Tag binary values in cbor if set

[matthewbauer]

CBOR has tags, which work similarly to "subtype"s:

https://www.iana.org/assignments/cbor-tags/cbor-tags.xhtml

Unsure if this makes sense. Note that the subtype must just be one
byte wide.

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[nlohmann]

I have one question (see comment). Furthermore, test cases are missing. Maybe with some examples, I understand the goal of this PR.

[matthewbauer]

Note this only works for encoding subtypes, not decoding. Decoding is hard because the tag can come for any data type - not just binary. So we would need to add more state to handle it properly.

[coveralls]

Coverage remained the same at 100.0% when pulling dd08f77 on matthewbauer:tag-cbor into efcc826 on nlohmann:develop.

[Ericson2314]

For context, here is an issue from a Rust library about this exact issue pyfisch/cbor#157 . Serde also wasn't originally made with CBOR tags in mind, so again the sticking point is derialization without polluting everything else with CBOR-specific concepts.

[nlohmann]

As the library does not support tags in the moment (#1968), it would fail to parse its own output, or am I mistaken?

[matthewbauer]

As the library does not support tags in the moment (#1968), it would fail to parse its own output, or am I mistaken?

Yes - you wouldn't be able to parse a cbor with a subtype since it would have that tag.

[Ericson2314]

Yes this change just attempts serialization for now, as a stop-gap which is good enough for our purposes.

[nlohmann]

Hm. Then I think it would be helpful to also adjust the parser to skip tags, because otherwise roundtripping would not work any more. This does not need to be done in this PR, of course, but I'm still re-opening #1968.

[Ericson2314]

Oh! We'll if you are fine doing it after is there anything more this PR needs?

[nlohmann]

@Ericson2314 @matthewbauer It would be great if you could have a look at #2273.

[nlohmann]

Looks good to me.

[nlohmann]

Thanks!

[nlohmann]

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🔖 Release item

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Type

• ✨ New Feature
• 🐛 Bug Fix
• ⚡️ Improvement
• 🔨 Further Change
• 🔥 Deprecated function

Description

• Use binary subtype as tag in CBOR if set. Tag binary values in cbor if set #2244

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[Ericson2314]

Thank you!