[DRAFT] Make async queries possible

[fabianfett]

This is a very early draft enabling async queries on a Postgres connection. It allows async/await in Postgres:

// swift-tools-version:5.5
import PackageDescription

let package = Package(
    name: "postgres-perf",
    platforms: [
        .macOS(.v12)
    ],
    dependencies: [
        .package(url: "https://github.com/fabianfett/postgres-nio.git", .branch("ff-async2")),
    ],
    targets: [
        .executableTarget(name: "PostgresExample", dependencies: [
            .product(name: "PostgresNIO", package: "postgres-nio"),
        ]),
    ]
)

And then use it like this:

import NIO
import Logging
import PostgresNIO
import struct Foundation.Date

@main
enum AsyncExample {
    static func main() async throws {
        let eventLoopGroup = MultiThreadedEventLoopGroup(numberOfThreads: 1)
        let eventLoop = eventLoopGroup.next()
        defer { try! eventLoopGroup.syncShutdownGracefully() }
        
        var logger = Logger(label: "psql")
        logger.logLevel = .info
        
        let configuration = PSQLConnection.Configuration(
            host: "postgres", port: 5432,
            username: "postgres",
            database: "postgres",
            password: "postgres",
            tlsConfiguration: nil,
            coders: .foundation
        )
        let connection = try await PSQLConnection.connect(configuration: configuration, logger: logger, on: eventLoop)
        
        let start = Date()
        var i = 0
        var result = 0
        
        let stream = try await connection.query("SELECT * FROM large_test LIMIT 2000000", logger: logger)
        for try await (column1, column2, column3) in stream.decode(Int.self, Double.self, Double.self) {
            result &+= column1
            i &+= 1
        }
        
        try await connection.close()
    }
}

[Jerry-Carter]

Gonna start kicking the tires on your ff-async2 branch. Anything I should know?

[codecov-commenter]

Codecov Report

Merging #188 (320581b) into main (f876692) will decrease coverage by 5.76%.
The diff coverage is 54.32%.

❗ Current head 320581b differs from pull request most recent head 02bb7ca. Consider uploading reports for the commit 02bb7ca to get more accurate results

@@            Coverage Diff             @@
##             main     #188      +/-   ##
==========================================
- Coverage   43.81%   38.05%   -5.77%     
==========================================
  Files         169      117      -52     
  Lines       12748     8449    -4299     
==========================================
- Hits         5586     3215    -2371     
+ Misses       7162     5234    -1928     

Flag	Coverage Δ
unittests	38.05% <54.32%> (-5.77%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...esNIO/Connection/PostgresConnection+Database.swift	0.00% <0.00%> (ø)
Sources/PostgresNIO/Data/PostgresData+Array.swift	0.00% <0.00%> (ø)
...es/PostgresNIO/Message/PostgresMessage+Error.swift	0.00% <0.00%> (ø)
...Message/PostgresMessage+ParameterDescription.swift	0.00% <0.00%> (ø)
...esNIO/Message/PostgresMessage+RowDescription.swift	0.00% <0.00%> (ø)
...rces/PostgresNIO/New/Extensions/Logging+PSQL.swift	18.18% <ø> (ø)
...rces/PostgresNIO/New/Messages/Authentication.swift	63.36% <ø> (ø)
Sources/PostgresNIO/New/PSQLBackendMessage.swift	92.89% <ø> (ø)
Sources/PostgresNIO/New/PSQLChannelHandler.swift	47.96% <ø> (ø)
Sources/PostgresNIO/New/PSQLTask.swift	35.13% <ø> (ø)
... and 93 more

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