Add test for Client cmd failure on textproto command

This commit introduces a new test case for the `Client`'s `cmd` method to ensure it fails correctly when the `textproto` command encounters a broken writer. It also adds a `failWriter` struct that simulates a write failure to facilitate this testing scenario.

smtp/smtp_test.go

@@ -1391,252 +1391,308 @@ func TestScramAuth_handleServerFirstResponse(t *testing.T) {
 			t.Errorf("expected error to be %q, got %q", expectedErr, err)
 		}
 	})
-
 }
 
-/*
+func TestCRAMMD5Auth(t *testing.T) {
-
+	t.Run("CRAM-MD5 on test server succeeds", func(t *testing.T) {
-
+		ctx, cancel := context.WithCancel(context.Background())
-
+		defer cancel()
-
+		PortAdder.Add(1)
-
+		serverPort := int(TestServerPortBase + PortAdder.Load())
-
+		featureSet := "250-AUTH CRAM-MD5\r\n250-8BITMIME\r\n250-DSN\r\n250 SMTPUTF8"
-func TestAuthSCRAMSHA1_OK(t *testing.T) {
-	hostname := "127.0.0.1"
-	port := "2585"
-
 		go func() {
-		startSMTPServer(false, hostname, port, sha1.New)
+			if err := simpleSMTPServer(ctx, t, &serverProps{
-	}()
+				FeatureSet: featureSet,
-	time.Sleep(time.Millisecond * 500)
+				ListenPort: serverPort,
-
+			},
-	conn, err := net.Dial("tcp", fmt.Sprintf("%s:%s", hostname, port))
+			); err != nil {
-	if err != nil {
+				t.Errorf("failed to start test server: %s", err)
-		t.Errorf("failed to dial server: %v", err)
-	}
-	client, err := NewClient(conn, hostname)
-	if err != nil {
-		t.Errorf("failed to create client: %v", err)
-	}
-	if err = client.Hello(hostname); err != nil {
-		t.Errorf("failed to send HELO: %v", err)
-	}
-	if err = client.Auth(ScramSHA1Auth("username", "password")); err != nil {
-		t.Errorf("failed to authenticate: %v", err)
-	}
-}
-
-func TestAuthSCRAMSHA256_OK(t *testing.T) {
-	hostname := "127.0.0.1"
-	port := "2586"
-
-	go func() {
-		startSMTPServer(false, hostname, port, sha256.New)
-	}()
-	time.Sleep(time.Millisecond * 500)
-
-	conn, err := net.Dial("tcp", fmt.Sprintf("%s:%s", hostname, port))
-	if err != nil {
-		t.Errorf("failed to dial server: %v", err)
-	}
-	client, err := NewClient(conn, hostname)
-	if err != nil {
-		t.Errorf("failed to create client: %v", err)
-	}
-	if err = client.Hello(hostname); err != nil {
-		t.Errorf("failed to send HELO: %v", err)
-	}
-	if err = client.Auth(ScramSHA256Auth("username", "password")); err != nil {
-		t.Errorf("failed to authenticate: %v", err)
-	}
-}
-
-func TestAuthSCRAMSHA1PLUS_OK(t *testing.T) {
-	hostname := "127.0.0.1"
-	port := "2590"
-
-	go func() {
-		startSMTPServer(true, hostname, port, sha1.New)
-	}()
-	time.Sleep(time.Millisecond * 500)
-
-	cert, err := tls.X509KeyPair(localhostCert, localhostKey)
-	if err != nil {
-		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:%s", hostname, port), &tlsConfig)
-	if err != nil {
-		t.Errorf("failed to dial server: %v", err)
-	}
-	client, err := NewClient(conn, hostname)
-	if err != nil {
-		t.Errorf("failed to create client: %v", err)
-	}
-	if err = client.Hello(hostname); err != nil {
-		t.Errorf("failed to send HELO: %v", err)
-	}
-
-	tlsConnState := conn.ConnectionState()
-	if err = client.Auth(ScramSHA1PlusAuth("username", "password", &tlsConnState)); err != nil {
-		t.Errorf("failed to authenticate: %v", err)
-	}
-}
-
-func TestAuthSCRAMSHA256PLUS_OK(t *testing.T) {
-	hostname := "127.0.0.1"
-	port := "2591"
-
-	go func() {
-		startSMTPServer(true, hostname, port, sha256.New)
 		}()
-	time.Sleep(time.Millisecond * 500)
+		time.Sleep(time.Millisecond * 30)
 
