archive/zip: remove unused special case

This removes a special case that was added to fix issue #10956, but that
was never actually effective. The code in the test case still fails to
read, so perhaps the zip64 support added in CL 6463050 inadvertently
caught this particular case.

It's possible that the original theorized bug still exists, but I'm not
convinced it was ever fixed.

Update #28700

Change-Id: I4854de616364510f64a6def30b308686563f8dbb
Reviewed-on: https://go-review.googlesource.com/c/go/+/179757
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/archive/zip/reader.go

@@ -8,7 +8,6 @@ import (
 	"bufio"
 	"encoding/binary"
 	"errors"
-	"fmt"
 	"hash"
 	"hash/crc32"
 	"io"
@@ -84,9 +83,6 @@ func (z *Reader) init(r io.ReaderAt, size int64) error {
 	if err != nil {
 		return err
 	}
-	if end.directoryRecords > uint64(size)/fileHeaderLen {
-		return fmt.Errorf("archive/zip: TOC declares impossible %d files in %d byte zip", end.directoryRecords, size)
-	}
 	z.r = r
 	z.File = make([]*File, 0, end.directoryRecords)
 	z.Comment = end.comment

src/archive/zip/reader_test.go

@@ -981,15 +981,17 @@ func TestIssue10957(t *testing.T) {
 	}
 }
 
-// Verify the number of files is sane.
+// Verify that this particular malformed zip file is rejected.
 func TestIssue10956(t *testing.T) {
 	data := []byte("PK\x06\x06PK\x06\a0000\x00\x00\x00\x00\x00\x00\x00\x00" +
 		"0000PK\x05\x06000000000000" +
 		"0000\v\x00000\x00\x00\x00\x00\x00\x00\x000")
-	_, err := NewReader(bytes.NewReader(data), int64(len(data)))
-	const want = "TOC declares impossible 3472328296227680304 files in 57 byte"
-	if err == nil && !strings.Contains(err.Error(), want) {
-		t.Errorf("error = %v; want %q", err, want)
+	r, err := NewReader(bytes.NewReader(data), int64(len(data)))
+	if err == nil {
+		t.Errorf("got nil error, want ErrFormat")
+	}
+	if r != nil {
+		t.Errorf("got non-nil Reader, want nil")
 	}
 }