2 files changed, 91 insertions, 1 deletions
diff --git a/src/archive/zip/reader.go b/src/archive/zip/reader.go
index 6b57f767fc..b2a4ed6042 100644
--- a/src/archive/zip/reader.go
+++ b/src/archive/zip/reader.go
@@ -834,7 +834,16 @@ func (r *Reader) initFileList() {
 				continue
 			}
 
-			for dir := path.Dir(name); dir != "."; dir = path.Dir(dir) {
+			dir := name
+			for {
+				if idx := strings.LastIndex(dir, "/"); idx < 0 {
+					break
+				} else {
+					dir = dir[:idx]
+				}
+				if dirs[dir] {
+					break
+				}
 				dirs[dir] = true
 			}
 
diff --git a/src/archive/zip/reader_test.go b/src/archive/zip/reader_test.go
index cb8a0c2871..5ce994e4dd 100644
--- a/src/archive/zip/reader_test.go
+++ b/src/archive/zip/reader_test.go
@@ -9,6 +9,7 @@ import (
 	"encoding/binary"
 	"encoding/hex"
 	"errors"
+	"fmt"
 	"internal/obscuretestdata"
 	"io"
 	"io/fs"
@@ -1874,3 +1875,83 @@ func TestBaseOffsetPlusOverflow(t *testing.T) {
 	// as the section reader offset & size were < 0.
 	NewReader(bytes.NewReader(data), int64(len(data))+1875)
 }
+
+func BenchmarkReaderOneDeepDir(b *testing.B) {
+	var buf bytes.Buffer
+	zw := NewWriter(&buf)
+
+	for i := range 4000 {
+		name := strings.Repeat("a/", i) + "data"
+		zw.CreateHeader(&FileHeader{
+			Name:   name,
+			Method: Store,
+		})
+	}
+
+	if err := zw.Close(); err != nil {
+		b.Fatal(err)
+	}
+	data := buf.Bytes()
+
+	for b.Loop() {
+		zr, err := NewReader(bytes.NewReader(data), int64(len(data)))
+		if err != nil {
+			b.Fatal(err)
+		}
+		zr.Open("does-not-exist")
+	}
+}
+
+func BenchmarkReaderManyDeepDirs(b *testing.B) {
+	var buf bytes.Buffer
+	zw := NewWriter(&buf)
+
+	for i := range 2850 {
+		name := fmt.Sprintf("%x", i)
+		name = strings.Repeat("/"+name, i+1)[1:]
+
+		zw.CreateHeader(&FileHeader{
+			Name:   name,
+			Method: Store,
+		})
+	}
+
+	if err := zw.Close(); err != nil {
+		b.Fatal(err)
+	}
+	data := buf.Bytes()
+
+	for b.Loop() {
+		zr, err := NewReader(bytes.NewReader(data), int64(len(data)))
+		if err != nil {
+			b.Fatal(err)
+		}
+		zr.Open("does-not-exist")
+	}
+}
+
+func BenchmarkReaderManyShallowFiles(b *testing.B) {
+	var buf bytes.Buffer
+	zw := NewWriter(&buf)
+
+	for i := range 310000 {
+		name := fmt.Sprintf("%v", i)
+		zw.CreateHeader(&FileHeader{
+			Name:   name,
+			Method: Store,
+		})
+	}
+
+	if err := zw.Close(); err != nil {
+		b.Fatal(err)
+	}
+	data := buf.Bytes()
+
+	for b.Loop() {
+		zr, err := NewReader(bytes.NewReader(data), int64(len(data)))
+		if err != nil {
+			b.Fatal(err)
+		}
+		zr.Open("does-not-exist")
+	}
+}