-	cert, err := tls.X509KeyPair(localhostCert, localhostKey)
+		auth := CRAMMD5Auth("username", "password")
+		client, err := Dial(fmt.Sprintf("%s:%d", TestServerAddr, serverPort))
 		if err != nil {
-		fmt.Printf("error creating TLS cert: %s", err)
+			t.Fatalf("failed to dial to test server: %s", err)
+		}
+		if err = client.Auth(auth); err != nil {
+			t.Errorf("failed to auth to test server: %s", err)
+		}
+	})
+	t.Run("CRAM-MD5 on test server fails", func(t *testing.T) {
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+		PortAdder.Add(1)
+		serverPort := int(TestServerPortBase + PortAdder.Load())
+		featureSet := "250-AUTH CRAM-MD5\r\n250-8BITMIME\r\n250-DSN\r\n250 SMTPUTF8"
+		go func() {
+			if err := simpleSMTPServer(ctx, t, &serverProps{
+				FailOnAuth: true,
+				FeatureSet: featureSet,
+				ListenPort: serverPort,
+			},
+			); err != nil {
+				t.Errorf("failed to start test server: %s", err)
 				return
 			}
-	tlsConfig := tls.Config{Certificates: []tls.Certificate{cert}, InsecureSkipVerify: true}
+		}()
+		time.Sleep(time.Millisecond * 30)
 
-	conn, err := tls.Dial("tcp", fmt.Sprintf("%s:%s", hostname, port), &tlsConfig)
+		auth := CRAMMD5Auth("username", "password")
+		client, err := Dial(fmt.Sprintf("%s:%d", TestServerAddr, serverPort))
 		if err != nil {
-		t.Errorf("failed to dial server: %v", err)
+			t.Fatalf("failed to dial to test server: %s", err)
 		}
-	client, err := NewClient(conn, hostname)
+		if err = client.Auth(auth); err == nil {
-	if err != nil {
+			t.Error("auth should fail on test server")
-		t.Errorf("failed to create client: %v", err)
-	}
-	if err = client.Hello(hostname); err != nil {
-		t.Errorf("failed to send HELO: %v", err)
-	}
-
-	tlsConnState := conn.ConnectionState()
-	if err = client.Auth(ScramSHA256PlusAuth("username", "password", &tlsConnState)); err != nil {
-		t.Errorf("failed to authenticate: %v", err)
 		}
+	})
 }
 
-func TestAuthSCRAMSHA1_fail(t *testing.T) {
+func TestNewClient(t *testing.T) {
-	hostname := "127.0.0.1"
+	t.Run("new client via Dial succeeds", func(t *testing.T) {
-	port := "2587"
+		ctx, cancel := context.WithCancel(context.Background())
-
+		defer cancel()
+		PortAdder.Add(1)
+		serverPort := int(TestServerPortBase + PortAdder.Load())
+		featureSet := "250-8BITMIME\r\n250-DSN\r\n250 SMTPUTF8"
 		go func() {
-		startSMTPServer(false, hostname, port, sha1.New)
+			if err := simpleSMTPServer(ctx, t, &serverProps{
-	}()
+				FeatureSet: featureSet,
-	time.Sleep(time.Millisecond * 500)
+				ListenPort: serverPort,
-
+			},
-	conn, err := net.Dial("tcp", fmt.Sprintf("%s:%s", hostname, port))
+			); err != nil {
-	if err != nil {
+				t.Errorf("failed to start test server: %s", err)
-		t.Errorf("failed to dial server: %v", err)
-	}
-	client, err := NewClient(conn, hostname)
-	if err != nil {
-		t.Errorf("failed to create client: %v", err)
-	}
-	if err = client.Hello(hostname); err != nil {
-		t.Errorf("failed to send HELO: %v", err)
-	}
-	if err = client.Auth(ScramSHA1Auth("username", "invalid")); err == nil {
-		t.Errorf("expected auth error, got nil")
-	}
-}
-
-func TestAuthSCRAMSHA256_fail(t *testing.T) {
-	hostname := "127.0.0.1"
-	port := "2588"
-
-	go func() {
-		startSMTPServer(false, hostname, port, sha256.New)
-	}()
-	time.Sleep(time.Millisecond * 500)
-
-	conn, err := net.Dial("tcp", fmt.Sprintf("%s:%s", hostname, port))
-	if err != nil {
-		t.Errorf("failed to dial server: %v", err)
-	}
-	client, err := NewClient(conn, hostname)
-	if err != nil {
-		t.Errorf("failed to create client: %v", err)
-	}
-	if err = client.Hello(hostname); err != nil {
-		t.Errorf("failed to send HELO: %v", err)
-	}
-	if err = client.Auth(ScramSHA256Auth("username", "invalid")); err == nil {
-		t.Errorf("expected auth error, got nil")
-	}
-}
-
-func TestAuthSCRAMSHA1PLUS_fail(t *testing.T) {
-	hostname := "127.0.0.1"
-	port := "2592"
-
-	go func() {
-		startSMTPServer(true, hostname, port, sha1.New)
-	}()
-	time.Sleep(time.Millisecond * 500)
-
-	cert, err := tls.X509KeyPair(localhostCert, localhostKey)
-	if err != nil {
-		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:%s", hostname, port), &tlsConfig)
-	if err != nil {
-		t.Errorf("failed to dial server: %v", err)
-	}
-	client, err := NewClient(conn, hostname)
-	if err != nil {
-		t.Errorf("failed to create client: %v", err)
-	}
-	if err = client.Hello(hostname); err != nil {
-		t.Errorf("failed to send HELO: %v", err)
-	}
-	tlsConnState := conn.ConnectionState()
-	if err = client.Auth(ScramSHA1PlusAuth("username", "invalid", &tlsConnState)); err == nil {
-		t.Errorf("expected auth error, got nil")
-	}
-}
-
-func TestAuthSCRAMSHA256PLUS_fail(t *testing.T) {
-	hostname := "127.0.0.1"
-	port := "2593"
-
-	go func() {
-		startSMTPServer(true, hostname, port, sha1.New)
 		}()
-	time.Sleep(time.Millisecond * 500)
+		time.Sleep(time.Millisecond * 30)
 
