hid: add a work in progress IRC daemon

The port is more than viable but it's also sort of all-or-nothing
and versioning needs have come before I've had a chance to finish it.

3 files changed, 1629 insertions, 0 deletions

diff --git a/xS/hid-gen-replies.sh b/xS/hid-gen-replies.sh
new file mode 100755
index 0000000..c32b000
--- /dev/null
+++ b/xS/hid-gen-replies.sh
@@ -0,0 +1,16 @@
+#!/bin/sh
+LC_ALL=C exec awk '
+	/^[0-9]+ *(ERR|RPL)_[A-Z]+ *".*"$/ {
+		match($0, /".*"/);
+		ids[$1] = $2;
+		texts[$2] = substr($0, RSTART, RLENGTH);
+	}
+	END {
+		print "package " ENVIRON["GOPACKAGE"] "\n\nconst ("
+		for (i in ids)
+			printf("\t%s = %s\n", ids[i], i)
+		print ")\n\nvar defaultReplies = map[int]string{"
+		for (i in ids)
+			print "\t" ids[i] ": " texts[ids[i]] ","
+		print "}"
+	}'
diff --git a/xS/hid-replies b/xS/hid-replies
new file mode 100644
index 0000000..24affae
--- /dev/null
+++ b/xS/hid-replies
@@ -0,0 +1,87 @@
+1 RPL_WELCOME ":Welcome to the Internet Relay Network %s!%s@%s"
+2 RPL_YOURHOST ":Your host is %s, running version %s"
+3 RPL_CREATED ":This server was created %s"
+4 RPL_MYINFO "%s %s %s %s"
+5 RPL_ISUPPORT "%s :are supported by this server"
+211 RPL_STATSLINKINFO "%s %zu %zu %zu %zu %zu %lld"
+212 RPL_STATSCOMMANDS "%s %zu %zu %zu"
+219 RPL_ENDOFSTATS "%c :End of STATS report"
+221 RPL_UMODEIS "+%s"
+242 RPL_STATSUPTIME ":Server Up %d days %d:%02d:%02d"
+251 RPL_LUSERCLIENT ":There are %d users and %d services on %d servers"
+252 RPL_LUSEROP "%d :operator(s) online"
+253 RPL_LUSERUNKNOWN "%d :unknown connection(s)"
+254 RPL_LUSERCHANNELS "%d :channels formed"
+255 RPL_LUSERME ":I have %d clients and %d servers"
+301 RPL_AWAY "%s :%s"
+302 RPL_USERHOST ":%s"
+303 RPL_ISON ":%s"
+305 RPL_UNAWAY ":You are no longer marked as being away"
+306 RPL_NOWAWAY ":You have been marked as being away"
+311 RPL_WHOISUSER "%s %s %s * :%s"
+312 RPL_WHOISSERVER "%s %s :%s"
+313 RPL_WHOISOPERATOR "%s :is an IRC operator"
+314 RPL_WHOWASUSER "%s %s %s * :%s"
+315 RPL_ENDOFWHO "%s :End of WHO list"
+317 RPL_WHOISIDLE "%s %d :seconds idle"
+318 RPL_ENDOFWHOIS "%s :End of WHOIS list"
+319 RPL_WHOISCHANNELS "%s :%s"
+322 RPL_LIST "%s %d :%s"
+323 RPL_LISTEND ":End of LIST"
+324 RPL_CHANNELMODEIS "%s +%s"
+329 RPL_CREATIONTIME "%s %lld"
+331 RPL_NOTOPIC "%s :No topic is set"
+332 RPL_TOPIC "%s :%s"
+333 RPL_TOPICWHOTIME "%s %s %lld"
+341 RPL_INVITING "%s %s"
+346 RPL_INVITELIST "%s %s"
+347 RPL_ENDOFINVITELIST "%s :End of channel invite list"
+348 RPL_EXCEPTLIST "%s %s"
+349 RPL_ENDOFEXCEPTLIST "%s :End of channel exception list"
+351 RPL_VERSION "%s.%d %s :%s"
+352 RPL_WHOREPLY "%s %s %s %s %s %s :%d %s"
+353 RPL_NAMREPLY "%c %s :%s"
+364 RPL_LINKS "%s %s :%d %s"
+365 RPL_ENDOFLINKS "%s :End of LINKS list"
+366 RPL_ENDOFNAMES "%s :End of NAMES list"
+367 RPL_BANLIST "%s %s"
+368 RPL_ENDOFBANLIST "%s :End of channel ban list"
+369 RPL_ENDOFWHOWAS "%s :End of WHOWAS"
+372 RPL_MOTD ":- %s"
+375 RPL_MOTDSTART ":- %s Message of the day - "
+376 RPL_ENDOFMOTD ":End of MOTD command"
+391 RPL_TIME "%s :%s"
+401 ERR_NOSUCHNICK "%s :No such nick/channel"
+402 ERR_NOSUCHSERVER "%s :No such server"
+403 ERR_NOSUCHCHANNEL "%s :No such channel"
+404 ERR_CANNOTSENDTOCHAN "%s :Cannot send to channel"
+406 ERR_WASNOSUCHNICK "%s :There was no such nickname"
+409 ERR_NOORIGIN ":No origin specified"
+410 ERR_INVALIDCAPCMD "%s :%s"
+411 ERR_NORECIPIENT ":No recipient given (%s)"
+412 ERR_NOTEXTTOSEND ":No text to send"
+421 ERR_UNKNOWNCOMMAND "%s: Unknown command"
+422 ERR_NOMOTD ":MOTD File is missing"
+423 ERR_NOADMININFO "%s :No administrative info available"
+431 ERR_NONICKNAMEGIVEN ":No nickname given"
+432 ERR_ERRONEOUSNICKNAME "%s :Erroneous nickname"
+433 ERR_NICKNAMEINUSE "%s :Nickname is already in use"
+441 ERR_USERNOTINCHANNEL "%s %s :They aren't on that channel"
+442 ERR_NOTONCHANNEL "%s :You're not on that channel"
+443 ERR_USERONCHANNEL "%s %s :is already on channel"
+445 ERR_SUMMONDISABLED ":SUMMON has been disabled"
+446 ERR_USERSDISABLED ":USERS has been disabled"
+451 ERR_NOTREGISTERED ":You have not registered"
+461 ERR_NEEDMOREPARAMS "%s :Not enough parameters"
+462 ERR_ALREADYREGISTERED ":Unauthorized command (already registered)"
+467 ERR_KEYSET "%s :Channel key already set"
+471 ERR_CHANNELISFULL "%s :Cannot join channel (+l)"
+472 ERR_UNKNOWNMODE "%c :is unknown mode char to me for %s"
+473 ERR_INVITEONLYCHAN "%s :Cannot join channel (+i)"
+474 ERR_BANNEDFROMCHAN "%s :Cannot join channel (+b)"
+475 ERR_BADCHANNELKEY "%s :Cannot join channel (+k)"
+476 ERR_BADCHANMASK "%s :Bad Channel Mask"
+481 ERR_NOPRIVILEGES ":Permission Denied- You're not an IRC operator"
+482 ERR_CHANOPRIVSNEEDED "%s :You're not channel operator"
+501 ERR_UMODEUNKNOWNFLAG ":Unknown MODE flag"
+502 ERR_USERSDONTMATCH ":Cannot change mode for other users"
diff --git a/xS/main.go b/xS/main.go
new file mode 100644
index 0000000..72a6df0
--- /dev/null
+++ b/xS/main.go
@@ -0,0 +1,1526 @@
+//
+// Copyright (c) 2014 - 2018, Přemysl Janouch <p@janouch.name>
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+// SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+// OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+//
+
+// hid is a straight-forward port of kike IRCd from C.
