ip/torrent and private trackers

[Nick Owens <mischief@9.offblast.org>]

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ip/torrent in certain circumstances will never make progress.
specifically, sl reported that no progress was made while contacting the
tracker at bakabt.me. investigation revealed that the tracker was
actually returing an error message:

d14:failure reason95:use of this client is not allowed on our tracker,
please see http://www.bakabt.me/whitelist.phpe

see http://www.bakabt.me/whitelist.php for the whitelist.

in short, they don't like our peerid, -NF9001-. i have just made a
request on their forum to whitelist the id, but the alternative is to
spoof the peerid. the patch below allows you to specify the 8
character peerid with the -i argument when invoking ip/torrent.

setting my peerid to '-TR282Z-', which is transmission 2.82+, allowed me
to connect to bakabt's tracker.

additionally, i'll patch ip/torrent to report errors from the tracker,
so that this situation is less confusing to the user.

diff -r 20c2c6fccfee sys/src/cmd/ip/torrent.c
--- a/sys/src/cmd/ip/torrent.c	Sat Jan 11 16:07:35 2014 +0100
+++ b/sys/src/cmd/ip/torrent.c	Fri Jan 31 03:28:25 2014 -0800
@@ -1174,13 +1174,14 @@
 {
 	int sflag, pflag, vflag, cflag, fd, i, n;
 	Dict *alist, *wlist, *info, *torrent, *d, *l;
-	char *p, *s, *e;
+	char *p, *s, *e, *pid;
 	File **fp, *f;
 	vlong len;
 
 	fmtinstall('H', Hfmt);
 	alist = wlist = nil;
 	sflag = pflag = vflag = cflag = 0;
+	pid = nil;
 	ARGBEGIN {
 	case 'm':
 		mntweb = EARGF(usage());
@@ -1206,6 +1207,9 @@
 	case 'd':
 		debug++;
 		break;
+	case 'i':
+		pid = EARGF(usage());
+		break;
 	default:
 		usage();
 	} ARGEND;
@@ -1339,7 +1343,10 @@
 	case -1:
 		sysfatal("fork: %r");
 	case 0:
-		memmove(peerid, "-NF9001-", 8);
+		if(pid)
+			memmove(peerid, pid, 8);
+		else
+			memmove(peerid, "-NF9001-", 8);
 		for(i=8; i<sizeof(peerid); i++)
 			peerid[i] = nrand(10)+'0';
 		server();


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