add darwin support for point-to-point TUN and update doc

syscalls_darwin.go

@@ -0,0 +1,123 @@
+// +build darwin
+
+package water
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"syscall"
+	"unsafe"
+)
+
+const appleUTUNCtl = "com.apple.net.utun_control"
+
+/*
+ * From ioctl.h:
+ * #define	IOCPARM_MASK	0x1fff		// parameter length, at most 13 bits
+ * ...
+ * #define	IOC_OUT		0x40000000	// copy out parameters
+ * #define	IOC_IN		0x80000000	// copy in parameters
+ * #define	IOC_INOUT	(IOC_IN|IOC_OUT)
+ * ...
+ * #define _IOC(inout,group,num,len) \
+ * 	(inout | ((len & IOCPARM_MASK) << 16) | ((group) << 8) | (num))
+ * ...
+ * #define	_IOWR(g,n,t)	_IOC(IOC_INOUT,	(g), (n), sizeof(t))
+ *
+ * From kern_control.h:
+ * #define CTLIOCGINFO     _IOWR('N', 3, struct ctl_info)	// get id from name
+ *
+ */
+
+const appleCTLIOCGINFO = (0x40000000 | 0x80000000) | ((100 & 0x1fff) << 16) | uint32(byte('N'))<<8 | 3
+
+/*
+ * #define _IOW(g,n,t) _IOC(IOC_IN, (g), (n), sizeof(t))
+ * #define TUNSIFMODE _IOW('t', 94, int)
+ */
+const appleTUNSIFMODE = (0x80000000) | ((4 & 0x1fff) << 16) | uint32(byte('t'))<<8 | 94
+
+/*
+ * struct sockaddr_ctl {
+ *     u_char sc_len; // depends on size of bundle ID string
+ *     u_char sc_family; // AF_SYSTEM
+ *     u_int16_t ss_sysaddr; // AF_SYS_KERNCONTROL
+ *     u_int32_t sc_id; // Controller unique identifier
+ *     u_int32_t sc_unit; // Developer private unit number
+ *     u_int32_t sc_reserved[5];
+ * };
+ */
+type sockaddrCtl struct {
+	scLen      uint8
+	scFamily   uint8
+	ssSysaddr  uint16
+	scID       uint32
+	scUnit     uint32
+	scReserved [5]uint32
+}
+
+var sockaddrCtlSize uintptr = 32
+
+func newTUN(string) (ifce *Interface, err error) {
+	var fd int
+	// Supposed to be socket(PF_SYSTEM, SOCK_DGRAM, SYSPROTO_CONTROL), but ...
+	//
+	// In sys/socket.h:
+	// #define PF_SYSTEM	AF_SYSTEM
+	//
+	// In sys/sys_domain.h:
+	// #define SYSPROTO_CONTROL       	2	/* kernel control protocol */
+	if fd, err = syscall.Socket(syscall.AF_SYSTEM, syscall.SOCK_DGRAM, 2); err != nil {
+		return nil, fmt.Errorf("error in syscall.Socket: %v", err)
+	}
+
+	var ctlInfo = &struct {
+		ctlID   uint32
+		ctlName [96]byte
+	}{}
+	copy(ctlInfo.ctlName[:], []byte(appleUTUNCtl))
+
+	if _, _, errno := syscall.Syscall(syscall.SYS_IOCTL, uintptr(fd), uintptr(appleCTLIOCGINFO), uintptr(unsafe.Pointer(ctlInfo))); errno != 0 {
+		err = errno
+		return nil, fmt.Errorf("error in syscall.Syscall(syscall.SYS_IOTL, ...): %v", err)
+	}
+
+	addrP := unsafe.Pointer(&sockaddrCtl{
+		scLen:    uint8(sockaddrCtlSize),
+		scFamily: syscall.AF_SYSTEM,
+
+		/* #define AF_SYS_CONTROL 2 */
+		ssSysaddr: 2,
+
+		scID:   ctlInfo.ctlID,
+		scUnit: 0,
+	})
+	if _, _, errno := syscall.RawSyscall(syscall.SYS_CONNECT, uintptr(fd), uintptr(addrP), uintptr(sockaddrCtlSize)); errno != 0 {
+		err = errno
+		return nil, fmt.Errorf("error in syscall.RawSyscall(syscall.SYS_CONNECT, ...): %v", err)
+	}
+
+	var ifName struct {
+		name [16]byte
+	}
+	ifNameSize := uintptr(16)
+	if _, _, errno := syscall.Syscall6(syscall.SYS_GETSOCKOPT, uintptr(fd),
+		2, /* #define SYSPROTO_CONTROL 2 */
+		2, /* #define UTUN_OPT_IFNAME 2 */
+		uintptr(unsafe.Pointer(&ifName)),
+		uintptr(unsafe.Pointer(&ifNameSize)), 0); errno != 0 {
+		err = errno
+		return nil, fmt.Errorf("error in syscall.Syscall6(syscall.SYS_GETSOCKOPT, ...): %v", err)
+	}
+
+	return &Interface{
+		isTAP:           false,
+		name:            string(ifName.name[:ifNameSize-1 /* -1 is for \0 */]),
+		ReadWriteCloser: os.NewFile(uintptr(fd), string(ifName.name[:])),
+	}, nil
+}
+
+func newTAP(ifName string) (ifce *Interface, err error) {
+	return nil, errors.New("tap interface not implemented on this platform")
+}