Initial Commit

pkg/config/config.go

@@ -0,0 +1,147 @@
+package config
+
+import (
+	_ "embed"
+	"encoding/json"
+	"fmt"
+	"net"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"git.cryptic.systems/volker.raschek/dyndns-client/pkg/types"
+	log "github.com/sirupsen/logrus"
+)
+
+//go:embed config.json
+var defaultConfig string
+
+// GetDefaultConfiguration returns a default configuration
+func GetDefaultConfiguration() (*types.Config, error) {
+	cnf := new(types.Config)
+	jsonDecoder := json.NewDecoder(strings.NewReader(defaultConfig))
+
+	err := jsonDecoder.Decode(cnf)
+	if err != nil {
+		return nil, fmt.Errorf("failed to decode default config: %w", err)
+	}
+
+	defaultInterface, err := getDefaultInterfaceByIP()
+	if err != nil {
+		return nil, err
+	}
+	cnf.Ifaces = []string{defaultInterface.Name}
+
+	return cnf, nil
+}
+
+// Read config from a file
+func Read(cnfFile string) (*types.Config, error) {
+
+	// Load burned in configuration if config not available
+	if _, err := os.Stat(cnfFile); os.IsNotExist(err) {
+		if err := os.MkdirAll(filepath.Dir(cnfFile), 0755); err != nil {
+			return nil, fmt.Errorf("failed to create directory: %w", err)
+		}
+		cnf, err := GetDefaultConfiguration()
+		if err != nil {
+			return nil, err
+		}
+
+		err = cnf.Validate()
+		if err != nil {
+			return nil, err
+		}
+
+		log.Infof("use embedded configuration")
+
+		return cnf, nil
+	}
+
+	f, err := os.Open(cnfFile)
+	if err != nil {
+		return nil, fmt.Errorf("failed to open file: %w", err)
+	}
+	defer f.Close()
+
+	cnf := new(types.Config)
+	jsonDecoder := json.NewDecoder(f)
+	err = jsonDecoder.Decode(cnf)
+	if err != nil {
+		return nil, fmt.Errorf("failed to decode json: %w", err)
+	}
+
+	for _, iface := range cnf.Ifaces {
+		if _, err := net.InterfaceByName(iface); err != nil {
+			return nil, fmt.Errorf("unknown interface: %v", iface)
+		}
+	}
+
+	err = cnf.Validate()
+	if err != nil {
+		return nil, err
+	}
+
+	log.Infof("use configuration from file %v", cnfFile)
+
+	return cnf, nil
+}
+
+// Write config into a file
+func Write(cnf *types.Config, cnfFile string) error {
+	if _, err := os.Stat(filepath.Dir(cnfFile)); os.IsNotExist(err) {
+		err := os.MkdirAll(filepath.Dir(cnfFile), 0755)
+		if err != nil {
+			return err
+		}
+	}
+
+	f, err := os.Create(cnfFile)
+	if err != nil {
+		return fmt.Errorf("failed to create file %v: %v", cnfFile, err)
+	}
+	defer f.Close()
+
+	jsonEncoder := json.NewEncoder(f)
+	jsonEncoder.SetIndent("", "  ")
+	err = jsonEncoder.Encode(cnf)
+	if err != nil {
+		return fmt.Errorf("failed to encode json: %w", err)
+	}
+	return nil
+}
+
+func getDefaultInterfaceByIP() (*net.Interface, error) {
+	ifaces, err := net.Interfaces()
+	if err != nil {
+		return nil, fmt.Errorf("failed to fet network interfaces from kernel: %w", err)
+	}
+
+	defaultIP := getOutboundIP()
+
+	for _, iface := range ifaces {
+		addrs, err := iface.Addrs()
+		if err != nil {
+			return nil, fmt.Errorf("failed to list ip addresses for interface %v: %w", iface.Name, err)
+		}
+
+		for _, addr := range addrs {
+			addrIP := strings.Split(addr.String(), "/")[0]
+			if addrIP == defaultIP.String() {
+				return &iface, nil
+			}
+		}
+	}
+
+	return nil, fmt.Errorf("no interface found fo ip address %v", defaultIP)
+}
+
+func getOutboundIP() net.IP {
+	conn, err := net.Dial("udp", "8.8.8.8:80")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer conn.Close()
+	localAddr := conn.LocalAddr().(*net.UDPAddr)
+	return localAddr.IP
+}

pkg/config/config.json

@@ -0,0 +1 @@
+{}