+package main
+
+/*
+
+// ANSI terminal formatting, would be better if we had isatty() available
+func tf(text string, ansi string) string {
+	return "\x1b[0;" + ansi + "m" + text + "\x1b[0m"
+}
+
+func logErrorf(format string, args ...interface{}) {
+	fmt.Fprintf(os.Stderr, tf("error: "+format+"\n", "1;31"), args...)
+}
+
+func logFatalf(format string, args ...interface{}) {
+	fmt.Fprintf(os.Stderr, tf("fatal: "+format+"\n", "1;31"), args...)
+	os.Exit(1)
+}
+
+func logFatal(object interface{}) {
+	logFatalf("%s", object)
+}
+
+func getHome() (home string) {
+	if u, _ := user.Current(); u != nil {
+		home = u.HomeDir
+	} else {
+		home = os.Getenv("HOME")
+	}
+	return
+}
+
+// Only handling the simple case as that's what one mostly wants.
+// TODO(p): Handle the generic case as well.
+func expandTilde(path string) string {
+	if strings.HasPrefix(path, "~/") {
+		return getHome() + path[1:]
+	}
+	return path
+}
+
+func getXdgHomeDir(name, def string) string {
+	env := os.Getenv(name)
+	if env != "" && env[0] == '/' {
+		return env
+	}
+	return filepath.Join(getHome(), def)
+}
+
+// Retrieve all XDG base directories for configuration files
+func getXdgConfigDirs() (result []string) {
+	home := getXdgHomeDir("XDG_CONFIG_HOME", ".config")
+	if home != "" {
+		result = append(result, home)
+	}
+	dirs := os.Getenv("XDG_CONFIG_DIRS")
+	if dirs == "" {
+		dirs = "/etc/xdg"
+	}
+	for _, path := range strings.Split(dirs, ":") {
+		if path != "" {
+			result = append(result, path)
+		}
+	}
+	return
+}
+
+// Read a configuration file with the given basename w/o extension
+func readConfigFile(name string, output interface{}) error {
+	var suffix = filepath.Join(projectName, name+".json")
+	for _, path := range getXdgConfigDirs() {
+		full := filepath.Join(path, suffix)
+		file, err := os.Open(full)
+		if err != nil {
+			if !os.IsNotExist(err) {
+				return err
+			}
+			continue
+		}
+		defer file.Close()
+
+		decoder := json.NewDecoder(file)
+		err = decoder.Decode(output)
+		if err != nil {
+			return fmt.Errorf("%s: %s", full, err)
+		}
+		return nil
+	}
+	return errors.New("configuration file not found")
+}
+
+*/
+
+import (
+	"bufio"
+	"crypto/sha256"
+	"crypto/tls"
+	"encoding/hex"
+	"flag"
+	"fmt"
+	"io"
+	"log"
+	"net"
+	"os"
+	"os/signal"
+	"path/filepath"
+	"regexp"
+	"strconv"
+	"strings"
+	"syscall"
+	"time"
+)
+
+var debugMode = false
+
+// --- Utilities ---------------------------------------------------------------
+
+//
+// Trivial SSL/TLS autodetection. The first block of data returned by Recvfrom
+// must be at least three octets long for this to work reliably, but that should
+// not pose a problem in practice. We might try waiting for them.
+//
+//  SSL2:      1xxx xxxx | xxxx xxxx |    <1>
+//                (message length)  (client hello)
+//  SSL3/TLS:    <22>    |    <3>    | xxxx xxxx
+//            (handshake)|  (protocol version)
+//
+func detectTLS(sysconn syscall.RawConn) (isTLS bool) {
+	sysconn.Read(func(fd uintptr) (done bool) {
+		var buf [3]byte
+		n, _, err := syscall.Recvfrom(int(fd), buf[:], syscall.MSG_PEEK)
+		switch {
+		case n == 3:
+			isTLS = buf[0]&0x80 != 0 && buf[2] == 1
+			fallthrough
+		case n == 2:
+			isTLS = buf[0] == 22 && buf[1] == 3
+		case n == 1:
+			isTLS = buf[0] == 22
+		case err == syscall.EAGAIN:
+			return false
+		}
+		return true
+	})
+	return isTLS
+}
+
+// --- Configuration -----------------------------------------------------------
+
+// XXX: Do we really want to support default nil values?
+var config = []struct {
+	key         string // INI key
+	def         []rune // default value, may be nil
+	description string // documentation
+}{
+	// XXX: I'm not sure if Go will cooperate here.
+	{"pid_file", nil, "Path or name of the PID file"},
+	{"bind", []rune(":6667"), "Address of the IRC server"},
+}
+
+// --- Rate limiter ------------------------------------------------------------
+
+type floodDetector struct {
+	interval   uint    // interval for the limit
+	limit      uint    // maximum number of events allowed
+	timestamps []int64 // timestamps of last events
+	pos        uint    // index of the oldest event
+}
+
+func newFloodDetector(interval, limit uint) *floodDetector {
+	return &floodDetector{
+		interval:   interval,
+		limit:      limit,
+		timestamps: make([]int64, limit+1),
+		pos:        0,
+	}
+}
+
+func (fd *floodDetector) check() bool {
+	now := time.Now().Unix()
+	fd.timestamps[fd.pos] = now
+
+	fd.pos++
+	if fd.pos > fd.limit {
+		fd.pos = 0
+	}
+
+	var count uint
+	begin := now - int64(fd.interval)
+	for _, ts := range fd.timestamps {
+		if ts >= begin {
+			count++
+		}
+	}
+	return count <= fd.limit
+}
+
+// --- IRC protocol ------------------------------------------------------------
+
+//go:generate sh -c "./hid-gen-replies.sh > hid-replies.go < hid-replies"
+
+func ircToLower(c byte) byte {
+	switch c {
+	case '[':
+		return '{'
+	case ']':
+		return '}'
+	case '\\':
+		return '|'
+	case '~':
+		return '^'
+	}
+	if c >= 'A' && c <= 'Z' {
+		return c + ('a' - 'A')
+	}
+	return c
+}
+
+// TODO: To support ALL CAPS initialization of maps, perhaps we should use
+// ircToUpper instead.
