice
3. embedded message

Its pretty straight forward to check for string or byte slice. Also, not all input is a valid message. That gives you this result:

valid string	valid message	result
no	no	byte slice
no	yes	message or byte slice
yes	no	string
yes	yes	message or string

Ideally the protocol would have an extra wire type, for example "type 6", to designate embedded messages. But without that, its not possible in every case to know the structure of the input, unless you have a schema. Other protocols such as JSON are self describing, nothing is stopping ProtoBuf from being self describing as well. Granted, you lose the field names, but even just having the field numbers and values, with a defined structure as read from the input, would be quite useful. Quoting from the spec:

in other words, the last three bits of the number store the wire type

So that gives you this currently:

000 Varint
001 64-bit
010 Length-delimited
011 Start group
100 End group
101 32-bit
110
111

So you have at least two extra types that could be added. Even a single extra type for embedded messages would essentially make ProtoBuf self describing.