4mARCHIVE_WRITE24m(3) Library Functions Manual 4mARCHIVE_WRITE24m(3) 1mNAME0m archive_write — functions for creating archives 1mLIBRARY0m Streaming Archive Library (libarchive, -larchive) 1mSYNOPSIS0m 1m#include 0m 1mDESCRIPTION0m These functions provide a complete API for creating streaming archive files. The general process is to first create the struct archive ob‐ ject, set any desired options, initialize the archive, append entries, then close the archive and release all resources. 1mCreate archive object0m See 4marchive_write_new24m(3). To write an archive, you must first obtain an initialized struct archive object from 1marchive_write_new22m(). 1mEnable filters and formats, configure block size and padding0m See 4marchive_write_filter24m(3), 4marchive_write_format24m(3) and 4marchive_write_blocksize24m(3). You can then modify this object for the desired operations with the various 1marchive_write_set_XXX22m() functions. In particular, you will need to invoke appropriate 1marchive_write_add_XXX22m() and 1marchive_write_set_XXX22m() functions to enable the corresponding compres‐ sion and format support. 1mSet options0m See 4marchive_write_set_options24m(3). 1mOpen archive0m See 4marchive_write_open24m(3). Once you have prepared the struct archive object, you call 1marchive_write_open22m() to actually open the archive and prepare it for writing. There are several variants of this function; the most basic expects you to provide pointers to several functions that can provide blocks of bytes from the archive. There are convenience forms that al‐ low you to specify a filename, file descriptor, 4mFILE24m 4m*24m object, or a block of memory from which to write the archive data. 1mProduce archive0m See 4marchive_write_header24m(3) and 4marchive_write_data24m(3). Individual archive entries are written in a three-step process: You first initialize a struct archive_entry structure with information about the new entry. At a minimum, you should set the pathname of the entry and provide a 4mstruct24m 4mstat24m with a valid 4mst_mode24m field, which spec‐ ifies the type of object and 4mst_size24m field, which specifies the size of the data portion of the object. 1mRelease resources0m See 4marchive_write_free24m(3). After all entries have been written, use the 1marchive_write_free22m() func‐ tion to release all resources. 1mEXAMPLES0m The following sketch illustrates basic usage of the library. In this example, the callback functions are simply wrappers around the standard 4mopen24m(2), 4mwrite24m(2), and 4mclose24m(2) system calls. #ifdef __linux__ #define _FILE_OFFSET_BITS 64 #endif #include #include #include #include #include #include struct mydata { const char *name; int fd; }; int myopen(struct archive *a, void *client_data) { struct mydata *mydata = client_data; mydata->fd = open(mydata->name, O_WRONLY | O_CREAT, 0644); if (mydata->fd >= 0) return (ARCHIVE_OK); else return (ARCHIVE_FATAL); } la_ssize_t mywrite(struct archive *a, void *client_data, const void *buff, size_t n) { struct mydata *mydata = client_data; return (write(mydata->fd, buff, n)); } int myclose(struct archive *a, void *client_data) { struct mydata *mydata = client_data; if (mydata->fd > 0) close(mydata->fd); return (0); } void write_archive(const char *outname, const char **filename) { struct mydata *mydata = malloc(sizeof(struct mydata)); struct archive *a; struct archive_entry *entry; struct stat st; char buff[8192]; int len; int fd; a = archive_write_new(); mydata->name = outname; /* Set archive format and filter according to output file extension. * If it fails, set default format. Platform depended function. * See supported formats in archive_write_set_format_filter_by_ext.c */ if (archive_write_set_format_filter_by_ext(a, outname) != ARCHIVE_OK) { archive_write_add_filter_gzip(a); archive_write_set_format_ustar(a); } archive_write_open(a, mydata, myopen, mywrite, myclose); while (*filename) { stat(*filename, &st); entry = archive_entry_new(); archive_entry_copy_stat(entry, &st); archive_entry_set_pathname(entry, *filename); archive_write_header(a, entry); if ((fd = open(*filename, O_RDONLY)) != -1) { len = read(fd, buff, sizeof(buff)); while (len > 0) { archive_write_data(a, buff, len); len = read(fd, buff, sizeof(buff)); } close(fd); } archive_entry_free(entry); filename++; } archive_write_free(a); } int main(int argc, const char **argv) { const char *outname; argv++; outname = *argv++; write_archive(outname, argv); return 0; } 1mSEE ALSO0m 4mtar24m(1), 4marchive_write_set_options24m(3), 4mlibarchive24m(3), 4mcpio24m(5), 4mmtree24m(5), 4mtar24m(5) 1mHISTORY0m The 1mlibarchive 22mlibrary first appeared in FreeBSD 5.3. 1mAUTHORS0m The 1mlibarchive 22mlibrary was written by Tim Kientzle . 1mBUGS0m There are many peculiar bugs in historic tar implementations that may cause certain programs to reject archives written by this library. For example, several historic implementations calculated header checksums incorrectly and will thus reject valid archives; GNU tar does not fully support pax interchange format; some old tar implementations required specific field terminations. The default pax interchange format eliminates most of the historic tar limitations and provides a generic key/value attribute facility for vendor-defined extensions. One oversight in POSIX is the failure to provide a standard attribute for large device numbers. This library uses “SCHILY.devminor” and “SCHILY.devmajor” for device numbers that exceed the range supported by the backwards-compatible ustar header. These keys are compatible with Joerg Schilling's 1mstar 22marchiver. Other implementations may not recognize these keys and will thus be unable to correctly restore device nodes with large device numbers from archives created by this library. Debian February 2, 2012 4mARCHIVE_WRITE24m(3)