dnsmasq-netbox-connector/internal/config/dnsmasq.go

package config

import (
	"fmt"
	"os"
	"path"
	"strings"
)

const (
	leaseFileKey = "dhcp-leasefile"
	rangeKey     = "dhcp-range"
	confFileKey  = "conf-file"
	confDirKey   = "conf-dir"
)

func tryParseLineOption(line, key string) (string, bool) {
	if !strings.HasPrefix(line, key) {
		return "", false
	}

	_, val, found := strings.Cut(line, "=")
	return val, found
}

type dnsmasqConfOptions struct {
	leaseFile  string
	rangeStart string
	rangeEnd   string
}

func defaultDNSMasqOptions() map[string]string {
	return map[string]string{
		confDirKey:   "/etc/dnsmasq.d",
		confFileKey:  "",
		leaseFileKey: "/var/lib/misc/dnsmasq.leases",
		rangeKey:     "",
	}
}

func parseDNSMasqConfFile(content string, options map[string]string) {
	for _, l := range strings.Split(content, "\n") {
		for key := range options {
			newVal, found := tryParseLineOption(l, key)
			if found {
				options[key] = newVal
			}
		}
	}
}

func parseDNSMasqOptions(rootFileContent string) (dnsmasqConfOptions, error) {
	rawOptions := defaultDNSMasqOptions()

	// start with parsing the root file
	parseDNSMasqConfFile(rootFileContent, rawOptions)

	// get all additional conf files in the provided directory
	confDir := rawOptions[confDirKey]
	if confDir != "" {
		entries, err := os.ReadDir(confDir)
		if err != nil {
			return dnsmasqConfOptions{}, fmt.Errorf("failed to get list of additional config files: %w", err)
		}
		for _, e := range entries {
			if e.IsDir() || !strings.HasSuffix(e.Name(), ".conf") {
				continue
			}
			fileContent, err := os.ReadFile(path.Join(confDir, e.Name()))
			if err != nil {
				return dnsmasqConfOptions{}, fmt.Errorf("failed to read sub config file: %w", err)
			}
			parseDNSMasqConfFile(string(fileContent), rawOptions)
		}
	}

	// get any additional config file
	if additionalFile := rawOptions[confFileKey]; additionalFile != "" {
		filecontent, err := os.ReadFile(additionalFile)
		if err != nil {
			return dnsmasqConfOptions{}, fmt.Errorf("failed to read additional config file: %w", err)
		}
		parseDNSMasqConfFile(string(filecontent), rawOptions)
	}

	dhcpRange := strings.Split(rawOptions[rangeKey], ",")
	if len(dhcpRange) < 2 {
		return dnsmasqConfOptions{}, fmt.Errorf("invalid value for DHCP range: %s", rawOptions[rangeKey])
	}

	return dnsmasqConfOptions{
		leaseFile:  rawOptions[leaseFileKey],
		rangeStart: dhcpRange[0],
		rangeEnd:   dhcpRange[1],
	}, nil
}