Fix panic closing file which is never read

Signed-off-by: Derek McGowan <derek@mcg.dev>

Author: dmcgowan

erofs.go

@@ -910,7 +910,10 @@ func (b *file) Read(p []byte) (int, error) {
 }
 
 func (b *file) Close() error {
-	b.info.cached = nil
+	if b.info != nil && b.info.cached != nil {
+		b.img.putBlock(b.info.cached)
+		b.info.cached = nil
+	}
 	return nil
 }
 

erofs_test.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"io/fs"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -140,10 +141,10 @@ func BenchmarkLookup(b *testing.B) {
 			for range b.N {
 				f, err := fsys.Open(bc.path)
 				if err != nil {
-					if bc.name == "bigdir-notfound" {
-						continue
+					if !errors.Is(err, fs.ErrNotExist) {
+						b.Fatal(err)
 					}
-					b.Fatal(err)
+					continue
 				}
 				_ = f.Close()
 			}

internal/erofstest/testcase.go

@@ -273,6 +273,10 @@ var Basic TestCase = &testCase{
 
 		// ReadLink on a regular file should return ErrInvalid.
 		CheckReadLinkFile(t, fsys, "in-root.txt")
+
+		// Close without reading should not panic.
+		CheckOpenClose(t, fsys, "in-root.txt")
+		CheckOpenClose(t, fsys, "usr/lib/testdir")
 	},
 }
 
@@ -766,3 +770,17 @@ func CheckReadLinkFile(t testing.TB, fsys fs.FS, name string) {
 		t.Errorf("ReadLink(%s): got %v, want fs.ErrInvalid", name, err)
 	}
 }
+
+// CheckOpenClose verifies that opening and immediately closing a file
+// without reading does not panic.
+func CheckOpenClose(t testing.TB, fsys fs.FS, name string) {
+	t.Helper()
+	f, err := fsys.Open(name)
+	if err != nil {
+		t.Errorf("Open(%s): %v", name, err)
+		return
+	}
+	if err := f.Close(); err != nil {
+		t.Errorf("Close(%s): %v", name, err)
+	}
+}