cmlibarchive/libarchive/archive_write.c

/*-
 * Copyright (c) 2003-2010 Tim Kientzle
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR(S) ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "archive_platform.h"
__FBSDID("$FreeBSD: head/lib/libarchive/archive_write.c 201099 2009-12-28 03:03:00Z kientzle $");

/*
 * This file contains the "essential" portions of the write API, that
 * is, stuff that will essentially always be used by any client that
 * actually needs to write an archive.  Optional pieces have been, as
 * far as possible, separated out into separate files to reduce
 * needlessly bloating statically-linked clients.
 */

#ifdef HAVE_SYS_WAIT_H
#include <sys/wait.h>
#endif
#ifdef HAVE_ERRNO_H
#include <errno.h>
#endif
#ifdef HAVE_LIMITS_H
#include <limits.h>
#endif
#include <stdio.h>
#ifdef HAVE_STDLIB_H
#include <stdlib.h>
#endif
#ifdef HAVE_STRING_H
#include <string.h>
#endif
#include <time.h>
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif

#include "archive.h"
#include "archive_entry.h"
#include "archive_private.h"
#include "archive_write_private.h"

static struct archive_vtable *archive_write_vtable(void);

static int	_archive_filter_code(struct archive *, int);
static const char *_archive_filter_name(struct archive *, int);
static int64_t	_archive_filter_bytes(struct archive *, int);
static int  _archive_write_filter_count(struct archive *);
static int	_archive_write_close(struct archive *);
static int	_archive_write_free(struct archive *);
static int	_archive_write_header(struct archive *, struct archive_entry *);
static int	_archive_write_finish_entry(struct archive *);
static ssize_t	_archive_write_data(struct archive *, const void *, size_t);

struct archive_none {
	size_t buffer_size;
	size_t avail;
	char *buffer;
	char *next;
};

static struct archive_vtable *
archive_write_vtable(void)
{
	static struct archive_vtable av;
	static int inited = 0;

	if (!inited) {
		av.archive_close = _archive_write_close;
		av.archive_filter_bytes = _archive_filter_bytes;
		av.archive_filter_code = _archive_filter_code;
		av.archive_filter_name = _archive_filter_name;
		av.archive_filter_count = _archive_write_filter_count;
		av.archive_free = _archive_write_free;
		av.archive_write_header = _archive_write_header;
		av.archive_write_finish_entry = _archive_write_finish_entry;
		av.archive_write_data = _archive_write_data;
		inited = 1;
	}
	return (&av);
}

/*
 * Allocate, initialize and return an archive object.
 */
struct archive *
archive_write_new(void)
{
	struct archive_write *a;
	unsigned char *nulls;

	a = (struct archive_write *)calloc(1, sizeof(*a));
	if (a == NULL)
		return (NULL);
	a->archive.magic = ARCHIVE_WRITE_MAGIC;
	a->archive.state = ARCHIVE_STATE_NEW;
	a->archive.vtable = archive_write_vtable();
	/*
	 * The value 10240 here matches the traditional tar default,
	 * but is otherwise arbitrary.
	 * TODO: Set the default block size from the format selected.
	 */
	a->bytes_per_block = 10240;
	a->bytes_in_last_block = -1;	/* Default */

	/* Initialize a block of nulls for padding purposes. */
	a->null_length = 1024;
	nulls = (unsigned char *)calloc(1, a->null_length);
	if (nulls == NULL) {
		free(a);
		return (NULL);
	}
	a->nulls = nulls;
	return (&a->archive);
}

/*
 * Set the block size.  Returns 0 if successful.
 */
int
archive_write_set_bytes_per_block(struct archive *_a, int bytes_per_block)
{
	struct archive_write *a = (struct archive_write *)_a;
	archive_check_magic(&a->archive, ARCHIVE_WRITE_MAGIC,
	    ARCHIVE_STATE_NEW, "archive_write_set_bytes_per_block");
	a->bytes_per_block = bytes_per_block;
	return (ARCHIVE_OK);
}

