DialerProxy: Fix SplitHTTP H3 dialerProxy (#3570)

* wip

* wip

* formatting

* cnc connection no longer needs to be a Packetconn

* dialerProxy: do not cancel connection when Dial context is cancelled

transport/internet/system_dialer.go

@@ -2,6 +2,7 @@ package internet
 
 import (
 	"context"
+	"math/rand"
 	"syscall"
 	"time"
 
@@ -48,7 +49,7 @@ func hasBindAddr(sockopt *SocketConfig) bool {
 }
 
 func (d *DefaultSystemDialer) Dial(ctx context.Context, src net.Address, dest net.Destination, sockopt *SocketConfig) (net.Conn, error) {
-	errors.LogDebug(ctx, "dialing to " + dest.String())
+	errors.LogDebug(ctx, "dialing to "+dest.String())
 
 	if dest.Network == net.Network_UDP && !hasBindAddr(sockopt) {
 		srcAddr := resolveSrcAddr(net.Network_UDP, src)
@@ -221,3 +222,29 @@ func RegisterDialerController(ctl control.Func) error {
 	dialer.controllers = append(dialer.controllers, ctl)
 	return nil
 }
+
+type FakePacketConn struct {
+	net.Conn
+}
+
+func (c *FakePacketConn) ReadFrom(p []byte) (n int, addr net.Addr, err error) {
+	n, err = c.Read(p)
+	return n, c.RemoteAddr(), err
+}
+
+func (c *FakePacketConn) WriteTo(p []byte, _ net.Addr) (n int, err error) {
+	return c.Write(p)
+}
+
+func (c *FakePacketConn) LocalAddr() net.Addr {
+	return &net.TCPAddr{
+		IP:   net.IP{byte(rand.Intn(256)), byte(rand.Intn(256)), byte(rand.Intn(256)), byte(rand.Intn(256))},
+		Port: rand.Intn(65536),
+	}
+}
+
+func (c *FakePacketConn) SetReadBuffer(bytes int) error {
+	// do nothing, this function is only there to suppress quic-go printing
+	// random warnings about UDP buffers to stdout
+	return nil
+}