Add proper support for Decimal (#194)

* Use `PostgresNumeric` for `Decimal` instead of String
* Make `Decimal` conform to `PSQLCodable`
* Fix support for text decimals
* Add integration test for decimal string serialization
* Test inserting decimal to text column

Co-authored-by: Gwynne Raskind <gwynne@darkrainfall.org>

Sources/PostgresNIO/Data/PostgresData+Decimal.swift

@@ -18,7 +18,7 @@ extension PostgresData {
 
 extension Decimal: PostgresDataConvertible {
     public static var postgresDataType: PostgresDataType {
-        return String.postgresDataType
+        return .numeric
     }
 
     public init?(postgresData: PostgresData) {
@@ -29,6 +29,6 @@ extension Decimal: PostgresDataConvertible {
     }
 
     public var postgresData: PostgresData? {
-        return .init(decimal: self)
+        return .init(numeric: PostgresNumeric(decimal: self))
     }
 }

Sources/PostgresNIO/New/Data/Decimal+PSQLCodable.swift

@@ -0,0 +1,39 @@
+import NIOCore
+import struct Foundation.Decimal
+
+extension Decimal: PSQLCodable {
+    var psqlType: PSQLDataType {
+        .numeric
+    }
+
+    var psqlFormat: PSQLFormat {
+        .binary
+    }
+
+    static func decode(from byteBuffer: inout ByteBuffer, type: PSQLDataType, format: PSQLFormat, context: PSQLDecodingContext) throws -> Decimal {
+        switch (format, type) {
+        case (.binary, .numeric):
+            guard let numeric = PostgresNumeric(buffer: &byteBuffer) else {
+                throw PSQLCastingError.failure(targetType: Self.self, type: type, postgresData: byteBuffer, context: context)
+            }
+            return numeric.decimal
+        case (.text, .numeric):
+            guard let string = byteBuffer.readString(length: byteBuffer.readableBytes), let value = Decimal(string: string) else {
+                throw PSQLCastingError.failure(targetType: Self.self, type: type, postgresData: byteBuffer, context: context)
+            }
+            return value
+        default:
+            throw PSQLCastingError.failure(targetType: Self.self, type: type, postgresData: byteBuffer, context: context)
+        }
+    }
+
+    func encode(into byteBuffer: inout ByteBuffer, context: PSQLEncodingContext) {
+        let numeric = PostgresNumeric(decimal: self)
+        byteBuffer.writeInteger(numeric.ndigits)
+        byteBuffer.writeInteger(numeric.weight)
+        byteBuffer.writeInteger(numeric.sign)
+        byteBuffer.writeInteger(numeric.dscale)
+        var value = numeric.value
+        byteBuffer.writeBuffer(&value)
+    }
+}

Tests/IntegrationTests/PSQLIntegrationTests.swift

@@ -251,6 +251,31 @@ final class IntegrationTests: XCTestCase {
         XCTAssertEqual(try row?.decode(column: "timestamptz", as: Date.self).description, "2016-01-18 00:20:03 +0000")
     }
 
+    func testDecodeDecimals() {
+        let eventLoopGroup = MultiThreadedEventLoopGroup(numberOfThreads: 1)
+        defer { XCTAssertNoThrow(try eventLoopGroup.syncShutdownGracefully()) }
+        let eventLoop = eventLoopGroup.next()
+
+        var conn: PSQLConnection?
+        XCTAssertNoThrow(conn = try PSQLConnection.test(on: eventLoop).wait())
+        defer { XCTAssertNoThrow(try conn?.close().wait()) }
+
+        var stream: PSQLRowStream?
+        XCTAssertNoThrow(stream = try conn?.query("""
+            SELECT
+                $1::numeric     as numeric,
+                $2::numeric     as numeric_negative
+            """, [Decimal(string: "123456.789123")!, Decimal(string: "-123456.789123")!], logger: .psqlTest).wait())
+
+        var rows: [PSQLRow]?
+        XCTAssertNoThrow(rows = try stream?.all().wait())
+        XCTAssertEqual(rows?.count, 1)
+        let row = rows?.first
+
+        XCTAssertEqual(try row?.decode(column: "numeric", as: Decimal.self), Decimal(string: "123456.789123")!)
+        XCTAssertEqual(try row?.decode(column: "numeric_negative", as: Decimal.self), Decimal(string: "-123456.789123")!)
+    }
+
     func testDecodeUUID() {
         let eventLoopGroup = MultiThreadedEventLoopGroup(numberOfThreads: 1)
         defer { XCTAssertNoThrow(try eventLoopGroup.syncShutdownGracefully()) }

