4mARCHIVE_READ24m(3) Library Functions Manual 4mARCHIVE_READ24m(3) 1mNAME0m archive_read — functions for reading streaming archives 1mLIBRARY0m Streaming Archive Library (libarchive, -larchive) 1mSYNOPSIS0m 1m#include 0m 1mDESCRIPTION0m These functions provide a complete API for reading streaming archives. The general process is to first create the struct archive object, set options, initialize the reader, iterate over the archive headers and associated data, then close the archive and release all resources. 1mCreate archive object0m See 4marchive_read_new24m(3). To read an archive, you must first obtain an initialized struct archive object from 1marchive_read_new22m(). 1mEnable filters and formats0m See 4marchive_read_filter24m(3) and 4marchive_read_format24m(3). You can then modify this object for the desired operations with the various 1marchive_read_set_XXX22m() and 1marchive_read_support_XXX22m() func‐ tions. In particular, you will need to invoke appropriate 1marchive_read_support_XXX22m() functions to enable the corresponding com‐ pression and format support. Note that these latter functions perform two distinct operations: they cause the corresponding support code to be linked into your program, and they enable the corresponding auto-de‐ tect code. Unless you have specific constraints, you will generally want to invoke 1marchive_read_support_filter_all22m() and 1marchive_read_support_format_all22m() to enable auto-detect for all formats and compression types currently supported by the library. 1mSet options0m See 4marchive_read_set_options24m(3). 1mOpen archive0m See 4marchive_read_open24m(3). Once you have prepared the struct archive object, you call 1marchive_read_open22m() to actually open the archive and prepare it for reading. 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 read the archive data. Note that the core library makes no assumptions about the size of the blocks read; callback functions are free to read whatever block size is most appro‐ priate for the medium. 1mConsume archive0m See 4marchive_read_header24m(3), 4marchive_read_data24m(3) and 4marchive_read_extract24m(3). Each archive entry consists of a header followed by a certain amount of data. You can obtain the next header with 1marchive_read_next_header22m(), which returns a pointer to an struct archive_entry structure with in‐ formation about the current archive element. If the entry is a regular file, then the header will be followed by the file data. You can use 1marchive_read_data22m() (which works much like the 4mread24m(2) system call) to read this data from the archive, or 1marchive_read_data_block22m() which provides a slightly more efficient interface. You may prefer to use the higher-level 1marchive_read_data_skip22m(), which reads and discards the data for this entry, 1marchive_read_data_into_fd22m(), which copies the data to the provided file descriptor, or 1marchive_read_extract22m(), which recreates the specified entry on disk and copies data from the archive. In particular, note that 1marchive_read_extract22m() uses the struct archive_entry structure that you provide it, which may differ from the entry just read from the archive. In particular, many applications will want to override the pathname, file permissions, or ownership. 1mRelease resources0m See 4marchive_read_free24m(3). Once you have finished reading data from the archive, you should call 1marchive_read_close22m() to close the archive, then call 1marchive_read_free22m() to release all resources, including all memory al‐ located by the library. 1mEXAMPLES0m The following illustrates basic usage of the library. In this example, the callback functions are simply wrappers around the standard 4mopen24m(2), 4mread24m(2), and 4mclose24m(2) system calls. void list_archive(const char *name) { struct mydata *mydata; struct archive *a; struct archive_entry *entry; mydata = malloc(sizeof(struct mydata)); a = archive_read_new(); mydata->name = name; archive_read_support_filter_all(a); archive_read_support_format_all(a); archive_read_open(a, mydata, myopen, myread, myclose); while (archive_read_next_header(a, &entry) == ARCHIVE_OK) { printf("%s\n",archive_entry_pathname(entry)); archive_read_data_skip(a); } archive_read_free(a); free(mydata); } la_ssize_t myread(struct archive *a, void *client_data, const void **buff) { struct mydata *mydata = client_data; *buff = mydata->buff; return (read(mydata->fd, mydata->buff, 10240)); } int myopen(struct archive *a, void *client_data) { struct mydata *mydata = client_data; mydata->fd = open(mydata->name, O_RDONLY); return (mydata->fd >= 0 ? ARCHIVE_OK : ARCHIVE_FATAL); } int myclose(struct archive *a, void *client_data) { struct mydata *mydata = client_data; if (mydata->fd > 0) close(mydata->fd); return (ARCHIVE_OK); } 1mSEE ALSO0m 4mtar24m(1), 4marchive_read_data24m(3), 4marchive_read_extract24m(3), 4marchive_read_filter24m(3), 4marchive_read_format24m(3), 4marchive_read_header24m(3), 4marchive_read_new24m(3), 4marchive_read_open24m(3), 4marchive_read_set_options24m(3), 4marchive_util24m(3), 4mlibarchive24m(3), 4mtar24m(5) 1mHISTORY0m The 1mlibarchive 22mlibrary first appeared in FreeBSD 5.3. 1mAUTHORS0m The 1mlibarchive 22mlibrary was written by Tim Kientzle . 1mBUGS0m Many traditional archiver programs treat empty files as valid empty archives. For example, many implementations of 4mtar24m(1) allow you to ap‐ pend entries to an empty file. Of course, it is impossible to deter‐ mine the format of an empty file by inspecting the contents, so this library treats empty files as having a special “empty” format. Debian February 2, 2012 4mARCHIVE_READ24m(3)