fix(dialer): prevent hang on HTTP+ICMP by enabling QUIC keepalive by default

The ICMP dialer required explicit keepalive:true to send QUIC PING frames,
while the regular QUIC dialer enabled keepalive by default (10s period).
Without PING frames, quic-go's 30s idle timeout silently killed connections,
causing HTTP+ICMP tunnels to hang after periods of inactivity.

Fixes go-gost/gost#352

Also in this commit:
- Release session mutex before calling GetConn() in both ICMP and QUIC
  dialers, so a dead session doesn't block all Dial() calls while
  OpenStreamSync blocks
- Add 30s timeout context to OpenStreamSync to prevent indefinite blocking
  if the QUIC session dies between liveness check and stream open
- Guard session cache deletion with pointer identity check to avoid
  evicting a newly created session during a race

dialer/icmp/conn.go

@@ -3,6 +3,7 @@ package quic
 import (
 	"context"
 	"net"
+	"time"
 
 	"github.com/quic-go/quic-go"
 )
@@ -12,7 +13,9 @@ type quicSession struct {
 }
 
 func (session *quicSession) GetConn() (*quicConn, error) {
-	stream, err := session.session.OpenStreamSync(context.Background())
+	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
+	defer cancel()
+	stream, err := session.session.OpenStreamSync(ctx)
 	if err != nil {
 		return nil, err
 	}

dialer/icmp/dialer.go

@@ -75,7 +75,6 @@ func (d *icmpDialer) Dial(ctx context.Context, addr string, opts ...dialer.DialO
 	}
 
 	d.sessionMutex.Lock()
-	defer d.sessionMutex.Unlock()
 
 	session, ok := d.sessions[addr]
 	if session != nil && session.IsClosed() {
@@ -95,6 +94,7 @@ func (d *icmpDialer) Dial(ctx context.Context, addr string, opts ...dialer.DialO
 			pc, err = icmp_pkg.ListenPacket("ip4:icmp", "")
 		}
 		if err != nil {
+			d.sessionMutex.Unlock()
 			return
 		}
 
@@ -109,16 +109,22 @@ func (d *icmpDialer) Dial(ctx context.Context, addr string, opts ...dialer.DialO
 		if err != nil {
 			d.logger.Error(err)
 			pc.Close()
+			d.sessionMutex.Unlock()
 			return nil, err
 		}
 
 		d.sessions[addr] = session
 	}
+	d.sessionMutex.Unlock()
 
 	conn, err = session.GetConn()
 	if err != nil {
+		d.sessionMutex.Lock()
+		if d.sessions[addr] == session {
+			delete(d.sessions, addr)
+		}
 		session.Close()
-		delete(d.sessions, addr)
+		d.sessionMutex.Unlock()
 		return nil, err
 	}
 

dialer/icmp/metadata.go

@@ -14,14 +14,21 @@ type metadata struct {
 }
 
 func (d *icmpDialer) parseMetadata(md mdata.Metadata) (err error) {
-	if mdutil.GetBool(md, "keepalive") {
-		d.md.keepAlivePeriod = mdutil.GetDuration(md, "ttl")
+	const (
+		keepAlive        = "keepAlive"
+		keepAlivePeriod  = "ttl"
+		handshakeTimeout = "handshakeTimeout"
+		maxIdleTimeout   = "maxIdleTimeout"
+	)
+
+	if md == nil || !md.IsExists(keepAlive) || mdutil.GetBool(md, keepAlive) {
+		d.md.keepAlivePeriod = mdutil.GetDuration(md, keepAlivePeriod)
 		if d.md.keepAlivePeriod <= 0 {
 			d.md.keepAlivePeriod = 10 * time.Second
 		}
 	}
-	d.md.handshakeTimeout = mdutil.GetDuration(md, "handshakeTimeout")
-	d.md.maxIdleTimeout = mdutil.GetDuration(md, "maxIdleTimeout")
+	d.md.handshakeTimeout = mdutil.GetDuration(md, handshakeTimeout)
+	d.md.maxIdleTimeout = mdutil.GetDuration(md, maxIdleTimeout)
 
 	return
 }

dialer/quic/conn.go

@@ -3,6 +3,7 @@ package quic
 import (
 	"context"
 	"net"
+	"time"
 
 	"github.com/quic-go/quic-go"
 )
@@ -12,7 +13,9 @@ type quicSession struct {
 }
 
 func (session *quicSession) GetConn() (*quicConn, error) {
-	stream, err := session.session.OpenStreamSync(context.Background())
+	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
+	defer cancel()
+	stream, err := session.session.OpenStreamSync(ctx)
 	if err != nil {
 		return nil, err
 	}

dialer/quic/dialer.go

@@ -58,7 +58,6 @@ func (d *quicDialer) Dial(ctx context.Context, addr string, opts ...dialer.DialO
 	}
 
 	d.sessionMutex.Lock()
-	defer d.sessionMutex.Unlock()
 
 	session, ok := d.sessions[addr]
 	if session != nil && session.IsClosed() {
@@ -73,11 +72,13 @@ func (d *quicDialer) Dial(ctx context.Context, addr string, opts ...dialer.DialO
 
 		c, err := options.Dialer.Dial(ctx, "udp", "")
 		if err != nil {
+			d.sessionMutex.Unlock()
 			return nil, err
 		}
 		pc, ok := c.(net.PacketConn)
 		if !ok {
 			c.Close()
+			d.sessionMutex.Unlock()
 			return nil, errors.New("quic: wrong connection type")
 		}
 
@@ -89,16 +90,22 @@ func (d *quicDialer) Dial(ctx context.Context, addr string, opts ...dialer.DialO
 		if err != nil {
 			d.logger.Error(err)
 			pc.Close()
+			d.sessionMutex.Unlock()
 			return nil, err
 		}
 
 		d.sessions[addr] = session
 	}
+	d.sessionMutex.Unlock()
 
 	conn, err = session.GetConn()
 	if err != nil {
+		d.sessionMutex.Lock()
+		if d.sessions[addr] == session {
+			delete(d.sessions, addr)
+		}
 		session.Close()
-		delete(d.sessions, addr)
+		d.sessionMutex.Unlock()
 		return nil, err
 	}