Basic platform?

Former-commit-id: 423e18edc3

dns/platform/windows.go

@@ -0,0 +1,247 @@
+//go:build windows
+
+package dns
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"net/netip"
+	"syscall"
+
+	"golang.org/x/sys/windows/registry"
+)
+
+var (
+	dnsapi                  = syscall.NewLazyDLL("dnsapi.dll")
+	dnsFlushResolverCacheFn = dnsapi.NewProc("DnsFlushResolverCache")
+)
+
+const (
+	interfaceConfigPath           = `SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces`
+	interfaceConfigNameServer     = "NameServer"
+	interfaceConfigDhcpNameServer = "DhcpNameServer"
+)
+
+// WindowsDNSConfigurator manages DNS settings on Windows using the registry
+type WindowsDNSConfigurator struct {
+	guid          string
+	originalState *DNSState
+}
+
+// NewWindowsDNSConfigurator creates a new Windows DNS configurator
+// guid is the network interface GUID
+func NewWindowsDNSConfigurator(guid string) (*WindowsDNSConfigurator, error) {
+	if guid == "" {
+		return nil, fmt.Errorf("interface GUID is required")
+	}
+
+	return &WindowsDNSConfigurator{
+		guid: guid,
+	}, nil
+}
+
+// Name returns the configurator name
+func (w *WindowsDNSConfigurator) Name() string {
+	return "windows-registry"
+}
+
+// SetDNS sets the DNS servers and returns the original servers
+func (w *WindowsDNSConfigurator) SetDNS(servers []netip.Addr) ([]netip.Addr, error) {
+	// Get current DNS settings before overriding
+	originalServers, err := w.GetCurrentDNS()
+	if err != nil {
+		return nil, fmt.Errorf("get current DNS: %w", err)
+	}
+
+	// Store original state
+	w.originalState = &DNSState{
+		OriginalServers:  originalServers,
+		ConfiguratorName: w.Name(),
+	}
+
+	// Set new DNS servers
+	if err := w.setDNSServers(servers); err != nil {
+		return nil, fmt.Errorf("set DNS servers: %w", err)
+	}
+
+	// Flush DNS cache
+	if err := w.flushDNSCache(); err != nil {
+		// Non-fatal, just log
+		fmt.Printf("warning: failed to flush DNS cache: %v\n", err)
+	}
+
+	return originalServers, nil
+}
+
+// RestoreDNS restores the original DNS configuration
+func (w *WindowsDNSConfigurator) RestoreDNS() error {
+	if w.originalState == nil {
+		return fmt.Errorf("no original state to restore")
+	}
+
+	// Clear the static DNS setting
+	if err := w.clearDNSServers(); err != nil {
+		return fmt.Errorf("clear DNS servers: %w", err)
+	}
+
+	// Flush DNS cache
+	if err := w.flushDNSCache(); err != nil {
+		fmt.Printf("warning: failed to flush DNS cache: %v\n", err)
+	}
+
+	return nil
+}
+
+// GetCurrentDNS returns the currently configured DNS servers
+func (w *WindowsDNSConfigurator) GetCurrentDNS() ([]netip.Addr, error) {
+	regKey, err := w.getInterfaceRegistryKey(registry.QUERY_VALUE)
+	if err != nil {
+		return nil, fmt.Errorf("get interface registry key: %w", err)
+	}
+	defer closeKey(regKey)
+
+	// Try to get static DNS first
+	nameServer, _, err := regKey.GetStringValue(interfaceConfigNameServer)
+	if err == nil && nameServer != "" {
+		return w.parseServerList(nameServer), nil
+	}
+
+	// Fall back to DHCP DNS
+	dhcpNameServer, _, err := regKey.GetStringValue(interfaceConfigDhcpNameServer)
+	if err == nil && dhcpNameServer != "" {
+		return w.parseServerList(dhcpNameServer), nil
+	}
+
+	return []netip.Addr{}, nil
+}
+
+// setDNSServers sets the DNS servers in the registry
+func (w *WindowsDNSConfigurator) setDNSServers(servers []netip.Addr) error {
