Add echo buffer to SMTP server tests

Refactored SMTP server tests to use an echo buffer for capturing responses. This allows for better validation of command responses without relying on error messages. Additionally, added a new test case to validate a full SendMail transaction with TLS and authentication.

smtp/smtp_test.go

@@ -2215,11 +2215,12 @@ func TestClient_Mail(t *testing.T) {
 		PortAdder.Add(1)
 		serverPort := int(TestServerPortBase + PortAdder.Load())
 		featureSet := "250-8BITMIME\r\n250 STARTTLS"
+		echoBuffer := bytes.NewBuffer(nil)
 		go func() {
 			if err := simpleSMTPServer(ctx, t, &serverProps{
-				EchoCommandAsError: "MAIL FROM:",
+				EchoBuffer: echoBuffer,
-				FeatureSet:         featureSet,
+				FeatureSet: featureSet,
-				ListenPort:         serverPort,
+				ListenPort: serverPort,
 			},
 			); err != nil {
 				t.Errorf("failed to start test server: %s", err)
@@ -2237,13 +2238,13 @@ func TestClient_Mail(t *testing.T) {
 				t.Errorf("failed to close client: %s", err)
 			}
 		})
-		if err = client.Mail("valid-from@domain.tld"); err == nil {
+		if err = client.Mail("valid-from@domain.tld"); err != nil {
-			t.Error("server should echo the command as error but didn't")
+			t.Errorf("failed to set mail from address: %s", err)
 		}
-		sent := strings.Replace(err.Error(), "500 ", "", -1)
 		expected := "MAIL FROM:<valid-from@domain.tld> BODY=8BITMIME"
-		if !strings.EqualFold(sent, expected) {
+		resp := strings.Split(echoBuffer.String(), "\r\n")
-			t.Errorf("expected mail from command to be %q, but sent %q", expected, sent)
+		if !strings.EqualFold(resp[5], expected) {
+			t.Errorf("expected mail from command to be %q, but sent %q", expected, resp[5])
 		}
 	})
 	t.Run("from address and server supports SMTPUTF8", func(t *testing.T) {
@@ -2252,11 +2253,12 @@ func TestClient_Mail(t *testing.T) {
 		PortAdder.Add(1)
 		serverPort := int(TestServerPortBase + PortAdder.Load())
 		featureSet := "250-SMTPUTF8\r\n250 STARTTLS"
+		echoBuffer := bytes.NewBuffer(nil)
 		go func() {
 			if err := simpleSMTPServer(ctx, t, &serverProps{
-				EchoCommandAsError: "MAIL FROM:",
+				EchoBuffer: echoBuffer,
-				FeatureSet:         featureSet,
+				FeatureSet: featureSet,
-				ListenPort:         serverPort,
+				ListenPort: serverPort,
 			},
 			); err != nil {
 				t.Errorf("failed to start test server: %s", err)
@@ -2274,13 +2276,13 @@ func TestClient_Mail(t *testing.T) {
 				t.Errorf("failed to close client: %s", err)
 			}
 		})
-		if err = client.Mail("valid-from@domain.tld"); err == nil {
+		if err = client.Mail("valid-from@domain.tld"); err != nil {
-			t.Error("server should echo the command as error but didn't")
+			t.Errorf("failed to set mail from address: %s", err)
 		}
-		sent := strings.Replace(err.Error(), "500 ", "", -1)
 		expected := "MAIL FROM:<valid-from@domain.tld> SMTPUTF8"
-		if !strings.EqualFold(sent, expected) {
+		resp := strings.Split(echoBuffer.String(), "\r\n")
-			t.Errorf("expected mail from command to be %q, but sent %q", expected, sent)
+		if !strings.EqualFold(resp[5], expected) {
+			t.Errorf("expected mail from command to be %q, but sent %q", expected, resp[5])
 		}
 	})
 	t.Run("from address and server supports DSN", func(t *testing.T) {
@@ -2289,11 +2291,12 @@ func TestClient_Mail(t *testing.T) {
 		PortAdder.Add(1)
 		serverPort := int(TestServerPortBase + PortAdder.Load())
 		featureSet := "250-DSN\r\n250 STARTTLS"
+		echoBuffer := bytes.NewBuffer(nil)
 		go func() {
 			if err := simpleSMTPServer(ctx, t, &serverProps{
-				EchoCommandAsError: "MAIL FROM:",
+				EchoBuffer: echoBuffer,
-				FeatureSet:         featureSet,
+				FeatureSet: featureSet,
-				ListenPort:         serverPort,
+				ListenPort: serverPort,
 			},
 			); err != nil {
 				t.Errorf("failed to start test server: %s", err)
@@ -2315,10 +2318,10 @@ func TestClient_Mail(t *testing.T) {
 		if err = client.Mail("valid-from@domain.tld"); err == nil {
 			t.Error("server should echo the command as error but didn't")
 		}
-		sent := strings.Replace(err.Error(), "500 ", "", -1)
 		expected := "MAIL FROM:<valid-from@domain.tld> RET=FULL"
-		if !strings.EqualFold(sent, expected) {
+		resp := strings.Split(echoBuffer.String(), "\r\n")
-			t.Errorf("expected mail from command to be %q, but sent %q", expected, sent)
+		if !strings.EqualFold(resp[5], expected) {
+			t.Errorf("expected mail from command to be %q, but sent %q", expected, resp[5])
 		}
 	})
 	t.Run("from address and server supports DSN, SMTPUTF8 and 8BITMIME", func(t *testing.T) {
@@ -2327,11 +2330,12 @@ func TestClient_Mail(t *testing.T) {
 		PortAdder.Add(1)
 		serverPort := int(TestServerPortBase + PortAdder.Load())
 		featureSet := "250-DSN\r\n250-8BITMIME\r\n250-SMTPUTF8\r\n250 STARTTLS"
+		echoBuffer := bytes.NewBuffer(nil)
 		go func() {
 			if err := simpleSMTPServer(ctx, t, &serverProps{
-				EchoCommandAsError: "MAIL FROM:",
+				EchoBuffer: echoBuffer,
-				FeatureSet:         featureSet,
+				FeatureSet: featureSet,
-				ListenPort:         serverPort,
+				ListenPort: serverPort,
 			},
 			); err != nil {
 				t.Errorf("failed to start test server: %s", err)
@@ -2353,10 +2357,10 @@ func TestClient_Mail(t *testing.T) {
 		if err = client.Mail("valid-from@domain.tld"); err == nil {
 			t.Error("server should echo the command as error but didn't")
 		}
-		sent := strings.Replace(err.Error(), "500 ", "", -1)
 		expected := "MAIL FROM:<valid-from@domain.tld> BODY=8BITMIME SMTPUTF8 RET=FULL"
-		if !strings.EqualFold(sent, expected) {
+		resp := strings.Split(echoBuffer.String(), "\r\n")
-			t.Errorf("expected mail from command to be %q, but sent %q", expected, sent)
+		if !strings.EqualFold(resp[7], expected) {
+			t.Errorf("expected mail from command to be %q, but sent %q", expected, resp[7])
 		}
 	})
 }
@@ -2428,11 +2432,12 @@ func TestClient_Rcpt(t *testing.T) {
 		PortAdder.Add(1)
 		serverPort := int(TestServerPortBase + PortAdder.Load())
 		featureSet := "250-DSN\r\n250 STARTTLS"
+		echoBuffer := bytes.NewBuffer(nil)
 		go func() {
 			if err := simpleSMTPServer(ctx, t, &serverProps{
-				EchoCommandAsError: "RCPT TO:",
+				EchoBuffer: echoBuffer,
-				FeatureSet:         featureSet,
+				FeatureSet: featureSet,
-				ListenPort:         serverPort,
+				ListenPort: serverPort,
 			},
 			); err != nil {
 				t.Errorf("failed to start test server: %s", err)
@@ -2456,10 +2461,10 @@ func TestClient_Rcpt(t *testing.T) {
 		if err = client.Rcpt("valid-to@domain.tld"); err == nil {
 			t.Error("recpient address with newlines should fail")
 		}
-		sent := strings.Replace(err.Error(), "500 ", "", -1)
 		expected := "RCPT TO:<valid-to@domain.tld> NOTIFY=SUCCESS"
-		if !strings.EqualFold(sent, expected) {
+		resp := strings.Split(echoBuffer.String(), "\r\n")
-			t.Errorf("expected rcpt to command to be %q, but sent %q", expected, sent)
+		if !strings.EqualFold(resp[5], expected) {
+			t.Errorf("expected rcpt to command to be %q, but sent %q", expected, resp[5])
 		}
 	})
 }
@@ -2537,6 +2542,45 @@ func TestClient_Data(t *testing.T) {
 	})
 }
 
