--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/cmd/sievemgr/common.go	Mon Oct 26 14:19:24 2020 +0100
@@ -0,0 +1,192 @@
+// Copyright (C) 2020 Guido Berhoerster <guido+managesieve@berhoerster.name>
+//
+// Permission is hereby granted, free of charge, to any person obtaining
+// a copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to
+// permit persons to whom the Software is furnished to do so, subject to
+// the following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+// IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+// CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+// TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+// SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+package main
+
+import (
+	"bufio"
+	"crypto/tls"
+	"errors"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net"
+	"os"
+	"os/user"
+	"runtime"
+	"strings"
+
+	"go.guido-berhoerster.org/managesieve"
+	"golang.org/x/crypto/ssh/terminal"
+)
+
+var errTooBig = errors.New("too big")
+
+func parseHostPort(s string) (string, string, error) {
+	var host string
+	host, port, err := net.SplitHostPort(s)
+	if err != nil {
+		// error may be due to a missing port but there is no usable
+		// error value to test for, thus try again with a port added
+		var tmpErr error
+		host, _, tmpErr = net.SplitHostPort(s + ":4190")
+		if tmpErr != nil {
+			return "", "", err
+		}
+	}
+	if port == "" {
+		// no port given, try to look up a SRV record for given domain
+		// and fall back to the domain and port 4190
+		services, err := managesieve.LookupService(host)
+		if err != nil {
+			return "", "", err
+		}
+		host, port, err = net.SplitHostPort(services[0])
+		if err != nil {
+			return "", "", err
+		}
+	}
+	return host, port, nil
+}
+
+func readPassword() (string, error) {
+	var tty *os.File
+	var fd int
+	var w io.Writer
+	if runtime.GOOS == "windows" {
+		fd = int(os.Stdin.Fd())
+		w = os.Stdout
+	} else {
+		var err error
+		tty, err = os.OpenFile("/dev/tty", os.O_RDWR, 0666)
+		if err != nil {
+			return "", err
+		}
+		defer tty.Close()
+		fd = int(tty.Fd())
+		w = tty
+	}
+
+	io.WriteString(w, "Password: ")
+	rawPassword, err := terminal.ReadPassword(fd)
+	io.WriteString(w, "\n")
+	if err != nil {
+		return "", fmt.Errorf("failed to read password: %s", err)
+	}
+	password := string(rawPassword)
+	if password == "" {
+		return "", fmt.Errorf("invalid password")
+	}
+	return password, nil
+}
+
+func readPasswordFile(filename string) (string, error) {
+	f, err := os.Open(filename)
+	if err != nil {
+		return "", err
+	}
+	defer f.Close()
+	scanner := bufio.NewScanner(f)
+	if !scanner.Scan() {
+		err := scanner.Err()
+		if err == nil {
+			err = fmt.Errorf("failed to read from %q: unexpected EOF",
+				filename)
+		}
+		return "", err
+	}
+	password := scanner.Text()
+	if password == "" {
+		return "", fmt.Errorf("invalid password")
+	}
+	return password, nil
+}
+
+func usernamePassword(host, port, username, passwordFile string) (string, string, error) {
+	// fall back to the system username
+	if username == "" {
+		u, err := user.Current()
+		if err != nil {
+			return "", "",
+				fmt.Errorf("failed to obtain username: %s", err)
+		}
+		username = u.Username
+	}
+
+	var password string
+	var err error
+	if passwordFile != "" {
+		password, err = readPasswordFile(passwordFilename)
+	} else {
+		password, err = readPassword()
+	}
+	if err != nil {
+		return "", "", err
+	}
+
+	return username, password, nil
+}
+
+func dialPlainAuth(hostport, username, password string) (*managesieve.Client, error) {
+	c, err := managesieve.Dial(hostport)
+	if err != nil {
+		return nil, fmt.Errorf("failed to connect: %s", err)
+	}
+
+	host, _, _ := net.SplitHostPort(hostport)
+	// switch to a TLS connection except for localhost
+	if host != "localhost" && host != "127.0.0.1" && host != "::1" {
+		tlsConf := &tls.Config{
+			ServerName:         host,
+			InsecureSkipVerify: skipCertVerify,
+		}
+		if err := c.StartTLS(tlsConf); err != nil {
+			return nil,
+				fmt.Errorf("failed to start TLS connection: %s",
+					err)
+		}
+	}
+
+	auth := managesieve.PlainAuth("", username, password, host)
+	if err := c.Authenticate(auth); err != nil {
+		return nil, fmt.Errorf("failed to authenticate user %s: %s",
+			username, err)
+	}
+
+	return c, nil
+}
+
+func readLimitedString(r io.Reader, n int64) (string, error) {
+	var s strings.Builder
+	_, err := io.CopyN(&s, r, n)
+	if err == nil {
+		// check for EOF
+		_, err = io.CopyN(ioutil.Discard, r, 1)
+		if err == nil {
+			return s.String(), errTooBig
+		}
+	}
+	if err != io.EOF {
+		return s.String(), err
+	}
+
+	return s.String(), nil
+}