-	cert, err := tls.X509KeyPair(localhostCert, localhostKey)
+		client, err := Dial(fmt.Sprintf("%s:%d", TestServerAddr, serverPort))
 		if err != nil {
-		fmt.Printf("error creating TLS cert: %s", err)
+			t.Errorf("failed to create client: %s", err)
+		}
+		if err := client.Close(); err != nil {
+			t.Errorf("failed to close client: %s", err)
+		}
+	})
+	t.Run("new client via Dial fails on server not started", func(t *testing.T) {
+		_, err := Dial(fmt.Sprintf("%s:%d", TestServerAddr, 64000))
+		if err == nil {
+			t.Error("dial on non-existant server should fail")
+		}
+	})
+	t.Run("new client fails on server not available", func(t *testing.T) {
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+		PortAdder.Add(1)
+		serverPort := int(TestServerPortBase + PortAdder.Load())
+		featureSet := "250-8BITMIME\r\n250-DSN\r\n250 SMTPUTF8"
+		go func() {
+			if err := simpleSMTPServer(ctx, t, &serverProps{
+				FailOnDial: true,
+				FeatureSet: featureSet,
+				ListenPort: serverPort,
+			},
+			); err != nil {
+				t.Errorf("failed to start test server: %s", err)
 				return
 			}
-	tlsConfig := tls.Config{Certificates: []tls.Certificate{cert}, InsecureSkipVerify: true}
+		}()
+		time.Sleep(time.Millisecond * 30)
 
