add numeric parsing for binary floating point, fixes vapor#56

Author: tanner0101

Sources/PostgreSQL/Data/PostgreSQLData+BinaryFloatingPoint.swift

@@ -11,6 +11,9 @@ extension BinaryFloatingPoint where Self: LosslessStringConvertible {
             case .int8: f = Self(value.as(Int64.self, default: 0).bigEndian)
             case .float4: f = Self(Data(value.reversed()).as(Float.self, default: 0))
             case .float8: f = Self(Data(value.reversed()).as(Double.self, default: 0))
+            case .numeric:
+                let string = try String.convertFromPostgreSQLData(data)
+                f = Self(string)
             default: throw PostgreSQLError.decode(self, from: data)
             }
             guard let value = f else {

Tests/PostgreSQLTests/PostgreSQLConnectionTests.swift

@@ -536,6 +536,20 @@ class PostgreSQLConnectionTests: XCTestCase {
         }
         try done.wait()
     }
+    
+    // https://github.com/vapor/postgresql/issues/56
+    func testSum() throws {
+        let conn = try PostgreSQLConnection.makeTest(transport: .cleartext)
+        struct Sum: Decodable {
+            var sum: Double
+        }
+        let rows = try conn.query("SELECT SUM(3.14) as sum", decoding: Sum.self).wait()
+        switch rows.count {
+        case 1:
+            XCTAssertEqual(rows[0].sum, 3.14)
+        default: XCTFail("invalid row count")
+        }
+    }
 
     static var allTests = [
         ("testVersion", testVersion),