fix: Fix connection interface binding, JSON lease DB

cmd/conn_unix.go

@@ -0,0 +1,70 @@
+// Copied with modifications from https://github.com/insomniacslk/dhcp/blob/master/dhcpv4/server4/conn_unix.go (under BSD-3-Clause license)
+//go:build !windows
+
+package cmd
+
+import (
+	"errors"
+	"fmt"
+	"net"
+	"os"
+
+	"github.com/adrianokf/go-dhcp/pkg/types"
+	"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, addr *net.UDPAddr) (*net.UDPConn, 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)
+	}
+	// Allow reusing the port to aid debugging and testing.
+	if err := unix.SetsockoptInt(fd, unix.SOL_SOCKET, unix.SO_REUSEPORT, 1); err != nil {
+		return nil, fmt.Errorf("cannot set reuseport on socket: %v", err)
+	}
+	if len(iface) != 0 {
+		// Bind directly to the interface.
+		if err := unix.BindToDevice(fd, iface); err != nil {
+			return nil, fmt.Errorf("cannot bind to interface %s: %v", iface, err)
+		}
+	}
+
+	if addr == nil {
+		addr = &net.UDPAddr{Port: types.ServerPort}
+	}
+	// Bind to the port.
+	saddr := unix.SockaddrInet4{Port: addr.Port}
+	if addr.IP != nil && addr.IP.To4() == nil {
+		return nil, fmt.Errorf("wrong address family (expected v4) for %s", addr.IP)
+	}
+	copy(saddr.Addr[:], addr.IP.To4())
+	if err := unix.Bind(fd, &saddr); err != nil {
+		return nil, fmt.Errorf("cannot bind to port %d: %v", addr.Port, err)
+	}
+
+	conn, err := net.FilePacketConn(f)
+	if err != nil {
+		return nil, err
+	}
+	udpconn, ok := conn.(*net.UDPConn)
+	if !ok {
+		return nil, errors.New("BUG: incorrect socket type, expected UDP")
+	}
+	return udpconn, nil
+}