Tunnel inbound: Support TPROXY on OpenBSD as well (#6546)

https://github.com/XTLS/Xray-core/pull/6546#issuecomment-5100711574

proxy/dokodemo/fakeudp_openbsd.go

@@ -0,0 +1,58 @@
+//go:build openbsd
+// +build openbsd
+
+package dokodemo
+
+import (
+	"fmt"
+	"net"
+	"os"
+
+	"golang.org/x/sys/unix"
+)
+
+func FakeUDP(addr *net.UDPAddr, mark int) (net.PacketConn, error) {
+	ip4 := addr.IP.To4()
+	if ip4 == nil {
+		return nil, &net.OpError{Op: "fake", Err: fmt.Errorf("IPv6 is not supported by the OpenBSD transparent UDP patch")}
+	}
+
+	fd, err := unix.Socket(unix.AF_INET, unix.SOCK_DGRAM, 0)
+	if err != nil {
+		return nil, &net.OpError{Op: "fake", Err: fmt.Errorf("socket open: %w", err)}
+	}
+
+	closeFD := true
+	defer func() {
+		if closeFD {
+			unix.Close(fd)
+		}
+	}()
+
+	if err = unix.SetsockoptInt(fd, unix.SOL_SOCKET, unix.SO_BINDANY, 1); err != nil {
+		return nil, &net.OpError{Op: "fake", Err: fmt.Errorf("set socket option SO_BINDANY: %w", err)}
+	}
+	if err = unix.SetsockoptInt(fd, unix.SOL_SOCKET, unix.SO_REUSEADDR, 1); err != nil {
+		return nil, &net.OpError{Op: "fake", Err: fmt.Errorf("set socket option SO_REUSEADDR: %w", err)}
+	}
+
+	sockaddr := &unix.SockaddrInet4{Port: addr.Port}
+	copy(sockaddr.Addr[:], ip4)
+	if err = unix.Bind(fd, sockaddr); err != nil {
+		return nil, &net.OpError{Op: "fake", Err: fmt.Errorf("bind %s: %w", addr.String(), err)}
+	}
+
+	fdFile := os.NewFile(uintptr(fd), fmt.Sprintf("net-udp-bindany-%s", addr.String()))
+	if fdFile == nil {
+		return nil, &net.OpError{Op: "fake", Err: fmt.Errorf("convert descriptor to file")}
+	}
+	defer fdFile.Close()
+
+	packetConn, err := net.FilePacketConn(fdFile)
+	if err != nil {
+		return nil, &net.OpError{Op: "fake", Err: fmt.Errorf("convert descriptor to packet connection: %w", err)}
+	}
+
+	closeFD = false
+	return packetConn, nil
+}

proxy/dokodemo/fakeudp_other.go

@@ -1,5 +1,5 @@
-//go:build !linux
-// +build !linux
+//go:build !linux && !openbsd
+// +build !linux,!openbsd
 
 package dokodemo