add SMTP support

it will be used in future update to add email sending capabilities

cmd/smtptest.go

@@ -0,0 +1,54 @@
+package cmd
+
+import (
+	"os"
+
+	"github.com/rs/zerolog"
+	"github.com/spf13/cobra"
+
+	"github.com/drakkan/sftpgo/v2/config"
+	"github.com/drakkan/sftpgo/v2/logger"
+	"github.com/drakkan/sftpgo/v2/smtp"
+	"github.com/drakkan/sftpgo/v2/util"
+)
+
+var (
+	smtpTestRecipient string
+	smtpTestCmd       = &cobra.Command{
+		Use:   "smtptest",
+		Short: "Test the SMTP configuration",
+		Long: `SFTPGo will try to send a test email to the specified recipient.
+If the SMTP configuration is correct you should receive this email.`,
+		Run: func(cmd *cobra.Command, args []string) {
+			logger.DisableLogger()
+			logger.EnableConsoleLogger(zerolog.DebugLevel)
+			configDir = util.CleanDirInput(configDir)
+			err := config.LoadConfig(configDir, configFile)
+			if err != nil {
+				logger.WarnToConsole("Unable to initialize data provider, config load error: %v", err)
+				os.Exit(1)
+			}
+			smtpConfig := config.GetSMTPConfig()
+			err = smtpConfig.Initialize()
+			if err != nil {
+				logger.ErrorToConsole("unable to initialize SMTP configuration: %v", err)
+				os.Exit(1)
+			}
+			err = smtp.SendEmail(smtpTestRecipient, "SFTPGo - Testing Email Settings", "It appears your SFTPGo email is setup correctly!",
+				smtp.EmailContentTypeTextPlain)
+			if err != nil {
+				logger.WarnToConsole("Error sending email: %v", err)
+				os.Exit(1)
+			}
+			logger.InfoToConsole("No errors were reported while sending an email. Please check your inbox to make sure.")
+		},
+	}
+)
+
+func init() {
+	addConfigFlags(smtpTestCmd)
+	smtpTestCmd.Flags().StringVar(&smtpTestRecipient, "recipient", "", `email address to send the test e-mail to`)
+	smtpTestCmd.MarkFlagRequired("recipient") //nolint:errcheck
+
+	rootCmd.AddCommand(smtpTestCmd)
+}