torrent.c

/* $Id: torrent.c,v 1.108 2008-10-06 18:47:11 niallo Exp $ */
/*
 * Copyright (c) 2006, 2007 Niall O'Higgins <niallo@unworkable.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <sys/types.h>
#include <sys/mman.h>
#include <sys/param.h>
#include <sys/stat.h>

#include <errno.h>
#include <fcntl.h>
#include <libgen.h>
#include <limits.h>
#include <sha1.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

#if defined(__linux__) || defined(__CYGWIN__) || defined(__GLIBC__)
#include <sys/file.h>
#endif

/* solaris 10 */
#if defined(__SVR4) && defined(__sun)
#include "/usr/ucbinclude/sys/file.h"
#endif


#include "includes.h"


/*
 * torrent_parse_infohash()
 *
 * Compute torrent file infohash, returning a 20 byte array.
 */
u_int8_t *
torrent_parse_infohash(const char *file, size_t infoend)
{
	SHA1_CTX sha;
	u_int8_t result[SHA1_DIGEST_LENGTH], *ret;
	char *p, *buf;
	BUF *b;
	size_t len;

	if (infoend == 0)
		errx(1, "torrent_parse_infohash: infoend is zero - error parsing torrent file");
	if ((b = buf_load(file, BUF_AUTOEXT)) == NULL)
		exit(1);

	len = buf_len(b);
	buf = buf_release(b);
	p = buf;
#define INFO_STR "4:info"
	p = strstr(buf, INFO_STR);
	if (p == NULL)
		errx(1, "torrent_parse_infohash: no info key found");
	p += strlen(INFO_STR);

	SHA1Init(&sha);
	SHA1Update(&sha, p, (infoend - (p - buf)));
	SHA1Final(result, &sha);

	len = SHA1_DIGEST_LENGTH;
	ret = xmalloc(len);
	memcpy(ret, result, SHA1_DIGEST_LENGTH);
	xfree(buf);

	return (ret);
}

/*
 * torrent_parse_file()
 *
 * Parse a .torrent data file, returning a discrete torrent structure.
 */
struct torrent *
torrent_parse_file(const char *file)
{
	struct torrent_file		*multi_file;
	struct torrent			*torrent;
	struct benc_node		*troot, *node, *lnode, *tnode;
	struct benc_node		*filenode, *childnode;
	BUF				*buf;
	int				l;
	size_t				ret;

	torrent = xmalloc(sizeof(*torrent));

	memset(torrent, 0, sizeof(*torrent));
	torrent->name = xstrdup(file);

	/* XXX need a way to free torrents and their node trees */
	torrent->broot = benc_root_create();

	if ((buf = buf_load(file, 0)) == NULL)
		err(1, "torrent_parse_file: buf_load");

	if ((troot = benc_parse_buf(buf, torrent->broot)) == NULL)
		errx(1, "torrent_parse_file: yyparse of %s", file);

	buf_free(in);
	if ((node = benc_node_find(troot, "info")) == NULL)
		errx(1, "no info data found in torrent");
	torrent->info_hash = torrent_parse_infohash(file, node->end);

	if ((node = benc_node_find(troot, "announce")) == NULL)
		errx(1, "no announce data found in torrent");

	if (node->flags & BSTRING)
		torrent->announce = node->body.string.value;
	else
		errx(1, "announce value is not a string");

	if ((node = benc_node_find(troot, "comment")) != NULL
	    && node->flags & BSTRING)
		torrent->comment = node->body.string.value;

	if ((filenode = benc_node_find(troot, "files")) == NULL) {
		torrent->type = SINGLEFILE;
		if ((node = benc_node_find(troot, "length")) == NULL)
			errx(1, "no length field");

		if (!(node->flags & BINT))
			errx(1, "length is not a number");

		torrent->body.singlefile.tfp.file_length = node->body.number;
		torrent->left = torrent->body.singlefile.tfp.file_length;

		if ((node = benc_node_find(troot, "name")) == NULL)
			errx(1, "no name field");

		if (!(node->flags & BSTRING))
			errx(1, "name is not a string");

