Support MongoDB 4.0 Multi-document transactions

[pierreis]

No description provided.

[why-not-try-calmer]

I would like to see multiple-document transactions implemented too. To the best of my knowledge the last MongoDB version that didn't support transactions was 3.6, EOL'ed in 2021 (the upcoming next stable, official version is 6.0 -- https://www.mongodb.com/docs/upcoming/release-notes/6.0/#std-label-release-notes-6.0). It's hard for this library to compete with librairies for other databases without transactions. This means that in the long run people are going to not use mongodb in Haskell at all.

That said, I would be willing to help. As far as I understand this library sends opcodes + document data as "notices" (bytestrings) formatted and transported as per MongoDB Wire Protocol; and Wire Protocol defines transactions using the OP_MSG opcode. This suggests that implementing transactions entails enabling this library to produce and consume "notices" written using this new opcode?

[VictorDenisov]

Yep. It means implementing operations using OP_MSG code according to https://www.mongodb.com/docs/manual/reference/mongodb-wire-protocol/

[why-not-try-calmer]

Yep. It means implementing operations using OP_MSG code according to https://www.mongodb.com/docs/manual/reference/mongodb-wire-protocol/

Okay. I don't want to promise anything but I'll look into it. If a maintainer of this library is already working on this please let me know.