/*
 * Get the current block size.  -1 if it has never been set.
 */
int
archive_write_get_bytes_per_block(struct archive *_a)
{
	struct archive_write *a = (struct archive_write *)_a;
	archive_check_magic(&a->archive, ARCHIVE_WRITE_MAGIC,
	    ARCHIVE_STATE_ANY, "archive_write_get_bytes_per_block");
	return (a->bytes_per_block);
}

/*
 * Set the size for the last block.
 * Returns 0 if successful.
 */
int
archive_write_set_bytes_in_last_block(struct archive *_a, int bytes)
{
	struct archive_write *a = (struct archive_write *)_a;
	archive_check_magic(&a->archive, ARCHIVE_WRITE_MAGIC,
	    ARCHIVE_STATE_ANY, "archive_write_set_bytes_in_last_block");
	a->bytes_in_last_block = bytes;
	return (ARCHIVE_OK);
}

/*
 * Return the value set above.  -1 indicates it has not been set.
 */
int
archive_write_get_bytes_in_last_block(struct archive *_a)
{
	struct archive_write *a = (struct archive_write *)_a;
	archive_check_magic(&a->archive, ARCHIVE_WRITE_MAGIC,
	    ARCHIVE_STATE_ANY, "archive_write_get_bytes_in_last_block");
	return (a->bytes_in_last_block);
}

/*
 * dev/ino of a file to be rejected.  Used to prevent adding
 * an archive to itself recursively.
 */
int
archive_write_set_skip_file(struct archive *_a, la_int64_t d, la_int64_t i)
{
	struct archive_write *a = (struct archive_write *)_a;
	archive_check_magic(&a->archive, ARCHIVE_WRITE_MAGIC,
	    ARCHIVE_STATE_ANY, "archive_write_set_skip_file");
	a->skip_file_set = 1;
	a->skip_file_dev = d;
	a->skip_file_ino = i;
	return (ARCHIVE_OK);
}

/*
 * Allocate and return the next filter structure.
 */
struct archive_write_filter *
__archive_write_allocate_filter(struct archive *_a)
{
	struct archive_write *a = (struct archive_write *)_a;
	struct archive_write_filter *f;

	f = calloc(1, sizeof(*f));
	f->archive = _a;
	f->state = ARCHIVE_WRITE_FILTER_STATE_NEW;
	if (a->filter_first == NULL)
		a->filter_first = f;
	else
		a->filter_last->next_filter = f;
	a->filter_last = f;
	return f;
}

/*
 * Write data to a particular filter.
 */
int
__archive_write_filter(struct archive_write_filter *f,
    const void *buff, size_t length)
{
	int r;
	/* Never write to non-open filters */
	if (f->state != ARCHIVE_WRITE_FILTER_STATE_OPEN)
		return(ARCHIVE_FATAL);
	if (length == 0)
		return(ARCHIVE_OK);
	if (f->write == NULL)
		/* If unset, a fatal error has already occurred, so this filter
		 * didn't open. We cannot write anything. */
		return(ARCHIVE_FATAL);
	r = (f->write)(f, buff, length);
	f->bytes_written += length;
	return (r);
}

/*
 * Recursive function for opening the filter chain
 * Last filter is opened first
 */
static int
__archive_write_open_filter(struct archive_write_filter *f)
{
	int ret;

	ret = ARCHIVE_OK;
	if (f->next_filter != NULL)
		ret = __archive_write_open_filter(f->next_filter);
	if (ret != ARCHIVE_OK)
		return (ret);
	if (f->state != ARCHIVE_WRITE_FILTER_STATE_NEW)
		return (ARCHIVE_FATAL);
	if (f->open == NULL) {
		f->state = ARCHIVE_WRITE_FILTER_STATE_OPEN;
		return (ARCHIVE_OK);
	}
	ret = (f->open)(f);
	if (ret == ARCHIVE_OK)
		f->state = ARCHIVE_WRITE_FILTER_STATE_OPEN;
	else
		f->state = ARCHIVE_WRITE_FILTER_STATE_FATAL;
	return (ret);
}

/*
 * Open all filters
 */
static int
__archive_write_filters_open(struct archive_write *a)
{
	return (__archive_write_open_filter(a->filter_first));
}

