sandboxed-api/oss-internship-2020/sapi_libarchive/examples/untar.cc
2020-09-07 14:11:39 +00:00

278 lines
6.4 KiB
C++

/*
* This file is in the public domain.
* Use it as you wish.
*/
/*
* This is a compact tar extraction program using libarchive whose
* primary goal is small executable size. Statically linked, it can
* be very small, depending in large part on how cleanly factored your
* system libraries are. Note that this uses the standard libarchive,
* without any special recompilation. The only functional concession
* is that this program uses the uid/gid from the archive instead of
* doing uname/gname lookups. (Add a call to
* archive_write_disk_set_standard_lookup() to enable uname/gname
* lookups, but be aware that this can add 500k or more to a static
* executable, depending on the system libraries, since user/group
* lookups frequently pull in password, YP/LDAP, networking, and DNS
* resolver libraries.)
*
* To build:
* $ gcc -static -Wall -o untar untar.c -larchive
* $ strip untar
*
* NOTE: On some systems, you may need to add additional flags
* to ensure that untar.c is compiled the same way as libarchive
* was compiled. In particular, Linux users will probably
* have to add -D_FILE_OFFSET_BITS=64 to the command line above.
*
* For fun, statically compile the following simple hello.c program
* using the same flags as for untar and compare the size:
*
* #include <stdio.h>
* int main(int argc, char **argv) {
* printf("hello, world\n");
* return(0);
* }
*
* You may be even more surprised by the compiled size of true.c listed here:
*
* int main(int argc, char **argv) {
* return (0);
* }
*
* On a slightly customized FreeBSD 5 system that I used around
* 2005, hello above compiled to 89k compared to untar of 69k. So at
* that time, libarchive's tar reader and extract-to-disk routines
* compiled to less code than printf().
*
* On my FreeBSD development system today (August, 2009):
* hello: 195024 bytes
* true: 194912 bytes
* untar: 259924 bytes
*/
#include <iostream>
#include <sys/types.h>
#include <sys/stat.h>
#include <archive.h>
#include <archive_entry.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
static void errmsg(const char *);
static void extract(const char *filename, int do_extract, int flags);
static void fail(const char *, const char *, int);
static int copy_data(struct archive *, struct archive *);
static void msg(const char *);
static void usage(void);
static void warn(const char *, const char *);
static int verbose = 0;
int
main(int argc, const char **argv)
{
const char *filename = NULL;
int compress, flags, mode, opt;
(void)argc;
mode = 'x';
verbose = 0;
compress = '\0';
flags = ARCHIVE_EXTRACT_TIME;
/* Among other sins, getopt(3) pulls in printf(3). */
while (*++argv != NULL && **argv == '-') {
const char *p = *argv + 1;
while ((opt = *p++) != '\0') {
switch (opt) {
case 'f':
if (*p != '\0')
filename = p;
else
filename = *++argv;
p += strlen(p);
break;
case 'p':
flags |= ARCHIVE_EXTRACT_PERM;
flags |= ARCHIVE_EXTRACT_ACL;
flags |= ARCHIVE_EXTRACT_FFLAGS;
break;
case 't':
mode = opt;
break;
case 'v':
verbose++;
break;
case 'x':
mode = opt;
break;
default:
usage();
}
}
}
std::cout << "begin\n";
switch (mode) {
case 't':
extract(filename, 0, flags);
break;
case 'x':
extract(filename, 1, flags);
break;
}
std::cout << "end";
return (0);
}
static void
extract(const char *filename, int do_extract, int flags)
{
struct archive *a;
struct archive *ext;
struct archive_entry *entry;
int r;
a = archive_read_new();
ext = archive_write_disk_new();
archive_write_disk_set_options(ext, flags);
/*
* Note: archive_write_disk_set_standard_lookup() is useful
* here, but it requires library routines that can add 500k or
* more to a static executable.
*/
archive_read_support_format_tar(a);
/*
* On my system, enabling other archive formats adds 20k-30k
* each. Enabling gzip decompression adds about 20k.
* Enabling bzip2 is more expensive because the libbz2 library
* isn't very well factored.
*/
std::cout <<"AAA\n";
if (filename != NULL && strcmp(filename, "-") == 0)
filename = NULL;
if ((r = archive_read_open_filename(a, filename, 10240)))
fail("archive_read_open_filename()",
archive_error_string(a), r);
std::cout << "BBB\n";
for (;;) {
r = archive_read_next_header(a, &entry);
if (r == ARCHIVE_EOF)
break;
if (r != ARCHIVE_OK)
fail("archive_read_next_header()",
archive_error_string(a), 1);
if (verbose && do_extract)
msg("x ");
if (verbose || !do_extract)
msg(archive_entry_pathname(entry));
if (do_extract) {
r = archive_write_header(ext, entry);
if (r != ARCHIVE_OK)
warn("archive_write_header()",
archive_error_string(ext));
else {
copy_data(a, ext);
r = archive_write_finish_entry(ext);
if (r != ARCHIVE_OK)
fail("archive_write_finish_entry()",
archive_error_string(ext), 1);
}
}
if (verbose || !do_extract)
msg("\n");
}
archive_read_close(a);
archive_read_free(a);
archive_write_close(ext);
archive_write_free(ext);
exit(0);
}
static int
copy_data(struct archive *ar, struct archive *aw)
{
int r;
const void *buff;
size_t size;
#if ARCHIVE_VERSION_NUMBER >= 3000000
int64_t offset;
#else
off_t offset;
#endif
for (;;) {
r = archive_read_data_block(ar, &buff, &size, &offset);
if (r == ARCHIVE_EOF)
return (ARCHIVE_OK);
if (r != ARCHIVE_OK)
return (r);
r = archive_write_data_block(aw, buff, size, offset);
if (r != ARCHIVE_OK) {
warn("archive_write_data_block()",
archive_error_string(aw));
return (r);
}
}
}
/*
* These reporting functions use low-level I/O; on some systems, this
* is a significant code reduction. Of course, on many server and
* desktop operating systems, malloc() and even crt rely on printf(),
* which in turn pulls in most of the rest of stdio, so this is not an
* optimization at all there. (If you're going to pay 100k or more
* for printf() anyway, you may as well use it!)
*/
static void
msg(const char *m)
{
write(1, m, strlen(m));
}
static void
errmsg(const char *m)
{
write(2, m, strlen(m));
}
static void
warn(const char *f, const char *m)
{
errmsg(f);
errmsg(" failed: ");
errmsg(m);
errmsg("\n");
}
static void
fail(const char *f, const char *m, int r)
{
warn(f, m);
exit(r);
}
static void
usage(void)
{
const char *m = "Usage: untar [-tvx] [-f file] [file]\n";
errmsg(m);
exit(1);
}