Tuesday, July 3, 2018

Making FreeBSD magnet links

For the last few years, I've been producing torrents and publishing magnet links, but there is some special work that I do to make these.  The first few releases, I inserted a bogus tracker into the torrent, because despite there being plenty of tools out there for producing trackerless (DHT) torrents, they were all GUI and I never found any that were command line based.  The other was there was/is no tool for extracting the info hash and building the magnet link.  There may be tools now, but I couldn't find any when I started 3 years ago.

The following steps are based upon the recent release of FreeBSD 11.2-R, adjust as necessary.

  1. Fetch FreeBSD into a directory (I create a per release directory).  There are a few directories that you have mirror, I use wget for this.  The mirroring feature for wget isn't great.  After each command I have to remove the CHECKSUM.SHA256, CHECKSUM.SHA512 and index.html* files.
    $ wget -c -r -l 1 -nd --limit-rate=800k https://download.freebsd.org/ftp/releases/ISO-IMAGES/11.2/
    $ wget -c -r -l 1 -nd --limit-rate=800k https://download.freebsd.org/ftp/releases/VM-IMAGES/11.2-RELEASE/aarch64/Latest/
    $ wget -c -r -l 1 -nd --limit-rate=800k https://download.freebsd.org/ftp/releases/VM-IMAGES/11.2-RELEASE/amd64/Latest/
    $ wget -c -r -l 1 -nd --limit-rate=800k https://download.freebsd.org/ftp/releases/VM-IMAGES/11.2-RELEASE/i386/Latest/
  2. Fetch the signature files:
    $ wget https://www.freebsd.org/releases/11.2R/CHECKSUM.SHA512-FreeBSD-11.2-RELEASE-{amd64,i386,powerpc,powerpc-powerpc64,sparc64,arm64-aarch64}.asc
    $ wget https://www.freebsd.org/releases/11.2R/CHECKSUM.SHA512-FreeBSD-11.2-RELEASE-{amd64,i386,arm64-aarch64}-vm.asc
    $ wget https://www.freebsd.org/releases/11.2R/CHECKSUM.SHA512-FreeBSD-11.2-RELEASE-arm-armv6-{BANANAPI,BEAGLEBONE,CUBIEBOARD,CUBIEBOARD2,CUBBOX-HUMMINGBOARD,GUMSTIX,PANDABOARD,RPI-B,RPI2,WANDBOARD}.asc
  3. Verify the GPG key that signed the above files.  This is usually Glen Barber's key, but not always.  I have met and verified his fingerprint in person,  If you have verified someone's key who has signed Glen's key, that is another good way.
  4. Verify the checksum files:
    $ for i in *.asc; do gpg --verify $i; done
    You should see a bunch of lines like:
    Warning: using insecure memory!
    gpg: Signature made Fri Jun 22 09:33:50 2018 PDT
    gpg:                using RSA key 0x031458A5478FE293
    gpg: Good signature from "Glen Barber <gjb@FreeBSD.org>" [full]
    gpg:                 aka "Glen Barber <glen.j.barber@gmail.com>" [full]
    gpg:                 aka "Glen Barber <gjb@glenbarber.us>" [full]
    gpg:                 aka "Glen Barber <gjb@keybase.io>" [unknown]
    gpg: WARNING: not a detached signature; file 'CHECKSUM.SHA512-FreeBSD-11.2-RELEASE-amd64-vm' was NOT verified!
    The last line can be ignored.  The non-.asc files were d/l'd and will not be used.  Make sure that all of the files report Good signature.
  5. In the past I have used BitTornado for other things, so I ended up using it as the basis to make the tool for creating trackerless torrent files.  The modifications were simple.  It appears that the original BitTornado CVS tree is off-line (anyways, it was served insecurely), but it looks like effigies/BitTornado is similar enough that it could be modified and used.  I copied btmakemetafile.py to btmaketrackerless.py and applied the following patch:
    $ diff -u btmakemetafile.py btmaketrackerless.py 
    --- btmakemetafile.py   2004-05-24 12:54:52.000000000 -0700
    +++ btmaketrackerless.py        2016-10-10 17:13:32.742081000 -0700
    @@ -23,9 +23,9 @@
     def prog(amount):
         print '%.1f%% complete\r' % (amount * 100),