-	conn, err := tls.Dial("tcp", fmt.Sprintf("%s:%s", hostname, port), &tlsConfig)
+		_, err := Dial(fmt.Sprintf("%s:%d", TestServerAddr, serverPort))
+		if err == nil {
+			t.Error("connection to non-available server should fail")
+		}
+	})
+	t.Run("new client fails on faker that fails on close", func(t *testing.T) {
+		server := "442 service not available\r\n"
+		var wrote strings.Builder
+		var fake faker
+		fake.failOnClose = true
+		fake.ReadWriter = struct {
+			io.Reader
+			io.Writer
+		}{
+			strings.NewReader(server),
+			&wrote,
+		}
+		_, err := NewClient(fake, "faker.host")
+		if err == nil {
+			t.Error("connection to non-available server should fail on close")
+		}
+	})
+}
+
+func TestClient_hello(t *testing.T) {
+	t.Run("client fails on EHLO but not on HELO", func(t *testing.T) {
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+		PortAdder.Add(1)
+		serverPort := int(TestServerPortBase + PortAdder.Load())
+		featureSet := "250-8BITMIME\r\n250-DSN\r\n250 SMTPUTF8"
+		go func() {
+			if err := simpleSMTPServer(ctx, t, &serverProps{
+				FailOnEhlo: true,
+				FailOnHelo: 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.Errorf("failed to dial server: %v", err)
+			t.Errorf("failed to dial to test server: %s", err)
 		}
-	client, err := NewClient(conn, hostname)
+		if err = client.hello(); err == nil {
+			t.Error("helo should fail on test server")
+		}
+	})
+}
+
+func TestClient_Hello(t *testing.T) {
+	t.Run("normal client HELO/EHLO", func(t *testing.T) {
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+		PortAdder.Add(1)
+		serverPort := int(TestServerPortBase + PortAdder.Load())
+		featureSet := "250-8BITMIME\r\n250-DSN\r\n250 SMTPUTF8"
+		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.Errorf("failed to create client: %v", err)
+			t.Errorf("failed to dial to test server: %s", err)
 		}
-	if err = client.Hello(hostname); err != nil {
+		if err = client.Hello(TestServerAddr); err != nil {
-		t.Errorf("failed to send HELO: %v", err)
+			t.Errorf("failed to send HELO/EHLO to test server: %s", err)
 		}
-	tlsConnState := conn.ConnectionState()
+	})
-	if err = client.Auth(ScramSHA256PlusAuth("username", "invalid", &tlsConnState)); err == nil {
+	t.Run("client HELO/EHLO with empty name should fail", func(t *testing.T) {
-		t.Errorf("expected auth error, got nil")
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+		PortAdder.Add(1)
+		serverPort := int(TestServerPortBase + PortAdder.Load())
+		featureSet := "250-8BITMIME\r\n250-DSN\r\n250 SMTPUTF8"
+		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.Errorf("failed to dial to test server: %s", err)
+		}
+		if err = client.Hello(""); err == nil {
+			t.Error("HELO/EHLO with empty name should fail")
+		}
+	})
+	t.Run("client HELO/EHLO with newline in name should fail", func(t *testing.T) {
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+		PortAdder.Add(1)
+		serverPort := int(TestServerPortBase + PortAdder.Load())
+		featureSet := "250-8BITMIME\r\n250-DSN\r\n250 SMTPUTF8"
+		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.Errorf("failed to dial to test server: %s", err)
+		}
+		if err = client.Hello(TestServerAddr + "\r\n"); err == nil {
+			t.Error("HELO/EHLO with newline should fail")
+		}
+	})
+	t.Run("client double HELO/EHLO should fail", func(t *testing.T) {
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+		PortAdder.Add(1)
+		serverPort := int(TestServerPortBase + PortAdder.Load())
+		featureSet := "250-8BITMIME\r\n250-DSN\r\n250 SMTPUTF8"
+		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.Errorf("failed to dial to test server: %s", err)
+		}
+		if err = client.Hello(TestServerAddr); err != nil {
+			t.Errorf("failed to send HELO/EHLO to test server: %s", err)
+		}
+		if err = client.Hello(TestServerAddr); err == nil {
+			t.Error("double HELO/EHLO should fail")
+		}
+	})
+}
+
+func TestClient_cmd(t *testing.T) {
+	t.Run("cmd fails on textproto cmd", func(t *testing.T) {
+		server := "220 server ready\r\n"
+		var fake faker
+		fake.failOnClose = true
+		fake.ReadWriter = struct {
+			io.Reader
+			io.Writer
+		}{
+			strings.NewReader(server),
+			&failWriter{},
+		}
+		client, err := NewClient(fake, "faker.host")
+		if err != nil {
+			t.Errorf("failed to create client: %s", err)
+		}
+		_, _, err = client.cmd(250, "HELO faker.host")
+		if err == nil {
+			t.Error("cmd should fail on textproto cmd with broken writer")
+		}
+	})
 }
 
 // Issue 17794: don't send a trailing space on AUTH command when there's no password.
-func TestClientAuthTrimSpace(t *testing.T) {
+func TestClient_Auth_trimSpace(t *testing.T) {
 	server := "220 hello world\r\n" +
 		"200 some more"
 	var wrote strings.Builder
@@ -1655,7 +1711,7 @@ func TestClientAuthTrimSpace(t *testing.T) {
 	c.tls = true
 	c.didHello = true
 	_ = c.Auth(toServerEmptyAuth{})
-	if err := c.Close(); err != nil {
+	if err = c.Close(); err != nil {
 		t.Errorf("close failed: %s", err)
 	}
 	if got, want := wrote.String(), "AUTH FOOAUTH\r\n*\r\nQUIT\r\n"; got != want {
@@ -1663,19 +1719,15 @@ func TestClientAuthTrimSpace(t *testing.T) {
 	}
 }
 
-// toServerEmptyAuth is an implementation of Auth that only implements
+/*
-// the Start method, and returns "FOOAUTH", nil, nil. Notably, it returns
+
-// zero bytes for "toServer" so we can test that we don't send spaces at
+
-// the end of the line. See TestClientAuthTrimSpace.
+
-type toServerEmptyAuth struct{}
+
+
+
 