		torrent->body.singlefile.tfp.path = node->body.string.value;

		if ((node = benc_node_find(troot, "piece length")) == NULL)
			errx(1, "no piece length field");

		if (!(node->flags & BINT))
			errx(1, "piece length is not a number");

		torrent->piece_length = node->body.number;

		if ((node = benc_node_find(troot, "pieces")) == NULL)
			errx(1, "no pieces field");

		if (!(node->flags & BSTRING))
			errx(1, "pieces is not a string");

		torrent->body.singlefile.pieces = node->body.string.value;
		torrent->num_pieces = node->body.string.len / SHA1_DIGEST_LENGTH;

		if ((node = benc_node_find(troot, "md5sum")) != NULL) {
			if (!(node->flags & BSTRING))
				errx(1, "md5sum is not a string");
			else
				torrent->body.singlefile.tfp.md5sum =
				    node->body.string.value;
		}
	} else {
		torrent->type = MULTIFILE;
		if ((node = benc_node_find(troot, "name")) == NULL)
			errx(1, "no name field");

		if (!(node->flags & BSTRING))
			errx(1, "name is not a string");

		torrent->body.multifile.name = node->body.string.value;

		if ((node = benc_node_find(troot, "piece length")) == NULL)
			errx(1, "no piece length field");

		if (!(node->flags & BINT))
			errx(1, "piece length is not a number");

		torrent->piece_length = node->body.number;

		if ((node = benc_node_find(troot, "pieces")) == NULL)
			errx(1, "no pieces field");

		if (!(node->flags & BSTRING))
			errx(1, "pieces is not a string");

		torrent->body.multifile.pieces = node->body.string.value;
		torrent->body.singlefile.pieces = node->body.string.value;
		torrent->num_pieces = node->body.string.len / SHA1_DIGEST_LENGTH;

		TAILQ_INIT(&torrent->body.multifile.files);

		/* iterate through sub-dictionaries */
		TAILQ_FOREACH(childnode, &filenode->children, benc_nodes) {
			multi_file = xmalloc(sizeof(*multi_file));

			memset(multi_file, 0, sizeof(*multi_file));
			if ((tnode = benc_node_find(childnode, "length")) == NULL)
				errx(1, "no length field");
			if (!(tnode->flags & BINT))
				errx(1, "length is not a number");
			multi_file->file_length = tnode->body.number;
			torrent->body.multifile.total_length +=
			    tnode->body.number;
			torrent->left = torrent->body.multifile.total_length;
			if ((tnode = benc_node_find(childnode, "md5sum")) != NULL
			    && tnode->flags & BSTRING)
				multi_file->md5sum = tnode->body.string.value;

			if ((tnode = benc_node_find(childnode, "path")) == NULL)
				errx(1, "no path field");
			if (!(tnode->flags & BLIST))
				errx(1, "path is not a list");

			multi_file->path = xmalloc(MAXPATHLEN);

			memset(multi_file->path, '\0', MAXPATHLEN);

			TAILQ_FOREACH(lnode, &tnode->children, benc_nodes) {
				if (!(lnode->flags & BSTRING))
					errx(1, "path element is not a string");
				if (*multi_file->path == '\0') {
					ret = strlcpy(multi_file->path,
					    lnode->body.string.value,
					    MAXPATHLEN);
					if (ret >= MAXPATHLEN)
						errx(1, "path too large");
				} else {
					l = snprintf(multi_file->path,
					    MAXPATHLEN, "%s/%s",
					    multi_file->path,
					    lnode->body.string.value);
					if (l == -1 || l >= MAXPATHLEN)
						errx(1, "path too large");
				}
			}

