dhcpv4: Move BindToInterface to interfaces package

This moves the implementations of the BindToInterface to the interfaces/
package, since they aren't ipv4-specific.
The BindToInterface function remains in dhcpv4 (simply wraps the one in
interfaces) to keep backwards-compatibility

Additionally, fold bindtodevice_darwin into bindtodevice_bsd: darwin is
mostly a BSD, and happens to support IP_RECVIF, so use that instead of
IP_BOUND_IF, which only affects sends, not receives according to the
code comments in bsd/netinet/ip_output.c as well as being v4-only

Signed-off-by: Anatole Denis <natolumin@unverle.fr>

2 files changed, 27 insertions, 0 deletions

diff --git a/interfaces/bindtodevice_bsd.go b/interfaces/bindtodevice_bsd.go
new file mode 100644
index 0000000..180c3eb
--- /dev/null
+++ b/interfaces/bindtodevice_bsd.go
@@ -0,0 +1,18 @@
+// +build freebsd openbsd netbsd darwin
+
+package interfaces
+
+import (
+	"net"
+	"syscall"
+)
+
+// BindToInterface emulates linux's SO_BINDTODEVICE option for a socket by using
+// IP_RECVIF.
+func BindToInterface(fd int, ifname string) error {
+	iface, err := net.InterfaceByName(ifname)
+	if err != nil {
+		return err
+	}
+	return syscall.SetsockoptInt(fd, syscall.IPPROTO_IP, syscall.IP_RECVIF, iface.Index)
+}
diff --git a/interfaces/bindtodevice_linux.go b/interfaces/bindtodevice_linux.go
new file mode 100644
index 0000000..52c7177
--- /dev/null
+++ b/interfaces/bindtodevice_linux.go
@@ -0,0 +1,9 @@
+// +build linux
+
+package interfaces
+
+import "golang.org/x/sys/unix"
+
+func BindToInterface(fd int, ifname string) error {
+	return unix.BindToDevice(fd, ifname)
+}