Comment by elcritch
5 months ago
> To me it looks more like Markdown vs. CommonMark disputes; John Gruber repeatedly refused to standardize Markdown or even any subset in spite of huge needs because he somehow believes that standardization ruins simplicity. I don't really agree---simple but correct standard is possible, albeit with efforts.
Right, that was my take after reading about it for a while. The way MessagePack and CBOR frame the problem is fairly different, with CBOR intentionally opting for an open tagging system.
Plus it feels a bit childish brining up the circumstances of the fork (correct or not) when they've clearly diverged bit in purpose and scope. The Markdown vs CommonMark is an apt comparison.
I've used both and both work very well. They're both stable, and be parsed into native objects at a speed nearing that of memory copy with the right implementations.
> CBOR intentionally opting for an open tagging system
CBOR's tags are MP's extension types
Not so much. (This response seems to repeat, please refrain from ignoring details in such bold claim.) MP extension types are opaque and applications can do nothing about them. CBOR tags are extensions to the existing data model and can be processed to some extent---for example unknown tags don't prevent implementations from inspecting their contents. And I don't think MP had any sort of registry for extension types, they are more like "reserved for future expansion" instead of "less used but still spec-worthy types to be defined with a reasonable proposal".
> Not so much. (This response seems to repeat, please refrain from ignoring details in such bold claim.)
I said what I meant; feel free to disagree but this policing is pretty condescending. I don't need to constantly repeat that the fundamental data format is lifted from MP and the extra features/process Bormann added on top of it are uniformly poorly thought out.
Just like CBOR's tags, extension types are additional, non core types. Bormann renamed them and bumped up the size so you can have way more of them in CBOR, but the tag also takes up more space, and since the odds of needing billions of extension types are basically zero it's not a good tradeoff.
> MP extension types are opaque and applications can do nothing about them. CBOR tags are extensions to the existing data model and can be processed to some extent
I think CBOR's "have your cake and eat it too" design has confused you. Yes CBOR establishes a tag registry, but implementations are free to ignore all tags. In practice what this means is if you can control the receiver you can use whatever tags you want, and if you don't control the receiver you have to either avoid tags or potentially limit your audience (i.e. do I use the "Standard date/time string" and eat the extra int8 or do I just send it as a string and note it as a date/time in my docs). You might think, "oh pish posh what can't process a date/time string", but the answer is "many embedded devices you'd want to use CBOR on". It's yet another feature added with no consideration for real world use cases.
> for example unknown tags don't prevent implementations from inspecting their contents. And I don't think MP had any sort of registry for extension types, they are more like "reserved for future expansion" instead of "less used but still spec-worthy types to be defined with a reasonable proposal".
You fundamentally misunderstand MP's extension types. Instead of guessing you can read about them in the MP spec [0]:
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Extension types
MessagePack allows applications to define application-specific types using the Extension type. Extension type consists of an integer and a byte array where the integer represents a kind of types and the byte array represents data.
Applications can assign 0 to 127 to store application-specific type information. An example usage is that application defines type = 0 as the application's unique type system, and stores name of a type and values of the type at the payload.
MessagePack reserves -1 to -128 for future extension to add predefined types. These types will be added to exchange more types without using pre-shared statically-typed schema across different programming environments.
[0, 127]: application-specific types
[-128, -1]: reserved for predefined types
Because extension types are intended to be added, old applications may not implement all of them. However, they can still handle such type as one of Extension types. Therefore, applications can decide whether they reject unknown Extension types, accept as opaque data, or transfer to another application without touching payload of them.
---
[0]: https://github.com/msgpack/msgpack/blob/master/spec.md#exten...
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