/*
 * Close all filtes
 */
static int
__archive_write_filters_close(struct archive_write *a)
{
	struct archive_write_filter *f;
	int ret, ret1;
	ret = ARCHIVE_OK;
	for (f = a->filter_first; f != NULL; f = f->next_filter) {
		/* Do not close filters that are not open */
		if (f->state == ARCHIVE_WRITE_FILTER_STATE_OPEN) {
			if (f->close != NULL) {
				ret1 = (f->close)(f);
				if (ret1 < ret)
					ret = ret1;
				if (ret1 == ARCHIVE_OK) {
					f->state =
					    ARCHIVE_WRITE_FILTER_STATE_CLOSED;
				} else {
					f->state =
					    ARCHIVE_WRITE_FILTER_STATE_FATAL;
				}
			} else
				f->state = ARCHIVE_WRITE_FILTER_STATE_CLOSED;
		}
	}
	return (ret);
}

int
__archive_write_output(struct archive_write *a, const void *buff, size_t length)
{
	return (__archive_write_filter(a->filter_first, buff, length));
}

int
__archive_write_nulls(struct archive_write *a, size_t length)
{
	if (length == 0)
		return (ARCHIVE_OK);

	while (length > 0) {
		size_t to_write = length < a->null_length ? length : a->null_length;
		int r = __archive_write_output(a, a->nulls, to_write);
		if (r < ARCHIVE_OK)
			return (r);
		length -= to_write;
	}
	return (ARCHIVE_OK);
}

static int
archive_write_client_open(struct archive_write_filter *f)
{
	struct archive_write *a = (struct archive_write *)f->archive;
	struct archive_none *state;
	void *buffer;
	size_t buffer_size;
	int ret;

	f->bytes_per_block = archive_write_get_bytes_per_block(f->archive);
	f->bytes_in_last_block =
	    archive_write_get_bytes_in_last_block(f->archive);
	buffer_size = f->bytes_per_block;

	state = (struct archive_none *)calloc(1, sizeof(*state));
	buffer = (char *)malloc(buffer_size);
	if (state == NULL || buffer == NULL) {
		free(state);
		free(buffer);
		archive_set_error(f->archive, ENOMEM,
		    "Can't allocate data for output buffering");
		return (ARCHIVE_FATAL);
	}

	state->buffer_size = buffer_size;
	state->buffer = buffer;
	state->next = state->buffer;
	state->avail = state->buffer_size;
	f->data = state;

	if (a->client_opener == NULL)
		return (ARCHIVE_OK);
	ret = a->client_opener(f->archive, a->client_data);
	if (ret != ARCHIVE_OK) {
		free(state->buffer);
		free(state);
		f->data = NULL;
	}
	return (ret);
}

static int
archive_write_client_write(struct archive_write_filter *f,
    const void *_buff, size_t length)
{
	struct archive_write *a = (struct archive_write *)f->archive;
        struct archive_none *state = (struct archive_none *)f->data;
	const char *buff = (const char *)_buff;
	ssize_t remaining, to_copy;
	ssize_t bytes_written;

	remaining = length;

	/*
	 * If there is no buffer for blocking, just pass the data
	 * straight through to the client write callback.  In
	 * particular, this supports "no write delay" operation for
	 * special applications.  Just set the block size to zero.
	 */
	if (state->buffer_size == 0) {
		while (remaining > 0) {
			bytes_written = (a->client_writer)(&a->archive,
			    a->client_data, buff, remaining);
			if (bytes_written <= 0)
				return (ARCHIVE_FATAL);
			remaining -= bytes_written;
			buff += bytes_written;
		}
		return (ARCHIVE_OK);
	}

	/* If the copy buffer isn't empty, try to fill it. */
	if (state->avail < state->buffer_size) {
		/* If buffer is not empty... */
		/* ... copy data into buffer ... */
		to_copy = ((size_t)remaining > state->avail) ?
			state->avail : (size_t)remaining;
		memcpy(state->next, buff, to_copy);
		state->next += to_copy;
		state->avail -= to_copy;
		buff += to_copy;
		remaining -= to_copy;
		/* ... if it's full, write it out. */
		if (state->avail == 0) {
			char *p = state->buffer;
			size_t to_write = state->buffer_size;
			while (to_write > 0) {
				bytes_written = (a->client_writer)(&a->archive,
				    a->client_data, p, to_write);
				if (bytes_written <= 0)
					return (ARCHIVE_FATAL);
				if ((size_t)bytes_written > to_write) {
					archive_set_error(&(a->archive),
					    -1, "write overrun");
					return (ARCHIVE_FATAL);
				}
				p += bytes_written;
				to_write -= bytes_written;
			}
			state->next = state->buffer;
			state->avail = state->buffer_size;
		}
	}

