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Diffstat (limited to 'examples/untar.c')
| -rw-r--r-- | examples/untar.c | 262 |
1 files changed, 262 insertions, 0 deletions
diff --git a/examples/untar.c b/examples/untar.c new file mode 100644 index 0000000..e77adf7 --- /dev/null +++ b/examples/untar.c @@ -0,0 +1,262 @@ +/* + * 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 <sys/types.h> +__FBSDID("$FreeBSD$"); + +#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(); + } + } + } + + switch (mode) { + case 't': + extract(filename, 0, flags); + break; + case 'x': + extract(filename, 1, flags); + break; + } + + 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. + */ + if (filename != NULL && strcmp(filename, "-") == 0) + filename = NULL; + if ((r = archive_read_open_file(a, filename, 10240))) + fail("archive_read_open_file()", + archive_error_string(a), r); + 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_finish(a); + exit(0); +} + +static int +copy_data(struct archive *ar, struct archive *aw) +{ + int r; + const void *buff; + size_t size; + off_t offset; + + 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); +} |
