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Refactor blk_match(). Fold the remaining data and empty file or no blocks
cases together since they are kind of the same.

OK tb@

/*	$OpenBSD: blocks.c,v 1.23 2024/02/28 09:36:11 claudio Exp $ */
/*
 * Copyright (c) 2019 Kristaps Dzonsons <kristaps@bsd.lv>
 *
 * 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/queue.h>
#include <sys/stat.h>

#include <assert.h>
#include <endian.h>
#include <errno.h>
#include <inttypes.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include <openssl/md4.h>

#include "extern.h"

struct	blkhash {
	const struct blk	*blk;
	TAILQ_ENTRY(blkhash)	 entries;
};

TAILQ_HEAD(blkhashq, blkhash);

/*
 * Table used by the sender for looking up blocks.
 * The blocks are those sent by the receiver; we're looking up using
 * hashes computed from our local file.
 */
struct	blktab {
	struct blkhashq	*q; /* entries in the hashtable */
	size_t		 qsz; /* size of the hashtable */
	struct blkhash	*blks; /* pre-allocated hashtable entries */
};

/*
 * This is the number of buckets in the hashtable.
 * Use the same that GPL rsync uses.
 * (It should be dynamic?)
 */
#define	BLKTAB_SZ	  65536

/*
 * Initialise an empty hashtable with BLKTAB_SZ entries in it.
 * Populate it for each file with blkhash_set.
 * When we've processed all files, call blkhash_free.
 * Returns NULL on allocation failure.
 */
struct blktab *
blkhash_alloc(void)
{
	struct blktab	*p;

	if ((p = calloc(1, sizeof(struct blktab))) == NULL) {
		ERR("calloc");
		return NULL;
	}
	p->qsz = BLKTAB_SZ;
	p->q = calloc(p->qsz, sizeof(struct blkhashq));
	if (p->q == NULL) {
		ERR("calloc");
		free(p);
		return NULL;
	}
	return p;
}

/*
 * Populate the hashtable with an incoming file's blocks.
 * This will clear out any existing hashed data.
 * Returns zero on allocation failure, non-zero otherwise.
 */
int
blkhash_set(struct blktab *p, const struct blkset *bset)
{
	size_t	 i, idx;

	if (bset == NULL)
		return 1;

	/* Wipe clean the table. */

	for (i = 0; i < p->qsz; i++)
		TAILQ_INIT(&p->q[i]);

	/* Fill in the hashtable. */

	p->blks = reallocarray(p->blks, bset->blksz, sizeof(struct blkhash));
	if (p->blks == NULL) {
		ERR("reallocarray");
		return 0;
	}
	for (i = 0; i < bset->blksz; i++) {
		p->blks[i].blk = &bset->blks[i];
		idx = bset->blks[i].chksum_short % p->qsz;
		assert(idx < p->qsz);
		TAILQ_INSERT_TAIL(&p->q[idx], &p->blks[i], entries);
	}

	return 1;
}

/*
 * Free as allocated with blkhash_alloc().
 */
void
blkhash_free(struct blktab *p)
{

	free(p->blks);
	free(p);
}

/*
 * From our current position of "offs" in buffer "buf" of total size
 * "size", see if we can find a matching block in our list of blocks.
 * The "hint" refers to the block that *might* work.
 * Returns the blk or NULL if no matching block was found.
 */
static const struct blk *
blk_find(struct sess *sess, struct blkstat *st,
	const struct blkset *blks, const char *path, int recomp)
{
	unsigned char	 md[MD4_DIGEST_LENGTH];
	uint32_t	 fhash;
	off_t		 remain, osz;
	int		 have_md = 0;
	char		*map;
	const struct blkhashq *q;
	const struct blkhash *ent;

	remain = st->mapsz - st->offs;
	assert(remain);
	osz = MINIMUM(remain, (off_t)blks->len);

