WIP: add SetFddhcp

1 files changed, 35 insertions, 2 deletions

diff --git a/tun/tun_linux.go b/tun/tun_linux.go
index 12cd49f..bbc1888 100644
--- a/tun/tun_linux.go
+++ b/tun/tun_linux.go
@@ -29,6 +29,8 @@ const (
 
 type NativeTun struct {
 	tunFile                 *os.File
+	tunRdFile               *os.File
+	nextTunFile             *os.File
 	index                   int32      // if index
 	errors                  chan error // async error handling
 	events                  chan Event // device related events
@@ -358,6 +360,16 @@ func (tun *NativeTun) Write(bufs [][]byte, offset int) (int, error) {
 		if errors.Is(err, syscall.EBADFD) {
 			return total, os.ErrClosed
 		}
+
+		if tun.tunFile != tun.nextTunFile && errors.Is(err, os.ErrDeadlineExceeded) {
+			// Switch to new tunFile
+			tun.tunFile = tun.nextTunFile
+			n, err = tun.tunFile.Write(bufs[bufsI][offset:])
+			if errors.Is(err, syscall.EBADFD) {
+				return total, os.ErrClosed
+			}
+		}
+
 		if err != nil {
 			errs = errors.Join(errs, err)
 		} else {
@@ -452,7 +464,14 @@ func (tun *NativeTun) Read(bufs [][]byte, sizes []int, offset int) (int, error)
 		if tun.vnetHdr {
 			readInto = tun.readBuff[:]
 		}
-		n, err := tun.tunFile.Read(readInto)
+		n, err := tun.tunRdFile.Read(readInto)
+		if tun.tunRdFile != tun.nextTunFile && errors.Is(err, os.ErrDeadlineExceeded) {
+			// Old tun is empty. Retry with new tun.
+			tun.tunRdFile.Close()
+			tun.tunRdFile = tun.nextTunFile
+			n, err = tun.tunRdFile.Read(readInto)
+		}
+
 		if errors.Is(err, syscall.EBADFD) {
 			err = os.ErrClosed
 		}
@@ -468,6 +487,18 @@ func (tun *NativeTun) Read(bufs [][]byte, sizes []int, offset int) (int, error)
 	}
 }
 
+func (tun *NativeTun) SetFd(fd int) error {
+	err := unix.SetNonblock(fd, true)
+	if err != nil {
+		return err
+	}
+	oldTun := tun.tunFile
+	tun.nextTunFile = os.NewFile(uintptr(fd), "/dev/tunB")
+	tun.tunFile = tun.nextTunFile
+	oldTun.SetDeadline(time.Now()) // Release blocked in Read and Write
+	return nil
+}
+
 func (tun *NativeTun) Events() <-chan Event {
 	return tun.events
 }
@@ -572,6 +603,7 @@ func CreateTUN(name string, mtu int) (Device, error) {
 func CreateTUNFromFile(file *os.File, mtu int) (Device, error) {
 	tun := &NativeTun{
 		tunFile:                 file,
+		tunRdFile:               file,
 		events:                  make(chan Event, 5),
 		errors:                  make(chan error, 5),
 		statusListenersShutdown: make(chan struct{}),
@@ -621,7 +653,7 @@ func CreateTUNFromFile(file *os.File, mtu int) (Device, error) {
 
 // CreateUnmonitoredTUNFromFD creates a Device from the provided file
 // descriptor.
-func CreateUnmonitoredTUNFromFD(fd int) (Device, string, error) {
+func CreateUnmonitoredTUNFromFD(fd int) (*NativeTun, string, error) {
 	err := unix.SetNonblock(fd, true)
 	if err != nil {
 		return nil, "", err
@@ -629,6 +661,7 @@ func CreateUnmonitoredTUNFromFD(fd int) (Device, string, error) {
 	file := os.NewFile(uintptr(fd), "/dev/tun")
 	tun := &NativeTun{
 		tunFile:      file,
+		tunRdFile:    file,
 		events:       make(chan Event, 5),
 		errors:       make(chan error, 5),
 		tcp4GROTable: newTCPGROTable(),