installpkg: Avoid using /install on target dir

Use a temporary randomly named directory named like 'installpkg-2052825695'
for the package's metadata in its '/install' directory.  It will help allow
running multiple instances on the same target root directory by removing
a point of conflict.

Attempt to place this directory in the host's default temporary directory.  If
it does not exist, use the host's root path.

1 files changed, 15 insertions, 0 deletions

diff --git a/filesystem.go b/filesystem.go
index c33df15..dec07f3 100644
--- a/filesystem.go
+++ b/filesystem.go
@@ -4,7 +4,9 @@ import (
 	"io/fs"
 	"math"
 	"os"
+	"path/filepath"
 	"strconv"
+	"strings"
 	"time"
 )
 
@@ -46,6 +48,19 @@ func IsDir(path string) (bool, error) {
 	return info.IsDir(), nil
 }
 
+func IsParentDir(parent, sub string) (bool, error) {
+	up := ".." + string(os.PathSeparator)
+
+	rel, err := filepath.Rel(parent, sub)
+	if err != nil {
+		return false, err
+	}
+	if !strings.HasPrefix(rel, up) && rel != ".." {
+		return true, nil
+	}
+	return false, nil
+}
+
 func IsSymlink(path string) (bool, error) {
 	info, err := os.Stat(path)
 	if err != nil {