			TAILQ_INSERT_TAIL(&torrent->body.multifile.files,
			    multi_file, files);
		}
	}

	if ((node = benc_node_find(troot, "created by")) != NULL
	    && node->flags & BSTRING)
		torrent->created_by = node->body.string.value;

	if ((node = benc_node_find(troot, "creation date")) != NULL
	    && node->flags & BINT)
		torrent->creation_date = node->body.number;

	return (torrent);
}

/*
 * torrent_print()
 *
 * Util function to print various details about the parsed torrent.
 */
void
torrent_print(struct torrent *torrent)
{
	struct torrent_file *tfile;
	int i;

	printf("announce url:\t%s\n", torrent->announce);
	printf("created by:\t");
	if (torrent->created_by == NULL)
		printf("NONE\n");
	else
		printf("%s\n", torrent->created_by);
	printf("creation date:\t");
	if (torrent->creation_date == 0)
		printf("NONE\n");
	else
		printf("%s", ctime(&torrent->creation_date));
	printf("comment:\t");
	if (torrent->comment == NULL)
		printf("NONE\n");
	else
		printf("%s\n", torrent->comment);
	printf("info hash:\t0x");
	for (i = 0; i < SHA1_DIGEST_LENGTH; i++)
		printf("%02x", torrent->info_hash[i]);
	putchar('\n');
	printf("pieces:\t\t%u\n", torrent->num_pieces);
	printf("type:\t\t");
	if (torrent->type == SINGLEFILE) {
		tfile = &torrent->body.singlefile.tfp;
		printf("single file\n");
		printf("length:\t\t%jd bytes\n", (intmax_t)tfile->file_length);
		printf("file name:\t%s\n", tfile->path);
		printf("piece length:\t%u bytes\n",
		    torrent->piece_length);
		printf("md5sum:\t\t");
		if (tfile->md5sum == NULL)
			printf("NONE\n");
		else
			printf("%s\n", tfile->md5sum);
	} else {
		printf("multi file\n");
		printf("base path:\t%s\n",
		    torrent->body.multifile.name);
		printf("piece length:\t%u bytes\n",
		    torrent->piece_length);
		printf("--files--\n");
		TAILQ_FOREACH(tfile, &torrent->body.multifile.files, files) {
			printf("file name:\t%s\n", tfile->path);
			printf("length:\t\t%jd bytes\n", (intmax_t)tfile->file_length);
			printf("md5sum:\t\t");
			if (tfile->md5sum == NULL)
				printf("NONE\n");
			else
				printf("%s\n", tfile->md5sum);
		}
	}
}

/*
 * torrent_block_write()
 *
 * Write arbitrary binary data to given piece at supplied offset.
 */
void
torrent_block_write(struct torrent_piece *tpp, off_t off, u_int32_t len, void *d)
{
	struct torrent_mmap *tmmp;
	off_t cntlen = 0, cntbase = 0;
	u_int8_t *aptr;
	u_int32_t tlen, bytesleft = len, diff = 0;

	trace("torrent_block_write tpp->idx: %u off: %u len: %u", tpp->index, off, len);
	TAILQ_FOREACH(tmmp, &tpp->mmaps, mmaps) {
		if (bytesleft < len) {
			diff = len - bytesleft;
			/* write as much as we can here and jump to next
			 * mapping if required*/
			if (bytesleft > tmmp->len) {
				memcpy(tmmp->addr, (u_int8_t *)d + diff,
				    tmmp->len);
				bytesleft -= tmmp->len;
				continue;
			}
			/* done once we make it here */
			memcpy(tmmp->addr, (u_int8_t *)d + diff, bytesleft);
			return;

		}
		cntlen += tmmp->len;
		if (cntlen < off) {
			cntbase += tmmp->len;
			continue;
		} else {
			aptr = tmmp->addr;
			for (; cntbase < off; cntbase++)
				aptr++;
			tlen = tmmp->len - (aptr - (u_int8_t *)tmmp->addr);
			/* its possible that we are writing more bytes than
			 * remain in this single mapping.  in this case,
			 * we need to write the remainder to the next
			 * mapping(s)*/
			if (len > tlen) {
				memcpy(aptr, d, tlen);
				bytesleft -= tlen;
				continue;
			}
			memcpy(aptr, d, len);
			return;
		}
	}
}

