minitar

Tiny C library to interact with tar archives

Example

#include <stdio.h>
#include <minitar.h>

int main(int argc, char** argv)
{
	if(argc == 1)
	{
		fprintf(stderr, "Usage: %s [file]\n", argv[0]);
		return 1;
	}
	struct minitar* mp = minitar_open(argv[1]);
	if(!mp)
	{
		perror(argv[1]);
		return 1;
	}
	struct minitar_entry* entry;
	do {
		entry = minitar_read_entry(mp);
		if(entry) { 
			printf("%s\n", entry->metadata.name);
			minitar_free_entry(entry);
		}
	} while(entry);
	minitar_close(mp);
}

The output of this example program when running it with an uncompressed tar archive is identical to that of tar --list -f archive.tar with the same uncompressed archive.

Functions

minitar_open

struct minitar* minitar_open(const char* pathname)

Opens a tar archive for reading, and returns a heap-allocated struct minitar which must be freed with minitar_close() after using it. If opening the file or allocating the struct fails, returns NULL.

A struct minitar is opaque, and should only be passed to other minitar functions. You should not care about its contents.

minitar_read_entry

struct minitar_entry* minitar_read_entry(struct minitar* mp)

Reads the next entry from a struct minitar which should be the return value of a previous call to minitar_open(). The return value is a heap-allocated struct minitar_entry, which should be freed with minitar_free_entry() when no longer needed.

This structure consists of the file metadata (in the metadata field), and a heap-allocated pointer to the file's contents (the ptr field), of size metadata.size + a NULL character, for convenience. This means you can use normal C string functions if you're expecting an ASCII file. Other kinds of files may have NULL characters before the end of the file, so you should assume the length of ptr is metadata.size and not strlen(ptr).

This pointer will be freed when calling minitar_free_entry(), so if you're intending to use the file's contents later, copy them somewhere else.

This function returns NULL on end-of-file (when all entries have been read).

minitar_free_entry

void minitar_free_entry(struct minitar_entry* entry)

Frees the heap-allocated struct minitar_entry and the file contents stored inside it. The pointer passed to minitar_free_entry() should be the return value of a previous call to minitar_read_entry(), minitar_find_by_name() or minitar_find_any_of().

minitar_rewind

void minitar_rewind(struct minitar* mp)

Rewinds the struct minitar back to the beginning of the archive file, which means that the next call to minitar_read_entry() will return the first entry instead of the entry after the last read entry.

minitar_find_by_name

struct minitar_entry* minitar_find_by_name(struct minitar* mp, const char* name)

Returns the first entry with a matching name, or NULL if none are found. The return value is a struct minitar_entry, which is heap-allocated and should be freed after use with minitar_free_entry(). This structure is already documented in the entry documenting minitar_read_entry().

This function starts searching from the current archive position, which means that to find a matching entry in the entire archive minitar_rewind() should be called on it first.

The state of mp after minitar_find_by_name() returns is unspecified, but a successive call to minitar_find_by_name() will return the next matching entry, if there is one. (Calling minitar_find_by_name() in a loop until it returns NULL will return all matching entries.)

In order to perform other minitar operations on the archive, minitar_rewind() should probably be called first, to get a known state.

minitar_find_any_of

struct minitar_entry* minitar_find_any_of(struct minitar* mp, enum minitar_file_type type)

Does the same thing as minitar_find_by_name(), but matches the file type instead of the name. As with minitar_find_by_name(), this function starts searching from the current archive position and calling it in a loop until it returns NULL will return all matching entries.

minitar_close

int minitar_close(struct minitar* mp)

Closes the tar archive file mp points to and frees the heap memory it was using. The pointer passed to minitar_close() should be the return value of a previous call to minitar_open().

Returns 0 on success, everything else is failure and you should check errno.

Types

minitar_file_type

enum minitar_file_type

This enum lists all supported file types:

MTAR_REGULAR: Regular files

MTAR_BLKDEV: Block special devices

MTAR_CHRDEV: Character special devices

MTAR_DIRECTORY: Directories

Other file types supported in tar archives, such as FIFOs or symlinks, are not supported and minitar will throw an error when encountering one of them.

minitar_entry_metadata

struct minitar_entry_metadata

This structure represents an entry's metadata, with the following fields:

name: A string representing the full path of the entry within the archive. (char[])

mode: An integer representing the permissions of the entry. (mode_t)

uid: An integer representing the user ID of the entry's owner. (uid_t)

gid: An integer representing the group ID of the entry's owner. (gid_t)

size: An integer representing the size of the entry's contents in bytes. (size_t)

mtime: A UNIX timestamp representing the last time the entry was modified. (time_t)

type: An enum representing the type of the entry. (enum minitar_file_type)

uname: A string representing the username of the entry's owner. (char[])

gname: A string representing the group name of the entry's owner. (char[])

minitar_entry

struct minitar_entry

An entry in a tar archive. Fields:

metadata: The entry's metadata. (struct minitar_entry_metadata)

ptr: A pointer to the entry's contents, heap-allocated. (char*)

More details about this structure are available in the documentation for minitar_read_entry().

Error handling

When a fatal error occurs, minitar calls the function minitar_handle_panic() with a message describing the error. The default implementation of this function prints the error message out to standard error and aborts.

You might want to handle errors differently. Well, you can override the panic function! Just create a function with the following signature:

noreturn void minitar_handle_panic(const char* message)

and put your error handling code in there. This function will automatically override the default one used by minitar.

This function needs to have C linkage and be unmangled. If you're using other languages, this might not be the case, for example, a C++ implementation would need the following signature:

extern "C" [[noreturn]] void minitar_handle_panic(const char* message)

and a Rust implementation would need:

#[no_mangle]
pub extern "C" fn minitar_handle_panic(message: *const u8) -> !

License

minitar is free and open-source software under the BSD-2-Clause license.