+// FIXME: This doesn't follow the meaning of strxfrm and perhaps should be
+// renamed to ircNormalize.
+func ircStrxfrm(ident string) string {
+	var canon []byte
+	for _, c := range []byte(ident) {
+		canon = append(canon, ircToLower(c))
+	}
+	return string(canon)
+}
+
+func ircFnmatch(pattern string, s string) bool {
+	pattern, s = ircStrxfrm(pattern), ircStrxfrm(s)
+	// FIXME: This should not support [] ranges and handle / specially.
+	// We could translate the pattern to a regular expression.
+	matched, _ := filepath.Match(pattern, s)
+	return matched
+}
+
+// TODO: We will need to add support for IRCv3 tags.
+var reMsg = regexp.MustCompile(
+	`^(?::([^! ]*)(?:!([^@]*)@([^ ]*))? +)?([^ ]+)(.*)?$`)
+var reArgs = regexp.MustCompile(`:.*| [^: ][^ ]*`)
+
+type message struct {
+	nick    string   // optional nickname
+	user    string   // optional username
+	host    string   // optional hostname or IP address
+	command string   // command name
+	params  []string // arguments
+}
+
+// Everything as per RFC 2812
+const (
+	ircMaxNickname      = 9
+	ircMaxHostname      = 63
+	ircMaxChannelName   = 50
+	ircMaxMessageLength = 510
+)
+
+// TODO: Port the IRC token validation part as needed.
+
+const reClassSpecial = "\\[\\]\\\\`_^{|}"
+
+var (
+	// Extending ASCII to the whole range of Unicode letters.
+	reNickname = regexp.MustCompile(
+		`^[\pL` + reClassSpecial + `][\pL` + reClassSpecial + `0-9-]*$`)
+
+	// Notably, this won't match invalid UTF-8 characters, although the
+	// behaviour seems to be unstated in the documentation.
+	reUsername = regexp.MustCompile(`^[^\0\r\n @]+$`)
+
+	reChannelName = regexp.MustCompile(`^[^\0\7\r\n ,:]+$`)
+)
+
+func ircIsValidNickname(nickname string) bool {
+	return len(nickname) <= ircMaxNickname && reNickname.MatchString(nickname)
+}
+
+func ircIsValidUsername(username string) bool {
+	// XXX: We really should put a limit on this
+	// despite the RFC not mentioning one.
+	return reUsername.MatchString(username)
+}
+
+func ircIsValidChannelName(name string) bool {
+	return len(name) <= ircMaxChannelName && reChannelName.MatchString(name)
+}
+
+// --- Clients (equals users) --------------------------------------------------
+
+type connCloseWrite interface {
+	net.Conn
+	CloseWrite() error
+}
+
+const ircSupportedUserModes = "aiwros"
+
+const (
+	ircUserModeInvisible = 1 << iota
+	ircUserModeRxWallops
+	ircUserModeRestricted
+	ircUserModeOperator
+	ircUserModeRxServerNotices
+)
+
+const (
+	ircCapMultiPrefix = 1 << iota
+	ircCapInviteNotify
+	ircCapEchoMessage
+	ircCapUserhostInNames
+	ircCapServerTime
+)
+
+type client struct {
+	transport net.Conn       // underlying connection
+	tls       *tls.Conn      // TLS, if detected
+	conn      connCloseWrite // high-level connection
+	inQ       []byte         // unprocessed input
+	outQ      []byte         // unprocessed output
+	reading   bool           // whether a reading goroutine is running
+	writing   bool           // whether a writing goroutine is running
+	closing   bool           // whether we're closing the connection
+	killTimer *time.Timer    // hard kill timeout
+
+	opened            int64 // when the connection was opened
+	nSentMessages     uint  // number of sent messages total
+	sentBytes         int   // number of sent bytes total
+	nReceivedMessages uint  // number of received messages total
+	receivedBytes     int   // number of received bytes total
+
+	hostname string // hostname or IP shown to the network
+	port     string // port of the peer as a string
+	address  string // full network address
+
+	pingTimer      *time.Timer // we should send a PING
+	timeoutTimer   *time.Timer // connection seems to be dead
+	registered     bool        // the user has registered
+	capNegotiating bool        // negotiating capabilities
+	capsEnabled    uint        // enabled capabilities
+	capVersion     uint        // CAP protocol version
+
+	tlsCertFingerprint string // client certificate fingerprint
+
+	nickname string // IRC nickname (main identifier)
+	username string // IRC username
+	realname string // IRC realname (or e-mail)
+
+	mode        uint            // user's mode
+	awayMessage string          // away message
+	lastActive  int64           // last PRIVMSG, to get idle time
+	invites     map[string]bool // channel invitations by operators
+	antiflood   floodDetector   // flood detector
+}
+
+// --- Channels ----------------------------------------------------------------
+
+const ircSupportedChanModes = "ov" + "beI" + "imnqpst" + "kl"
+
+const (
+	ircChanModeInviteOnly = 1 << iota
+	ircChanModeModerated
+	ircChanModeNoOutsideMsgs
+	ircChanModeQuiet
+	ircChanModePrivate
+	ircChanModeSecret
+	ircChanModeProtectedTopic
+
+	ircChanModeOperator
+	ircChanModeVoice
+)
+
+type channel struct {
+	name      string // channel name
+	modes     uint   // channel modes
+	key       string // channel key
+	userLimit int    // user limit or -1
+	created   int64  // creation time
+
+	topic     string // channel topic
+	topicWho  string // who set the topic
+	topicTime int64  // when the topic was set
+
+	userModes map[*client]uint // modes for all channel users
+
+	banList       []string // ban list
+	exceptionList []string // exceptions from bans
+	inviteList    []string // exceptions from +I
+}
+
+func newChannel() *channel {
+	return &channel{userLimit: -1}
+}
+
+// TODO: Port struct channel methods.
+
+// --- IRC server context ------------------------------------------------------
+
+type whowasInfo struct {
+	nickname, username, realname, hostname string
+}
+
+func newWhowasInfo(c *client) *whowasInfo {
+	return &whowasInfo{
+		nickname: c.nickname,
+		username: c.username,
+		realname: c.realname,
+		hostname: c.hostname,
+	}
+}
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+type ircCommand struct {
+	name                 string
+	requiresRegistration bool
+	handler              func(*message, *client)
+
+	nReceived     uint // number of commands received
+	bytesReceived uint // number of bytes received total
+}
+
+type preparedEvent struct {
+	client *client
+	host   string // client's hostname or literal IP address
+	isTLS  bool   // the client seems to use TLS
+}
+
+type readEvent struct {
+	client *client
+	data   []byte // new data from the client
+	err    error  // read error
+}
+
+type writeEvent struct {
+	client  *client
+	written int   // amount of bytes written
+	err     error // write error
+}
+
+// TODO: Port server_context. Maybe we want to keep it in a struct?
