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pop3_server.go
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pop3_server.go
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package main
import (
"bufio"
"crypto/rand"
"crypto/tls"
"errors"
"fmt"
"net"
"os"
"strings"
)
type popState int
const (
stateUnauthorized popState = iota
stateTransaction
stateUpdate
)
const (
eol = "\r\n"
)
// POP3Server spawn a simple pop3 server which acts as a proxy to KUmail
func POP3Server(port int, secure bool) {
var err error
var netlistener net.Listener
tcpPort := fmt.Sprintf(":%d", port)
if secure {
var certificate tls.Certificate
certificate, err = tls.LoadX509KeyPair(Conf.POP.Cert, Conf.POP.Key)
if err != nil {
Log.Errorf("unable to load certificate: %s", err)
os.Exit(1)
}
config := tls.Config{
Certificates: []tls.Certificate{certificate},
ClientAuth: tls.NoClientCert,
MinVersion: tls.VersionTLS10,
}
config.Rand = rand.Reader
netlistener, err = tls.Listen("tcp", tcpPort, &config)
} else {
netlistener, err = net.Listen("tcp", tcpPort)
}
if err != nil {
Log.Errorf("listen error: %s", err)
os.Exit(1)
}
Log.Infof("POP3 server listening on port: %d", port)
if secure {
Log.Info("Using TLS")
}
for {
conn, err := netlistener.Accept()
if err != nil {
Log.Errorf("accept error: %s", err)
}
go handleConn(conn)
}
}
func handleConn(conn net.Conn) {
defer conn.Close()
kumailClient := new(KUmail)
var (
state = stateUnauthorized
)
reader := bufio.NewReader(conn)
writeClient(conn, "+OK simple KUmail POP3 -> IMAP proxy")
for {
line, err := reader.ReadString('\n')
if err != nil {
Log.Error(err.Error())
return
}
Log.Debugf("-> %s", line)
// Parse command
cmd, args := readCommand(line)
if cmd == "USER" && state == stateUnauthorized {
// accept username and wait for PASS command
username, _ := getSafeArgs(args, 0)
kumailClient.User = username
writeClient(conn, "+OK user accepted")
} else if cmd == "PASS" && state == stateUnauthorized {
pass, _ := getSafeArgs(args, 0)
settings, err := GetSettings(kumailClient.User)
if err != nil {
writeClient(conn, "-ERR unable to get user settings!")
return
}
if settings == nil {
writeClient(conn, "-ERR account not registered!")
return
}
kumailClient.Pass = pass
if kumailClient.Init(settings) {
writeClient(conn, "+OK pass accepted")
state = stateTransaction
} else {
writeClient(conn, "-ERR Username or password incorrect!")
}
} else if cmd == "CAPA" && state == stateTransaction {
writeClient(conn, "+OK Capability list follows")
writeClient(conn, "UIDL")
writeClient(conn, "USER")
writeClient(conn, ".")
} else if cmd == "UIDL" && state == stateTransaction {
list, err := kumailClient.UIDL()
if err != nil {
kumailClient.Close()
Log.Error(err.Error())
writeClient(conn, "-ERR unable to perform UIDL")
return
}
writeClient(conn, "+OK")
// TODO buffer this stuff and send as a single command?
for _, msg := range list {
writeClient(conn, "%s %d", msg.ID, msg.UID)
}
writeClient(conn, ".")
} else if cmd == "LIST" && state == stateTransaction {
list, total, err := kumailClient.ListAll()
if err != nil {
kumailClient.Close()
Log.Error(err.Error())
writeClient(conn, "-ERR unable to perform LIST")
return
}
writeClient(conn, "+OK %d messages (%d octets)", len(list), total)
// TODO buffer this stuff and send as a single command?
for _, msg := range list {
writeClient(conn, "%s %d", msg.ID, msg.size)
}
writeClient(conn, ".")
} else if cmd == "RETR" && state == stateTransaction {
id, _ := getSafeArgs(args, 0)
msg, octets, err := kumailClient.GetMessage(id)
if err != nil {
kumailClient.Close()
Log.Error(err.Error())
writeClient(conn, "-ERR no such message")
return
}
writeClient(conn, "+OK %d octets", octets)
// send message
fmt.Fprintf(conn, msg+eol)
writeClient(conn, ".")
} else if cmd == "DELE" && state == stateTransaction {
writeClient(conn, "-ERR you are not allowed to delete messages on this server")
} else if cmd == "QUIT" {
// take down IMAP connection
kumailClient.Close()
writeClient(conn, "+OK Bye bye!")
return
} else {
writeClient(conn, "-ERR invalid command")
return // close connection on invalid command
}
}
}
// read commands send by client
func readCommand(line string) (string, []string) {
line = strings.Trim(line, "\r \n")
cmd := strings.Split(line, " ")
return cmd[0], cmd[1:]
}
func getSafeArgs(args []string, n int) (string, error) {
if n < len(args) {
return args[n], nil
}
return "", errors.New("out of range")
}
// write message to client and print the message in the server log
func writeClient(conn net.Conn, msg string, args ...interface{}) {
fmt.Fprintf(conn, msg+eol, args...)
Log.Debugf("<- "+msg+eol, args...)
}