feat: introduce DNS intercept mode infrastructure

cmd/cli/service_args_darwin.go

@@ -0,0 +1,134 @@
+//go:build darwin
+
+package cli
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"strings"
+)
+
+const launchdPlistPath = "/Library/LaunchDaemons/ctrld.plist"
+
+// serviceConfigFileExists returns true if the launchd plist for ctrld exists on disk.
+// This is more reliable than checking launchctl status, which may report "not found"
+// if the service was unloaded but the plist file still exists.
+func serviceConfigFileExists() bool {
+	_, err := os.Stat(launchdPlistPath)
+	return err == nil
+}
+
+// appendServiceFlag appends a CLI flag (e.g., "--intercept-mode") to the installed
+// service's launch arguments. This is used when upgrading an existing installation
+// to intercept mode without losing the existing --cd flag and other arguments.
+//
+// On macOS, this modifies the launchd plist at /Library/LaunchDaemons/ctrld.plist
+// using the "defaults" command, which is the standard way to edit plists.
+//
+// The function is idempotent: if the flag already exists, it's a no-op.
+func appendServiceFlag(flag string) error {
+	// Read current ProgramArguments from plist.
+	out, err := exec.Command("defaults", "read", launchdPlistPath, "ProgramArguments").CombinedOutput()
+	if err != nil {
+		return fmt.Errorf("failed to read plist ProgramArguments: %w (output: %s)", err, strings.TrimSpace(string(out)))
+	}
+
+	// Check if the flag is already present (idempotent).
+	args := string(out)
+	if strings.Contains(args, flag) {
+		mainLog.Load().Debug().Msgf("Service flag %q already present in plist, skipping", flag)
+		return nil
+	}
+
+	// Use PlistBuddy to append the flag to ProgramArguments array.
+	// PlistBuddy is more reliable than "defaults" for array manipulation.
+	addCmd := exec.Command(
+		"/usr/libexec/PlistBuddy",
+		"-c", fmt.Sprintf("Add :ProgramArguments: string %s", flag),
+		launchdPlistPath,
+	)
+	if out, err := addCmd.CombinedOutput(); err != nil {
+		return fmt.Errorf("failed to append %q to plist ProgramArguments: %w (output: %s)", flag, err, strings.TrimSpace(string(out)))
+	}
+
+	mainLog.Load().Info().Msgf("Appended %q to service launch arguments", flag)
+	return nil
+}
+
+// verifyServiceRegistration is a no-op on macOS (launchd plist verification not needed).
+func verifyServiceRegistration() error {
+	return nil
+}
+
+// removeServiceFlag removes a CLI flag (and its value, if the next argument is not
+// a flag) from the installed service's launch arguments. For example, removing
+// "--intercept-mode" also removes the following "dns" or "hard" value argument.
+//
+// The function is idempotent: if the flag doesn't exist, it's a no-op.
+func removeServiceFlag(flag string) error {
+	// Read current ProgramArguments to find the index.
+	out, err := exec.Command("/usr/libexec/PlistBuddy", "-c", "Print :ProgramArguments", launchdPlistPath).CombinedOutput()
+	if err != nil {
+		return fmt.Errorf("failed to read plist ProgramArguments: %w (output: %s)", err, strings.TrimSpace(string(out)))
+	}
+
+	// Parse the PlistBuddy output to find the flag's index.
+	// PlistBuddy prints arrays as:
+	//   Array {
+	//       /path/to/ctrld
+	//       run
+	//       --cd=xxx
+	//       --intercept-mode
+	//       dns
+	//   }
+	lines := strings.Split(string(out), "\n")
+	var entries []string
+	for _, line := range lines {
+		trimmed := strings.TrimSpace(line)
+		if trimmed == "Array {" || trimmed == "}" || trimmed == "" {
+			continue
+		}
+		entries = append(entries, trimmed)
+	}
+
+	index := -1
+	for i, entry := range entries {
+		if entry == flag {
+			index = i
+			break
+		}
+	}
+
+	if index < 0 {
+		mainLog.Load().Debug().Msgf("Service flag %q not present in plist, skipping removal", flag)
+		return nil
+	}
+
+	// Check if the next entry is a value (not a flag). If so, delete it first
+	// (deleting by index shifts subsequent entries down, so delete value before flag).
+	hasValue := index+1 < len(entries) && !strings.HasPrefix(entries[index+1], "-")
+	if hasValue {
+		delVal := exec.Command(
+			"/usr/libexec/PlistBuddy",
+			"-c", fmt.Sprintf("Delete :ProgramArguments:%d", index+1),
+			launchdPlistPath,
+		)
+		if out, err := delVal.CombinedOutput(); err != nil {
+			return fmt.Errorf("failed to remove value for %q from plist: %w (output: %s)", flag, err, strings.TrimSpace(string(out)))
+		}
+	}
+
+	// Delete the flag itself.
+	delCmd := exec.Command(
+		"/usr/libexec/PlistBuddy",
+		"-c", fmt.Sprintf("Delete :ProgramArguments:%d", index),
+		launchdPlistPath,
+	)
+	if out, err := delCmd.CombinedOutput(); err != nil {
+		return fmt.Errorf("failed to remove %q from plist ProgramArguments: %w (output: %s)", flag, err, strings.TrimSpace(string(out)))
+	}
+
+	mainLog.Load().Info().Msgf("Removed %q from service launch arguments", flag)
+	return nil
+}