Expand UserDefined to include Subtype as defined in the BSON spec

[antarestrader]

Proposal

In the Notes section of the BSON spec the seventh bullet described BinData. The third sub-bullet describes the user-defined type, "\x80-\xFF "User defined" subtypes. The binary data can be anything."

Our implementation limits this to only 0x80 and throws and error on other subtypes.

I propose that the UserDefined type be redefined to include a Word8 subtype field and that accompanying changes be made to the binary get and put functions.

data UserDefined = UserDefined Word8 ByteString

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Use Case

The BSON format while more compact than JSON is still a rather verbose document particularly with the way it encodes arrays. I would like to leverage the UserDefined binary part of the spec to store packed vectors of data. Using the subtype field would allow me to identify what was in the packed date without having to use a separate field of tag.

[antarestrader]

I will create a pull request for this, but as it is a breaking change to the API, I would like to hear from the maintainer before doing so.

[VictorDenisov]

Looking into it. I'll get back to you.

[VictorDenisov]

Sorry for the delay. It looks like the right thing to do. We will bump the major version. Go ahead with the PR.