+func TestSendMail(t *testing.T) {
+	t.Run("full SendMail transaction with TLS and auth", func(t *testing.T) {
+		ctx, cancel := context.WithCancel(context.Background())
+		defer cancel()
+		PortAdder.Add(1)
+		serverPort := int(TestServerPortBase + PortAdder.Load())
+		featureSet := "250-AUTH LOGIN\r\n250-DSN\r\n250 STARTTLS"
+		echoBuffer := bytes.NewBuffer(nil)
+		go func() {
+			if err := simpleSMTPServer(ctx, t, &serverProps{
+				EchoBuffer: echoBuffer,
+				FeatureSet: featureSet,
+				ListenPort: serverPort,
+			},
+			); err != nil {
+				t.Errorf("failed to start test server: %s", err)
+				return
+			}
+		}()
+		time.Sleep(time.Millisecond * 30)
+		addr := fmt.Sprintf("%s:%d", TestServerAddr, serverPort)
+		testHookStartTLS = func(config *tls.Config) {
+			testConfig := getTLSConfig(t)
+			config.ServerName = testConfig.ServerName
+			config.RootCAs = testConfig.RootCAs
+			config.Certificates = testConfig.Certificates
+		}
+		auth := LoginAuth("username", "password", TestServerAddr, false)
+		if err := SendMail(addr, auth, "valid-from@domain.tld", []string{"valid-to@domain.tld"},
+			[]byte("test message")); err != nil {
+			t.Fatalf("failed to send mail: %s", err)
+		}
+		resp := strings.Split(echoBuffer.String(), "\r\n")
+		for i, line := range resp {
+			t.Logf("response line %d: %q", i, line)
+		}
+	})
+}
+
 /*
 func TestBasic(t *testing.T) {
 	server := strings.Join(strings.Split(basicServer, "\n"), "\r\n")
@@ -4055,28 +4099,28 @@ func testingKey(s string) string { return strings.ReplaceAll(s, "TESTING KEY", "
 