/*
 * torrent_block_read()
 *
 * Read a given block of a piece.  This handles pieces which overlap
 * multiple files.  Data copies may be necessary under certain circumstances.
 * For this reason, caller should check the value of "hint".  If it is 1,
 * caller must free the data returned when done with it.
 */
void *
torrent_block_read(struct torrent_piece *tpp, off_t off, u_int32_t len, int *hint)
{
	void *block;
	u_int8_t *aptr, *bptr;
	struct torrent_mmap *tmmp;
	off_t cntlen = 0, cntbase = 0;
	u_int32_t tlen = len, ilen;

	*hint = 0;
	block = NULL;
	bptr = NULL;

	trace("torrent_block_read tpp->idx: %u off: %u len: %u", tpp->index, off, len);
	TAILQ_FOREACH(tmmp, &tpp->mmaps, mmaps) {
		/* sum the lengths of the mappings we visit. if the offset is
		   greater than the current sum, then the requested data is
		   not within this mapping so continue to next mapping */
		cntlen += tmmp->len;
		if (cntlen < off) {
			/* we need to maintain a base length so that we
			   know how far we need to move the pointer to reach
			   the offset */
			cntbase += tmmp->len;
			continue;
		} else {
			/* our offset is within this mapping, but we still
			   might need to bring the pointer up to it */
			aptr = tmmp->addr;
			/* (off - cntbase) is the distance from the start of
			 * mapping that we need to traverse to get to the
			 * offset. */
			/* ilen is the length remaining in the mapping, after
			 * the walk */
			ilen = tmmp->len - (off - cntbase);
			if (ilen > tmmp->len)
				errx(1, "overflow: ilen > tmmp->len");
			for(; cntbase < off; cntbase++)
				aptr++;

			trace("torrent_block_read: off: %jd len: %u ilen: %u (off - cntbase): %jd tmmp->len: %u tlen: %u file: %s md5sum: %s", off, len, ilen, off - cntbase, tmmp->len, tlen, tmmp->tfp->path, tmmp->tfp->md5sum);
			/* this mapping might not contain as many bytes as
			   we requested.  in that case, copy as many as
			   possible and continue to next mapping */
			if (ilen < tlen) {
				/* make sure we only malloc once */
				if (*hint == 0) {
					block = xmalloc(len);
					bptr = block;
					*hint = 1;
				}
				memcpy(bptr, aptr, ilen);
				bptr += ilen;
				tlen -= ilen;
			} else {
				/* if possible, do not do a buffer copy,
				 * but return the mmaped base address directly
				 */
				if (*hint == 0) {
					return (aptr);
				}
				memcpy(bptr, aptr, tlen);
				return (block);
			}
		}
	}
	if (*hint == 1) {
		return (block);
	}

	return (NULL);
}

/*
 * torrent_piece_find()
 *
 * Look up the torrent piece at a given index.
 */
struct torrent_piece *
torrent_piece_find(struct torrent *tp, u_int32_t idx)
{
	struct torrent_piece *tpp;
	if (idx > tp->num_pieces - 1)
		errx(1, "torrent_piece_find: index %u out of bounds", idx);
	tpp = tp->piece_array + idx;

	return (tpp);
}

/*
 * torrent_mmap_create()
 *
 * Create the mmap corresponding to a given offset and length of a supplied
 * torrent file.  Also handles zero'ing the file if necessary.
 */
struct torrent_mmap *
torrent_mmap_create(struct torrent *tp, struct torrent_file *tfp, off_t off,
    u_int32_t len)
{
	struct torrent_mmap *tmmp;
	struct stat sb;
	char buf[MAXPATHLEN], *buf2, zero = 0x00, *basedir;
	int openflags, mmapflags, fd = 0, l;
	long pagesize;
	u_int8_t *nearest_page = NULL;
	off_t page_off = 0;

