From 2713779ee64250b16314355f76cb90d40b64e4b2 Mon Sep 17 00:00:00 2001
From: cinap_lenrek <cinap_lenrek@felloff.net>
Date: Mon, 1 May 2017 00:01:14 +0200
Subject: 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.
---
 sys/src/cmd/ip/torrent.c | 47 ++++++++++++++++++++++++++---------------------
 1 file changed, 26 insertions(+), 21 deletions(-)

diff --git a/sys/src/cmd/ip/torrent.c b/sys/src/cmd/ip/torrent.c
index 3cc1aeb09..5ce321b4c 100644
--- a/sys/src/cmd/ip/torrent.c
+++ b/sys/src/cmd/ip/torrent.c
@@ -55,7 +55,7 @@ int port = 6881;
 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 @@ rwpiece(int wr, int index, uchar *data, int len, int poff)
 }
 
 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 @@ havepiece(int x)
 	}
 	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 @@ havepiece(int x)
 		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 @@ peer(int fd, int incoming, char *addr)
 	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 @@ peer(int fd, int incoming, char *addr)
 	mewant = 0;
 	hewant = 0;
 	workpiece = -1;
+	workoffset = 0;
+
 	map = mallocz(nhavemap, 1);
 	told = malloc(nhavemap);
 
@@ -451,18 +458,15 @@ peer(int fd, int incoming, char *addr)
 		}
 		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 @@ peer(int fd, int incoming, char *addr)
 			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 @@ Error:
 			o += m;
 			n -= m;
 			p = 0;
-			if(havepiece(x++))
+			if(havepiece(x++, w->str))
 				continue;
 			if(++err > 10){
 				close(fd);
@@ -806,8 +811,8 @@ Error:
 			}
 		}
 	}
-	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 @@ Hfmt(Fmt *f)
 int
 mktorrent(int fd, Dict *alist, Dict *wlist)
 {
-	uchar *b, h[20];
+	uchar *b, h[SHA1dlen];
 	Dir *d;
 	int n;
 
@@ -1321,14 +1326,14 @@ main(int argc, char *argv[])
 	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 @@ main(int argc, char *argv[])
 			sysfatal("fork: %r");
 		case 0:
 			for(; i<npieces; i+=nproc)
-				havepiece(i);
+				havepiece(i, nil);
 			exits(0);
 		}
 	}
-- 
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