+// XXX: Beware that maps with identifier keys need to be indexed correctly.
+// We might want to enforce accessor functions for users and channels.
+var (
+	started int64 // when has the server been started
+
+	users       map[string]*client  // maps nicknames to clients
+	channels    map[string]*channel // maps channel names to data
+	handlers    map[string]bool     // TODO message handlers
+	capHandlers map[string]bool     // TODO CAP message handlers
+
+	whowas map[string]*whowasInfo // WHOWAS registry
+
+	serverName     string          // our server name
+	pingInterval   uint            // ping interval in seconds
+	maxConnections int             // max connections allowed or 0
+	motd           []string        // MOTD (none if empty)
+	operators      map[string]bool // TLS certificate fingerprints for IRCops
+)
+
+var (
+	sigs     = make(chan os.Signal, 1)
+	conns    = make(chan net.Conn)
+	prepared = make(chan preparedEvent)
+	reads    = make(chan readEvent)
+	writes   = make(chan writeEvent)
+	timeouts = make(chan *client)
+
+	tlsConf  *tls.Config
+	clients  = make(map[*client]bool)
+	listener net.Listener
+	// TODO: quitting, quitTimer as they are named in kike?
+	inShutdown    bool
+	shutdownTimer <-chan time.Time
+)
+
+// Forcefully tear down all connections.
+func forceShutdown(reason string) {
+	if !inShutdown {
+		log.Fatalln("forceShutdown called without initiateShutdown")
+	}
+
+	log.Printf("forced shutdown (%s)\n", reason)
+	for c := range clients {
+		c.destroy("TODO")
+	}
+}
+
+// Initiate a clean shutdown of the whole daemon.
+func initiateShutdown() {
+	log.Println("shutting down")
+	if err := listener.Close(); err != nil {
+		log.Println(err)
+	}
+	for c := range clients {
+		c.closeLink("TODO")
+	}
+
+	shutdownTimer = time.After(5 * time.Second)
+	inShutdown = true
+}
+
+// TODO: ircChannelCreate
+
+func ircChannelDestroyIfEmpty(ch *channel) {
+	// TODO
+}
+
+// TODO: ircSendToRoommates
+// Broadcast to all /other/ clients (telnet-friendly, also in accordance to
+// the plan of extending this to an IRCd).
+func broadcast(line string, except *client) {
+	for c := range clients {
+		if c != except {
+			c.send(line)
+		}
+	}
+}
+
+func ircSendToRoommates(c *client, message string) {
+	// TODO
+}
+
+// --- Clients (continued) -----------------------------------------------------
+
+// TODO: Perhaps we should append to *[]byte for performance.
+func clientModeToString(m uint, mode *string) {
+	if 0 != m&ircUserModeInvisible {
+		*mode += "i"
+	}
+	if 0 != m&ircUserModeRxWallops {
+		*mode += "w"
+	}
+	if 0 != m&ircUserModeRestricted {
+		*mode += "r"
+	}
+	if 0 != m&ircUserModeOperator {
+		*mode += "o"
+	}
+	if 0 != m&ircUserModeRxServerNotices {
+		*mode += "s"
+	}
+}
+
+func (c *client) getMode() string {
+	mode := ""
+	if c.awayMessage != "" {
+		mode += "a"
+	}
+	clientModeToString(c.mode, &mode)
+	return mode
+}
+
+func (c *client) send(line string) {
+	if c.conn == nil || c.closing {
+		return
+	}
+
+	// TODO: Rename inQ and outQ to recvQ and sendQ as they are usually named.
+	oldOutQ := len(c.outQ)
+
+	// So far there's only one message tag we use, so we can do it simple;
+	// note that a 1024-character limit applies to messages with tags on.
+	if 0 != c.capsEnabled&ircCapServerTime {
+		c.outQ = time.Now().UTC().
+			AppendFormat(c.outQ, "@time=2006-01-02T15:04:05.000Z ")
+	}
+
+	bytes := []byte(line)
+	if len(bytes) > ircMaxMessageLength {
+		bytes = bytes[:ircMaxMessageLength]
+	}
+
+	// TODO: Kill the connection above some "SendQ" threshold (careful!)
+	c.outQ = append(c.outQ, bytes...)
+	c.outQ = append(c.outQ, "\r\n"...)
+	c.flushOutQ()
+
+	// Technically we haven't sent it yet but that's a minor detail
+	c.nSentMessages++
+	c.sentBytes += len(c.outQ) - oldOutQ
+}
+
+func (c *client) sendf(format string, a ...interface{}) {
+	c.send(fmt.Sprintf(format, a...))
+}
+
+func (c *client) addToWhowas() {
+	// Only keeping one entry for each nickname.
+	// TODO: Make sure this list doesn't get too long, for example by
+	// putting them in a linked list ordered by time.
+	whowas[ircStrxfrm(c.nickname)] = newWhowasInfo(c)
+}
+
+func (c *client) unregister(reason string) {
+	if !c.registered {
+		return
+	}
+
+	ircSendToRoommates(c, fmt.Sprintf(":%s!%s@%s QUIT :%s",
+		c.nickname, c.username, c.hostname, reason))
+
+	// The eventual QUIT message will take care of state at clients.
+	for _, ch := range channels {
+		delete(ch.userModes, c)
+		ircChannelDestroyIfEmpty(ch)
+	}
+
+	c.addToWhowas()
+	delete(users, ircStrxfrm(c.nickname))
+	c.nickname = ""
+	c.registered = false
+}
+
+// TODO: Rename to kill.
+// Close the connection and forget about the client.
+func (c *client) destroy(reason string) {
+	if reason == "" {
+		reason = "Client exited"
+	}
+	c.unregister(reason)
+
+	// TODO: Log the address; seems like we always have c.address.
+	log.Println("client destroyed")
+
+	// Try to send a "close notify" alert if the TLS object is ready,
+	// otherwise just tear down the transport.
+	if c.conn != nil {
+		_ = c.conn.Close()
+	} else {
+		_ = c.transport.Close()
+	}
+
+	// Clean up the goroutine, although a spurious event may still be sent.
+	// TODO: Other timers if needed.
+	if c.killTimer != nil {
+		c.killTimer.Stop()
+	}
+
+	delete(clients, c)
+}
+
+// Tear down the client connection, trying to do so in a graceful manner.