	if ((pagesize = sysconf(_SC_PAGESIZE)) == -1)
		err(1, "torrent_mmap_create: sysconf");
	open:
	if (tfp->fd == 0) {
		if (tp->type == SINGLEFILE)
			l = snprintf(buf, sizeof(buf), "%s", tfp->path);
		else {
			l = snprintf(buf, sizeof(buf), "%s/%s",
			    tp->body.multifile.name, tfp->path);
			if (l == -1 || l >= (int)sizeof(buf))
				errx(1, "torrent_mmap_create: path too long");
			/* Linux dirname() modifies the buffer, so make a copy */
			buf2 = xstrdup(buf);
			if ((basedir = dirname(buf2)) == NULL)
				err(1, "torrent_mmap_create: basename");
			if (mkpath(basedir, 0755) == -1)
				if (errno != EEXIST)
					err(1, "torrent_mmap_create \"%s\": mkdir", basedir);
			xfree(buf2);
			basedir = NULL;
		}
		openflags = (tp->good_pieces == tp->num_pieces ? O_RDONLY : O_RDWR|O_CREAT);
		if ((fd = open(buf, openflags, 0600)) == -1)
			err(1, "torrent_mmap_create: open `%s'", buf);

		if (flock(fd, LOCK_EX | LOCK_NB) == -1)
			err(1, "torrent_mmap_create: flock()");
		tfp->fd = fd;
	}
	if (fstat(tfp->fd, &sb) == -1)
		err(1, "torrent_mmap_create: fstat `%d'", tfp->fd);
	/* trace("size: %u vs. len+off: %u", sb.st_size, (off_t)len + off); */
	if (sb.st_size < ((off_t)len + off)) {
		/* trace("%llu offset zeroed, len %u, size: %u", off, len, sb.st_size); */
		tp->isnew = 1;
		/* seek to the expected size of file ... */
		if (lseek(tfp->fd, (off_t)len + off - 1, SEEK_SET) == -1)
			err(1, "torrent_mmap_create: lseek() failure");
		/* and write a byte there */
		if (write(tfp->fd, &zero, 1) < 1)
			err(1, "torrent_mmap_create: write() failure");
		if (flock(tfp->fd, LOCK_UN) == -1)
			err(1, "torrent_mmap_create: flock()");
		close(tfp->fd);
		tfp->fd = 0;
		goto open;
	}
	/* OpenBSD does not require us to align our mmap to page-size boundaries,
	 * but Linux and no doubt other platforms do.
	 */
	tmmp = xmalloc(sizeof(*tmmp));
	memset(tmmp, 0, sizeof(*tmmp));
	tmmp->len = len;
	if (off > 0) {
		page_off = ((off / pagesize) * pagesize);
		len += off - page_off;
	}
	/* trace("mmap: len: %u off: %u sbsiz: %u fd: %d aligned off: %u pagesize: %d", len, off, sb.st_size, tfp->fd, page_off, pagesize); */

	tmmp->tfp = tfp;
	mmapflags = (tp->good_pieces == tp->num_pieces ? PROT_READ : PROT_READ|PROT_WRITE);
	tmmp->aligned_addr = mmap(0, len, mmapflags, MAP_SHARED, tfp->fd, page_off);
	if (tmmp->aligned_addr == MAP_FAILED)
		err(1, "torrent_mmap_create: mmap");
/* cygwin doesn't provide madvise() */
#if !defined(__CYGWIN__)
	if (madvise(tmmp->aligned_addr, len, MADV_SEQUENTIAL|MADV_WILLNEED) == -1)
		err(1, "torrent_mmap_create: madvise");
#endif
	nearest_page = tmmp->aligned_addr + (off - page_off);
	tmmp->addr = nearest_page;

	tfp->refs++;
	return (tmmp);
}

/*
 * torrent_pieces_create()
 *
 * Initialize the flat array of piece descriptors, one for each
 * piece in the torrent.  This facilitates extremely fast
 * random access for piece metadata.
 */
struct torrent_piece *
torrent_pieces_create(struct torrent *tp)
{
	struct torrent_piece *tpp;
	u_int32_t len, i;
	off_t off;

	tpp = xcalloc(tp->num_pieces, sizeof(*tpp));
	for (i = 0; i < tp->num_pieces; i++) {
		tpp[i].tp = tp;
		tpp[i].index = i;
		TAILQ_INIT(&tpp[i].mmaps);

		off = tp->piece_length * (off_t)i;
		/* nice and simple */
		if (tp->type == SINGLEFILE) {
			/* last piece is irregular */
			if (i == tp->num_pieces - 1) {
				len = tp->body.singlefile.tfp.file_length - off;
			} else {
				len = tp->piece_length;
			}
			tpp[i].len = len;