+	if len(servers) == 0 {
+		return fmt.Errorf("no DNS servers provided")
+	}
+
+	regKey, err := w.getInterfaceRegistryKey(registry.SET_VALUE)
+	if err != nil {
+		return fmt.Errorf("get interface registry key: %w", err)
+	}
+	defer closeKey(regKey)
+
+	// Build comma-separated or space-separated list of servers
+	var serverList string
+	for i, server := range servers {
+		if i > 0 {
+			serverList += ","
+		}
+		serverList += server.String()
+	}
+
+	if err := regKey.SetStringValue(interfaceConfigNameServer, serverList); err != nil {
+		return fmt.Errorf("set NameServer: %w", err)
+	}
+
+	return nil
+}
+
+// clearDNSServers clears the static DNS server setting
+func (w *WindowsDNSConfigurator) clearDNSServers() error {
+	regKey, err := w.getInterfaceRegistryKey(registry.SET_VALUE)
+	if err != nil {
+		return fmt.Errorf("get interface registry key: %w", err)
+	}
+	defer closeKey(regKey)
+
+	// Set empty string to revert to DHCP
+	if err := regKey.SetStringValue(interfaceConfigNameServer, ""); err != nil {
+		return fmt.Errorf("clear NameServer: %w", err)
+	}
+
+	return nil
+}
+
+// getInterfaceRegistryKey opens the registry key for the network interface
+func (w *WindowsDNSConfigurator) getInterfaceRegistryKey(access uint32) (registry.Key, error) {
+	regKeyPath := interfaceConfigPath + `\` + w.guid
+
+	regKey, err := registry.OpenKey(registry.LOCAL_MACHINE, regKeyPath, access)
+	if err != nil {
+		return 0, fmt.Errorf("open HKEY_LOCAL_MACHINE\\%s: %w", regKeyPath, err)
+	}
+
+	return regKey, nil
+}
+
+// parseServerList parses a comma or space-separated list of DNS servers
+func (w *WindowsDNSConfigurator) parseServerList(serverList string) []netip.Addr {
+	var servers []netip.Addr
+
+	// Split by comma or space
+	parts := splitByDelimiters(serverList, []rune{',', ' '})
+
+	for _, part := range parts {
+		if addr, err := netip.ParseAddr(part); err == nil {
+			servers = append(servers, addr)
+		}
+	}
+
+	return servers
+}
+
+// flushDNSCache flushes the Windows DNS resolver cache
+func (w *WindowsDNSConfigurator) flushDNSCache() error {
+	// dnsFlushResolverCacheFn.Call() may panic if the func is not found
+	defer func() {
+		if rec := recover(); rec != nil {
+			fmt.Printf("warning: DnsFlushResolverCache panicked: %v\n", rec)
+		}
+	}()
+
+	ret, _, err := dnsFlushResolverCacheFn.Call()
+	if ret == 0 {
+		if err != nil && !errors.Is(err, syscall.Errno(0)) {
+			return fmt.Errorf("DnsFlushResolverCache failed: %w", err)
+		}
+		return fmt.Errorf("DnsFlushResolverCache failed")
+	}
+
+	return nil
+}
+
+// splitByDelimiters splits a string by multiple delimiters
+func splitByDelimiters(s string, delimiters []rune) []string {
+	var result []string
+	var current []rune
+
+	for _, char := range s {
+		isDelimiter := false
+		for _, delim := range delimiters {
+			if char == delim {
+				isDelimiter = true
+				break
+			}
+		}
+
+		if isDelimiter {
+			if len(current) > 0 {
+				result = append(result, string(current))
+				current = []rune{}
+			}
+		} else {
+			current = append(current, char)
+		}
+	}
+
+	if len(current) > 0 {
+		result = append(result, string(current))
+	}
+
+	return result
+}
+
+// closeKey closes a registry key and logs errors
+func closeKey(closer io.Closer) {
+	if err := closer.Close(); err != nil {
+		fmt.Printf("warning: failed to close registry key: %v\n", err)
+	}
+}