+func (c *client) closeLink(reason string) {
+	// Let's just cut the connection, the client can try again later.
+	// We also want to avoid accidentally writing to the socket before
+	// address resolution has finished.
+	if c.conn == nil {
+		c.destroy(reason)
+		return
+	}
+	if c.closing {
+		return
+	}
+
+	nickname := c.nickname
+	if nickname == "" {
+		nickname = "*"
+	}
+
+	// We push an "ERROR" message to the write buffer and let the writer send
+	// it, with some arbitrary timeout. The "closing" state makes sure
+	// that a/ we ignore any successive messages, and b/ that the connection
+	// is killed after the write buffer is transferred and emptied.
+	// (Since we send this message, we don't need to call CloseWrite here.)
+	c.sendf("ERROR :Closing link: %s[%s] (%s)",
+		nickname, c.hostname /* TODO host IP? */, reason)
+	c.closing = true
+
+	c.unregister(reason)
+	c.killTimer = time.AfterFunc(3*time.Second, func() {
+		timeouts <- c
+	})
+}
+
+func (c *client) inMaskList(masks []string) bool {
+	client := fmt.Sprintf("%s!%s@%s", c.nickname, c.username, c.hostname)
+	for _, mask := range masks {
+		if ircFnmatch(mask, client) {
+			return true
+		}
+	}
+	return false
+}
+
+func (c *client) getTLSCertFingerprint() string {
+	if c.tls == nil {
+		return ""
+	}
+
+	peerCerts := c.tls.ConnectionState().PeerCertificates
+	if len(peerCerts) == 0 {
+		return ""
+	}
+
+	hash := sha256.Sum256(peerCerts[0].Raw)
+	return hex.EncodeToString(hash[:])
+}
+
+// --- Timers ------------------------------------------------------------------
+
+// TODO
+
+// --- IRC command handling ----------------------------------------------------
+
+// XXX: ap doesn't really need to be a slice.
+func (c *client) makeReply(id int, ap []interface{}) string {
+	nickname := c.nickname
+	if nickname == "" {
+		nickname = "*"
+	}
+
+	s := fmt.Sprintf(":%s %03d %s ", serverName, id, nickname)
+	a := fmt.Sprintf(defaultReplies[id], ap...)
+	return s + a
+}
+
+// XXX: This way we cannot typecheck the arguments, so we must be careful.
+func (c *client) sendReply(id int, args ...interface{}) {
+	c.send(c.makeReply(id, args))
+}
+
+/// Send a space-separated list of words across as many replies as needed.
+func (c *client) sendReplyVector(id int, items []string, args ...interface{}) {
+	common := c.makeReply(id, args)
+
+	// We always send at least one message (there might be a client that
+	// expects us to send this message at least once).
+	for len(items) > 0 {
+		// If not even a single item fits in the limit (which may happen,
+		// in theory) it just gets cropped. We could also skip it.
+		reply := append([]byte(common), items[0]...)
+
+		// Append as many items as fits in a single message.
+		for len(items) > 0 &&
+			len(reply)+1+len(items[0]) <= ircMaxMessageLength {
+			reply = append(reply, ' ')
+			reply = append(reply, items[0]...)
+			items = items[1:]
+		}
+
+		c.send(string(reply))
+	}
+}
+
+func (c *client) sendMOTD() {
+	if len(motd) == 0 {
+		c.sendReply(ERR_NOMOTD)
+		return
+	}
+
+	c.sendReply(RPL_MOTDSTART, serverName)
+	for _, line := range motd {
+		c.sendReply(RPL_MOTD, line)
+	}
+	c.sendReply(RPL_ENDOFMOTD)
+}
+
+func (c *client) sendLUSERS() {
+	nUsers, nServices, nOpers, nUnknown := 0, 0, 0, 0
+	for c := range clients {
+		if c.registered {
+			nUsers++
+		} else {
+			nUnknown++
+		}
+		if 0 != c.mode&ircUserModeOperator {
+			nOpers++
+		}
+	}
+
+	nChannels := 0
+	for _, ch := range channels {
+		if 0 != ch.modes&ircChanModeSecret {
+			nChannels++
+		}
+	}
+
+	c.sendReply(RPL_LUSERCLIENT, nUsers, nServices, 1 /* servers total */)
+	if nOpers != 0 {
+		c.sendReply(RPL_LUSEROP, nOpers)
+	}
+	if nUnknown != 0 {
+		c.sendReply(RPL_LUSERUNKNOWN, nUnknown)
+	}
+	if nChannels != 0 {
+		c.sendReply(RPL_LUSERCHANNELS, nChannels)
+	}
+	c.sendReply(RPL_LUSERME, nUsers+nServices+nUnknown, 0 /* peer servers */)
+}
+
+func isThisMe(target string) bool {
+	// Target servers can also be matched by their users
+	if ircFnmatch(target, serverName) {
+		return true
+	}
+	_, ok := users[ircStrxfrm(target)]
+	return ok
+}
+
+func (c *client) sendISUPPORT() {
+	// Only # channels, +e supported, +I supported, unlimited arguments to MODE
+	c.sendReply(RPL_ISUPPORT, "CHANTYPES=# EXCEPTS INVEX MODES"+
+		" TARGMAX=WHOIS:,LIST:,NAMES:,PRIVMSG:1,NOTICE:1,KICK:"+
+		" NICKLEN=%d CHANNELLEN=%d", ircMaxNickname, ircMaxChannelName)
+}
+
+func (c *client) tryFinishRegistration() {
+	// TODO: Check if the realname is really required.
+	if c.nickname == "" || c.username == "" || c.realname == "" {
+		return
+	}
+	if c.registered || c.capNegotiating {
+		return
+	}
+
+	c.registered = true
+	c.sendReply(RPL_WELCOME, c.nickname, c.username, c.hostname)
+
+	c.sendReply(RPL_YOURHOST, serverName, "TODO version")
+	// The purpose of this message eludes me.
+	c.sendReply(RPL_CREATED, time.Unix(started, 0).Format("Mon, 02 Jan 2006"))
+	c.sendReply(RPL_MYINFO, serverName, "TODO version",
+		ircSupportedUserModes, ircSupportedChanModes)
+
+	c.sendISUPPORT()
+	c.sendLUSERS()
+	c.sendMOTD()
+
+	if mode := c.getMode(); mode != "" {
+		c.sendf(":%s MODE %s :+%s", c.nickname, c.nickname, mode)
+	}
+
+	c.tlsCertFingerprint = c.getTLSCertFingerprint()
+	if c.tlsCertFingerprint != "" {
+		c.sendf(":%s NOTICE %s :Your TLS client certificate fingerprint is %s",
+			serverName, c.nickname, c.tlsCertFingerprint)
+	}
+
+	delete(whowas, ircStrxfrm(c.nickname))
+}
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+// IRCv3 capability negotiation. See http://ircv3.org for details.
