Working with Archives

Table of Contents

• Introduction
• Reading files in the archive
  • Simple
  • Advanced: File Iterators
  • Advanced: File Reader
• Reading xattrs
  • Simple

Introduction

The SqshArchive struct represents a squashfs archive. It is created by calling sqsh_archive_open() and is destroyed by calling sqsh_archive_close().

Opening and cleaning up an archive is simple:

struct SqshArchive *archive = sqsh_archive_open("archive.squashfs", NULL, NULL);
assert(archive != NULL);
 
sqsh_archive_close(archive);

Opening with more control:

int err = 0;
struct SqshConfig config = {
    .max_symlink_depth = 10,
    // ...
};
struct SqshArchive *archive = sqsh_archive_open("archive.sqsh", &config, &err);
if (err != 0) {
    sqsh_perror(err, NULL);
    exit(1);
}
 
sqsh_archive_close(archive);

Reading files in the archive

Simple

The simplest way to read a file in the archive is to use sqsh_easy_file_content(). This function returns a pointer to the contents of the file in the archive. The pointer is heap allocated and must be free'd by the caller. The allocated buffer is null terminated. If the file itself contains null bytes, you can get the file size by calling sqsh_easy_file_size().

struct SqshArchive *archive = sqsh_archive_open("archive.squashfs", NULL, NULL);
assert(archive != NULL);
 
uint8_t *content = sqsh_easy_file_content(archive, "/path/to/file.txt", NULL);
uint64_t size = sqsh_easy_file_size2(archive, "/path/to/file.txt", NULL);
fwrite(content, 1, size, stdout);
free(content);
 
sqsh_archive_close(archive);

Advanced: File Iterators

The simple API is fine for small files, but for larger files it is better to use the SqshFileIterator. The iterator allows you to read the file in chunks, which is more efficient than reading the entire file into memory at once.

struct SqshArchive *archive = sqsh_archive_open("archive.squashfs", NULL, NULL);
 
int err = 0;
struct SqshFile *file = sqsh_open(archive, "/path/to/file.txt", &err);
assert(err == 0);
struct SqshFileIterator *it = sqsh_file_iterator_new(file, &err);
assert(err == 0);
while ((err = sqsh_file_iterator_next(it, SIZE_MAX, &err)) > 0) {
    const uint8_t *data = sqsh_file_iterator_data(it);
    size_t size = sqsh_file_iterator_size(it);
    fwrite(data, 1, size, stdout);
}
assert(err == 0);
sqsh_file_iterator_free(it);
sqsh_close(file);
sqsh_archive_close(archive);

Advanced: File Reader

If you need more control over the ranges to be read from the file, you can use the SqshFileReader API. This API allows you to read arbitrary ranges from the file.

struct SqshArchive *archive = sqsh_archive_open("archive.squashfs", NULL, NULL);
 
int err = 0;
struct SqshFile *file = sqsh_open(archive, "/path/to/file.txt", &err);
assert(err == 0);
struct SqshFileReader *reader = sqsh_file_reader_new(file, &err);
assert(err == 0);
err = sqsh_file_reader_advance2(reader, 0, 10);
assert(err == 0);
 
const uint8_t *data = sqsh_file_reader_data(reader);
size_t size = sqsh_file_reader_size(reader);
 
fwrite(data, 1, size, stdout);
sqsh_file_reader_free(reader);
sqsh_close(file);
sqsh_archive_close(archive);

This example reads the first 10 bytes of the file.

Reading xattrs

libsqsh is able to handle handle xattrs of files in the archive.

Simple

The simple way to get an xattr is to use sqsh_easy_xattr_get().

int err = 0;
struct SqshArchive *archive = sqsh_archive_open("archive.squashfs", NULL, NULL);
assert(err == 0);
char *xattr = sqsh_easy_xattr_get(archive, "/path/to/file.txt", "user.myxattr", &err);
assert(err == 0);
puts(xattr);
free(xattr);
sqsh_archive_close(archive);

To get a list of all xattr on a file you can use sqsh_easy_xattr_list "sqsh_easy_xattr_list()".

int err = 0;
struct SqshArchive *archive = sqsh_archive_open("archive.squashfs", NULL, NULL);
assert(err == 0);
char **list = sqsh_easy_xattr_keys(archive, "/path/to/file.txt", &err);
assert(err == 0);
for(int i = 0; list[i] != NULL; i++) {
    puts(list[i]);
}
free(list);
sqsh_archive_close(archive);