First implementation of DHCP server, compiles but not tested yet.

dhcpd/helpers.go

@@ -0,0 +1,101 @@
+package dhcpd
+
+import (
+	"fmt"
+	"log"
+	"net"
+	"os"
+	"path"
+	"runtime"
+	"strings"
+
+	"github.com/joomcode/errorx"
+)
+
+func trace(format string, args ...interface{}) {
+	pc := make([]uintptr, 10) // at least 1 entry needed
+	runtime.Callers(2, pc)
+	f := runtime.FuncForPC(pc[0])
+	var buf strings.Builder
+	buf.WriteString(fmt.Sprintf("%s(): ", path.Base(f.Name())))
+	text := fmt.Sprintf(format, args...)
+	buf.WriteString(text)
+	if len(text) == 0 || text[len(text)-1] != '\n' {
+		buf.WriteRune('\n')
+	}
+	fmt.Fprint(os.Stderr, buf.String())
+}
+
+func isTimeout(err error) bool {
+	operr, ok := err.(*net.OpError)
+	if !ok {
+		return false
+	}
+	return operr.Timeout()
+}
+
+// return first IPv4 address of an interface, if there is any
+func getIfaceIPv4(iface *net.Interface) *net.IPNet {
+	ifaceAddrs, err := iface.Addrs()
+	if err != nil {
+		panic(err)
+	}
+
+	for _, addr := range ifaceAddrs {
+		ipnet, ok := addr.(*net.IPNet)
+		if !ok {
+			// not an IPNet, should not happen
+			log.Fatalf("SHOULD NOT HAPPEN: got iface.Addrs() element %s that is not net.IPNet", addr)
+		}
+
+		if ipnet.IP.To4() == nil {
+			log.Printf("Got IP that is not IPv4: %v", ipnet.IP)
+			continue
+		}
+
+		log.Printf("Got IP that is IPv4: %v", ipnet.IP)
+		return &net.IPNet{
+			IP:   ipnet.IP.To4(),
+			Mask: ipnet.Mask,
+		}
+	}
+	return nil
+}
+
+func isConnClosed(err error) bool {
+	if err == nil {
+		return false
+	}
+	nerr, ok := err.(*net.OpError)
+	if !ok {
+		return false
+	}
+
+	if strings.Contains(nerr.Err.Error(), "use of closed network connection") {
+		return true
+	}
+
+	return false
+}
+
+func wrapErrPrint(err error, message string, args ...interface{}) error {
+	var errx error
+	if err == nil {
+		errx = fmt.Errorf(message, args...)
+	} else {
+		errx = errorx.Decorate(err, message, args...)
+	}
+	log.Println(errx.Error())
+	return errx
+}
+
+func parseIPv4(text string) (net.IP, error) {
+	result := net.ParseIP(text)
+	if result == nil {
+		return nil, fmt.Errorf("%s is not an IP address", text)
+	}
+	if result.To4() == nil {
+		return nil, fmt.Errorf("%s is not an IPv4 address", text)
+	}
+	return result.To4(), nil
+}