+
+type ircCapArgs struct {
+	subcommand string   // the subcommand being processed
+	fullParams string   // whole parameter string
+	params     []string // split parameters
+	target     string   // target parameter for replies
+}
+
+var ircCapTable = []struct {
+	flag uint   // flag
+	name string // name of the capability
+}{
+	{ircCapMultiPrefix, "multi-prefix"},
+	{ircCapInviteNotify, "invite-notify"},
+	{ircCapEchoMessage, "echo-message"},
+	{ircCapUserhostInNames, "userhost-in-names"},
+	{ircCapServerTime, "server-time"},
+}
+
+func (c *client) handleCAPLS(a *ircCapArgs) {
+	if len(a.params) == 1 {
+		if ver, err := strconv.ParseUint(a.params[0], 10, 32); err != nil {
+			c.sendReply(ERR_INVALIDCAPCMD, a.subcommand,
+				"Ignoring invalid protocol version number")
+		} else {
+			c.capVersion = uint(ver)
+		}
+	}
+
+	c.capNegotiating = true
+	c.sendf(":%s CAP %s LS :multi-prefix invite-notify echo-message"+
+		" userhost-in-names server-time", serverName, a.target)
+}
+
+func (c *client) handleCAPLIST(a *ircCapArgs) {
+	caps := []string{}
+	for _, cap := range ircCapTable {
+		if 0 != c.capsEnabled&cap.flag {
+			caps = append(caps, cap.name)
+		}
+	}
+
+	c.sendf(":%s CAP %s LIST :%s", serverName, a.target,
+		strings.Join(caps, " "))
+}
+
+func ircDecodeCapability(name string) uint {
+	for _, cap := range ircCapTable {
+		if cap.name == name {
+			return cap.flag
+		}
+	}
+	return 0
+}
+
+func (c *client) handleCAPREQ(a *ircCapArgs) {
+	c.capNegotiating = true
+
+	newCaps := c.capsEnabled
+	ok := true
+	for _, param := range a.params {
+		removing := false
+		name := param
+		if name[:1] == "-" {
+			removing = true
+			name = name[1:]
+		}
+
+		if cap := ircDecodeCapability(name); cap == 0 {
+			ok = false
+		} else if removing {
+			newCaps &= ^cap
+		} else {
+			newCaps |= cap
+		}
+	}
+
+	if ok {
+		c.capsEnabled = newCaps
+		c.sendf(":%s CAP %s ACK :%s", serverName, a.target, a.fullParams)
+	} else {
+		c.sendf(":%s CAP %s NAK :%s", serverName, a.target, a.fullParams)
+	}
+}
+
+func (c *client) handleCAPACK(a *ircCapArgs) {
+	if len(a.params) > 0 {
+		c.sendReply(ERR_INVALIDCAPCMD, a.subcommand,
+			"No acknowledgable capabilities supported")
+	}
+}
+
+func (c *client) handleCAPEND(a *ircCapArgs) {
+	c.capNegotiating = false
+	c.tryFinishRegistration()
+}
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+// TODO: Beware of case sensitivity, probably need to index it by ircStrxfrm,
+// which should arguably be named ircToLower and ircToUpper or something.
+var ircCapHandlers = map[string]func(*client, *ircCapArgs){
+	"LS":   (*client).handleCAPLS,
+	"LIST": (*client).handleCAPLIST,
+	"REQ":  (*client).handleCAPREQ,
+	"ACK":  (*client).handleCAPACK,
+	"END":  (*client).handleCAPEND,
+}
+
+// XXX: Maybe these also deserve to be methods for client?  They operato on
+// global state, though.
+
+func ircHandleCAP(msg *message, c *client) {
+	if len(msg.params) < 1 {
+		c.sendReply(ERR_NEEDMOREPARAMS, msg.command)
+		return
+	}
+
+	// TODO: This really does seem to warrant a method.
+	nickname := c.nickname
+	if nickname == "" {
+		nickname = "*"
+	}
+
+	args := &ircCapArgs{
+		target:     nickname,
+		subcommand: msg.params[0],
+		fullParams: "",
+		params:     []string{},
+	}
+
+	if len(msg.params) > 1 {
+		args.fullParams = msg.params[1]
+		// TODO: ignore_empty, likely create SplitSkipEmpty
+		args.params = strings.Split(args.fullParams, " ")
+	}
+
+	// FIXME: We should ASCII ToUpper the subcommand.
+	if fn, ok := ircCapHandlers[ircStrxfrm(args.subcommand)]; !ok {
+		c.sendReply(ERR_INVALIDCAPCMD, args.subcommand,
+			"Invalid CAP subcommand")
+	} else {
+		fn(c, args)
+	}
+}
+
+func ircHandlePASS(msg *message, c *client) {
+	if c.registered {
+		c.sendReply(ERR_ALREADYREGISTERED)
+	} else if len(msg.params) < 1 {
+		c.sendReply(ERR_NEEDMOREPARAMS, msg.command)
+	}
+
+	// We have TLS client certificates for this purpose; ignoring.
+}
+
+func ircHandleNICK(msg *message, c *client) {
+	if len(msg.params) < 1 {
+		c.sendReply(ERR_NONICKNAMEGIVEN)
+		return
+	}
+
+	nickname := msg.params[0]
+	if !ircIsValidNickname(nickname) {
+		c.sendReply(ERR_ERRONEOUSNICKNAME, nickname)
+		return
+	}
+
+	nicknameNormalized := ircStrxfrm(nickname)
+	if client, ok := users[nicknameNormalized]; ok && client != c {
+		c.sendReply(ERR_NICKNAMEINUSE, nickname)
+		return
+	}
+
+	if c.registered {
+		c.addToWhowas()
+
+		message := fmt.Sprintf(":%s!%s@%s NICK :%s",
+			c.nickname, c.username, c.hostname, nickname)
+		ircSendToRoommates(c, message)
+		c.send(message)
+	}
+
+	// Release the old nickname and allocate a new one.