	/*
	 * First, compute our fast hash the hard way (if we're
	 * reentering this function from a previous block match, or the
	 * first time) or from our existing s1 and s2 values.
	 */

	if (!recomp) {
		fhash = (st->s1 & 0xFFFF) | (st->s2 << 16);
	} else {
		fhash = hash_fast(st->map + st->offs, (size_t)osz);
		st->s1 = fhash & 0xFFFF;
		st->s2 = fhash >> 16;
	}

	/*
	 * Start with our match hint.
	 * This just runs the fast and slow check with the hint.
	 */

	if (st->hint < blks->blksz &&
	    fhash == blks->blks[st->hint].chksum_short &&
	    (size_t)osz == blks->blks[st->hint].len) {
		hash_slow(st->map + st->offs, (size_t)osz, md, sess);
		have_md = 1;
		if (memcmp(md, blks->blks[st->hint].chksum_long, blks->csum) == 0) {
			LOG4("%s: found matching hinted match: "
			    "position %jd, block %zu (position %jd, size %zu)",
			    path,
			    (intmax_t)st->offs, blks->blks[st->hint].idx,
			    (intmax_t)blks->blks[st->hint].offs,
			    blks->blks[st->hint].len);
			return &blks->blks[st->hint];
		}
	}

	/*
	 * Look for the fast hash modulus in our hashtable, filter for
	 * those matching the full hash and length, then move to the
	 * slow hash.
	 * The slow hash is computed only once.
	 */

	q = &st->blktab->q[fhash % st->blktab->qsz];

	TAILQ_FOREACH(ent, q, entries) {
		if (fhash != ent->blk->chksum_short ||
		    (size_t)osz != ent->blk->len)
			continue;

		LOG4("%s: found matching fast match: "
		    "position %jd, block %zu (position %jd, size %zu)",
		    path, (intmax_t)st->offs, ent->blk->idx,
		    (intmax_t)ent->blk->offs, ent->blk->len);

		if (have_md == 0) {
			hash_slow(st->map + st->offs, (size_t)osz, md, sess);
			have_md = 1;
		}

		if (memcmp(md, ent->blk->chksum_long, blks->csum))
			continue;

		LOG4("%s: sender verifies slow match", path);
		return ent->blk;
	}

	/*
	 * Adjust our partial sums for the hashing.
	 * We first remove the first byte from the sum.
	 * We then, if we have space, add the first byte of the next
	 * block in the sequence.
	 */

	map = st->map + st->offs;
	st->s1 -= map[0];
	st->s2 -= osz * map[0];

	if (osz < remain) {
		st->s1 += map[osz];
		st->s2 += st->s1;
	}

	return NULL;
}

/*
 * Given a local file "path" and the blocks created by a remote machine,
 * find out which blocks of our file they don't have and send them.
 * This function is reentrant: it must be called while there's still
 * data to send.
 */
void
blk_match(struct sess *sess, const struct blkset *blks,
	const char *path, struct blkstat *st)
{
	off_t		  last, end = 0, sz;
	int32_t		  tok;
	size_t		  i;
	const struct blk *blk;

	/*
	 * If the file's empty or we don't have any blocks from the
	 * sender, then simply send the whole file.
	 * Otherwise, run the hash matching routine and send raw chunks
	 * and subsequent matching tokens.
	 */

	if (st->mapsz && blks->blksz) {
		/*
		 * Stop searching at the length of the file minus the
		 * size of the last block.
		 * The reason for this being that we don't need to do an
		 * incremental hash within the last block---if it
		 * doesn't match, it doesn't match.
		 */

		end = st->mapsz + 1 - blks->blks[blks->blksz - 1].len;
	}

	last = st->offs;
	for (i = 0; st->offs < end; st->offs++, i++) {
		blk = blk_find(sess, st, blks, path, i == 0);
		if (blk == NULL)
			continue;

		sz = st->offs - last;
		st->dirty += sz;
		st->total += sz;
		LOG4("%s: flushing %jd B before %zu B block %zu",
		    path, (intmax_t)sz,
		    blk->len, blk->idx);
		tok = -(blk->idx + 1);

		hash_file_buf(&st->ctx, st->map + last, sz + blk->len);

