Hi everyone. As an educational exercise I decided ...
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Arjan van Wieringen
09/26/2025, 12:44 PMHi everyone. As an educational exercise I decided to implement (part of) the Postgres Wire Protocol in pure Kotlin. So I have a pure Kotlin Postgres Client now that uses coroutines and have tested it on JVM, JS Node, JS WASM and Apple ARM64. Take a look! https://github.com/helico-tech/postgreskt
Most of the coroutine and network programming was pretty new to me, so I probably made quite some errors there, so I don't mind any feedback and pointers. It is not my plan at all to use this in production AND YOU SHOULDN'T EITHER and this was purely an exercise.
To be honest, it wasn't that hard. I spent most time figuring out bugs in byte encoding and decoding. I found out the Jetbrains AI / Junie is actually pretty good in pointing those out.
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Stefan Oltmann
09/26/2025, 12:54 PMOh great, going to use this in production... 😆
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Arjan van Wieringen
09/26/2025, 1:29 PMI omitted SASL auth because I thought it was too difficult (and out of scope). I just asked Junie and she(?) implemented it, so I've updated that 😄
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Stefan Oltmann
09/26/2025, 1:31 PMIndeed. I refer to basically all AIs as "he" (and sometimes "it"), but Junie sounds like a female name to me, so it's the only AI I call "she".
Stefan Oltmann
09/26/2025, 1:32 PMMy female trainee, however, refers all AIs as "she".
Stefan Oltmann
09/26/2025, 1:35 PMIn German you would say "die künstliche Intelligenz" where "die" is "she". So I can see where she's coming from.
I consider ChatGPT somehow as my coding Bro, so it's obviously a dude. 🫣
Stefan Oltmann
09/26/2025, 1:36 PMSee how a single
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Arjan van Wieringen
09/26/2025, 1:36 PMDutch is, 'de kunstmatige intelligentie', so same 😉
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CLOVIS
09/26/2025, 1:57 PMNice, I'm soon going to do the same for MongoDB 👀 ktmongo.opensavvy.dev
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CLOVIS
09/26/2025, 1:58 PMI'm planning on going with Ktor Sockets and KotlinX.IO, are there any footguns/lessons you would have wanted to know before you started?
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Arjan van Wieringen
09/26/2025, 2:02 PMI also use Ktor Sockets and Kotlinx IO. I must say it worked pretty good and easy! Just don't do anything too fancy with the Buffers, because you empty them before you know it.
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CLOVIS
09/26/2025, 2:03 PMAt this point I have the code to read/write most data from buffers, the next steps are to finish plugging KotlinX.Serialization on top, and then it's TCP fun
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Arjan van Wieringen
09/26/2025, 2:05 PMNice. I can't say anything about the Mongo TCP implementation. But Postgres was basically some custom serialization and pushing messages over the wire. The only caveat was that it isn't request - response, but a full async protocol which is also pretty stateful. So that's why I've implemented it as a very tiny state machine.
Arjan van Wieringen
09/26/2025, 2:05 PMPostgres can send you messages to give you updates about server parameters etc at any moment.
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CLOVIS
09/26/2025, 2:06 PMnice, interesting
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Arjan van Wieringen
09/26/2025, 2:07 PMWhat was interesting from this approach was that LISTEN/NOTIFY comes naturally from this implementation and you have a multi-producer fan-out message bus for free
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CLOVIS
09/26/2025, 2:11 PMThanks to coroutines channels, right?
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Arjan van Wieringen
09/26/2025, 2:56 PMNo I mean on Postgres level on how notifications work. With my client you can have multiple client listen and notify to a postgres channel.
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