		} else {
			/* last piece is irregular */
			if (i == tp->num_pieces - 1) {
				len = tp->body.multifile.total_length
				    - ((tp->num_pieces - 1) * tp->piece_length);
			} else {
				len = tp->piece_length;
			}
			tpp[i].len = len;
		}
	}

	tp->piece_array = tpp;
	return (tpp);
}

/*
 * torrent_piece_map()
 *
 * Creates the mmap region(s) corresponding to this piece.  For multi-file
 * torrents, this can be quite complicated.
 *
 * Returns 1 on success, 0 on failure.
 */
int
torrent_piece_map(struct torrent_piece *tpp)
{
	struct torrent_file  *tfp, *nxttfp;
	struct torrent_mmap  *tmmp;
	u_int32_t len;
	off_t off;

	off = tpp->tp->piece_length * (off_t)tpp->index;
	/* nice and simple */
	if (tpp->tp->type == SINGLEFILE) {
		tmmp = torrent_mmap_create(tpp->tp, &tpp->tp->body.singlefile.tfp, off, tpp->len);
		TAILQ_INSERT_TAIL(&tpp->mmaps, tmmp, mmaps);
		tpp->flags |= TORRENT_PIECE_MAPPED;

		return (0);
	} else {
		/*
		 * From: http://wiki.theory.org/BitTorrentSpecification
		 *
		 * "For the purposes of piece boundaries in the multi-file case,
		 * consider the file data as one long continuous stream,
		 * composed of the concatenation of each file in the order
		 * listed in the files list. The number of pieces and their
		 * boundaries are then determined in the same manner as the
		 * case of a single file. Pieces may overlap file boundaries."
		 *
		 * So, find which file(s) this piece should be mapped within.
		 * Or, if files are too small to make up a whole piece, which
		 * files should be mapped within the piece.
		 * This is kind of complicated.
		 */

		len = tpp->len;
		tpp->len = 0;
		TAILQ_FOREACH(tfp, &tpp->tp->body.multifile.files, files) {
			/* piece offset puts it outside the current
			   file, may be mapped to next file */
			if (off > tfp->file_length) {
				off -= tfp->file_length;
				continue;
			}
			/* file is too small for one piece
			   and this piece is not yet full */
			if (tfp->file_length < (off_t)len
			    && tpp->len < len) {
				if (tfp->file_length - off == 0)
					continue;
				tmmp = torrent_mmap_create(tpp->tp, tfp, off,
				    tfp->file_length - off);
				TAILQ_INSERT_TAIL(&tpp->mmaps, tmmp, mmaps);
				tpp->len += tfp->file_length - off;
				len -= tfp->file_length - off;
				off = 0;
				continue;
			}
			if (off + (off_t)len > tfp->file_length) {
				if (tfp->file_length == off) {
					off = 0;
					continue;
				}
				if (tfp->file_length - off == 0)
					continue;
				tmmp = torrent_mmap_create(tpp->tp, tfp, off,
				    tfp->file_length - off);
				tpp->len += tmmp->len;
				TAILQ_INSERT_TAIL(&tpp->mmaps, tmmp, mmaps);
				nxttfp = TAILQ_NEXT(tfp, files);
				len -= tmmp->len;
				off++;
				if (nxttfp->file_length < (off_t)len) {
					if (nxttfp->file_length == 0)
						continue;
					tmmp = torrent_mmap_create(tpp->tp, nxttfp,
					    0, nxttfp->file_length);
					tpp->len += tmmp->len;
					TAILQ_INSERT_TAIL(&tpp->mmaps, tmmp,
					    mmaps);
					off++;
					len -= tmmp->len;
					tfp = nxttfp;
					off = 0;
					continue;
				} else {
					if (len == 0)
						continue;
					tmmp = torrent_mmap_create(tpp->tp, nxttfp,
					    0, len);
				}
				tpp->len += tmmp->len;
				TAILQ_INSERT_TAIL(&tpp->mmaps, tmmp, mmaps);
				off++;
				break;
			} else if (off < tfp->file_length) {
				/* piece lies within this file */
				if (len == 0)
					continue;
				tmmp = torrent_mmap_create(tpp->tp, tfp, off, len);
				off++;
				TAILQ_INSERT_TAIL(&tpp->mmaps, tmmp, mmaps);
				tpp->len += len;
				break;
			}
		}
		tpp->flags |= TORRENT_PIECE_MAPPED;
		return (0);
	}
	return (1);
}

