path: root/serve_imap.go

package main

import (
	"bufio"
	"fmt"
	"context"
	"crypto/tls"
	"io"
	"net"
	"strings"

	"github.com/jackc/pgx/v5/pgxpool"
	"go.lindenii.runxiyu.org/lindenii-common/clog"
)

type imap_server_state_t uint

const (
	imap_server_state_begin imap_server_state_t = iota
	imap_server_state_helo
	imap_server_state_mail
	imap_server_state_rcpt
)

type imap_recv_session struct {
	buf_conn       *bufio.ReadWriter
	net_conn       net.Conn
	tls_conn       *tls.Conn
	my_server_name string
	db             *pgxpool.Pool
}

func (session *imap_recv_session) handle(ctx context.Context) error {
	session.buf_conn = bufio.NewReadWriter(bufio.NewReader(session.net_conn), bufio.NewWriter(session.net_conn))
	session.buf_conn.WriteString("* OK [CAPABILITY IMAP4rev2 AUTH=PLAIN] " + VERSION + "\r\n")
	session.buf_conn.Flush()

	for {
		var tag, cmd, param string
		{
			line, err := session.buf_conn.ReadString('\n')
			if err != nil {
				if err == io.EOF {
					return err_connection_handler_eof
				}
				return err
			}
			line = strings.TrimSuffix(line, "\n")
			line = strings.TrimSuffix(line, "\r")
			tag_end := strings.IndexByte(line, ' ')
			if tag_end == -1 {
				session.buf_conn.WriteString(line+" BAD Error in IMAP command received by server.\r\n")
				session.buf_conn.Flush()
				continue
			}
			tag = line[:tag_end]
			rest := line[tag_end+1:]
			cmd_end := strings.IndexByte(rest, ' ')
			var param_start int
			if cmd_end == -1 {
				cmd_end = len(rest)
				param_start = len(rest)
			} else {
				param_start = cmd_end + 1
			}
			cmd = strings.ToUpper(rest[:cmd_end])
			param = rest[param_start:]
		}
		fmt.Printf("received tag=%s, cmd=%s, param=%s\n", tag, cmd, param)
	}
}

func imap_new_session(ctx context.Context, net_conn net.Conn) error {
	session := imap_recv_session{
		net_conn: net_conn,
	}
	return session.handle(ctx)
}

func serve_imap() {
	var imap_net, imap_addr string
	config_consistent_run(func() {
		imap_net = config.IMAP.Net
		imap_addr = config.IMAP.Addr
	})
	listener, err := net.Listen(imap_net, imap_addr)
	if err != nil {
		clog.Fatal(1, "IMAP: Cannot listen: "+err.Error())
	}
	defer listener.Close()
	clog.Info("IMAP: Listening via " + imap_net + " on " + imap_addr)

	for {
		conn, err := listener.Accept()
		if err != nil {
			clog.Error("IMAP: Cannot accept connection: " + err.Error())
		}
		clog.Info("IMAP: Accepted connection from " + conn.RemoteAddr().String())

		go func() {
			ctx, cancel := context.WithCancel(context.Background())
			defer cancel()
			err := imap_new_session(ctx, conn)
			if err != nil {
				if err == err_connection_handler_eof {
					clog.Info("IMAP: Connection for " + conn.RemoteAddr().String() + " closed with EOF")
				} else {
					clog.Error("IMAP: Connection handler for " + conn.RemoteAddr().String() + " returned error: " + err.Error())
				}
			} else {
				clog.Info("IMAP: Connection for " + conn.RemoteAddr().String() + " closed gracefully")
			}
		}()
	}
}