perf(key): Use string builder for path concatenation

By leveraging the string builder and establishing the
capacity of the underlying slice, we can reduce a few
unnecessary allocations per event.

Author: rabbitstack

pkg/util/key/key.go

@@ -22,11 +22,12 @@
 package key
 
 import (
-	"github.com/rabbitstack/fibratus/pkg/sys"
-	"golang.org/x/sys/windows/registry"
 	"path/filepath"
 	"regexp"
 	"strings"
+
+	"github.com/rabbitstack/fibratus/pkg/sys"
+	"golang.org/x/sys/windows/registry"
 )
 
 var (
@@ -202,6 +203,18 @@ func Format(key string) (Key, string) {
 	return Invalid, key
 }
 
+// ConcatPaths concatenates root and subkey registry paths.
+func ConcatPaths(root, path string) string {
+	var b strings.Builder
+	b.Grow(len(root) + len(path) + 1)
+	if root != "" {
+		b.WriteString(root)
+		b.WriteByte('\\')
+	}
+	b.WriteString(path)
+	return b.String()
+}
+
 func subkey(key string, prefix string) string {
 	if len(key) > len(prefix) {
 		return key[len(prefix)+1:]

pkg/util/key/key_test.go

@@ -22,11 +22,12 @@
 package key
 
 import (
+	"testing"
+
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"golang.org/x/sys/windows"
 	"golang.org/x/sys/windows/registry"
-	"testing"
 )
 
 func init() {
@@ -182,3 +183,33 @@ func TestReadValue(t *testing.T) {
 		})
 	}
 }
+
+func TestConcatPaths(t *testing.T) {
+	var tests = []struct {
+		root     string
+		subkey   string
+		expected string
+	}{
+		{
+			root:     "HKEY_LOCAL_MACHINE",
+			subkey:   `Software\Microsoft\Windows\CurrentVersion\CapabilityAccessManager\Capabilities`,
+			expected: `HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\CapabilityAccessManager\Capabilities`,
+		},
+		{
+			root:     "",
+			subkey:   `Software\Microsoft\Windows\CurrentVersion\CapabilityAccessManager\Capabilities`,
+			expected: `Software\Microsoft\Windows\CurrentVersion\CapabilityAccessManager\Capabilities`,
+		},
+		{
+			root:     "HKEY_LOCAL_MACHINE",
+			subkey:   "",
+			expected: "HKEY_LOCAL_MACHINE\\",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.root+tt.subkey, func(t *testing.T) {
+			assert.Equal(t, tt.expected, ConcatPaths(tt.root, tt.subkey))
+		})
+	}
+}