	while ((size_t)remaining >= state->buffer_size) {
		/* Write out full blocks directly to client. */
		bytes_written = (a->client_writer)(&a->archive,
		    a->client_data, buff, state->buffer_size);
		if (bytes_written <= 0)
			return (ARCHIVE_FATAL);
		buff += bytes_written;
		remaining -= bytes_written;
	}

	if (remaining > 0) {
		/* Copy last bit into copy buffer. */
		memcpy(state->next, buff, remaining);
		state->next += remaining;
		state->avail -= remaining;
	}
	return (ARCHIVE_OK);
}

static int
archive_write_client_free(struct archive_write_filter *f)
{
	struct archive_write *a = (struct archive_write *)f->archive;

	if (a->client_freer)
		(*a->client_freer)(&a->archive, a->client_data);
	a->client_data = NULL;

	/* Clear passphrase. */
	if (a->passphrase != NULL) {
		memset(a->passphrase, 0, strlen(a->passphrase));
		free(a->passphrase);
		a->passphrase = NULL;
	}

	return (ARCHIVE_OK);
}

static int
archive_write_client_close(struct archive_write_filter *f)
{
	struct archive_write *a = (struct archive_write *)f->archive;
	struct archive_none *state = (struct archive_none *)f->data;
	ssize_t block_length;
	ssize_t target_block_length;
	ssize_t bytes_written;
	int ret = ARCHIVE_OK;

	/* If there's pending data, pad and write the last block */
	if (state->next != state->buffer) {
		block_length = state->buffer_size - state->avail;

		/* Tricky calculation to determine size of last block */
		if (a->bytes_in_last_block <= 0)
			/* Default or Zero: pad to full block */
			target_block_length = a->bytes_per_block;
		else
			/* Round to next multiple of bytes_in_last_block. */
			target_block_length = a->bytes_in_last_block *
			    ( (block_length + a->bytes_in_last_block - 1) /
			        a->bytes_in_last_block);
		if (target_block_length > a->bytes_per_block)
			target_block_length = a->bytes_per_block;
		if (block_length < target_block_length) {
			memset(state->next, 0,
			    target_block_length - block_length);
			block_length = target_block_length;
		}
		bytes_written = (a->client_writer)(&a->archive,
		    a->client_data, state->buffer, block_length);
		ret = bytes_written <= 0 ? ARCHIVE_FATAL : ARCHIVE_OK;
	}
	if (a->client_closer)
		(*a->client_closer)(&a->archive, a->client_data);
	free(state->buffer);
	free(state);

	/* Clear the close handler myself not to be called again. */
	f->state = ARCHIVE_WRITE_FILTER_STATE_CLOSED;
	return (ret);
}

/*
 * Open the archive using the current settings.
 */
int
archive_write_open2(struct archive *_a, void *client_data,
    archive_open_callback *opener, archive_write_callback *writer,
    archive_close_callback *closer, archive_free_callback *freer)
{
	struct archive_write *a = (struct archive_write *)_a;
	struct archive_write_filter *client_filter;
	int ret, r1;

	archive_check_magic(&a->archive, ARCHIVE_WRITE_MAGIC,
	    ARCHIVE_STATE_NEW, "archive_write_open");
	archive_clear_error(&a->archive);

	a->client_writer = writer;
	a->client_opener = opener;
	a->client_closer = closer;
	a->client_freer = freer;
	a->client_data = client_data;

	client_filter = __archive_write_allocate_filter(_a);
	client_filter->open = archive_write_client_open;
	client_filter->write = archive_write_client_write;
	client_filter->close = archive_write_client_close;
	client_filter->free = archive_write_client_free;

	ret = __archive_write_filters_open(a);
	if (ret < ARCHIVE_WARN) {
		r1 = __archive_write_filters_close(a);
		__archive_write_filters_free(_a);
		return (r1 < ret ? r1 : ret);
	}

	a->archive.state = ARCHIVE_STATE_HEADER;
	if (a->format_init)
		ret = (a->format_init)(a);
	return (ret);
}

int
archive_write_open(struct archive *_a, void *client_data,
    archive_open_callback *opener, archive_write_callback *writer,
    archive_close_callback *closer)
{
	return archive_write_open2(_a, client_data, opener, writer,
	    closer, NULL);
}