		/*
		 * Write the data we have, then follow it with
		 * the tag of the block that matches.
		 */

		st->curpos = last;
		st->curlen = st->curpos + sz;
		st->curtok = tok;
		assert(st->curtok != 0);
		st->curst = sz ? BLKSTAT_DATA : BLKSTAT_TOK;
		st->total += blk->len;
		st->offs += blk->len;
		st->hint = blk->idx + 1;

		return;
	}

	/* Emit remaining data and send terminator token. */

	sz = st->mapsz - last;
	LOG4("%s: flushing %s %jd B", path,
	    last == 0 ? "whole" : "remaining", (intmax_t)sz);

	hash_file_buf(&st->ctx, st->map + last, sz);

	st->total += sz;
	st->dirty += sz;
	st->curpos = last;
	st->curlen = st->curpos + sz;
	st->curtok = 0;
	st->curst = sz ? BLKSTAT_DATA : BLKSTAT_TOK;
}

/*
 * Buffer the message from sender to the receiver indicating that the
 * block set has been received.
 * Symmetrises blk_send_ack().
 */
void
blk_recv_ack(char buf[20], const struct blkset *blocks, int32_t idx)
{
	size_t	 pos = 0, sz;

	sz = sizeof(int32_t) + /* index */
	    sizeof(int32_t) + /* block count */
	    sizeof(int32_t) + /* block length */
	    sizeof(int32_t) + /* checksum length */
	    sizeof(int32_t); /* block remainder */
	assert(sz == 20);

	io_buffer_int(buf, &pos, sz, idx);
	io_buffer_int(buf, &pos, sz, blocks->blksz);
	io_buffer_int(buf, &pos, sz, blocks->len);
	io_buffer_int(buf, &pos, sz, blocks->csum);
	io_buffer_int(buf, &pos, sz, blocks->rem);
	assert(pos == sz);
}

/*
 * Read all of the checksums for a file's blocks.
 * Returns the set of blocks or NULL on failure.
 */
struct blkset *
blk_recv(struct sess *sess, int fd, const char *path)
{
	struct blkset	*s;
	int32_t		 i;
	size_t		 j;
	struct blk	*b;
	off_t		 offs = 0;

	if ((s = calloc(1, sizeof(struct blkset))) == NULL) {
		ERR("calloc");
		return NULL;
	}

	/*
	 * The block prologue consists of a few values that we'll need
	 * in reading the individual blocks for this file.
	 * FIXME: read into buffer and unbuffer.
	 */

	if (!io_read_size(sess, fd, &s->blksz)) {
		ERRX1("io_read_size");
		goto out;
	} else if (!io_read_size(sess, fd, &s->len)) {
		ERRX1("io_read_size");
		goto out;
	} else if (!io_read_size(sess, fd, &s->csum)) {
		ERRX1("io_read_int");
		goto out;
	} else if (!io_read_size(sess, fd, &s->rem)) {
		ERRX1("io_read_int");
		goto out;
	} else if (s->rem && s->rem >= s->len) {
		ERRX("block remainder is "
			"greater than block size");
		goto out;
	}

	LOG3("%s: read block prologue: %zu blocks of "
	    "%zu B, %zu B remainder, %zu B checksum", path,
	    s->blksz, s->len, s->rem, s->csum);

	if (s->blksz) {
		s->blks = calloc(s->blksz, sizeof(struct blk));
		if (s->blks == NULL) {
			ERR("calloc");
			goto out;
		}
	}

	/*
	 * Read each block individually.
	 * FIXME: read buffer and unbuffer.
	 */

	for (j = 0; j < s->blksz; j++) {
		b = &s->blks[j];
		if (!io_read_int(sess, fd, &i)) {
			ERRX1("io_read_int");
			goto out;
		}
		b->chksum_short = i;

		assert(s->csum <= sizeof(b->chksum_long));
		if (!io_read_buf(sess,
		    fd, b->chksum_long, s->csum)) {
			ERRX1("io_read_buf");
			goto out;
		}