+	if c.nickname != "" {
+		delete(users, ircStrxfrm(c.nickname))
+	}
+
+	c.nickname = nickname
+	users[nicknameNormalized] = c
+
+	c.tryFinishRegistration()
+}
+
+func ircHandleUSER(msg *message, c *client) {
+	if c.registered {
+		c.sendReply(ERR_ALREADYREGISTERED)
+		return
+	}
+	if len(msg.params) < 4 {
+		c.sendReply(ERR_NEEDMOREPARAMS, msg.command)
+		return
+	}
+
+	username, mode, realname := msg.params[0], msg.params[1], msg.params[3]
+
+	// Unfortunately the protocol doesn't give us any means of rejecting it
+	if !ircIsValidUsername(username) {
+		username = "*"
+	}
+
+	c.username = username
+	c.realname = realname
+
+	c.mode = 0
+	if m, err := strconv.ParseUint(mode, 10, 32); err != nil {
+		if 0 != m&4 {
+			c.mode |= ircUserModeRxWallops
+		}
+		if 0 != m&8 {
+			c.mode |= ircUserModeInvisible
+		}
+	}
+
+	c.tryFinishRegistration()
+}
+
+func ircHandleUSERHOST(msg *message, c *client) {
+	if len(msg.params) < 1 {
+		c.sendReply(ERR_NEEDMOREPARAMS, msg.command)
+		return
+	}
+
+	// TODO
+}
+
+func ircHandleLUSERS(msg *message, c *client) {
+	if len(msg.params) > 1 && !isThisMe(msg.params[1]) {
+		c.sendReply(ERR_NOSUCHSERVER, msg.params[1])
+		return
+	}
+	c.sendLUSERS()
+}
+
+func ircHandleMOTD(msg *message, c *client) {
+	if len(msg.params) > 0 && !isThisMe(msg.params[0]) {
+		c.sendReply(ERR_NOSUCHSERVER, msg.params[1])
+		return
+	}
+	c.sendMOTD()
+}
+
+func ircHandlePING(msg *message, c *client) {
+	// XXX: The RFC is pretty incomprehensible about the exact usage.
+	if len(msg.params) > 1 && !isThisMe(msg.params[1]) {
+		c.sendReply(ERR_NOSUCHSERVER, msg.params[1])
+	} else if len(msg.params) < 1 {
+		c.sendReply(ERR_NOORIGIN)
+	} else {
+		c.sendf(":%s PONG :%s", serverName, msg.params[0])
+	}
+}
+
+func ircHandlePONG(msg *message, c *client) {
+	// We are the only server, so we don't have to care too much.
+	if len(msg.params) < 1 {
+		c.sendReply(ERR_NOORIGIN)
+		return
+	}
+
+	// Set a new timer to send another PING
+	// TODO
+}
+
+func ircHandleQUIT(msg *message, c *client) {
+	reason := c.nickname
+	if len(msg.params) > 0 {
+		reason = msg.params[0]
+	}
+
+	c.closeLink("Quit: " + reason)
+}
+
+func ircHandleTIME(msg *message, c *client) {
+	if len(msg.params) > 0 && !isThisMe(msg.params[0]) {
+		c.sendReply(ERR_NOSUCHSERVER, msg.params[0])
+		return
+	}
+
+	c.sendReply(RPL_TIME, serverName,
+		time.Now().Format("Mon Jan _2 2006 15:04:05"))
+}
+
+func ircHandleVERSION(msg *message, c *client) {
+	if len(msg.params) > 0 && !isThisMe(msg.params[0]) {
+		c.sendReply(ERR_NOSUCHSERVER, msg.params[0])
+		return
+	}
+
+	postVersion := 0
+	if debugMode {
+		postVersion = 1
+	}
+
+	c.sendReply(RPL_VERSION, "TODO version", postVersion, serverName,
+		"TODO program name"+" "+"TODO version")
+	c.sendISUPPORT()
+}
+
+/*
+func ircChannelMulticast(ch *channel, msg string, except *client) {
+	for c, m := range ch.userModes {
+		if c != except {
+			c.send(msg)
+		}
+	}
+}
+
+func ircModifyMode(mask *uint, mode uint, add bool) bool {
+	orig := *mask
+	if add {
+		*mask |= mode
+	} else {
+		*mask &= ^mode
+	}
+	return *mask != orig
+}
+
+func ircUpdateUserMode(c *client, newMode uint) {
+	// TODO: Port, as well as all the other kike functions.
+}
+*/
+
+func ircHandleMODE(msg *message, c *client) {
+	if len(msg.params) < 1 {
+		c.sendReply(ERR_NEEDMOREPARAMS, msg.command)
+		return
+	}
+
+	// TODO
+	target := msg.params[0]
+	client := users[ircStrxfrm(target)]
+	ch := users[ircStrxfrm(target)]
+
+	if client != nil {
+		// TODO: Think about strcmp.
+		//if ircStrcmp(target, c.nickname) != 0 {
+		//}
+	} else if ch != nil {
+		// TODO
+	}
+}
+
+func ircHandleUserMessage(msg *message, c *client,
+	command string, allowAwayReply bool) {
+	if len(msg.params) < 1 {
+		c.sendReply(ERR_NORECIPIENT, msg.command)
+		return
+	}
+	if len(msg.params) < 2 || msg.params[1] == "" {
+		c.sendReply(ERR_NOTEXTTOSEND)
+		return
+	}
+
+	target, text := msg.params[0], msg.params[1]
+	if client, ok := users[ircStrxfrm(target)]; ok {
+		// TODO
+		_ = client
+		_ = text
+	} else if ch, ok := channels[ircStrxfrm(target)]; ok {
+		// TODO
+		_ = ch
+	} else {
+		c.sendReply(ERR_NOSUCHNICK, target)
+	}
+}
+
+// TODO: All the various real command handlers.
+
+func ircHandleX(msg *message, c *client) {
+}
+
+// --- ? -----------------------------------------------------------------------
+
+// Handle the results from initializing the client's connection.
+func (c *client) onPrepared(host string, isTLS bool) {
+	if isTLS {
+		c.tls = tls.Server(c.transport, tlsConf)
+		c.conn = c.tls
+	} else {
+		c.conn = c.transport.(connCloseWrite)
+	}
+
+	c.hostname = host
+	c.address = net.JoinHostPort(host, c.port)
+
+	// TODO: If we've tried to send any data before now, we need to flushOutQ.
+	go read(c)
+	c.reading = true
+}
+
+// Handle the results from trying to read from the client connection.
+func (c *client) onRead(data []byte, readErr error) {
+	if !c.reading {
+		// Abusing the flag to emulate CloseRead and skip over data, see below.
+		return
+	}
+
+	c.inQ = append(c.inQ, data...)
+	for {
+		// XXX: This accepts even simple LF newlines, even though they're not
+		// really allowed by the protocol.
+		advance, token, _ := bufio.ScanLines(c.inQ, false /* atEOF */)
+		if advance == 0 {
+			break
+		}
+
+		c.inQ = c.inQ[advance:]
+		line := string(token)
+		log.Printf("-> %s\n", line)
+
+		m := reMsg.FindStringSubmatch(line)
+		if m == nil {
+			log.Println("error: invalid line")
+			continue
+		}
+
+		msg := message{m[1], m[2], m[3], m[4], nil}
+		for _, x := range reArgs.FindAllString(m[5], -1) {
+			msg.params = append(msg.params, x[1:])
+		}
+
+		broadcast(line, c)
+	}
+
+	if readErr != nil {
+		c.reading = false
+
+		if readErr != io.EOF {
+			log.Println(readErr)
+			c.destroy("TODO")
+		} else if c.closing {
+			// Disregarding whether a clean shutdown has happened or not.