-func (toServerEmptyAuth) Start(_ *ServerInfo) (proto string, toServer []byte, err error) {
-	return "FOOAUTH", nil, nil
-}
 
-func (toServerEmptyAuth) Next(_ []byte, _ bool) (toServer []byte, err error) {
-	panic("unexpected call")
-}
 
 func TestBasic(t *testing.T) {
 	server := strings.Join(strings.Split(basicServer, "\n"), "\r\n")
@@ -3158,46 +3210,6 @@ func sendMail(hostPort string) error {
 	return SendMail(hostPort, nil, from, to, []byte("Subject: test\n\nhowdy!"))
 }
 
-// localhostCert is a PEM-encoded TLS cert generated from src/crypto/tls:
-//
-//	go run generate_cert.go --rsa-bits 1024 --host 127.0.0.1,::1,example.com \
-//		--ca --start-date "Jan 1 00:00:00 1970" --duration=1000000h
-var localhostCert = []byte(`
------BEGIN CERTIFICATE-----
-MIICFDCCAX2gAwIBAgIRAK0xjnaPuNDSreeXb+z+0u4wDQYJKoZIhvcNAQELBQAw
-EjEQMA4GA1UEChMHQWNtZSBDbzAgFw03MDAxMDEwMDAwMDBaGA8yMDg0MDEyOTE2
-MDAwMFowEjEQMA4GA1UEChMHQWNtZSBDbzCBnzANBgkqhkiG9w0BAQEFAAOBjQAw
-gYkCgYEA0nFbQQuOWsjbGtejcpWz153OlziZM4bVjJ9jYruNw5n2Ry6uYQAffhqa
-JOInCmmcVe2siJglsyH9aRh6vKiobBbIUXXUU1ABd56ebAzlt0LobLlx7pZEMy30
-LqIi9E6zmL3YvdGzpYlkFRnRrqwEtWYbGBf3znO250S56CCWH2UCAwEAAaNoMGYw
-DgYDVR0PAQH/BAQDAgKkMBMGA1UdJQQMMAoGCCsGAQUFBwMBMA8GA1UdEwEB/wQF
-MAMBAf8wLgYDVR0RBCcwJYILZXhhbXBsZS5jb22HBH8AAAGHEAAAAAAAAAAAAAAA
-AAAAAAEwDQYJKoZIhvcNAQELBQADgYEAbZtDS2dVuBYvb+MnolWnCNqvw1w5Gtgi
-NmvQQPOMgM3m+oQSCPRTNGSg25e1Qbo7bgQDv8ZTnq8FgOJ/rbkyERw2JckkHpD4
-n4qcK27WkEDBtQFlPihIM8hLIuzWoi/9wygiElTy/tVL3y7fGCvY2/k1KBthtZGF
-tN8URjVmyEo=
------END CERTIFICATE-----`)
-
-// localhostKey is the private key for localhostCert.
-var localhostKey = []byte(testingKey(`
------BEGIN RSA TESTING KEY-----
-MIICXgIBAAKBgQDScVtBC45ayNsa16NylbPXnc6XOJkzhtWMn2Niu43DmfZHLq5h
-AB9+Gpok4icKaZxV7ayImCWzIf1pGHq8qKhsFshRddRTUAF3np5sDOW3QuhsuXHu
-lkQzLfQuoiL0TrOYvdi90bOliWQVGdGurAS1ZhsYF/fOc7bnRLnoIJYfZQIDAQAB
-AoGBAMst7OgpKyFV6c3JwyI/jWqxDySL3caU+RuTTBaodKAUx2ZEmNJIlx9eudLA
-kucHvoxsM/eRxlxkhdFxdBcwU6J+zqooTnhu/FE3jhrT1lPrbhfGhyKnUrB0KKMM
-VY3IQZyiehpxaeXAwoAou6TbWoTpl9t8ImAqAMY8hlULCUqlAkEA+9+Ry5FSYK/m
-542LujIcCaIGoG1/Te6Sxr3hsPagKC2rH20rDLqXwEedSFOpSS0vpzlPAzy/6Rbb
-PHTJUhNdwwJBANXkA+TkMdbJI5do9/mn//U0LfrCR9NkcoYohxfKz8JuhgRQxzF2
-6jpo3q7CdTuuRixLWVfeJzcrAyNrVcBq87cCQFkTCtOMNC7fZnCTPUv+9q1tcJyB
-vNjJu3yvoEZeIeuzouX9TJE21/33FaeDdsXbRhQEj23cqR38qFHsF1qAYNMCQQDP
-QXLEiJoClkR2orAmqjPLVhR3t2oB3INcnEjLNSq8LHyQEfXyaFfu4U9l5+fRPL2i
-jiC0k/9L5dHUsF0XZothAkEA23ddgRs+Id/HxtojqqUT27B8MT/IGNrYsp4DvS/c
-qgkeluku4GjxRlDMBuXk94xOBEinUs+p/hwP1Alll80Tpg==
------END RSA TESTING KEY-----`))
-
-func testingKey(s string) string { return strings.ReplaceAll(s, "TESTING KEY", "PRIVATE KEY") }
-
 var flaky = flag.Bool("flaky", false, "run known-flaky tests too")
 