/*
 * Close out the archive.
 */
static int
_archive_write_close(struct archive *_a)
{
	struct archive_write *a = (struct archive_write *)_a;
	int r = ARCHIVE_OK, r1 = ARCHIVE_OK;

	archive_check_magic(&a->archive, ARCHIVE_WRITE_MAGIC,
	    ARCHIVE_STATE_ANY | ARCHIVE_STATE_FATAL,
	    "archive_write_close");
	if (a->archive.state == ARCHIVE_STATE_NEW
	    || a->archive.state == ARCHIVE_STATE_CLOSED)
		return (ARCHIVE_OK); /* Okay to close() when not open. */

	archive_clear_error(&a->archive);

	/* Finish the last entry if a finish callback is specified */
	if (a->archive.state == ARCHIVE_STATE_DATA
	    && a->format_finish_entry != NULL)
		r = ((a->format_finish_entry)(a));

	/* Finish off the archive. */
	/* TODO: have format closers invoke compression close. */
	if (a->format_close != NULL) {
		r1 = (a->format_close)(a);
		if (r1 < r)
			r = r1;
	}

	/* Finish the compression and close the stream. */
	r1 = __archive_write_filters_close(a);
	if (r1 < r)
		r = r1;

	if (a->archive.state != ARCHIVE_STATE_FATAL)
		a->archive.state = ARCHIVE_STATE_CLOSED;
	return (r);
}

static int
_archive_write_filter_count(struct archive *_a)
{
	struct archive_write *a = (struct archive_write *)_a;
	struct archive_write_filter *p = a->filter_first;
	int count = 0;
	while(p) {
		count++;
		p = p->next_filter;
	}
	return count;
}

void
__archive_write_filters_free(struct archive *_a)
{
	struct archive_write *a = (struct archive_write *)_a;
	int r = ARCHIVE_OK, r1;

	while (a->filter_first != NULL) {
		struct archive_write_filter *next
		    = a->filter_first->next_filter;
		if (a->filter_first->free != NULL) {
			r1 = (*a->filter_first->free)(a->filter_first);
			if (r > r1)
				r = r1;
		}
		free(a->filter_first);
		a->filter_first = next;
	}
	a->filter_last = NULL;
}

/*
 * Destroy the archive structure.
 *
 * Be careful: user might just call write_new and then write_free.
 * Don't assume we actually wrote anything or performed any non-trivial
 * initialization.
 */
static int
_archive_write_free(struct archive *_a)
{
	struct archive_write *a = (struct archive_write *)_a;
	int r = ARCHIVE_OK, r1;

	if (_a == NULL)
		return (ARCHIVE_OK);
	/* It is okay to call free() in state FATAL. */
	archive_check_magic(&a->archive, ARCHIVE_WRITE_MAGIC,
	    ARCHIVE_STATE_ANY | ARCHIVE_STATE_FATAL, "archive_write_free");
	if (a->archive.state != ARCHIVE_STATE_FATAL)
		r = archive_write_close(&a->archive);

	/* Release format resources. */
	if (a->format_free != NULL) {
		r1 = (a->format_free)(a);
		if (r1 < r)
			r = r1;
	}

	__archive_write_filters_free(_a);

	/* Release various dynamic buffers. */
	free((void *)(uintptr_t)(const void *)a->nulls);
	archive_string_free(&a->archive.error_string);
	if (a->passphrase != NULL) {
		/* A passphrase should be cleaned. */
		memset(a->passphrase, 0, strlen(a->passphrase));
		free(a->passphrase);
	}
	a->archive.magic = 0;
	__archive_clean(&a->archive);
	free(a);
	return (r);
}

