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ip/torrent: avoid requesting same chunks

instead of always just requesting the missing range
of the current piece, remember the workpiece offset
and request sequential chunks from the workpiece.

this avoids double requests of the same ranges when
the peer does not respond with the data immidiately.

--- a/sys/src/cmd/ip/torrent.c

+++ b/sys/src/cmd/ip/torrent.c

@@ -55,7 +55,7 @@

 char *deftrack = "http://exodus.desync.com/announce";

 char *mntweb = "/mnt/web";

 char *useragent = "torrent";

-uchar infohash[20];

+uchar infohash[SHA1dlen];

 uchar peerid[20];

 int blocksize;

@@ -212,9 +212,9 @@

 }

 int

-havepiece(int x)

+havepiece(int x, char *from)

 {

-	uchar *p, m, hash[20];

+	uchar *p, m, hash[SHA1dlen];

 	int n;

 	m = 0x80>>(x&7);

@@ -228,8 +228,11 @@

 	}

 	sha1(p, n, hash, nil);

 	free(p);

-	if(memcmp(hash, pieces[x].hash, 20))

+	if(memcmp(hash, pieces[x].hash, sizeof(hash))){

+		if(debug && from != nil)

+			fprint(2, "peer %s: damaged piece %d\n", from, x);

 		return 0;

+	}

 	lock(&stats);

 	if((havemap[x>>3] & m) == 0){

 		havemap[x>>3] |= m;

@@ -237,6 +240,8 @@

 		stats.left -= pieces[x].len;

 	}

 	unlock(&stats);

+	if(debug && from != nil)

+		fprint(2, "peer %s: completed piece %d\n", from, x);

 	return 1;

 }

@@ -382,7 +387,7 @@

 	uchar buf[64+MAXIO], *map, *told, *p, m;

 	int mechoking, hechoking;

 	int mewant, hewant;

-	int workpiece;

+	int workpiece, workoffset;

 	int i, o, l, x, n;

 	if(debug) fprint(2, "peer %s: %s connected\n", addr, incoming ? "incoming" : "outgoing");

@@ -419,6 +424,8 @@

 	mewant = 0;

 	hewant = 0;

 	workpiece = -1;

+	workoffset = 0;

+

 	map = mallocz(nhavemap, 1);

 	told = malloc(nhavemap);

@@ -451,18 +458,15 @@

 		}

 		if(!hechoking && mewant){

 			x = workpiece;

-			if(x < 0 || (havemap[x>>3]&(0x80>>(x&7))) != 0)

+			if(x < 0 || (havemap[x>>3]&(0x80>>(x&7))) != 0 || workoffset >= pieces[x].len)

 				x = pickpiece(map);

 			if(x >= 0){

-				workpiece = x;

-				o = pieces[x].brk;

-				if(o < 0 || o >= pieces[x].len){

-					pieces[x].brk = 0;

-					o = 0;

-				}

+				o = workpiece != x ? pieces[x].brk : workoffset;

 				l = pieces[x].len - o;

 				if(l > MAXIO)

 					l = MAXIO;

+				workpiece = x;

+				workoffset = o + l; 

 				if(debug) fprint(2, "peer %s: -> request %d %d %d\n", addr, x, o, l);

 				n = pack(buf, sizeof(buf), "lblll", 1+4+4+4, 0x06, x, o, l);

 				if(write(fd, buf, n) != n)

@@ -566,7 +570,8 @@

 			if(n <= 0)

 				continue;

 			pieces[x].brk = o+n;

-			if(o+n >= pieces[x].len && !havepiece(x)){

+			if(o+n >= pieces[x].len && !havepiece(x, addr)){

+				pieces[x].brk = 0;

 				/* backoff from this piece for a while */

 				if(x == workpiece)

 					workpiece = -1;

@@ -797,7 +802,7 @@

 			o += m;

 			n -= m;

 			p = 0;

-			if(havepiece(x++))

+			if(havepiece(x++, w->str))

 				continue;

 			if(++err > 10){

 				close(fd);

@@ -806,8 +811,8 @@

 			}

 		}

 	}

-	havepiece(off / blocksize);

-	havepiece(f->off / blocksize);

+	havepiece(off / blocksize, w->str);

+	havepiece(f->off / blocksize, w->str);

 	close(fd);

 	exits(0);

 }

@@ -1033,7 +1038,7 @@

 int

 mktorrent(int fd, Dict *alist, Dict *wlist)

 {

-	uchar *b, h[20];

+	uchar *b, h[SHA1dlen];

 	Dir *d;

 	int n;

@@ -1321,14 +1326,14 @@

 	if((blocksize = atoi(s)) <= 0)

 		sysfatal("bogus piece length in meta info");

 	d = dlook(info, "pieces");

-	if(d == nil || d->typ != 's' || d->len <= 0 || d->len % 20)

+	if(d == nil || d->typ != 's' || d->len <= 0 || d->len % SHA1dlen)

 		sysfatal("bad or no pices in meta info");

-	npieces = d->len / 20;

+	npieces = d->len / SHA1dlen;

 	pieces = mallocz(sizeof(Piece) * npieces, 1);

 	nhavemap = (npieces+7) / 8;

 	havemap = mallocz(nhavemap, 1);

 	for(i = 0; i<npieces; i++){

-		pieces[i].hash = (uchar*)d->str + i*20;

+		pieces[i].hash = (uchar*)d->str + i*SHA1dlen;

 		if(len < blocksize)

 			pieces[i].len = len;

 		else

@@ -1345,7 +1350,7 @@

 			sysfatal("fork: %r");

 		case 0:

 			for(; i<npieces; i+=nproc)

-				havepiece(i);

+				havepiece(i, nil);

 			exits(0);

 		}

 	}

-- 

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