		/*
		 * If we're the last block, then we're assigned the
		 * remainder of the data.
		 */

		b->offs = offs;
		b->idx = j;
		b->len = (j == (s->blksz - 1) && s->rem) ?
			s->rem : s->len;
		offs += b->len;

		LOG4("%s: read block %zu, length %zu B",
		    path, b->idx, b->len);
	}

	s->size = offs;
	LOG3("%s: read blocks: %zu blocks, %jd B total blocked data",
	    path, s->blksz, (intmax_t)s->size);
	return s;
out:
	free(s->blks);
	free(s);
	return NULL;
}

/*
 * Symmetrise blk_recv_ack(), except w/o the leading identifier.
 * Return zero on failure, non-zero on success.
 */
int
blk_send_ack(struct sess *sess, int fd, struct blkset *p)
{
	char	 buf[16];
	size_t	 pos = 0, sz;

	/* Put the entire send routine into a buffer. */

	sz = sizeof(int32_t) + /* block count */
	    sizeof(int32_t) + /* block length */
	    sizeof(int32_t) + /* checksum length */
	    sizeof(int32_t); /* block remainder */
	assert(sz <= sizeof(buf));

	if (!io_read_buf(sess, fd, buf, sz)) {
		ERRX1("io_read_buf");
		return 0;
	}

	if (!io_unbuffer_size(buf, &pos, sz, &p->blksz))
		ERRX1("io_unbuffer_size");
	else if (!io_unbuffer_size(buf, &pos, sz, &p->len))
		ERRX1("io_unbuffer_size");
	else if (!io_unbuffer_size(buf, &pos, sz, &p->csum))
		ERRX1("io_unbuffer_size");
	else if (!io_unbuffer_size(buf, &pos, sz, &p->rem))
		ERRX1("io_unbuffer_size");
	else if (p->len && p->rem >= p->len)
		ERRX1("non-zero length is less than remainder");
	else if (p->csum == 0 || p->csum > 16)
		ERRX1("inappropriate checksum length");
	else
		return 1;

	return 0;
}

/*
 * Transmit the metadata for set and blocks.
 * Return zero on failure, non-zero on success.
 */
int
blk_send(struct sess *sess, int fd, size_t idx,
	const struct blkset *p, const char *path)
{
	char	*buf;
	size_t	 i, pos = 0, sz;
	int	 rc = 0;

	/* Put the entire send routine into a buffer. */

	sz = sizeof(int32_t) + /* identifier */
	    sizeof(int32_t) + /* block count */
	    sizeof(int32_t) + /* block length */
	    sizeof(int32_t) + /* checksum length */
	    sizeof(int32_t) + /* block remainder */
	    p->blksz *
	    (sizeof(int32_t) + /* short checksum */
		p->csum); /* long checksum */

	if ((buf = malloc(sz)) == NULL) {
		ERR("malloc");
		return 0;
	}

	io_buffer_int(buf, &pos, sz, idx);
	io_buffer_int(buf, &pos, sz, p->blksz);
	io_buffer_int(buf, &pos, sz, p->len);
	io_buffer_int(buf, &pos, sz, p->csum);
	io_buffer_int(buf, &pos, sz, p->rem);

	for (i = 0; i < p->blksz; i++) {
		io_buffer_int(buf, &pos, sz, p->blks[i].chksum_short);
		io_buffer_buf(buf, &pos, sz, p->blks[i].chksum_long, p->csum);
	}

	assert(pos == sz);

	if (!io_write_buf(sess, fd, buf, sz)) {
		ERRX1("io_write_buf");
		goto out;
	}

	LOG3("%s: sent block prologue: %zu blocks of %zu B, "
	    "%zu B remainder, %zu B checksum",
	    path, p->blksz, p->len, p->rem, p->csum);
	rc = 1;
out:
	free(buf);
	return rc;
}