 func SkipFlaky(t testing.TB, issue int) {
@@ -3207,271 +3219,22 @@ func SkipFlaky(t testing.TB, issue int) {
 	}
 }
 
-// testSCRAMSMTPServer represents a test server for SCRAM-based SMTP authentication.
-// It does not do any acutal computation of the challenges but verifies that the expected
-// fields are present. We have actual real authentication tests for all SCRAM modes in the
-// go-mail client_test.go
-type testSCRAMSMTPServer struct {
-	authMechanism string
-	nonce         string
-	hostname      string
-	port          string
-	tlsServer     bool
-	h             func() hash.Hash
-}
-
-func (s *testSCRAMSMTPServer) handleConnection(conn net.Conn) {
-	defer func() {
-		_ = conn.Close()
-	}()
-
-	reader := bufio.NewReader(conn)
-	writer := bufio.NewWriter(conn)
-	writeLine := func(data string) error {
-		_, err := writer.WriteString(data + "\r\n")
-		if err != nil {
-			return fmt.Errorf("unable to write line: %w", err)
-		}
-		return writer.Flush()
-	}
-	writeOK := func() {
-		_ = writeLine("250 2.0.0 OK")
-	}
-
-	if err := writeLine("220 go-mail test server ready ESMTP"); err != nil {
-		return
-	}
-
-	data, err := reader.ReadString('\n')
-	if err != nil {
-		return
-	}
-	data = strings.TrimSpace(data)
-	if strings.HasPrefix(data, "EHLO") {
-		_ = writeLine(fmt.Sprintf("250-%s", s.hostname))
-		_ = writeLine("250-AUTH SCRAM-SHA-1 SCRAM-SHA-256")
-		writeOK()
-	} else {
-		_ = writeLine("500 Invalid command")
-		return
-	}
-
-	for {
-		data, err = reader.ReadString('\n')
-		if err != nil {
-			fmt.Printf("failed to read data: %v", err)
-		}
-		data = strings.TrimSpace(data)
-		if strings.HasPrefix(data, "AUTH") {
-			parts := strings.Split(data, " ")
-			if len(parts) < 2 {
-				_ = writeLine("500 Syntax error")
-				return
-			}
-
-			authMechanism := parts[1]
-			if authMechanism != "SCRAM-SHA-1" && authMechanism != "SCRAM-SHA-256" &&
-				authMechanism != "SCRAM-SHA-1-PLUS" && authMechanism != "SCRAM-SHA-256-PLUS" {
-				_ = writeLine("504 Unrecognized authentication mechanism")
-				return
-			}
-			s.authMechanism = authMechanism
-			_ = writeLine("334 ")
-			s.handleSCRAMAuth(conn)
-			return
-		} else {
-			_ = writeLine("500 Invalid command")
-		}
-	}
-}
-
-func (s *testSCRAMSMTPServer) handleSCRAMAuth(conn net.Conn) {
-	reader := bufio.NewReader(conn)
-	writer := bufio.NewWriter(conn)
-	writeLine := func(data string) error {
-		_, err := writer.WriteString(data + "\r\n")
-		if err != nil {
-			return fmt.Errorf("unable to write line: %w", err)
-		}
-		return writer.Flush()
-	}
-	var authMsg string
-
-	data, err := reader.ReadString('\n')
-	if err != nil {
-		_ = writeLine("535 Authentication failed")
-		return
-	}
-	data = strings.TrimSpace(data)
-	decodedMessage, err := base64.StdEncoding.DecodeString(data)
-	if err != nil {
-		_ = writeLine("535 Authentication failed")
-		return
-	}
-	splits := strings.Split(string(decodedMessage), ",")
-	if len(splits) != 4 {
-		_ = writeLine("535 Authentication failed - expected 4 parts")
-		return
-	}
-	if !s.tlsServer && splits[0] != "n" {
-		_ = writeLine("535 Authentication failed - expected n to be in the first part")
-		return
-	}
-	if s.tlsServer && !strings.HasPrefix(splits[0], "p=") {
-		_ = writeLine("535 Authentication failed - expected p= to be in the first part")
-		return
-	}
-	if splits[2] != "n=username" {
-		_ = writeLine("535 Authentication failed - expected n=username to be in the third part")
-		return
-	}
-	if !strings.HasPrefix(splits[3], "r=") {
-		_ = writeLine("535 Authentication failed - expected r= to be in the fourth part")
-		return
-	}
-	authMsg = splits[2] + "," + splits[3]
-
-	clientNonce := s.extractNonce(string(decodedMessage))
-	if clientNonce == "" {
-		_ = writeLine("535 Authentication failed")
-		return
-	}
-
-	s.nonce = clientNonce + "server_nonce"
