healthcheck: check if drbd reactor reload units differ

The bundled drbd-reactor-reload.{path,service} recently got updated, so
we need to check if the user actually has the most recent version.

pkg/healthcheck/healthcheck.go

@@ -10,6 +10,7 @@ import (
 )
 
 var bold = color.New(color.Bold).SprintfFunc()
+var faint = color.New(color.Faint).SprintfFunc()
 var errNotFound = errors.New("not found")
 
 type checker interface {

pkg/healthcheck/reactor.go

@@ -4,13 +4,28 @@ import (
 	"fmt"
 	"github.com/fatih/color"
 	log "github.com/sirupsen/logrus"
+	"os"
 	"path/filepath"
 	"strings"
 )
 
 type checkReactorAutoReload struct {
 }
 
+func fileContentsEqual(filenameA, filenameB string) (bool, error) {
+	a, err := os.ReadFile(filenameA)
+	if err != nil {
+		return false, fmt.Errorf("could not read %s: %w", filenameA, err)
+	}
+
+	b, err := os.ReadFile(filenameB)
+	if err != nil {
+		return false, fmt.Errorf("could not read %s: %w", filenameB, err)
+	}
+
+	return string(a) == string(b), nil
+}
+
 func (c *checkReactorAutoReload) check(prevError bool) error {
 	if prevError {
 		// reactor not installed, no need to check
@@ -23,6 +38,24 @@ func (c *checkReactorAutoReload) check(prevError bool) error {
 	if status.ActiveState != "active" {
 		return fmt.Errorf("service drbd-reactor-reload.path is not started")
 	}
+
+	dir := guessReactorReloadDir()
+	sourcePath := filepath.Join(dir, "drbd-reactor-reload.path")
+	sourceService := filepath.Join(dir, "drbd-reactor-reload.service")
+
+	destPath := "/etc/systemd/system/drbd-reactor-reload.path"
+	destService := "/etc/systemd/system/drbd-reactor-reload.service"
+
+	for _, path := range [][]string{{sourcePath, destPath}, {sourceService, destService}} {
+		equal, err := fileContentsEqual(path[0], path[1])
+		if err != nil {
+			return fmt.Errorf("could not compare %s and %s: %w", path[0], path[1], err)
+		}
+		if !equal {
+			return fmt.Errorf("%s differs from %s", path[0], path[1])
+		}
+	}
+
 	return nil
 }
 
@@ -47,10 +80,11 @@ func guessReactorReloadDir() string {
 	return ""
 }
 
-func (c *checkReactorAutoReload) format(_ error) string {
+func (c *checkReactorAutoReload) format(err error) string {
 	dir := guessReactorReloadDir()
 	var b strings.Builder
 	fmt.Fprintf(&b, "    %s drbd-reactor is not configured to automatically reload\n", color.RedString("✗"))
+	fmt.Fprintf(&b, "      %s\n", faint("→ %s", err.Error()))
 	if dir != "" {
 		path := filepath.Join(dir, "drbd-reactor-reload.{path,service}")
 		fmt.Fprintf(&b, "      Please execute:\n")