/*
 * C implementation of a bencode decoder.
 * This is the format defined by BitTorrent:
 *  http://wiki.theory.org/BitTorrentSpecification#bencoding
 *
 * The only external requirements are a few [standard] function calls and
 * the long long type.  Any sane system should provide all of these things.
 *
 * See the bencode.h header file for usage information.
 *
 * This is released into the public domain:
 *  http://en.wikipedia.org/wiki/Public_Domain
 *
 * Written by:
 *   Mike Frysinger <vapier@gmail.com>
 * And improvements from:
 *   Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
 */

/*
 * This implementation isn't optimized at all as I wrote it to support a bogus
 * system.  I have no real interest in this format.  Feel free to send me
 * patches (so long as you don't copyright them and you release your changes
 * into the public domain as well).
 */

#include <stdlib.h> /* malloc() realloc() free() strtoll() */
#include <string.h> /* memset() */

#include "bencode.h"

static be_node *be_alloc(be_type type)
{
	be_node *ret = (be_node*)malloc(sizeof(*ret));
	if (ret) {
		memset(ret, 0x00, sizeof(*ret));
		ret->type = type;
	}
	return ret;
}

static long long _be_decode_int(const char **data, long long *data_len)
{
	char *endp;
	long long ret = strtoll(*data, &endp, 10);
	*data_len -= (endp - *data);
	*data = endp;
	return ret;
}

long long be_str_len(be_node *node)
{
	long long ret = 0;
	if (node->val.s)
		memcpy(&ret, node->val.s - sizeof(ret), sizeof(ret));
	return ret;
}

static char *_be_decode_str(const char **data, long long *data_len)
{
	long long sllen = _be_decode_int(data, data_len);
	long slen = sllen;
	unsigned long len;
	char *ret = NULL;

	/* slen is signed, so negative values get rejected */
	if (sllen < 0)
		return ret;

	/* reject attempts to allocate large values that overflow the
	 * size_t type which is used with malloc()
	 */
	if (sizeof(long long) != sizeof(long))
		if (sllen != slen)
			return ret;

	/* make sure we have enough data left */
	if (sllen > *data_len - 1)
		return ret;

	/* switch from signed to unsigned so we don't overflow below */
	len = slen;

	if (**data == ':') {
		char *_ret = (char*)malloc(sizeof(sllen) + len + 1);
		memcpy(_ret, &sllen, sizeof(sllen));
		ret = _ret + sizeof(sllen);
		memcpy(ret, *data + 1, len);
		ret[len] = '\0';
		*data += len + 1;
		*data_len -= len + 1;
	}
	return ret;
}

static be_node *_be_decode(const char **data, long long *data_len)
{
	be_node *ret = NULL;

	if (!*data_len)
		return ret;

	switch (**data) {
		/* lists */
	case 'l': {
		unsigned int i = 0;

		ret = be_alloc(BE_LIST);

		--(*data_len);
		++(*data);
		while (**data != 'e') {
			ret->val.l = (be_node**)realloc(ret->val.l, (i + 2) * sizeof(*ret->val.l));
			ret->val.l[i] = _be_decode(data, data_len);
			if (!ret->val.l[i])
				break;
			++i;
		}
		--(*data_len);
		++(*data);

		ret->val.l[i] = NULL;

		return ret;
	}

	/* dictionaries */
	case 'd': {
		unsigned int i = 0;

		ret = be_alloc(BE_DICT);

		--(*data_len);
		++(*data);
		while (**data != 'e') {
			ret->val.d = (be_dict*)realloc(ret->val.d, (i + 2) * sizeof(*ret->val.d));
			ret->val.d[i].key = _be_decode_str(data, data_len);
			ret->val.d[i].val = _be_decode(data, data_len);
			if (!ret->val.l[i])
				break;
			++i;
		}
		--(*data_len);
		++(*data);

		ret->val.d[i].val = NULL;

		return ret;
	}

	/* integers */
	case 'i': {
		ret = be_alloc(BE_INT);

		--(*data_len);
		++(*data);
		ret->val.i = _be_decode_int(data, data_len);
		if (**data != 'e') {
			be_free(ret);
			return NULL;
		}
		--(*data_len);
		++(*data);

		return ret;
	}

	/* byte strings */
	case '0':
	case '1':
	case '2':
	case '3':
	case '4':
	case '5':
	case '6':
	case '7':
	case '8':
	case '9':
	{
		ret = be_alloc(BE_STR);

		ret->val.s = _be_decode_str(data, data_len);

		return ret;
	}

	/* invalid */
	default:
		break;
	}

	return ret;
}

be_node *be_decoden(const char *data, long long len)
{
	return _be_decode(&data, &len);
}

be_node *be_decode(const char *data)
{
	return be_decoden(data, strlen(data));
}

static inline void _be_free_str(char *str)
{
	if (str)
		free(str - sizeof(long long));
}
void be_free(be_node *node)
{
	switch (node->type) {
	case BE_STR:
		_be_free_str(node->val.s);
		break;

	case BE_INT:
		break;

	case BE_LIST: {
		unsigned int i;
		for (i = 0; node->val.l[i]; ++i)
			be_free(node->val.l[i]);
		free(node->val.l);
		break;
	}

	case BE_DICT: {
		unsigned int i;
		for (i = 0; node->val.d[i].val; ++i) {
			_be_free_str(node->val.d[i].key);
			be_free(node->val.d[i].val);
		}
		free(node->val.d);
		break;
	}
	}
	free(node);
}

