Add separate handshake timeout

This PR adds a new setting to the config: `network.timeout`. This setting
defines a time period during which all handshake procedures and
ceremonies must be completed. If not - connection is aborted. This
should help in situations when connection is established but client
cannot continue for some reason (for example, RST sent by some middle box).

mtglib/proxy.go

@@ -28,6 +28,7 @@ type Proxy struct {
 	allowFallbackOnUnknownDC    bool
 	tolerateTimeSkewness        time.Duration
 	idleTimeout                 time.Duration
+	handshakeTimeout            time.Duration
 	domainFrontingPort          int
 	domainFrontingIP            string
 	domainFrontingProxyProtocol bool
@@ -66,6 +67,11 @@ func (p *Proxy) ServeConn(conn essentials.Conn) {
 	ctx := newStreamContext(p.ctx, p.logger, conn)
 	defer ctx.Close()
 
+	if err := ctx.clientConn.SetDeadline(time.Now().Add(p.handshakeTimeout)); err != nil {
+		ctx.logger.WarningError("cannot set handshake timeout", err)
+		return
+	}
+
 	stop := context.AfterFunc(ctx, func() {
 		ctx.Close()
 	})
@@ -97,6 +103,11 @@ func (p *Proxy) ServeConn(conn essentials.Conn) {
 		return
 	}
 
+	if err := ctx.clientConn.SetDeadline(time.Time{}); err != nil {
+		ctx.logger.WarningError("cannot set deadline", err)
+		return
+	}
+
 	if err := p.doTelegramCall(ctx); err != nil {
 		ctx.logger.WarningError("cannot dial to telegram", err)
 		return
@@ -346,6 +357,7 @@ func NewProxy(opts ProxyOpts) (*Proxy, error) {
 		domainFrontingIP:         opts.DomainFrontingIP,
 		tolerateTimeSkewness:     opts.getTolerateTimeSkewness(),
 		idleTimeout:              opts.getIdleTimeout(),
+		handshakeTimeout:         opts.getHandshakeTimeout(),
 		allowFallbackOnUnknownDC: opts.AllowFallbackOnUnknownDC,
 		telegram:                 tg,
 		doppelGanger: doppel.NewGanger(