config: writing how the config file should look

config/config.go

@@ -0,0 +1,147 @@
+package config
+
+import (
+	"fmt"
+	"io/ioutil"
+	"net"
+
+	"git.wntrmute.dev/kyle/kdhcp/log"
+	"gopkg.in/yaml.v2"
+)
+
+const (
+	CurrentVersion = 1
+)
+
+func ensureV4(ip net.IP) (net.IP, error) {
+	ip4 := ip.To4()
+	if ip4 == nil {
+		return ip4, fmt.Errorf("%s isn't an IPv4 address", ip)
+	}
+
+	return ip4, nil
+}
+
+type IPRange struct {
+	Start net.IP
+	End   net.IP
+}
+
+func (r *IPRange) ensureV4() (err error) {
+	if r.Start, err = ensureV4(r.Start); err != nil {
+		return fmt.Errorf("config: range start address %w", err)
+	}
+
+	if r.End, err = ensureV4(r.End); err != nil {
+		return fmt.Errorf("config: range end address %w", err)
+	}
+
+	return nil
+}
+
+type Network struct {
+	Gateway   net.IP   `yaml:"gateway"`
+	Mask      net.IP   `yaml:"mask"`
+	Broadcast net.IP   `yaml:"broadcast"`
+	DNS       []net.IP `yaml:"dns"`
+	Domain    string   `yaml:"domain"`
+}
+
+func (n *Network) ensureV4() (err error) {
+	n.Gateway, err = ensureV4(n.Gateway)
+	if err != nil {
+		return fmt.Errorf("config: gateway %w", err)
+	}
+
+	n.Mask, err = ensureV4(n.Mask)
+	if err != nil {
+		return fmt.Errorf("config: mask  %w", err)
+	}
+
+	n.Broadcast, err = ensureV4(n.Broadcast)
+	if err != nil {
+		return fmt.Errorf("config: broadcast  %w", err)
+	}
+
+	for i := range n.DNS {
+		n.DNS[i], err = ensureV4(n.DNS[i])
+		if err != nil {
+			return fmt.Errorf("config: DNS address %w", err)
+		}
+	}
+
+	return nil
+}
+
+type ConfigFile struct {
+	Server *Config `yaml:"kdhcp"`
+}
+
+type Config struct {
+	Version   int                 `yaml:"version"`
+	Interface string              `yaml:"interface"`
+	LeaseFile string              `yaml:"lease_file"`
+	Network   *Network            `yaml:"network"`
+	Pools     map[string]*IPRange `yaml:"pools"`
+	Statics   map[string]net.IP   `yaml:"statics"`
+	Device    *net.Interface
+}
+
+func (cfg *Config) process() (err error) {
+	switch {
+	case cfg.Version == 0:
+		log.Warningln("config: Version is 0, which indicates it hasn't been set. The config may be invalid.")
+	case cfg.Version > CurrentVersion:
+		log.Warningf("config: Version is greater than the current version %d. The config may not behave as expected.", CurrentVersion)
+	}
+
+	cfg.Device, err = net.InterfaceByName(cfg.Interface)
+	if err != nil {
+		return fmt.Errorf("config: while looking up interface %s: %w", cfg.Interface, err)
+	}
+
+	err = cfg.Network.ensureV4()
+	if err != nil {
+		return err
+	}
+
+	for k, v := range cfg.Pools {
+		if err = v.ensureV4(); err != nil {
+			return fmt.Errorf("config: pool %s %w", k, err)
+		}
+
+		cfg.Pools[k] = v
+	}
+
+	for k, v := range cfg.Statics {
+		cfg.Statics[k], err = ensureV4(v)
+		if err != nil {
+			return fmt.Errorf("config: %s %w", k, err)
+		}
+	}
+
+	return nil
+}
+
+func Load(path string) (*Config, error) {
+	data, err := ioutil.ReadFile(path)
+	if err != nil {
+		return nil, fmt.Errorf("config: loading %s: %w", path, err)
+	}
+
+	configFile := &ConfigFile{}
+	err = yaml.Unmarshal(data, configFile)
+	if err != nil {
+		return nil, fmt.Errorf("config: while unmarshaling %s: %w", path, err)
+	}
+
+	if configFile.Server == nil {
+		log.Fatal("missing `kdhcp` section of config")
+	}
+	config := configFile.Server
+	if err = config.process(); err != nil {
+		return nil, err
+	}
+
+	return config, nil
+}