Handle NULLs when decoding arrays (#142)

* Add crashing test for decoding an array with NULL values

* Fix crash on NULL values inside arrays

Sources/PostgreSQL/Codable/PostgreSQLDataDecoder.swift

@@ -63,6 +63,13 @@ struct PostgreSQLDataDecoder {
                     let _ = value.extract(Int32.self).bigEndian
                     for _ in 0..<count {
                         let count = Int(value.extract(Int32.self).bigEndian)
+
+                        // Postgres sends -1 to distinguish an empty byte sequence from NULLs
+                        guard count != -1 else {
+                            array.append(.null)
+                            continue
+                        }
+
                         let subValue = value.extract(count: count)
                         let psqlData = PostgreSQLData(type, binary: subValue)
                         array.append(psqlData)

Tests/PostgreSQLTests/ConnectionTests.swift

@@ -670,6 +670,22 @@ class ConnectionTests: XCTestCase {
             XCTAssertEqual(polygon.polygon.points[3].y, 200)
         }.wait()
     }
+
+    func testGH141() throws {
+        let conn = try PostgreSQLConnection.makeTest()
+        defer { conn.close() }
+
+        struct Test: Decodable {
+            let arr: [String?]
+        }
+
+        let result = try conn.raw("SELECT ARRAY[NULL, 'foo', NULL, 'bar'] AS arr")
+            .all(decoding: Test.self)
+            .wait()
+
+        XCTAssertEqual(1, result.count)
+        XCTAssertEqual([nil, "foo", nil, "bar"], result[0].arr)
+    }
 }
 
 extension PostgreSQLConnection {

Tests/PostgreSQLTests/XCTestManifests.swift

@@ -11,6 +11,7 @@ extension ConnectionTests {
         ("testDataDecoder", testDataDecoder),
         ("testEmptyArray", testEmptyArray),
         ("testGH125", testGH125),
+        ("testGH141", testGH141),
         ("testGH24", testGH24),
         ("testGH46", testGH46),
         ("testInvalidDate", testInvalidDate),