is zip_file_is_seekable reliable ?

[remicollet]

Describe the Bug
zip_file_is_seekable seems unreliable

Expected Behavior
zip_file_is_seekable return 0 when seek not doable

Observed Behavior
zip_file_is_seekable return 1 but zip_fseek fails

To Reproduce
Using https://github.com/pierrejoye/php_zip/blob/master/tests/test.zip

Using "bar" entry, zip_file_is_seekable returns 1 and zip_fseek works
Using "entry1.txt" entry (compressed), zip_file_is_seekable returns 1 but zip_fseek fails

libzip Version
1.9.0

Operating System
Fedora 35

Additional information
zip_file_is_seekable is missing in documentation and test coverage

[remicollet]

FYI WIP in the PHP extension where I discover this problem
https://github.com/pierrejoye/php_zip/commits/feature_stream_seek

[remicollet]

Minimal test:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <zip.h>

#define ARCHIVE "test.zip"

int main(int argc, char *argv[]) {
	zip_t *z;
	zip_file_t *f;
	int i, err = 0;
	struct zip_stat s;

	z = zip_open(ARCHIVE, ZIP_RDONLY, &err);
	if (err || !z) exit(1);
	printf("Open Archive %s\n", ARCHIVE);
	for(i=0 ; f = zip_fopen_index(z, i, 0) ; i++) {
		zip_stat_index(z, i, 0, &s);
		printf(" Open File %d: %s (compress=%d)\n", i, s.name, s.comp_method);
		
		printf("  is_seekable: %d\n", zip_file_is_seekable(f));
		if (s.name[strlen(s.name)-1] == '/')  // directory
			printf("  directory\n");
		else
			printf("  fseek:       %d\n", zip_fseek(f, SEEK_SET, 0));
		zip_fclose(f);
	}
	zip_close(z);
	return 0;
}

Using https://github.com/pierrejoye/php_zip/raw/master/tests/test.zip

Output:

Open Archive phptest.zip
 Open File 0: bar (compress=0)
  is_seekable: 1
  fseek:       0
 Open File 1: foobar/ (compress=0)
  is_seekable: 1
  directory
 Open File 2: foobar/baz (compress=8)
  is_seekable: 1
  fseek:       -1
 Open File 3: entry1.txt (compress=8)
  is_seekable: 1
  fseek:       -1

We can expect zip_file_is_seekable to return 0 for directory (#301) and compressed files.

[remicollet]

Thanks, I confirm the fix is OK

Open Archive phptest.zip
 Open File 0: bar (compress=0)
  is_seekable: 1
  fseek:       0
 Open File 1: foobar/ (compress=0)
  is_seekable: 1
  fseek:       0
 Open File 2: foobar/baz (compress=8)
  is_seekable: 0
  fseek:       -1
 Open File 3: entry1.txt (compress=8)
  is_seekable: 0
  fseek:       -1

Do you plan a 1.9.1 bug release soon?

[dillof]

Just did 😉.

[remicollet]

Just did wink.

Thanks!

[remicollet]

@dillof btw, 1.9.1 still have 1.9.0 :(

#define LIBZIP_VERSION "1.9.0"
#define LIBZIP_VERSION_MAJOR 1
#define LIBZIP_VERSION_MINOR 9
#define LIBZIP_VERSION_MICRO 0