skunk-core

'''Skunk''' is a functional data access layer for Postgres.

Design principles:

• Skunk doesn't use JDBC. It speaks the Postgres wire protocol. It will not work with any other database back end.
• Skunk is asynchronous all the way down, via cats-effect, fs2, and ultimately nio. The high-level network layers (Protocol and Session) are safe to use concurrently.
• Serialization to and from schema types is not typeclass-based, so there are no implicit derivations. Codecs are explicit, like parser combinators.
• I'm not sweating arity abstraction that much. Pass a ~ b ~ c for three args and Void if there are no args. This may change in the future but it's fine for now.
• Skunk uses Resource for lifetime-managed objects, which means it takes some discipline to avoid leaks, especially when working concurrently. May or may not end up being problematic.
• I'm trying to write good Scaladoc this time.

A minimal example follows. We construct a Resource that yields a Session, then use it.

package example

import cats.effect._
import skunk._
import skunk.implicits._
import skunk.codec.numeric._

object Minimal extends IOApp {

 val session: Resource[IO, Session[IO]] =
   Session.single(
     host     = "localhost",
     port     = 5432,
     user     = "postgres",
     database = "world",
   )

 def run(args: List[String]): IO[ExitCode] =
   session.use { s =>
     for {
       n <- s.unique(sql"select 42".query(int4))
       _ <- IO(println(s"The answer is $n."))
     } yield ExitCode.Success
   }

}

Continue reading for an overview of the library. It's pretty small.

Skunk network stack, starting with BitVectorSocket at the bottom and ending with Protocol at the top (Session delegates all its work to Protocol). Everything is non-blocking.

Definitions of Postgres messages, with binary encoders and decoders. Doc for this package isn't very good yet, but the message formats are well documented at the linked pages below. It's a straightforward mapping.

It's probably useful to point out that Codec, Encoder, and Decoder in this package are from scodec. They're '''not''' the data types of the same name and same general design that are defined above in the skunk package. I realize this is confusing, but it shouldn't be a concern for anyone other than people working on the wire protocol, which never changes (heh-heh) so it shouldn't be a big deal.