Tests/IntegrationTests/PostgresNIOTests.swift

@@ -466,17 +466,41 @@ final class PostgresNIOTests: XCTestCase {
         var rows: PostgresQueryResult?
         XCTAssertNoThrow(rows = try conn?.query("""
         select
-            $1::numeric::text as a,
-            $2::numeric::text as b,
-            $3::numeric::text as c
+            $1::numeric as a,
+            $2::numeric as b,
+            $3::numeric as c
         """, [
             .init(numeric: a),
             .init(numeric: b),
             .init(numeric: c)
         ]).wait())
-        XCTAssertEqual(rows?.first?.column("a")?.string, "123456.789123")
-        XCTAssertEqual(rows?.first?.column("b")?.string, "-123456.789123")
-        XCTAssertEqual(rows?.first?.column("c")?.string, "3.14159265358979")
+        XCTAssertEqual(rows?.first?.column("a")?.decimal, Decimal(string: "123456.789123")!)
+        XCTAssertEqual(rows?.first?.column("b")?.decimal, Decimal(string: "-123456.789123")!)
+        XCTAssertEqual(rows?.first?.column("c")?.decimal, Decimal(string: "3.14159265358979")!)
+    }
+
+    func testDecimalStringSerialization() {
+        var conn: PostgresConnection?
+        XCTAssertNoThrow(conn = try PostgresConnection.test(on: eventLoop).wait())
+        defer { XCTAssertNoThrow( try conn?.close().wait() ) }
+
+        XCTAssertNoThrow(_ = try conn?.simpleQuery("DROP TABLE IF EXISTS \"table1\"").wait())
+        XCTAssertNoThrow(_ = try conn?.simpleQuery("""
+        CREATE TABLE table1 (
+            "balance" text NOT NULL
+        );
+        """).wait())
+        defer { XCTAssertNoThrow(_ = try conn?.simpleQuery("DROP TABLE \"table1\"").wait()) }
+
+        XCTAssertNoThrow(_ = try conn?.query("INSERT INTO table1 VALUES ($1)", [.init(decimal: Decimal(string: "123456.789123")!)]).wait())
+
+        var rows: PostgresQueryResult?
+        XCTAssertNoThrow(rows = try conn?.query("""
+        SELECT
+            "balance"
+        FROM table1
+        """).wait())
+        XCTAssertEqual(rows?.first?.column("balance")?.decimal, Decimal(string: "123456.789123")!)
     }
 
     func testMoney() {

Tests/PostgresNIOTests/New/Data/Decimal+PSQLCodableTests.swift

@@ -0,0 +1,32 @@
+import XCTest
+import NIOCore
+@testable import PostgresNIO
+
+class Decimal_PSQLCodableTests: XCTestCase {
+
+    func testRoundTrip() {
+        let values: [Decimal] = [1.1, .pi, -5e-12]
+
+        for value in values {
+            var buffer = ByteBuffer()
+            value.encode(into: &buffer, context: .forTests())
+            XCTAssertEqual(value.psqlType, .numeric)
+            let data = PSQLData(bytes: buffer, dataType: .numeric, format: .binary)
+
+            var result: Decimal?
+            XCTAssertNoThrow(result = try data.decode(as: Decimal.self, context: .forTests()))
+            XCTAssertEqual(value, result)
+        }
+    }
+
+    func testDecodeFailureInvalidType() {
+        var buffer = ByteBuffer()
+        buffer.writeInteger(Int64(0))
+        let data = PSQLData(bytes: buffer, dataType: .int8, format: .binary)
+
+        XCTAssertThrowsError(try data.decode(as: Decimal.self, context: .forTests())) { error in
+            XCTAssert(error is PSQLCastingError)
+        }
+    }
+
+}