Support AWS Redshift queries - SELECT Metadata without row number (vapor#167)

- Allow only one part in metadata response (Support AWS Redshift)

Co-authored-by: Fabian Fett <fabianfett@apple.com>

Author: grennis

Diff for: Sources/PostgresNIO/PostgresDatabase+Query.swift

@@ -74,7 +74,13 @@ public struct PostgresQueryMetadata {
             self.command = .init(parts[0])
             self.oid = Int(parts[1])
             self.rows = Int(parts[2])
-        case "DELETE", "UPDATE", "SELECT", "MOVE", "FETCH", "COPY":
+        case "SELECT" where parts.count == 1:
+            // AWS Redshift does not return the actual row count as defined in the postgres wire spec for SELECT:
+            // https://www.postgresql.org/docs/13/protocol-message-formats.html in section `CommandComplete`
+            self.command = "SELECT"
+            self.oid = nil
+            self.rows = nil
+        case "SELECT", "DELETE", "UPDATE", "MOVE", "FETCH", "COPY":
             // <cmd> rows
             guard parts.count == 2 else {
                 return nil

Diff for: Tests/PostgresNIOTests/New/PSQLMetadataTests.swift

@@ -0,0 +1,18 @@
+import NIO
+import XCTest
+@testable import PostgresNIO
+
+class PSQLMetadataTests: XCTestCase {
+    func testSelect() {
+        XCTAssertEqual(100, PostgresQueryMetadata(string: "SELECT 100")?.rows)
+        XCTAssertNotNil(PostgresQueryMetadata(string: "SELECT"))
+        XCTAssertNil(PostgresQueryMetadata(string: "SELECT")?.rows)
+        XCTAssertNil(PostgresQueryMetadata(string: "SELECT 100 100"))
+    }
+
+    func testUpdate() {
+        XCTAssertEqual(100, PostgresQueryMetadata(string: "UPDATE 100")?.rows)
+        XCTAssertNil(PostgresQueryMetadata(string: "UPDATE"))
+        XCTAssertNil(PostgresQueryMetadata(string: "UPDATE 100 100"))
+    }
+}