add go-tun2socks code

core/input.go

@@ -0,0 +1,127 @@
+package core
+
+/*
+#cgo CFLAGS: -I./c/include
+#include "lwip/pbuf.h"
+#include "lwip/tcp.h"
+
+err_t
+input(struct pbuf *p)
+{
+	return (*netif_list).input(p, netif_list);
+}
+*/
+import "C"
+import (
+	"encoding/binary"
+	"errors"
+	"unsafe"
+)
+
+type ipver byte
+
+const (
+	ipv4 = 4
+	ipv6 = 6
+)
+
+type proto byte
+
+const (
+	proto_icmp = 1
+	proto_tcp  = 6
+	proto_udp  = 17
+)
+
+func peekIPVer(p []byte) (ipver, error) {
+	if len(p) < 1 {
+		return 0, errors.New("short IP packet")
+	}
+	return ipver((p[0] & 0xf0) >> 4), nil
+}
+
+func moreFrags(ipv ipver, p []byte) bool {
+	switch ipv {
+	case ipv4:
+		if (p[6] & 0x20) > 0 /* has MF (More Fragments) bit set */ {
+			return true
+		}
+	case ipv6:
+		// FIXME Just too lazy to implement this for IPv6, for now
+		// returning true simply indicate do the copy anyway.
+		return true
+	}
+	return false
+}
+
+func fragOffset(ipv ipver, p []byte) uint16 {
+	switch ipv {
+	case ipv4:
+		return binary.BigEndian.Uint16(p[6:8]) & 0x1fff
+	case ipv6:
+		// FIXME Just too lazy to implement this for IPv6, for now
+		// returning a value greater than 0 simply indicate do the
+		// copy anyway.
+		return 1
+	}
+	return 0
+}
+
+func peekNextProto(ipv ipver, p []byte) (proto, error) {
+	switch ipv {
+	case ipv4:
+		if len(p) < 9 {
+			return 0, errors.New("short IPv4 packet")
+		}
+		return proto(p[9]), nil
+	case ipv6:
+		if len(p) < 6 {
+			return 0, errors.New("short IPv6 packet")
+		}
+		return proto(p[6]), nil
+	default:
+		return 0, errors.New("unknown IP version")
+	}
+}
+
+func Input(pkt []byte) (int, error) {
+	if len(pkt) == 0 {
+		return 0, nil
+	}
+
+	ipv, err := peekIPVer(pkt)
+	if err != nil {
+		return 0, err
+	}
+
+	nextProto, err := peekNextProto(ipv, pkt)
+	if err != nil {
+		return 0, err
+	}
+
+	lwipMutex.Lock()
+	defer lwipMutex.Unlock()
+
+	var buf *C.struct_pbuf
+
+	if nextProto == proto_udp && (!moreFrags(ipv, pkt) || fragOffset(ipv, pkt) > 0) {
+		// Copying data is not necessary for unfragmented UDP packets, and we would like to
+		// have all data in one pbuf.
+		buf = C.pbuf_alloc_reference(unsafe.Pointer(&pkt[0]), C.u16_t(len(pkt)), C.PBUF_REF)
+	} else {
+		// TODO Copy the data only when lwip need to keep it, e.g. in
+		// case we are returning ERR_CONN in tcpRecvFn.
+		//
+		// Allocating from PBUF_POOL results in a pbuf chain that may
+		// contain multiple pbufs.
+		buf = C.pbuf_alloc(C.PBUF_RAW, C.u16_t(len(pkt)), C.PBUF_POOL)
+		C.pbuf_take(buf, unsafe.Pointer(&pkt[0]), C.u16_t(len(pkt)))
+	}
+
+	ierr := C.input(buf)
+	if ierr != C.ERR_OK {
+		C.pbuf_free(buf)
+		return 0, errors.New("packet not handled")
+	}
+	return len(pkt), nil
+}