/*
 * torrent_piece_checkhash()
 *
 * Checksum the supplied piece.  Set the piece's checksum bit to true
 * if it is good, and also return 1.  Returns 0 if the hash check fails.
 */
int
torrent_piece_checkhash(struct torrent *tp, struct torrent_piece *tpp)
{
	SHA1_CTX sha;
	u_int8_t *d, *s, results[SHA1_DIGEST_LENGTH];
	int hint, res;

	if (!(tpp->flags & TORRENT_PIECE_MAPPED))
		errx(1, "torrent_piece_checkhash: unmapped piece: %u", tpp->index);
	d = torrent_block_read(tpp, 0, tpp->len, &hint);
	if (d == NULL)
		return (-1);

	SHA1Init(&sha);
	SHA1Update(&sha, d, tpp->len);
	SHA1Final(results, &sha);

	if (tp->type == MULTIFILE) {
		s = tp->body.multifile.pieces
		    + (SHA1_DIGEST_LENGTH * tpp->index);
	} else {
		s = tp->body.singlefile.pieces
		    + (SHA1_DIGEST_LENGTH * tpp->index);
	}

	res = memcmp(results, s, SHA1_DIGEST_LENGTH);
	if (res == 0) {
		tpp->flags |= TORRENT_PIECE_CKSUMOK;
	}
	if (hint == 1)
		xfree(d);

	return (res);
}

/*
 * torrent_piece_sync()
 *
 * Sync given piece to disk.
 */
void
torrent_piece_sync(struct torrent *tp, u_int32_t idx)
{
	struct torrent_piece *tpp;
	struct torrent_mmap *tmmp;

	tpp = torrent_piece_find(tp, idx);

	if (tpp == NULL)
		errx(1, "torrent_piece_sync: NULL piece");

	TAILQ_FOREACH(tmmp, &tpp->mmaps, mmaps)
		if (msync(tmmp->aligned_addr, tmmp->len, MS_SYNC) == -1)
			err(1, "torrent_piece_sync: msync");

}

/*
 * torrent_piece_unmap()
 *
 * Unmap the supplied piece, flushing it to disk and
 * closing the file descriptor if necessary.
 */
void
torrent_piece_unmap(struct torrent_piece *tpp)
{
	struct torrent_mmap *tmmp;

	TAILQ_FOREACH(tmmp, &tpp->mmaps, mmaps) {
		tmmp->tfp->refs--;
		if (tmmp->tfp->refs == 0) {
			flock(tmmp->tfp->fd, LOCK_UN);
			(void)  close(tmmp->tfp->fd);
			tmmp->tfp->fd = 0;
		}
		if (msync(tmmp->aligned_addr, tmmp->len, MS_SYNC) == -1)
			err(1, "torrent_piece_unmap: msync");
		if (munmap(tmmp->aligned_addr, tmmp->len) == -1)
			err(1, "torrent_piece_unmap: munmap");
	}
	while ((tmmp = TAILQ_FIRST(&tpp->mmaps))) {
		TAILQ_REMOVE(&tpp->mmaps, tmmp, mmaps);
		xfree(tmmp);
	}
	tpp->flags &= ~TORRENT_PIECE_MAPPED;
}

