From fd248c6cb1873229b5e487045accdf7ed7ac822e Mon Sep 17 00:00:00 2001
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Wed, 28 Feb 2018 12:40:56 +0100
Subject: Support nopi mode

---
 tun_linux.go | 43 +++++++++++++++++++++++++++----------------
 1 file changed, 27 insertions(+), 16 deletions(-)

(limited to 'tun_linux.go')

diff --git a/tun_linux.go b/tun_linux.go
index 97973a7..da53907 100644
--- a/tun_linux.go
+++ b/tun_linux.go
@@ -27,6 +27,7 @@ type NativeTun struct {
 	name   string        // name of interface
 	errors chan error    // async error handling
 	events chan TUNEvent // device related events
+	nopi   bool          // the device was pased IFF_NO_PI
 }
 
 func toRTMGRP(sc uint) uint {
@@ -242,21 +243,25 @@ func (tun *NativeTun) MTU() (int, error) {
 
 func (tun *NativeTun) Write(buff []byte, offset int) (int, error) {
 
-	// reserve space for header
+	if tun.nopi {
+		buff = buff[offset:]
+	} else {
+		// reserve space for header
 
-	buff = buff[offset-4:]
+		buff = buff[offset-4:]
 
-	// add packet information header
+		// add packet information header
 
-	buff[0] = 0x00
-	buff[1] = 0x00
+		buff[0] = 0x00
+		buff[1] = 0x00
 
-	if buff[4] == ipv6.Version<<4 {
-		buff[2] = 0x86
-		buff[3] = 0xdd
-	} else {
-		buff[2] = 0x08
-		buff[3] = 0x00
+		if buff[4] == ipv6.Version<<4 {
+			buff[2] = 0x86
+			buff[3] = 0xdd
+		} else {
+			buff[2] = 0x08
+			buff[3] = 0x00
+		}
 	}
 
 	// write
@@ -269,12 +274,16 @@ func (tun *NativeTun) Read(buff []byte, offset int) (int, error) {
 	case err := <-tun.errors:
 		return 0, err
 	default:
-		buff := buff[offset-4:]
-		n, err := tun.fd.Read(buff[:])
-		if n < 4 {
-			return 0, err
+		if tun.nopi {
+			return tun.fd.Read(buff[offset:])
+		} else {
+			buff := buff[offset-4:]
+			n, err := tun.fd.Read(buff[:])
+			if n < 4 {
+				return 0, err
+			}
+			return n - 4, err
 		}
-		return n - 4, err
 	}
 }
 
@@ -292,6 +301,7 @@ func CreateTUNFromFile(name string, fd *os.File) (TUNDevice, error) {
 		name:   name,
 		events: make(chan TUNEvent, 5),
 		errors: make(chan error, 5),
+		nopi:   false,
 	}
 
 	// start event listener
@@ -349,6 +359,7 @@ func CreateTUN(name string) (TUNDevice, error) {
 		name:   newName,
 		events: make(chan TUNEvent, 5),
 		errors: make(chan error, 5),
+		nopi:   false,
 	}
 
 	// start event listener
-- 
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