+			log.Println("client finished shutdown")
+			c.destroy("TODO")
+		} else {
+			log.Println("client EOF")
+			c.closeLink("")
+		}
+	} else if len(c.inQ) > 8192 {
+		log.Println("client inQ overrun")
+		c.closeLink("inQ overrun")
+
+		// tls.Conn doesn't have the CloseRead method (and it needs to be able
+		// to read from the TCP connection even for writes, so there isn't much
+		// sense in expecting the implementation to do anything useful),
+		// otherwise we'd use it to block incoming packet data.
+		c.reading = false
+	}
+}
+
+// Spawn a goroutine to flush the outQ if possible and necessary.
+func (c *client) flushOutQ() {
+	if !c.writing && c.conn != nil {
+		go write(c, c.outQ)
+		c.writing = true
+	}
+}
+
+// Handle the results from trying to write to the client connection.
+func (c *client) onWrite(written int, writeErr error) {
+	c.outQ = c.outQ[written:]
+	c.writing = false
+
+	if writeErr != nil {
+		log.Println(writeErr)
+		c.destroy("TODO")
+	} else if len(c.outQ) > 0 {
+		c.flushOutQ()
+	} else if c.closing {
+		if c.reading {
+			c.conn.CloseWrite()
+		} else {
+			c.destroy("TODO")
+		}
+	}
+}
+
+// --- Worker goroutines -------------------------------------------------------
+
+func accept(ln net.Listener) {
+	for {
+		if conn, err := ln.Accept(); err != nil {
+			// TODO: Consider specific cases in error handling, some errors
+			// are transitional while others are fatal.
+			log.Println(err)
+			break
+		} else {
+			conns <- conn
+		}
+	}
+}
+
+func prepare(client *client) {
+	conn := client.transport
+	host, _, err := net.SplitHostPort(conn.RemoteAddr().String())
+	if err != nil {
+		// In effect, we require TCP/UDP, as they have port numbers.
+		log.Fatalln(err)
+	}
+
+	// The Cgo resolver doesn't pthread_cancel getnameinfo threads, so not
+	// bothering with pointless contexts.
+	ch := make(chan string, 1)
+	go func() {
+		defer close(ch)
+		if names, err := net.LookupAddr(host); err != nil {
+			log.Println(err)
+		} else {
+			ch <- names[0]
+		}
+	}()
+
+	// While we can't cancel it, we still want to set a timeout on it.
+	select {
+	case <-time.After(5 * time.Second):
+	case resolved, ok := <-ch:
+		if ok {
+			host = resolved
+		}
+	}
+
+	// Note that in this demo application the autodetection prevents non-TLS
+	// clients from receiving any messages until they send something.
+	isTLS := false
+	if sysconn, err := conn.(syscall.Conn).SyscallConn(); err != nil {
+		// This is just for the TLS detection and doesn't need to be fatal.
+		log.Println(err)
+	} else {
+		isTLS = detectTLS(sysconn)
+	}
+
+	// FIXME: When the client sends no data, we still initialize its conn.
+	prepared <- preparedEvent{client, host, isTLS}
+}
+
+func read(client *client) {
+	// A new buffer is allocated each time we receive some bytes, because of
+	// thread-safety. Therefore the buffer shouldn't be too large, or we'd
+	// need to copy it each time into a precisely sized new buffer.
+	var err error
+	for err == nil {
+		var (
+			buf [512]byte
+			n   int
+		)
+		n, err = client.conn.Read(buf[:])
+		reads <- readEvent{client, buf[:n], err}
+	}
+}
+
+// Flush outQ, which is passed by parameter so that there are no data races.
+func write(client *client, data []byte) {
+	// We just write as much as we can, the main goroutine does the looping.
+	n, err := client.conn.Write(data)
+	writes <- writeEvent{client, n, err}
+}
+
+// --- Main --------------------------------------------------------------------
+
+func processOneEvent() {
+	select {
+	case <-sigs:
+		if inShutdown {
+			forceShutdown("requested by user")
+		} else {
+			initiateShutdown()
+		}
+
+	case <-shutdownTimer:
+		forceShutdown("timeout")
+
+	case conn := <-conns:
+		log.Println("accepted client connection")
+
+		// In effect, we require TCP/UDP, as they have port numbers.
+		address := conn.RemoteAddr().String()
+		host, port, err := net.SplitHostPort(address)
+		if err != nil {
+			log.Fatalln(err)
+		}
+
+		c := &client{
+			transport: conn,
+			address:   address,
+			hostname:  host,
+			port:      port,
+		}
+		clients[c] = true
+		go prepare(c)
+
+	case ev := <-prepared:
+		log.Println("client is ready:", ev.host)
+		if _, ok := clients[ev.client]; ok {
+			ev.client.onPrepared(ev.host, ev.isTLS)
+		}
+
+	case ev := <-reads:
+		log.Println("received data from client")
+		if _, ok := clients[ev.client]; ok {
+			ev.client.onRead(ev.data, ev.err)
+		}
+
+	case ev := <-writes:
+		log.Println("sent data to client")
+		if _, ok := clients[ev.client]; ok {
+			ev.client.onWrite(ev.written, ev.err)
+		}
+
+	case c := <-timeouts:
+		if _, ok := clients[c]; ok {
+			log.Println("client timeouted")
+			c.destroy("TODO")
+		}
+	}
+}
+
+func main() {
+	flag.BoolVar(&debugMode, "debug", false, "debug mode")
+	version := flag.Bool("version", false, "show version and exit")
+	flag.Parse()
+
+	// TODO: Consider using the same version number for all subprojects.
+	if *version {
+		fmt.Printf("%s %s\n", "hid", "0")
+		return
+	}
+
+	// TODO: Configuration--create an INI parser, probably;
+	//   lift XDG_CONFIG_HOME from gitlab-notifier.
+	if len(flag.Args()) != 3 {
+		log.Fatalf("usage: %s KEY CERT ADDRESS\n", os.Args[0])
+	}
+
+	cert, err := tls.LoadX509KeyPair(flag.Arg(1), flag.Arg(0))
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	tlsConf = &tls.Config{
+		Certificates:           []tls.Certificate{cert},
+		ClientAuth:             tls.RequestClientCert,
+		SessionTicketsDisabled: true,
+	}
+	listener, err = net.Listen("tcp", flag.Arg(2))
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	go accept(listener)
+	signal.Notify(sigs, syscall.SIGINT, syscall.SIGTERM)
+
+	for !inShutdown || len(clients) > 0 {
+		processOneEvent()
+	}
+}