-	serverFirstMessage := fmt.Sprintf("r=%s,s=%s,i=4096", s.nonce,
-		base64.StdEncoding.EncodeToString([]byte("salt")))
-	_ = writeLine(fmt.Sprintf("334 %s", base64.StdEncoding.EncodeToString([]byte(serverFirstMessage))))
-	authMsg = authMsg + "," + serverFirstMessage
-
-	data, err = reader.ReadString('\n')
-	if err != nil {
-		_ = writeLine("535 Authentication failed")
-		return
-	}
-	data = strings.TrimSpace(data)
-	decodedFinalMessage, err := base64.StdEncoding.DecodeString(data)
-	if err != nil {
-		_ = writeLine("535 Authentication failed")
-		return
-	}
-	splits = strings.Split(string(decodedFinalMessage), ",")
-
-	if !s.tlsServer && splits[0] != "c=biws" {
-		_ = writeLine("535 Authentication failed - expected c=biws to be in the first part")
-		return
-	}
-	if s.tlsServer {
-		if !strings.HasPrefix(splits[0], "c=") {
-			_ = writeLine("535 Authentication failed - expected c= to be in the first part")
-			return
-		}
-		channelBind, err := base64.StdEncoding.DecodeString(splits[0][2:])
-		if err != nil {
-			_ = writeLine("535 Authentication failed - base64 channel bind is not valid - " + err.Error())
-			return
-		}
-		if !strings.HasPrefix(string(channelBind), "p=") {
-			_ = writeLine("535 Authentication failed - expected channel binding to start with p=-")
-			return
-		}
-		cbType := string(channelBind[2:])
-		if !strings.HasPrefix(cbType, "tls-unique") && !strings.HasPrefix(cbType, "tls-exporter") {
-			_ = writeLine("535 Authentication failed - expected channel binding type tls-unique or tls-exporter")
-			return
-		}
-	}
-
-	if !strings.HasPrefix(splits[1], "r=") {
-		_ = writeLine("535 Authentication failed - expected r to be in the second part")
-		return
-	}
-	if !strings.Contains(splits[1], "server_nonce") {
-		_ = writeLine("535 Authentication failed - expected server_nonce to be in the second part")
-		return
-	}
-	if !strings.HasPrefix(splits[2], "p=") {
-		_ = writeLine("535 Authentication failed - expected p to be in the third part")
-		return
-	}
-
-	authMsg = authMsg + "," + splits[0] + "," + splits[1]
-	saltedPwd := pbkdf2.Key([]byte("password"), []byte("salt"), 4096, s.h().Size(), s.h)
-	mac := hmac.New(s.h, saltedPwd)
-	mac.Write([]byte("Server Key"))
-	skey := mac.Sum(nil)
-	mac.Reset()
-
-	mac = hmac.New(s.h, skey)
-	mac.Write([]byte(authMsg))
-	ssig := mac.Sum(nil)
-	mac.Reset()
-
-	serverFinalMessage := fmt.Sprintf("v=%s", base64.StdEncoding.EncodeToString(ssig))
-	_ = writeLine(fmt.Sprintf("334 %s", base64.StdEncoding.EncodeToString([]byte(serverFinalMessage))))
-
-	_, err = reader.ReadString('\n')
-	if err != nil {
-		_ = writeLine("535 Authentication failed")
-		return
-	}
-
-	_ = writeLine("235 Authentication successful")
-}
-
-func (s *testSCRAMSMTPServer) extractNonce(message string) string {
-	parts := strings.Split(message, ",")
-	for _, part := range parts {
-		if strings.HasPrefix(part, "r=") {
-			return part[2:]
-		}
-	}
-	return ""
-}
-
-func startSMTPServer(tlsServer bool, hostname, port string, h func() hash.Hash) {
-	server := &testSCRAMSMTPServer{
-		hostname:  hostname,
-		port:      port,
-		tlsServer: tlsServer,
-		h:         h,
-	}
-	listener, err := net.Listen("tcp", fmt.Sprintf("%s:%s", hostname, port))
-	if err != nil {
-		fmt.Printf("Failed to start SMTP server: %v", err)
-	}
-	defer func() {
-		_ = listener.Close()
-	}()
-
-	cert, err := tls.X509KeyPair(localhostCert, localhostKey)
-	if err != nil {
-		fmt.Printf("error creating TLS cert: %s", err)
-		return
-	}
-	tlsConfig := tls.Config{Certificates: []tls.Certificate{cert}}
-
-	for {
-		conn, err := listener.Accept()
-		if err != nil {
-			fmt.Printf("Failed to accept connection: %v", err)
-			continue
-		}
-		if server.tlsServer {
-			conn = tls.Server(conn, &tlsConfig)
-		}
-		go server.handleConnection(conn)
-	}
-}
-
 
