Basic platform?

Former-commit-id: 423e18edc3

dns/platform/detect_unix.go

@@ -0,0 +1,92 @@
+//go:build (linux && !android) || freebsd
+
+package dns
+
+import (
+	"fmt"
+	"net/netip"
+	"os"
+	"strings"
+)
+
+// DetectBestConfigurator detects and returns the most appropriate DNS configurator for the system
+// ifaceName is optional and only used for NetworkManager, systemd-resolved, and resolvconf
+func DetectBestConfigurator(ifaceName string) (DNSConfigurator, error) {
+	// Try systemd-resolved first (most modern)
+	if IsSystemdResolvedAvailable() && ifaceName != "" {
+		if configurator, err := NewSystemdResolvedDNSConfigurator(ifaceName); err == nil {
+			return configurator, nil
+		}
+	}
+
+	// Try NetworkManager (common on desktops)
+	if IsNetworkManagerAvailable() && ifaceName != "" {
+		if configurator, err := NewNetworkManagerDNSConfigurator(ifaceName); err == nil {
+			return configurator, nil
+		}
+	}
+
+	// Try resolvconf (common on older systems)
+	if IsResolvconfAvailable() && ifaceName != "" {
+		if configurator, err := NewResolvconfDNSConfigurator(ifaceName); err == nil {
+			return configurator, nil
+		}
+	}
+
+	// Fall back to direct file manipulation
+	return NewFileDNSConfigurator()
+}
+
+// Helper functions for checking system state
+
+// IsSystemdResolvedRunning checks if systemd-resolved is running
+func IsSystemdResolvedRunning() bool {
+	// Check if stub resolver is configured
+	servers, err := readResolvConfDNS()
+	if err != nil {
+		return false
+	}
+
+	// systemd-resolved uses 127.0.0.53
+	stubAddr := netip.MustParseAddr("127.0.0.53")
+	for _, server := range servers {
+		if server == stubAddr {
+			return true
+		}
+	}
+
+	return false
+}
+
+// readResolvConfDNS reads DNS servers from /etc/resolv.conf
+func readResolvConfDNS() ([]netip.Addr, error) {
+	content, err := os.ReadFile("/etc/resolv.conf")
+	if err != nil {
+		return nil, fmt.Errorf("read resolv.conf: %w", err)
+	}
+
+	var servers []netip.Addr
+	lines := strings.Split(string(content), "\n")
+	for _, line := range lines {
+		line = strings.TrimSpace(line)
+		if line == "" || strings.HasPrefix(line, "#") {
+			continue
+		}
+
+		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, nil
+}
+
+// GetSystemDNS returns the current system DNS servers
+func GetSystemDNS() ([]netip.Addr, error) {
+	return readResolvConfDNS()
+}