fileutil: add directory helpers, atomic file writing (#5477)

internal/fileutil/directories.go

@@ -0,0 +1,36 @@
+package fileutil
+
+import (
+	"os"
+	"path/filepath"
+
+	"github.com/rs/zerolog/log"
+)
+
+// CacheDir returns $XDG_CACHE_HOME/pomerium, or $HOME/.cache/pomerium, or /tmp/pomerium/cache
+func CacheDir() string {
+	dir, err := os.UserCacheDir()
+	if err == nil {
+		dir = filepath.Join(dir, "pomerium")
+	} else {
+		dir = filepath.Join(os.TempDir(), "pomerium", "cache")
+		log.Error().Msgf("user cache directory not set, defaulting to %s", dir)
+	}
+	return dir
+}
+
+// DataDir returns $XDG_DATA_HOME/pomerium, or $HOME/.local/share/pomerium, or /tmp/pomerium/data
+func DataDir() string {
+	dir := os.Getenv("XDG_DATA_HOME")
+	if dir != "" {
+		dir = filepath.Join(dir, "pomerium")
+	} else {
+		if home, err := os.UserHomeDir(); err == nil {
+			dir = filepath.Join(home, ".local", "share", "pomerium")
+		} else {
+			dir = filepath.Join(os.TempDir(), "pomerium", "data")
+		}
+		log.Error().Msgf("user data directory not set, defaulting to %s", dir)
+	}
+	return dir
+}