/*
 * torrent_bitfield_get()
 *
 * Allocate and return a byte-array corresponding to our bitmap representation
 * of the data we have in the torrent.  Caller is responsible for freeing
 * the memory, and must figure out itself how long the buffer is.
 */
u_int8_t *
torrent_bitfield_get(struct torrent *tp)
{
	struct torrent_piece *tpp;
	u_int32_t i, len;
	u_int8_t *bitfield;

	len = (tp->num_pieces + 7u) / 8u;
	bitfield = xmalloc(len);
	memset(bitfield, 0, len);
	for (i = 0; i < tp->num_pieces; i++) {
		tpp = torrent_piece_find(tp, i);
		if (tpp->flags & TORRENT_PIECE_CKSUMOK)
			util_setbit(bitfield, i);
	}

	return (bitfield);
}

/*
 * torrent_empty()
 *
 * Returns 1 if the torrent is empty, that is, contains no checksummed
 * pieces.  Returns 0 if there is at least 1 good piece.
 */
int
torrent_empty(struct torrent *tp)
{
	struct torrent_piece *tpp;
	u_int32_t i;
	for (i = 0; i < tp->num_pieces; i++) {
		tpp = torrent_piece_find(tp, i);
		if (tpp->flags & TORRENT_PIECE_CKSUMOK)
			return (0);
	}
	return (1);
}

/*
 * torrent_fastresume_dump()
 *
 * Write out the bitfield and some other metadata to a file in the same
 * dir as the torrent file, named <torrent_file>.funresume.
 */
void
torrent_fastresume_dump(struct torrent *tp)
{
	char resumename[MAXPATHLEN];
	FILE *fp;
	u_int32_t bitfieldlen;
	u_int8_t *bitfield;
	size_t bytes;
	int l;

	bitfieldlen = (tp->num_pieces + 7u) / 8u;
	bitfield = torrent_bitfield_get(tp);

	l = snprintf(resumename, sizeof(resumename), "%s.funresume", tp->name);
	if (l == -1 || l >= (int)sizeof(resumename))
		errx(1, "torrent_fastresume_dump: snprintf truncation");

	if ((fp = fopen(resumename, "w")) == NULL)
		err(1, "torrent_fastresume_dump: fopen");

	bytes = fwrite(bitfield, bitfieldlen, 1, fp);
	if (bytes != bitfieldlen
	    && ferror(fp))
		errx(1, "torrent_fastresume_dump: fwrite failure");
	fclose(fp);
	xfree(bitfield);
}

/*
 * torrent_fastresume_load()
 *
 * Load the fast resume data produced by torrent_fastresume_dump().
 * Returns -1 if it could not load the fast resume data, 0 otherwise.
 */
int
torrent_fastresume_load(struct torrent *tp)
{
	struct torrent_piece *tpp;
	char resumename[MAXPATHLEN];
	FILE *fp;
	u_int32_t i, bitfieldlen;
	u_int8_t *bitfield;
	size_t bytes;
	int l;

	bitfieldlen = (tp->num_pieces + 7u) / 8u;

	l = snprintf(resumename, sizeof(resumename), "%s.funresume", tp->name);
	if (l == -1 || l >= (int)sizeof(resumename))
		errx(1, "torrent_fastresume_load: snprintf truncation");

	if ((fp = fopen(resumename, "r")) == NULL)
		return (-1);

	bitfield = xmalloc(bitfieldlen);
	memset(bitfield, 0, bitfieldlen);

	bytes = fread(bitfield, bitfieldlen, 1, fp);
	if (bytes != bitfieldlen
	    && ferror(fp))
		errx(1, "torrent_fastresume_load: fread failure");
	fclose(fp);
	/* there are faster ways to do this, but this is pretty readable */
	for (i = 0; i < tp->num_pieces; i++) {
		tpp = torrent_piece_find(tp, i);
		if (util_getbit(bitfield, i) == 1) {
			tpp->flags |= TORRENT_PIECE_CKSUMOK;
			tp->good_pieces++;
			tp->downloaded += tpp->len;
		}
	}
	xfree(bitfield);

	return (0);
}