Refactor code structure for improved readability and maintainability

platform/network_windows.go

@@ -0,0 +1,151 @@
+//go:build windows
+
+package platform
+
+import (
+	"bufio"
+	"fmt"
+	"net"
+	"os/exec"
+	"regexp"
+	"strconv"
+	"strings"
+)
+
+// WindowsNetworkDiscoverer discovers network configuration using netsh commands.
+// It does not require elevated privileges or PowerShell.
+type WindowsNetworkDiscoverer struct{}
+
+var ipv4Re = regexp.MustCompile(`(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})`)
+var dnsLineRe = regexp.MustCompile(`^\s*(?:\S.*:\s+)?(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})\s*$`)
+
+// Discover returns the gateway IP and DNS servers for the default IPv4 route.
+func (d *WindowsNetworkDiscoverer) Discover() (NetworkInfo, error) {
+	info := NetworkInfo{}
+
+	// Step 1: Find default route — extract interface index and gateway IP.
+	ifIdx, gateway, err := windowsDefaultRoute()
+	if err != nil {
+		return info, fmt.Errorf("reading default IPv4 route: %w", err)
+	}
+	info.Gateway = gateway
+
+	// Step 2: Map interface index to name.
+	ifName, err := windowsInterfaceName(ifIdx)
+	if err != nil {
+		return info, fmt.Errorf("resolving interface name for index %d: %w", ifIdx, err)
+	}
+	info.Interface = ifName
+
+	// Step 3: Enumerate DNS servers for that interface.
+	servers, err := windowsDNSServers(ifName)
+	if err != nil {
+		return info, fmt.Errorf("reading DNS servers for interface %q: %w", ifName, err)
+	}
+	info.DNSServers = servers
+
+	return info, nil
+}
+
+// windowsDefaultRoute runs "netsh interface ipv4 show route" and returns the
+// interface index and gateway IP for the best (lowest-metric) 0.0.0.0/0 route.
+func windowsDefaultRoute() (ifIdx int, gateway string, err error) {
+	out, err := exec.Command("netsh", "interface", "ipv4", "show", "route").Output()
+	if err != nil {
+		return 0, "", fmt.Errorf("netsh interface ipv4 show route: %w", err)
+	}
+
+	bestMetric := -1
+	bestIdx := 0
+	bestGateway := ""
+
+	scanner := bufio.NewScanner(strings.NewReader(string(out)))
+	for scanner.Scan() {
+		line := scanner.Text()
+		if !strings.Contains(line, "0.0.0.0/0") {
+			continue
+		}
+		// Format: <Publish> <Type> <Metric> <Prefix> <Idx> <Gateway or Iface Name...>
+		fields := strings.Fields(line)
+		if len(fields) < 6 {
+			continue
+		}
+		metric, err := strconv.Atoi(fields[2])
+		if err != nil {
+			continue
+		}
+		idx, err := strconv.Atoi(fields[4])
+		if err != nil {
+			continue
+		}
+		// Gateway field is field 5+ — join and extract first IPv4.
+		gatewayField := strings.Join(fields[5:], " ")
+		m := ipv4Re.FindString(gatewayField)
+		if m == "" {
+			continue
+		}
+		if bestMetric < 0 || metric < bestMetric {
+			bestMetric = metric
+			bestIdx = idx
+			bestGateway = m
+		}
+	}
+
+	if bestIdx == 0 {
+		return 0, "", fmt.Errorf("no default IPv4 route found")
+	}
+	return bestIdx, bestGateway, nil
+}
+
+// windowsInterfaceName runs "netsh interface ipv4 show interfaces" and maps
+// the given interface index to the interface name.
+func windowsInterfaceName(idx int) (string, error) {
+	out, err := exec.Command("netsh", "interface", "ipv4", "show", "interfaces").Output()
+	if err != nil {
+		return "", fmt.Errorf("netsh interface ipv4 show interfaces: %w", err)
+	}
+
+	idxStr := strconv.Itoa(idx)
+	scanner := bufio.NewScanner(strings.NewReader(string(out)))
+	// Skip two header lines.
+	for i := 0; i < 2; i++ {
+		scanner.Scan()
+	}
+	for scanner.Scan() {
+		line := scanner.Text()
+		fields := strings.Fields(line)
+		if len(fields) < 5 {
+			continue
+		}
+		if fields[0] != idxStr {
+			continue
+		}
+		// Name is fields[4:] joined — may contain spaces.
+		return strings.Join(fields[4:], " "), nil
+	}
+	return "", fmt.Errorf("interface index %d not found", idx)
+}
+
+// windowsDNSServers runs "netsh interface ipv4 show dnsservers name=<ifName>"
+// and returns all IPv4 DNS server addresses in order.
+func windowsDNSServers(ifName string) ([]string, error) {
+	out, err := exec.Command("netsh", "interface", "ipv4", "show", "dnsservers",
+		"name="+ifName).Output()
+	if err != nil {
+		return nil, fmt.Errorf("netsh interface ipv4 show dnsservers: %w", err)
+	}
+
+	var servers []string
+	scanner := bufio.NewScanner(strings.NewReader(string(out)))
+	for scanner.Scan() {
+		m := dnsLineRe.FindStringSubmatch(scanner.Text())
+		if len(m) < 2 {
+			continue
+		}
+		ip := m[1]
+		if net.ParseIP(ip) != nil {
+			servers = append(servers, ip)
+		}
+	}
+	return servers, nil
+}