Refactor TLS config initialization in tests

Replace repetitive TLS configuration code with a reusable `getTLSConfig` helper function for consistency and maintainability. Additionally, update port configuration and add new tests for mail data transmission.

smtp/smtp_test.go

@@ -22,6 +22,7 @@ import (
 	"crypto/sha1"
 	"crypto/sha256"
 	"crypto/tls"
+	"crypto/x509"
 	"encoding/base64"
 	"errors"
 	"fmt"
@@ -42,7 +43,7 @@ const (
 	// TestServerAddr is the address the simple SMTP test server listens on
 	TestServerAddr = "127.0.0.1"
 	// TestServerPortBase is the base port for the simple SMTP test server
-	TestServerPortBase = 12025
+	TestServerPortBase = 30025
 )
 
 // PortAdder is an atomic counter used to increment port numbers for the test SMTP server instances.
@@ -1087,13 +1088,8 @@ func TestScramAuth(t *testing.T) {
 			var client *Client
 			switch tt.tls {
 			case true:
-				cert, err := tls.X509KeyPair(localhostCert, localhostKey)
+				tlsConfig := getTLSConfig(t)
-				if err != nil {
+				conn, err := tls.Dial("tcp", fmt.Sprintf("%s:%d", TestServerAddr, serverPort), tlsConfig)
-					fmt.Printf("error creating TLS cert: %s", err)
-					return
-				}
-				tlsConfig := tls.Config{Certificates: []tls.Certificate{cert}, InsecureSkipVerify: true}
-				conn, err := tls.Dial("tcp", fmt.Sprintf("%s:%d", TestServerAddr, serverPort), &tlsConfig)
 				if err != nil {
 					t.Fatalf("failed to dial TLS server: %v", err)
 				}
@@ -1161,13 +1157,8 @@ func TestScramAuth(t *testing.T) {
 			var client *Client
 			switch tt.tls {
 			case true:
-				cert, err := tls.X509KeyPair(localhostCert, localhostKey)
+				tlsConfig := getTLSConfig(t)
-				if err != nil {
+				conn, err := tls.Dial("tcp", fmt.Sprintf("%s:%d", TestServerAddr, serverPort), tlsConfig)
-					fmt.Printf("error creating TLS cert: %s", err)
-					return
-				}
-				tlsConfig := tls.Config{Certificates: []tls.Certificate{cert}, InsecureSkipVerify: true}
-				conn, err := tls.Dial("tcp", fmt.Sprintf("%s:%d", TestServerAddr, serverPort), &tlsConfig)
 				if err != nil {
 					t.Fatalf("failed to dial TLS server: %v", err)
 				}
@@ -1719,7 +1710,7 @@ func TestClient_StartTLS(t *testing.T) {
 				t.Errorf("failed to close client: %s", err)
 			}
 		})
-		tlsConfig := &tls.Config{InsecureSkipVerify: true}
+		tlsConfig := getTLSConfig(t)
 		if err = client.StartTLS(tlsConfig); err != nil {
 			t.Errorf("failed to initialize STARTTLS session: %s", err)
 		}
@@ -1753,7 +1744,7 @@ func TestClient_StartTLS(t *testing.T) {
 				t.Errorf("failed to close client: %s", err)
 			}
 		})
-		tlsConfig := &tls.Config{InsecureSkipVerify: true}
+		tlsConfig := getTLSConfig(t)
 		if err = client.StartTLS(tlsConfig); err == nil {
 			t.Error("STARTTLS should fail on EHLO")
 		}
@@ -1786,7 +1777,7 @@ func TestClient_StartTLS(t *testing.T) {
 				t.Errorf("failed to close client: %s", err)
 			}
 		})
-		tlsConfig := &tls.Config{InsecureSkipVerify: true}
+		tlsConfig := getTLSConfig(t)
 		if err = client.StartTLS(tlsConfig); err == nil {
 			t.Error("STARTTLS should fail for server not supporting it")
 		}
@@ -1821,7 +1812,8 @@ func TestClient_TLSConnectionState(t *testing.T) {
 				t.Errorf("failed to close client: %s", err)
 			}
 		})
-		tlsConfig := &tls.Config{InsecureSkipVerify: true, MinVersion: tls.VersionTLS12}
+		tlsConfig := getTLSConfig(t)
+		tlsConfig.MinVersion = tls.VersionTLS12
 		if err = client.StartTLS(tlsConfig); err != nil {
 			t.Errorf("failed to initialize STARTTLS session: %s", err)
 		}
@@ -2472,6 +2464,79 @@ func TestClient_Rcpt(t *testing.T) {
 	})
 }
 