 */
 
 // faker is a struct embedding io.ReadWriter to simulate network connections for testing purposes.
 type faker struct {
 	io.ReadWriter
+	failOnRead  bool
+	failOnClose bool
 }
 
-func (f faker) Close() error                     { return nil }
+func (f faker) Close() error {
+	if f.failOnClose {
+		return fmt.Errorf("faker: failed to close connection")
+	}
+	return nil
+}
 func (f faker) LocalAddr() net.Addr              { return nil }
 func (f faker) RemoteAddr() net.Addr             { return nil }
 func (f faker) SetDeadline(time.Time) error      { return nil }
@@ -3486,6 +3249,8 @@ type serverProps struct {
 	FailOnAuth      bool
 	FailOnDataInit  bool
 	FailOnDataClose bool
+	FailOnDial      bool
+	FailOnEhlo      bool
 	FailOnHelo      bool
 	FailOnMailFrom  bool
 	FailOnNoop      bool
@@ -3582,6 +3347,10 @@ func handleTestServerConnection(connection net.Conn, t *testing.T, props *server
 	}
 
 	if !props.IsTLS {
+		if props.FailOnDial {
+			writeLine("421 4.4.1 Service not available")
+			return
+		}
 		writeLine("220 go-mail test server ready ESMTP")
 	}
 
@@ -3595,9 +3364,9 @@ func handleTestServerConnection(connection net.Conn, t *testing.T, props *server
 		var datastring string
 		data = strings.TrimSpace(data)
 		switch {
-		case strings.HasPrefix(data, "EHLO"), strings.HasPrefix(data, "HELO"):
+		case strings.HasPrefix(data, "HELO"):
 			if len(strings.Split(data, " ")) != 2 {
-				writeLine("501 Syntax: EHLO hostname")
+				writeLine("501 Syntax: HELO hostname")
 				break
 			}
 			if props.FailOnHelo {
@@ -3605,6 +3374,16 @@ func handleTestServerConnection(connection net.Conn, t *testing.T, props *server
 				break
 			}
 			writeLine("250-localhost.localdomain\r\n" + props.FeatureSet)
+		case strings.HasPrefix(data, "EHLO"):
+			if len(strings.Split(data, " ")) != 2 {
+				writeLine("501 Syntax: EHLO hostname")
+				break
+			}
+			if props.FailOnEhlo {
+				writeLine("500 5.5.2 Error: fail on EHLO")
+				break
+			}
+			writeLine("250-localhost.localdomain\r\n" + props.FeatureSet)
 		case strings.HasPrefix(data, "MAIL FROM:"):
 			if props.FailOnMailFrom {
 				writeLine("500 5.5.2 Error: fail on MAIL FROM")
@@ -3886,3 +3665,24 @@ type randReader struct{}
 func (r *randReader) Read([]byte) (int, error) {
 	return 0, errors.New("broken reader")
 }
+
+// toServerEmptyAuth is an implementation of Auth that only implements
+// the Start method, and returns "FOOAUTH", nil, nil. Notably, it returns
+// zero bytes for "toServer" so we can test that we don't send spaces at
+// the end of the line. See TestClientAuthTrimSpace.
+type toServerEmptyAuth struct{}
+
+func (toServerEmptyAuth) Start(_ *ServerInfo) (proto string, toServer []byte, err error) {
+	return "FOOAUTH", nil, nil
+}
+
+func (toServerEmptyAuth) Next(_ []byte, _ bool) (toServer []byte, err error) {
+	return nil, fmt.Errorf("unexpected call")
+}
+
+// failWriter is a struct type that implements the io.Writer interface, but always returns an error on Write.
+type failWriter struct{}
+
+func (w *failWriter) Write([]byte) (int, error) {
+	return 0, errors.New("broken writer")
+}