    -if len(argv) < 3:
    +if len(argv) < 2:
         a,b = split(argv[0])
    -    print 'Usage: ' + b + ' <trackerurl> <file> [file...] [params...]'
    +    print 'Usage: ' + b + ' <file> [file...] [params...]'
         print
         print formatDefinitions(defaults, 80)
         print_announcelist_details()
    @@ -33,9 +33,9 @@
         exit(2)

     try:
    -    config, args = parseargs(argv[1:], defaults, 2, None)
    -    for file in args[1:]:
    -        make_meta_file(file, args[0], config, progress = prog)
    +    config, args = parseargs(argv[1:], defaults, 1, None)
    +    for file in args[0:]:
    +        make_meta_file(file, None, config, progress = prog)
     except ValueError, e:
         print 'error: ' + str(e)
         print 'run with no args for parameter explanations'

    If you notice, the only thing that is done is to drop the first argument, and instead of passing it into make_meta_file, a None is passed instead.  This will simply not add trackers to the torrent file.
  6. I then run the following script to verify the downloaded files, and generate the torrent files:
    $ cat cmp.sh 
    #!/bin/sh -
    # wget -c -r -l 1 -nd --limit-rate=800k https://download.freebsd.org/ftp/releases/ISO-IMAGES/11.2/
    # wget -c -r -l 1 -nd --limit-rate=800k https://download.freebsd.org/ftp/releases/VM-IMAGES/11.2-RELEASE/aarch64/Latest/
    # wget -c -r -l 1 -nd --limit-rate=800k https://download.freebsd.org/ftp/releases/VM-IMAGES/11.2-RELEASE/amd64/Latest/
    # wget -c -r -l 1 -nd --limit-rate=800k https://download.freebsd.org/ftp/releases/VM-IMAGES/11.2-RELEASE/i386/Latest/
    # wget https://www.freebsd.org/releases/11.2R/CHECKSUM.SHA512-FreeBSD-11.2-RELEASE-{amd64,i386,powerpc,powerpc-powerpc64,sparc64,arm64-aarch64}.asc
    # wget https://www.freebsd.org/releases/11.2R/CHECKSUM.SHA512-FreeBSD-11.2-RELEASE-{amd64,i386,arm64-aarch64}-vm.asc
    # wget https://www.freebsd.org/releases/11.2R/CHECKSUM.SHA512-FreeBSD-11.2-RELEASE-arm-armv6-{BANANAPI,BEAGLEBONE,CUBIEBOARD,CUBIEBOARD2,CUBBOX-HUMMINGBOARD,GUMSTIX,PANDABOARD,RPI-B,RPI2,WANDBOARD}.asc

    grep -h '^SHA512' CHECK*.asc | sed -e 's/SHA512 (\(.*\)) = \(.*\)/\2 \1/' | sort -k 2 > sha512.from.asc

    while read hash fname; do
            if [ -e "$fname" ]; then
                    sigfile=`grep -l -- "$fname" *.asc | head -n 1`
                    echo checking "$fname", sig in: "$sigfile"
                    #res=`sha512 -q "$fname"`
                    res=`shasum -a 512 "$fname" | awk '{ print $1 }'`
                    echo "File is: $res"
                    if [ x"$res" != x"$hash" ]; then
                            echo missmatch!  "$fname"
                            exit 1
                    fi
                    if ! [ -e "$fname".torrent ]; then
                            btmaketrackerless.py "$fname"
                    fi
            else
                    echo missing "$fname"
                    exit 1
            fi
    done < sha512.from.asc
  7. Once all the torrents have been generated, I then make the magnet links:
    $ cat btmakemagnet.sh 
    #!/bin/sh -

    # metainfo file.: FreeBSD-10.3-RELEASE-sparc64-bootonly.iso.torrent
    # info hash.....: 06091dabce1296d11d1758ffd071e7109a92934f
    # file name.....: FreeBSD-10.3-RELEASE-sparc64-bootonly.iso
    # file size.....: 203161600 (775 * 262144 + 0)
    # announce url..: udp://tracker.openbittorrent.com:80
    # btshowmetainfo 20030621 - decode BitTorrent metainfo files

    for i in *.torrent; do
            btshowmetainfo.py "$i" | awk '
    $0 ~ "^info hash" { info = $3 }
    $0 ~ "^file name" { name = $3 }
    END {
            print "magnet:?xt=urn:btih:" info "&dn=" name
    }'
    done
  8. I then create the magnet links file, and update the Torrents wiki page.
Sorry about the code formatting.  I don't know how to make it look better in blogger.