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package main
import (
"bufio"
"bytes"
"crypto/tls"
"net"
"slices"
"strings"
"go.lindenii.runxiyu.org/lindenii-common/mailkit"
)
type server_state_t uint
const (
server_state_begin server_state_t = iota
server_state_helo
server_state_mail
server_state_rcpt
)
func handle_incoming_server_connection(buf_conn *bufio.ReadWriter, net_conn *net.Conn) error {
var tls_conn *tls.Conn
var my_server_name string
var routes map[string]string
var tls_config *tls.Config
config_consistent_run(func() {
my_server_name = config.Server_name
routes = config.Routes
tls_config = config._tls_config
})
_, _ = buf_conn.WriteString("220 " + my_server_name + " " + VERSION + "\r\n")
_ = buf_conn.Flush()
server_state := server_state_begin
var remote_server_name string
var current_mail_from string
var current_rcpt_to []string
for {
line, err := buf_conn.ReadString('\n')
if err != nil {
return err
}
line = strings.TrimSuffix(line, "\n")
line = strings.TrimSuffix(line, "\r")
cmd_end := strings.IndexByte(line, ' ')
var param_start int
if cmd_end == -1 {
cmd_end = len(line)
param_start = len(line)
} else {
param_start = cmd_end + 1
}
cmd := strings.ToUpper(line[:cmd_end])
param := line[param_start:]
switch_cmd:
switch cmd {
case "STARTTLS":
if param != "" {
_, _ = buf_conn.WriteString("501 5.5.4 Syntax error (no parameters allowed)\r\n")
_ = buf_conn.Flush()
break
}
if tls_conn != nil {
_, _ = buf_conn.WriteString("554 5.5.1 Error: TLS already active\r\n")
_ = buf_conn.Flush()
break
}
_, _ = buf_conn.WriteString("220 2.0.0 Ready to start TLS\r\n")
_ = buf_conn.Flush()
tls_conn = tls.Server(*net_conn, tls_config)
buf_conn = bufio.NewReadWriter(bufio.NewReader(tls_conn), bufio.NewWriter(tls_conn))
server_state = server_state_begin
current_mail_from = ""
current_rcpt_to = []string{""}
case "HELO":
if param == "" { // TODO: actually validate the hostname
_, _ = buf_conn.WriteString("501 Syntax: HELO hostname\r\n")
_ = buf_conn.Flush()
break
}
remote_server_name = param
_ = remote_server_name // TODO
server_state = server_state_helo
_, _ = buf_conn.WriteString("250 " + my_server_name + "\r\n")
_ = buf_conn.Flush()
case "MAIL":
switch server_state {
case server_state_begin:
_, _ = buf_conn.WriteString("503 5.5.1 Error: send HELO/EHLO first\r\n")
_ = buf_conn.Flush()
break switch_cmd
case server_state_helo:
break
case server_state_mail:
_, _ = buf_conn.WriteString("503 5.5.1 Error: nested MAIL command\r\n")
_ = buf_conn.Flush()
break switch_cmd
}
if len(param) <= len("FROM:") || strings.ToUpper(param[:len("FROM:")]) != "FROM:" {
_, _ = buf_conn.WriteString("501 5.5.4 Syntax: MAIL FROM:<address>\r\n")
_ = buf_conn.Flush()
break
}
current_mail_from = param[len("FROM:"):]
current_rcpt_to = []string{}
server_state = server_state_mail
_, _ = buf_conn.WriteString("250 2.1.0 Ok\r\n")
_ = buf_conn.Flush()
// TODO: Address validation
case "RCPT":
if server_state != server_state_mail && server_state != server_state_rcpt {
_, _ = buf_conn.WriteString("503 5.5.1 Error: need MAIL command\r\n")
_ = buf_conn.Flush()
break
}
if len(param) <= len("TO:") || strings.ToUpper(param[:len("TO:")]) != "TO:" {
_, _ = buf_conn.WriteString("501 5.5.4 Syntax: RCPT TO:<address>\r\n")
_ = buf_conn.Flush()
break
}
recipient, _, _ := mailkit.Strip_angle_brackets(param[len("TO:"):])
_, ok := routes[recipient]
if !ok {
_, _ = buf_conn.WriteString("550 5.1.1 <" + recipient + ">: Recipient address rejected: User unknown in local recipient table\r\n")
_ = buf_conn.Flush()
break switch_cmd
}
current_rcpt_to = append(current_rcpt_to, recipient)
server_state = server_state_rcpt
_, _ = buf_conn.WriteString("250 2.1.5 Ok\r\n")
_ = buf_conn.Flush()
case "DATA":
if server_state != server_state_rcpt {
_, _ = buf_conn.WriteString("503 5.5.1 Error: need RCPT command\r\n")
_ = buf_conn.Flush()
break
}
_, _ = buf_conn.WriteString("354 End data with <CR><LF>.<CR><LF>\r\n")
_ = buf_conn.Flush()
var current_data []byte
for {
tmp, err := buf_conn.ReadSlice('\r')
if err != nil {
return err
}
// buf_conn.ReadSlice returns an internal buffer that gets
// overwritten on the next reader operation. So we must
// make a copy; also we have to allocate data_part to
// the correct length because [[builtin.copy]] copies
// min(len(dst), len(src)) items.
data_part := make([]byte, len(tmp))
copy(data_part, tmp)
next_four, err := buf_conn.Peek(4)
if err != nil {
return err
}
if bytes.Equal(next_four, []byte{'\n', '.', '\r', '\n'}) {
current_data = slices.Concat(current_data, data_part[:len(data_part)-1])
break
}
current_data = slices.Concat(current_data, data_part)
}
_, err := buf_conn.Discard(4)
if err != nil {
return err
}
{
inboxes_to_deliver_to := make(map[string]struct{})
for _, recipient := range current_rcpt_to {
inbox, ok := routes[recipient]
if !ok {
_, _ = buf_conn.WriteString("550 5.1.1 <" + recipient + ">: Recipient address rejected: User unknown in local recipient table\r\n")
break switch_cmd
}
inboxes_to_deliver_to[inbox] = struct{}{}
}
for inbox := range inboxes_to_deliver_to {
err = deliver_to_local_directory(current_mail_from, current_rcpt_to, current_data, inbox)
}
}
if err == nil {
_, _ = buf_conn.WriteString("250 2.0.0 Ok: Accepted\r\n")
} else {
_, _ = buf_conn.WriteString("500 2.0.0 Error: " + err.Error() + "\r\n")
}
_ = buf_conn.Flush()
server_state = server_state_helo
case "QUIT":
_, _ = buf_conn.WriteString("221 2.0.0 Bye\r\n")
_ = buf_conn.Flush()
return nil
case "NOOP":
_, _ = buf_conn.WriteString("250 2.0.0 Ok\r\n")
_ = buf_conn.Flush()
case "RSET":
if server_state != server_state_begin {
server_state = server_state_helo
}
_, _ = buf_conn.WriteString("250 2.0.0 Ok\r\n")
_ = buf_conn.Flush()
default:
_, _ = buf_conn.WriteString("500 5.5.2 Error: command not recognized\r\n")
_ = buf_conn.Flush()
}
}
}
|
