feat: Search for existing NodeJS runtime in the Windows Registry

installer/go/pkg/nodejs/system.go

@@ -19,30 +19,6 @@ import (
 // not to the machine, so the service account cannot be expected to reach it.
 var userPathPrefixes = []string{"/home/", "/Users/", "/root", `c:\users\`}
 
-// systemNodeCandidates returns the fixed locations a system-wide Node.js is
-// accepted from, for the current operating system.
-//
-// Returns:
-//   - []string: The absolute candidate paths, empty on an unsupported system
-func systemNodeCandidates() []string {
-	switch runtime.GOOS {
-	case "linux":
-		return []string{"/usr/bin/node", "/usr/local/bin/node"}
-	case "darwin":
-		return []string{"/usr/local/bin/node", "/opt/homebrew/bin/node"}
-	case "windows":
-		var candidates []string
-		for _, envVar := range []string{"ProgramFiles", "ProgramFiles(x86)"} {
-			if programFiles := os.Getenv(envVar); programFiles != "" {
-				candidates = append(candidates, filepath.Join(programFiles, "nodejs", "node.exe"))
-			}
-		}
-		return candidates
-	default:
-		return nil
-	}
-}
-
 // npmExecutableName returns the name of the npm executable on this platform.
 //
 // Returns:

installer/go/pkg/nodejs/system_unix.go

@@ -0,0 +1,21 @@
+//go:build linux || darwin
+
+package nodejs
+
+import "runtime"
+
+// systemNodeCandidates returns the fixed locations a system-wide Node.js is
+// accepted from, for the current operating system.
+//
+// Returns:
+//   - []string: The absolute candidate paths, empty on an unsupported system
+//
+func systemNodeCandidates() []string {
+	switch runtime.GOOS {
+	case "linux":
+		return []string{"/usr/bin/node", "/usr/local/bin/node"}
+	case "darwin":
+		return []string{"/usr/local/bin/node", "/opt/homebrew/bin/node"}
+	}
+	return nil
+}

installer/go/pkg/nodejs/system_windows.go

@@ -0,0 +1,132 @@
+//go:build windows
+
+package nodejs
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/flowfuse/device-agent-installer/pkg/logger"
+
+	"golang.org/x/sys/windows/registry"
+)
+
+// nodeRegistryValueNames lists the value names under SOFTWARE\Node.js that may
+// hold the Node.js installation directory or executable path.
+var nodeRegistryValueNames = []string{"InstallPath", "InstallDir", "Path"}
+
+// normaliseRegistryNodePath turns a registry value describing a Node.js
+// installation into a candidate node.exe path. Surrounding whitespace and
+// quotes are trimmed; a directory is completed with node.exe, a value that
+// already names an executable is kept as-is.
+//
+// Parameters:
+//   - raw: The registry value, a Node.js directory or node.exe path
+//
+// Returns:
+//   - string: The normalised path, "" when the value holds nothing usable
+func normaliseRegistryNodePath(raw string) string {
+	path := strings.TrimSpace(raw)
+	path = strings.Trim(path, `"`)
+	path = strings.TrimSpace(path)
+	if path == "" {
+		return ""
+	}
+	if !strings.EqualFold(filepath.Ext(path), ".exe") {
+		path = filepath.Join(path, "node.exe")
+	}
+	return path
+}
+
+// nodePathsFromRegistry returns node.exe candidates read from the Windows
+// registry, in the order they were found. MSI installs register their
+// installation in SOFTWARE\Node.js, and some installs only leave an App Paths
+// entry pointing straight at node.exe behind. Both 64-bit and 32-bit registry
+// views are consulted, so a 32-bit Node.js stays visible from a 64-bit
+// installer. The current-user hive is read as well, but a per-user install it
+// reveals is rejected later by the user-path check in DetectSystemNode.
+//
+// Returns:
+//   - []string: The unique candidate paths, empty when the registry names none
+func nodePathsFromRegistry() []string {
+	var candidates []string
+	seen := map[string]bool{}
+
+	add := func(raw string) {
+		path := normaliseRegistryNodePath(raw)
+		if path == "" {
+			return
+		}
+		key := strings.ToLower(path)
+		if seen[key] {
+			return
+		}
+		seen[key] = true
+		candidates = append(candidates, path)
+	}
+
+	roots := []registry.Key{registry.LOCAL_MACHINE, registry.CURRENT_USER}
+	keyPaths := []string{`SOFTWARE\Node.js`, `SOFTWARE\WOW6432Node\Node.js`}
+	accesses := []uint32{
+		registry.QUERY_VALUE | registry.WOW64_64KEY,
+		registry.QUERY_VALUE | registry.WOW64_32KEY,
+	}
+
+	for _, root := range roots {
+		for _, keyPath := range keyPaths {
+			for _, access := range accesses {
+				key, err := registry.OpenKey(root, keyPath, access)
+				if err != nil {
+					continue
+				}
+				for _, valueName := range nodeRegistryValueNames {
+					if value, _, err := key.GetStringValue(valueName); err == nil {
+						add(value)
+					}
+				}
+				key.Close()
+			}
+		}
+	}
+
+	// App Paths fallback for installs that registered one without leaving
+	// SOFTWARE\Node.js behind. Its default value points directly at node.exe.
+	appPathsKey := `SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths\node.exe`
+	for _, access := range accesses {
+		key, err := registry.OpenKey(registry.LOCAL_MACHINE, appPathsKey, access)
+		if err != nil {
+			continue
+		}
+		if value, _, err := key.GetStringValue(""); err == nil {
+			add(value)
+		}
+		key.Close()
+	}
+
+	if len(candidates) > 0 {
+		logger.Debug("Node.js install paths found in the Windows registry: %s", strings.Join(candidates, ", "))
+	}
+
+	return candidates
+}
+
+// systemNodeCandidates returns the locations a system-wide Node.js is accepted
+// from: the install paths registered in the Windows registry by MSI installs
+// first, then the conventional %ProgramFiles% locations covering non-MSI and
+// portable installs. Every candidate still has to pass the checks in
+// DetectSystemNode, so a registered path that is invalid, user-owned or too
+// old is skipped there.
+//
+// Returns:
+//   - []string: The absolute candidate node.exe paths, empty when none is known
+//
+func systemNodeCandidates() []string {
+	candidates := nodePathsFromRegistry()
+	for _, envVar := range []string{"ProgramFiles", "ProgramFiles(x86)"} {
+		if programFiles := os.Getenv(envVar); programFiles != "" {
+			candidates = append(candidates, filepath.Join(programFiles, "nodejs", "node.exe"))
+		}
+	}
+	return candidates
+}