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Comment by dbyte | Hacker News Reader

The grandfather of protobuf. Lost in the tales of time.

Grandfather of Protobuf is ASN.1

Very much so. Pretty much all of these protocols are simplifications of asn1 and in some cases (like protobuf) there are a handful of things that got lost because the wire formats didn’t have them as they didn’t need them. A schema indicator being the single biggest flaw in protobuf.

Why is the lack of a schema indicator the biggest flaw of protobuf?

If you parse a serialized protobuf byte array without having a .proto file, you have no way to dustinguish a byte string field from a nested message field. Thus you have no way to know how deep your parser should go.

Semi-related, one of the `imessage-exporter` contributors provided a great write-up on reverse engineering the handwritten and digital touch message protobufs [0]. The reconstructed proto files are [1] [2].

[0]: https://github.com/trymoose/handwriting2svg/blob/0eb56cf4582...

[1]: https://github.com/ReagentX/imessage-exporter/blob/beeb853b2...

[2]: https://github.com/ReagentX/imessage-exporter/blob/beeb853b2...

It makes it impossible to write a general purpose dissector that takes captured messages or bytes and figure out how to parse it.

All they needed was a varint at the head of any marshaled from to at least provide some scoping clue.

One usually has two grandfathers, so it still works out.

The telco industry, including GSM and its successors, uses ASN.1 widely.

iMessage uses a very strange amalgamation of typedstream (message content), keyed archives (app messages, sticker data), and protobufs (Digital Touch, handwriting) for different features. I wonder what motivated all of those design decisions.

This is stuff is such a PIA to parse. I assume it's just different teams doing different features over the years, and being alternately repulsed/seduced by each format. Probably features are implemented as libraries so there isn't a master oversight - they aren't trying to make iMessage's internal formats follow a consistent plan, just let all the libs coexist...

As someone who used to work on that team, it’s so interesting hearing thoughts from external public on the team.

I would love to hear your thoughts as an insider.

Maybe they should be repulsed, considering all of the journalists that are getting persecuted and/or murdered because they are getting pwned through iMessage serialization bugs :)

"Those who don't understand ASN.1 are doomed to reinvent it, poorly."

That said, it could be much worse --- JSON, or XML.

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