path: root/serve_imap.go

package main

import (
	"bufio"
	"context"
	"crypto/tls"
	"encoding/base64"
	"fmt"
	"io"
	"net"
	"strings"

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

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

const IMAP_CAPABILITIES = "CAPABILITY IMAP4rev2 AUTH=PLAIN"

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 [" + IMAP_CAPABILITIES + "] " + VERSION + "\r\n")
	_ = session.buf_conn.Flush()

	for {
		line, err := session.buf_conn.ReadString('\n')
		if err != nil {
			if err == io.EOF {
				return err_connection_handler_eof
			}
			return err
		}
		tag, cmd, param, err := parse_imap_line(line)
		if err != nil {
			_, _ = session.buf_conn.WriteString(line + " BAD " + err.Error() + "\r\n")
			_ = session.buf_conn.Flush()
			continue
		}
		clog.Debug(fmt.Sprintf("tag=%#v, cmd=%#v, param=%#v", tag, cmd, param))
	switch_cmd:
		switch cmd {
		case "CAPABILITY":
			_, _ = session.buf_conn.WriteString("* CAPABILITY " + IMAP_CAPABILITIES + "\r\n")
			_, _ = session.buf_conn.WriteString(tag + " OK CAPABILITY completed\r\n")
			_ = session.buf_conn.Flush()
		case "AUTHENTICATE":
			space_that_ends_the_method := strings.IndexByte(param, ' ')
			method := param[:space_that_ends_the_method]
			switch method {
			case "PLAIN":
				argument_base64 := param[space_that_ends_the_method+1:]
				if strings.IndexByte(argument_base64, ' ') != -1 {
					_, _ = session.buf_conn.WriteString(tag + " TODO too many parameters\r\n")
					_ = session.buf_conn.Flush()
					break switch_cmd
				}
				argument := make([]byte, base64.StdEncoding.DecodedLen(len(argument_base64)))
				_, err := base64.StdEncoding.Decode(argument, []byte(argument_base64))
				if err != nil {
					_, _ = session.buf_conn.WriteString(tag + " TODO cannot decode base64\r\n")
					_ = session.buf_conn.Flush()
					break switch_cmd
				}
				clog.Debug(fmt.Sprintf("argumetn=%#v", string(argument)))
			default:
				_, _ = session.buf_conn.WriteString(line + " TODO i don't know this authentication method\r\n")
				_ = session.buf_conn.Flush()
				break switch_cmd
			}
		}
	}
}

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, imap_trans string
	var tls_config *tls.Config
	config_consistent_run(func() {
		imap_net = config.IMAP.Net
		imap_addr = config.IMAP.Addr
		imap_trans = config.IMAP.Trans
		tls_config = config._tls_config
	})
	var listener net.Listener
	var err error
	switch imap_trans {
	case "tls", "":
		listener, err = tls.Listen(imap_net, imap_addr, tls_config)
		if err != nil {
			clog.Fatal(1, "IMAP: Cannot listen TLS: "+err.Error())
		}
	case "plain":
		listener, err = net.Listen(imap_net, imap_addr)
		if err != nil {
			clog.Fatal(1, "IMAP: Cannot listen plain: "+err.Error())
		}
	default:
		clog.Fatal(1, "IMAP: Invalid transport for listening")
	}

	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")
			}
		}()
	}
}