/*
 * Write the appropriate header.
 */
static int
_archive_write_header(struct archive *_a, struct archive_entry *entry)
{
	struct archive_write *a = (struct archive_write *)_a;
	int ret, r2;

	archive_check_magic(&a->archive, ARCHIVE_WRITE_MAGIC,
	    ARCHIVE_STATE_DATA | ARCHIVE_STATE_HEADER, "archive_write_header");
	archive_clear_error(&a->archive);

	if (a->format_write_header == NULL) {
		archive_set_error(&(a->archive), -1,
		    "Format must be set before you can write to an archive.");
		a->archive.state = ARCHIVE_STATE_FATAL;
		return (ARCHIVE_FATAL);
	}

	/* In particular, "retry" and "fatal" get returned immediately. */
	ret = archive_write_finish_entry(&a->archive);
	if (ret == ARCHIVE_FATAL) {
		a->archive.state = ARCHIVE_STATE_FATAL;
		return (ARCHIVE_FATAL);
	}
	if (ret < ARCHIVE_OK && ret != ARCHIVE_WARN)
		return (ret);

	if (a->skip_file_set &&
	    archive_entry_dev_is_set(entry) &&
	    archive_entry_ino_is_set(entry) &&
	    archive_entry_dev(entry) == (dev_t)a->skip_file_dev &&
	    archive_entry_ino64(entry) == a->skip_file_ino) {
		archive_set_error(&a->archive, 0,
		    "Can't add archive to itself");
		return (ARCHIVE_FAILED);
	}

	/* Format and write header. */
	r2 = ((a->format_write_header)(a, entry));
	if (r2 == ARCHIVE_FAILED) {
		return (ARCHIVE_FAILED);
	}
	if (r2 == ARCHIVE_FATAL) {
		a->archive.state = ARCHIVE_STATE_FATAL;
		return (ARCHIVE_FATAL);
	}
	if (r2 < ret)
		ret = r2;

	a->archive.state = ARCHIVE_STATE_DATA;
	return (ret);
}

static int
_archive_write_finish_entry(struct archive *_a)
{
	struct archive_write *a = (struct archive_write *)_a;
	int ret = ARCHIVE_OK;

	archive_check_magic(&a->archive, ARCHIVE_WRITE_MAGIC,
	    ARCHIVE_STATE_HEADER | ARCHIVE_STATE_DATA,
	    "archive_write_finish_entry");
	if (a->archive.state & ARCHIVE_STATE_DATA
	    && a->format_finish_entry != NULL)
		ret = (a->format_finish_entry)(a);
	a->archive.state = ARCHIVE_STATE_HEADER;
	return (ret);
}

/*
 * Note that the compressor is responsible for blocking.
 */
static ssize_t
_archive_write_data(struct archive *_a, const void *buff, size_t s)
{
	struct archive_write *a = (struct archive_write *)_a;
	const size_t max_write = INT_MAX;

	archive_check_magic(&a->archive, ARCHIVE_WRITE_MAGIC,
	    ARCHIVE_STATE_DATA, "archive_write_data");
	/* In particular, this catches attempts to pass negative values. */
	if (s > max_write)
		s = max_write;
	archive_clear_error(&a->archive);
	return ((a->format_write_data)(a, buff, s));
}

static struct archive_write_filter *
filter_lookup(struct archive *_a, int n)
{
	struct archive_write *a = (struct archive_write *)_a;
	struct archive_write_filter *f = a->filter_first;
	if (n == -1)
		return a->filter_last;
	if (n < 0)
		return NULL;
	while (n > 0 && f != NULL) {
		f = f->next_filter;
		--n;
	}
	return f;
}

static int
_archive_filter_code(struct archive *_a, int n)
{
	struct archive_write_filter *f = filter_lookup(_a, n);
	return f == NULL ? -1 : f->code;
}

static const char *
_archive_filter_name(struct archive *_a, int n)
{
	struct archive_write_filter *f = filter_lookup(_a, n);
	return f != NULL ? f->name : NULL;
}

static int64_t
_archive_filter_bytes(struct archive *_a, int n)
{
	struct archive_write_filter *f = filter_lookup(_a, n);
	return f == NULL ? -1 : f->bytes_written;
}