feat: implement SMTP server with authentication, port validation, and email storage

5 files changed, 157 insertions, 0 deletions

diff --git a/utils/smtp/constants.go b/utils/smtp/constants.go
new file mode 100644
index 0000000..cc6d173
--- /dev/null
+++ b/utils/smtp/constants.go
@@ -0,0 +1,5 @@
+package smtp
+
+const (
+	LOG_PREFIX = "SMTP"
+)
diff --git a/utils/smtp/server.go b/utils/smtp/server.go
new file mode 100644
index 0000000..0092c16
--- /dev/null
+++ b/utils/smtp/server.go
@@ -0,0 +1,56 @@
+package smtp
+
+import (
+	"dove/config"
+	"dove/messages"
+	"dove/utils/logger"
+	"fmt"
+	"time"
+
+	gosmtp "github.com/emersion/go-smtp"
+)
+
+var activeServers []serverInstance
+
+func Start() {
+	plainAddress := fmt.Sprintf("%s:%d", config.SMTP.Host, config.SMTP.Port)
+	plainServer := createServer(plainAddress)
+
+	activeServers = append(activeServers, serverInstance{server: plainServer, label: LOG_PREFIX})
+
+	go startListener(plainServer, LOG_PREFIX, plainAddress)
+}
+
+func Shutdown() {
+	for _, instance := range activeServers {
+		if shutdownError := instance.server.Close(); shutdownError != nil {
+			logger.Errorf(LOG_PREFIX, messages.SMTPShutdownFailed, instance.label, shutdownError)
+		}
+	}
+
+	logger.Infof(LOG_PREFIX, messages.SMTPShutdownComplete)
+}
+
+func createServer(address string) *gosmtp.Server {
+	smtpServer := gosmtp.NewServer(gosmtp.BackendFunc(func(connection *gosmtp.Conn) (gosmtp.Session, error) {
+		logger.Debugf(LOG_PREFIX, messages.SMTPSessionStarted, connection.Hostname())
+		return &session{}, nil
+	}))
+
+	smtpServer.Addr = address
+	smtpServer.Domain = config.SMTP.Domain
+	smtpServer.ReadTimeout = time.Duration(config.SMTP.ReadTimeout) * time.Second
+	smtpServer.WriteTimeout = time.Duration(config.SMTP.WriteTimeout) * time.Second
+	smtpServer.MaxMessageBytes = int64(config.SMTP.MaxMessageSize)
+	smtpServer.AllowInsecureAuth = true
+
+	return smtpServer
+}
+
+func startListener(smtpServer *gosmtp.Server, label string, address string) {
+	logger.Successf(LOG_PREFIX, messages.SMTPServerStarting, label, address)
+
+	if listenError := smtpServer.ListenAndServe(); listenError != nil {
+		logger.Fatalf(LOG_PREFIX, messages.SMTPListenFailed, label, listenError)
+	}
+}
diff --git a/utils/smtp/session.go b/utils/smtp/session.go
new file mode 100644
index 0000000..029c257
--- /dev/null
+++ b/utils/smtp/session.go
@@ -0,0 +1,61 @@
+package smtp
+
+import (
+	"dove/config"
+	"dove/messages"
+	"dove/utils/logger"
+	"dove/utils/errors"
+	"io"
+
+	gosmtp "github.com/emersion/go-smtp"
+)
+
+func (self *session) AuthPlain(username string, password string) error {
+	if !config.SMTP.AuthRequired {
+		return nil
+	}
+
+	if username != config.SMTP.Username || password != config.SMTP.Password {
+		logger.Warnf(LOG_PREFIX, messages.SMTPAuthFailed, username)
+		return errors.Error(messages.SMTPInvalidCredentials)
+	}
+
+	return nil
+}
+
+func (self *session) Mail(senderAddress string, mailOptions *gosmtp.MailOptions) error {
+	logger.Debugf(LOG_PREFIX, messages.SMTPMailFrom, senderAddress)
+	self.fromAddress = senderAddress
+	return nil
+}
+
+func (self *session) Rcpt(recipientAddress string, recipientOptions *gosmtp.RcptOptions) error {
+	logger.Debugf(LOG_PREFIX, messages.SMTPRecipient, recipientAddress)
+	self.toAddresses = append(self.toAddresses, recipientAddress)
+	return nil
+}
+
+func (self *session) Data(messageReader io.Reader) error {
+	rawMessage, readError := io.ReadAll(messageReader)
+	if readError != nil {
+		return readError
+	}
+
+	logger.Infof(LOG_PREFIX, messages.SMTPMessageReceived, len(rawMessage))
+
+	if storeError := storeMessage(self.fromAddress, self.toAddresses, rawMessage); storeError != nil {
+		logger.Errorf(LOG_PREFIX, messages.SMTPMessageStoreFailed, storeError)
+		return storeError
+	}
+
+	return nil
+}
+
+func (self *session) Reset() {
+	self.fromAddress = ""
+	self.toAddresses = nil
+}
+
+func (self *session) Logout() error {
+	return nil
+}
diff --git a/utils/smtp/storage.go b/utils/smtp/storage.go
new file mode 100644
index 0000000..b580d67
--- /dev/null
+++ b/utils/smtp/storage.go
@@ -0,0 +1,22 @@
+package smtp
+
+import (
+	"dove/config"
+	"fmt"
+	"os"
+	"path/filepath"
+	"time"
+)
+
+func storeMessage(fromAddress string, toAddresses []string, rawMessage []byte) error {
+	emailDirectory := filepath.Join(config.DataDir, "emails")
+
+	if directoryError := os.MkdirAll(emailDirectory, 0750); directoryError != nil {
+		return directoryError
+	}
+
+	filename := fmt.Sprintf("%d.eml", time.Now().UnixNano())
+	filePath := filepath.Join(emailDirectory, filename)
+
+	return os.WriteFile(filePath, rawMessage, 0640)
+}
\ No newline at end of file
diff --git a/utils/smtp/types.go b/utils/smtp/types.go
new file mode 100644
index 0000000..38c6504
--- /dev/null
+++ b/utils/smtp/types.go
@@ -0,0 +1,13 @@
+package smtp
+
+import gosmtp "github.com/emersion/go-smtp"
+
+type session struct {
+	fromAddress string
+	toAddresses []string
+}
+
+type serverInstance struct {
+	server *gosmtp.Server
+	label  string
+}