Bind interface fix (#310)

Added a bind to interface functionality.

1 files changed, 45 insertions, 0 deletions

diff --git a/dhcpv4/server4/conn.go b/dhcpv4/server4/conn.go
new file mode 100644
index 0000000..84d6aa3
--- /dev/null
+++ b/dhcpv4/server4/conn.go
@@ -0,0 +1,45 @@
+package server4
+
+import (
+	"fmt"
+	"net"
+	"os"
+
+	"github.com/insomniacslk/dhcp/dhcpv4"
+	"golang.org/x/sys/unix"
+)
+
+// NewIPv4UDPConn returns a UDP connection bound to both the interface and port
+// given based on a IPv4 DGRAM socket. The UDP connection allows broadcasting.
+//
+// The interface must already be configured.
+func NewIPv4UDPConn(iface string, port int) (net.PacketConn, error) {
+	fd, err := unix.Socket(unix.AF_INET, unix.SOCK_DGRAM, unix.IPPROTO_UDP)
+	if err != nil {
+		return nil, fmt.Errorf("cannot get a UDP socket: %v", err)
+	}
+	f := os.NewFile(uintptr(fd), "")
+	// net.FilePacketConn dups the FD, so we have to close this in any case.
+	defer f.Close()
+
+	// Allow broadcasting.
+	if err := unix.SetsockoptInt(fd, unix.SOL_SOCKET, unix.SO_BROADCAST, 1); err != nil {
+		return nil, fmt.Errorf("cannot set broadcasting on socket: %v", err)
+	}
+	// Allow reusing the addr to aid debugging.
+	if err := unix.SetsockoptInt(fd, unix.SOL_SOCKET, unix.SO_REUSEADDR, 1); err != nil {
+		return nil, fmt.Errorf("cannot set reuseaddr on socket: %v", err)
+	}
+	if len(iface) != 0 {
+		// Bind directly to the interface.
+		if err := dhcpv4.BindToInterface(fd, iface); err != nil {
+			return nil, fmt.Errorf("cannot bind to interface %s: %v", iface, err)
+		}
+	}
+	// Bind to the port.
+	if err := unix.Bind(fd, &unix.SockaddrInet4{Port: port}); err != nil {
+		return nil, fmt.Errorf("cannot bind to port %d: %v", port, err)
+	}
+
+	return net.FilePacketConn(f)
+}