+func TestClient_Data(t *testing.T) {
+	t.Run("normal mail data transmission succeeds", func(t *testing.T) {
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+		PortAdder.Add(1)
+		serverPort := int(TestServerPortBase + PortAdder.Load())
+		featureSet := "250-DSN\r\n250 STARTTLS"
+		go func() {
+			if err := simpleSMTPServer(ctx, t, &serverProps{
+				FeatureSet: featureSet,
+				ListenPort: serverPort,
+			},
+			); err != nil {
+				t.Errorf("failed to start test server: %s", err)
+				return
+			}
+		}()
+		time.Sleep(time.Millisecond * 30)
+		client, err := Dial(fmt.Sprintf("%s:%d", TestServerAddr, serverPort))
+		if err != nil {
+			t.Fatalf("failed to dial to test server: %s", err)
+		}
+		t.Cleanup(func() {
+			if err = client.Close(); err != nil {
+				t.Errorf("failed to close client: %s", err)
+			}
+		})
+		writer, err := client.Data()
+		if err != nil {
+			t.Fatalf("failed to create data writer: %s", err)
+		}
+		t.Cleanup(func() {
+			if err = writer.Close(); err != nil {
+				t.Errorf("failed to close data writer: %s", err)
+			}
+		})
+		if _, err = writer.Write([]byte("test message")); err != nil {
+			t.Errorf("failed to write data to test server: %s", err)
+		}
+	})
+	t.Run("mail data transmission fails on DATA command", func(t *testing.T) {
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+		PortAdder.Add(1)
+		serverPort := int(TestServerPortBase + PortAdder.Load())
+		featureSet := "250-DSN\r\n250 STARTTLS"
+		go func() {
+			if err := simpleSMTPServer(ctx, t, &serverProps{
+				FailOnDataInit: true,
+				FeatureSet:     featureSet,
+				ListenPort:     serverPort,
+			},
+			); err != nil {
+				t.Errorf("failed to start test server: %s", err)
+				return
+			}
+		}()
+		time.Sleep(time.Millisecond * 30)
+		client, err := Dial(fmt.Sprintf("%s:%d", TestServerAddr, serverPort))
+		if err != nil {
+			t.Fatalf("failed to dial to test server: %s", err)
+		}
+		t.Cleanup(func() {
+			if err = client.Close(); err != nil {
+				t.Errorf("failed to close client: %s", err)
+			}
+		})
+		if _, err = client.Data(); err == nil {
+			t.Error("expected data writer to fail")
+		}
+	})
+}
+
 /*
 func TestBasic(t *testing.T) {
 	server := strings.Join(strings.Split(basicServer, "\n"), "\r\n")
@@ -4251,7 +4316,7 @@ func handleTestServerConnection(connection net.Conn, t *testing.T, props *server
 				break
 			}
 			writeLine("220 Ready to start TLS")
-			tlsConfig := &tls.Config{Certificates: []tls.Certificate{keypair}}
+			tlsConfig := &tls.Config{Certificates: []tls.Certificate{keypair}, ServerName: "example.com"}
 			connection = tls.Server(connection, tlsConfig)
 			props.IsTLS = true
 			handleTestServerConnection(connection, t, props)
@@ -4444,3 +4509,18 @@ type failWriter struct{}
 func (w *failWriter) Write([]byte) (int, error) {
 	return 0, errors.New("broken writer")
 }
+
+func getTLSConfig(t *testing.T) *tls.Config {
+	t.Helper()
+	cert, err := tls.X509KeyPair(localhostCert, localhostKey)
+	if err != nil {
+		t.Fatalf("unable to load host certifcate: %s", err)
+	}
+	testRootCAs := x509.NewCertPool()
+	testRootCAs.AppendCertsFromPEM(localhostCert)
+	return &tls.Config{
+		Certificates: []tls.Certificate{cert},
+		RootCAs:      testRootCAs,
+		ServerName:   "example.com",
+	}
+}