Basic platform?

Former-commit-id: 423e18edc3

dns/platform/resolvconf.go

@@ -0,0 +1,192 @@
+//go:build (linux && !android) || freebsd
+
+package dns
+
+import (
+	"bytes"
+	"fmt"
+	"net/netip"
+	"os/exec"
+	"strings"
+)
+
+const resolvconfCommand = "resolvconf"
+
+// ResolvconfDNSConfigurator manages DNS settings using the resolvconf utility
+type ResolvconfDNSConfigurator struct {
+	ifaceName     string
+	implType      string
+	originalState *DNSState
+}
+
+// NewResolvconfDNSConfigurator creates a new resolvconf DNS configurator
+func NewResolvconfDNSConfigurator(ifaceName string) (*ResolvconfDNSConfigurator, error) {
+	if ifaceName == "" {
+		return nil, fmt.Errorf("interface name is required")
+	}
+
+	// Detect resolvconf implementation type
+	implType, err := detectResolvconfType()
+	if err != nil {
+		return nil, fmt.Errorf("detect resolvconf type: %w", err)
+	}
+
+	return &ResolvconfDNSConfigurator{
+		ifaceName: ifaceName,
+		implType:  implType,
+	}, nil
+}
+
+// Name returns the configurator name
+func (r *ResolvconfDNSConfigurator) Name() string {
+	return fmt.Sprintf("resolvconf-%s", r.implType)
+}
+
+// SetDNS sets the DNS servers and returns the original servers
+func (r *ResolvconfDNSConfigurator) SetDNS(servers []netip.Addr) ([]netip.Addr, error) {
+	// Get current DNS settings before overriding
+	originalServers, err := r.GetCurrentDNS()
+	if err != nil {
+		// If we can't get current DNS, proceed anyway
+		originalServers = []netip.Addr{}
+	}
+
+	// Store original state
+	r.originalState = &DNSState{
+		OriginalServers:  originalServers,
+		ConfiguratorName: r.Name(),
+	}
+
+	// Apply new DNS servers
+	if err := r.applyDNSServers(servers); err != nil {
+		return nil, fmt.Errorf("apply DNS servers: %w", err)
+	}
+
+	return originalServers, nil
+}
+
+// RestoreDNS restores the original DNS configuration
+func (r *ResolvconfDNSConfigurator) RestoreDNS() error {
+	var cmd *exec.Cmd
+
+	switch r.implType {
+	case "openresolv":
+		// Force delete with -f
+		cmd = exec.Command(resolvconfCommand, "-f", "-d", r.ifaceName)
+	default:
+		cmd = exec.Command(resolvconfCommand, "-d", r.ifaceName)
+	}
+
+	if out, err := cmd.CombinedOutput(); err != nil {
+		return fmt.Errorf("delete resolvconf config: %w, output: %s", err, out)
+	}
+
+	return nil
+}
+
+// GetCurrentDNS returns the currently configured DNS servers
+func (r *ResolvconfDNSConfigurator) GetCurrentDNS() ([]netip.Addr, error) {
+	// resolvconf doesn't provide a direct way to query per-interface DNS
+	// We can try to read /etc/resolv.conf but it's merged from all sources
+	content, err := exec.Command(resolvconfCommand, "-l").CombinedOutput()
+	if err != nil {
+		// Fall back to reading resolv.conf
+		return readResolvConfServers()
+	}
+
+	// Parse the output (format varies by implementation)
+	return parseResolvconfOutput(string(content)), nil
+}
+
+// applyDNSServers applies DNS server configuration via resolvconf
+func (r *ResolvconfDNSConfigurator) applyDNSServers(servers []netip.Addr) error {
+	if len(servers) == 0 {
+		return fmt.Errorf("no DNS servers provided")
+	}
+
+	// Build resolv.conf content
+	var content bytes.Buffer
+	content.WriteString("# Generated by Olm DNS Manager\n\n")
+
+	for _, server := range servers {
+		content.WriteString("nameserver ")
+		content.WriteString(server.String())
+		content.WriteString("\n")
+	}
+
+	// Apply via resolvconf
+	var cmd *exec.Cmd
+	switch r.implType {
+	case "openresolv":
+		// OpenResolv supports exclusive mode with -x
+		cmd = exec.Command(resolvconfCommand, "-x", "-a", r.ifaceName)
+	default:
+		cmd = exec.Command(resolvconfCommand, "-a", r.ifaceName)
+	}
+
+	cmd.Stdin = &content
+	if out, err := cmd.CombinedOutput(); err != nil {
+		return fmt.Errorf("apply resolvconf config: %w, output: %s", err, out)
+	}
+
+	return nil
+}
+
+// detectResolvconfType detects which resolvconf implementation is being used
+func detectResolvconfType() (string, error) {
+	cmd := exec.Command(resolvconfCommand, "--version")
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		return "", fmt.Errorf("detect resolvconf type: %w", err)
+	}
+
+	if strings.Contains(string(out), "openresolv") {
+		return "openresolv", nil
+	}
+
+	return "resolvconf", nil
+}
+
+// parseResolvconfOutput parses resolvconf -l output for DNS servers
+func parseResolvconfOutput(output string) []netip.Addr {
+	var servers []netip.Addr
+
+	lines := strings.Split(output, "\n")
+	for _, line := range lines {
+		line = strings.TrimSpace(line)
+
+		// Skip comments and empty lines
+		if line == "" || strings.HasPrefix(line, "#") {
+			continue
+		}
+
+		// Look for nameserver lines
+		if strings.HasPrefix(line, "nameserver") {
+			fields := strings.Fields(line)
+			if len(fields) >= 2 {
+				if addr, err := netip.ParseAddr(fields[1]); err == nil {
+					servers = append(servers, addr)
+				}
+			}
+		}
+	}
+
+	return servers
+}
+
+// readResolvConfServers reads DNS servers from /etc/resolv.conf
+func readResolvConfServers() ([]netip.Addr, error) {
+	cmd := exec.Command("cat", "/etc/resolv.conf")
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		return nil, fmt.Errorf("read resolv.conf: %w", err)
+	}
+
+	return parseResolvconfOutput(string(out)), nil
+}
+
+// IsResolvconfAvailable checks if resolvconf is available
+func IsResolvconfAvailable() bool {
+	cmd := exec.Command(resolvconfCommand, "--version")
+	return cmd.Run() == nil
+}