 // serverProps represents the configuration properties for the SMTP server.
 type serverProps struct {
-	EchoCommandAsError string
+	EchoBuffer      io.Writer
-	FailOnAuth         bool
+	FailOnAuth      bool
-	FailOnDataInit     bool
+	FailOnDataInit  bool
-	FailOnDataClose    bool
+	FailOnDataClose bool
-	FailOnDial         bool
+	FailOnDial      bool
-	FailOnEhlo         bool
+	FailOnEhlo      bool
-	FailOnHelo         bool
+	FailOnHelo      bool
-	FailOnMailFrom     bool
+	FailOnMailFrom  bool
-	FailOnNoop         bool
+	FailOnNoop      bool
-	FailOnQuit         bool
+	FailOnQuit      bool
-	FailOnReset        bool
+	FailOnReset     bool
-	FailOnSTARTTLS     bool
+	FailOnSTARTTLS  bool
-	FailTemp           bool
+	FailTemp        bool
-	FeatureSet         string
+	FeatureSet      string
-	ListenPort         int
+	ListenPort      int
-	HashFunc           func() hash.Hash
+	HashFunc        func() hash.Hash
-	IsSCRAMPlus        bool
+	IsSCRAMPlus     bool
-	IsTLS              bool
+	IsTLS           bool
-	SupportDSN         bool
+	SupportDSN      bool
-	SSLListener        bool
+	SSLListener     bool
-	TestSCRAM          bool
+	TestSCRAM       bool
-	VRFYUserUnknown    bool
+	VRFYUserUnknown bool
 }
 
 // simpleSMTPServer starts a simple TCP server that resonds to SMTP commands.
@@ -4151,6 +4195,11 @@ func handleTestServerConnection(connection net.Conn, t *testing.T, props *server
 		if err != nil {
 			t.Logf("failed to write line: %s", err)
 		}
+		if props.EchoBuffer != nil {
+			if _, err := props.EchoBuffer.Write([]byte(data + "\r\n")); err != nil {
+				t.Errorf("failed write to echo buffer: %s", err)
+			}
+		}
 		_ = writer.Flush()
 	}
 	writeOK := func() {
@@ -4171,13 +4220,15 @@ func handleTestServerConnection(connection net.Conn, t *testing.T, props *server
 			break
 		}
 		time.Sleep(time.Millisecond)
+		if props.EchoBuffer != nil {
+			if _, err = props.EchoBuffer.Write([]byte(data)); err != nil {
+				t.Errorf("failed write to echo buffer: %s", err)
+			}
+		}
 
 		var datastring string
 		data = strings.TrimSpace(data)
 		switch {
-		case props.EchoCommandAsError != "" && strings.HasPrefix(data, props.EchoCommandAsError):
-			writeLine("500 " + data)
-			break
 		case strings.HasPrefix(data, "HELO"):
 			if len(strings.Split(data, " ")) != 2 {
 				writeLine("501 Syntax: HELO hostname")
@@ -4260,6 +4311,11 @@ func handleTestServerConnection(connection net.Conn, t *testing.T, props *server
 					t.Logf("failed to read data from connection: %s", derr)
 					break
 				}
+				if props.EchoBuffer != nil {
+					if _, err = props.EchoBuffer.Write([]byte(ddata)); err != nil {
+						t.Errorf("failed write to echo buffer: %s", err)
+					}
+				}
 				ddata = strings.TrimSpace(ddata)
 				if ddata == "." {
 					if props.FailOnDataClose {