original code repository

Author: ximellon

.gitignore

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+*.o
+*.exe
+torrentcheck

Makefile

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+CFLAGS := -O
+
+all: torrentcheck
+
+clean:
+	rm *.o
+
+torrentcheck: torrentcheck.o sha1.o
+	$(CC) -o $@ $^ $(CFLAGS)

README

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+torrentcheck - catalog a .torrent file and optionally verify content hashes
+Usage: torrentcheck -t torrent-file [-p content-path] [-n] [-h] [-c] [-d]
+Options: -n suppresses progress count, -h shows all hash values,
+         -c or -d uses comma or dot formatted byte counts.
+Returns 0 if successful, nonzero return code if errors found.
+
+Option: -sha1 [optional hash] acts as a simple SHA1 filter.
+If -sha1 is followed by a hex hash, the return code will be zero
+on match and nonzero otherwise.
+
+Summary
+-------
+This program is a command-line utility to catalog and verify torrent files.
+Run with only the -t option, it displays the metadata, name, and size of
+each file in the torrent. Run with the -t and -p options, it computes the
+hashes of all files in the torrent, compares them against the hashes stored
+in the metadata, and warns of any errors.
+
+If torrentcheck returns "torrent is good" at the end of its output, every
+byte of every file in the torrent is present and correct, to a high degree of
+certainty as explained below.
+
+For example, if you run torrents on a fast external server and then download
+the files, this utility will verify that the files you received are complete
+and uncorrupted. It can also be used to verify backups or to automatically
+check a series of torrents using scripting.
+
+The -t parameter should be the path to the .torrent metadata file. The -p path
+should point to the file or files. It can include or leave out the torrent name.
+The -n option suppresses the running count, which is useful if you are writing
+the output to a file. The -h option shows all piece hash values. The -c or -d
+options produce comma or dot formatted byte counts for readability.
+
+The -sha1 option disables torrent checking, and instead acts as a SHA1 filter.
+Most Windows machines do not have a SHA1 utility, so I included this mode as a
+convenience feature. It reads in binary data from standard input until end of
+file, and prints the SHA1 hash. If a SHA1 hash is provided on the command line,
+it will return 0 if the hashes match or nonzero if they do not. This mode
+should agree with the output of "openssl dgst -sha1" or "digest -a sha1"
+
+Examples
+--------
+torrentcheck -t \torrents\ubuntu-10.10-desktop-i386.iso.torrent
+torrentcheck -t \torrents\ubuntu-10.10-desktop-i386.iso.torrent -p \download
+torrentcheck -t \torrents\ubuntu-10.10-desktop-i386.iso.torrent -p \download && echo good
+torrentcheck -t \torrents\ubuntu-10.10-desktop-i386.iso.torrent -p \download || echo bad
+torrentcheck -t \torrents\ubuntu-10.10-desktop-i386.iso.torrent -p \download\ubuntu-10.10-desktop-i386.iso
+torrentcheck -sha1 < \download\ubuntu-10.10-desktop-i386.iso
+torrentcheck -sha1 b28bbd742aff85d21b9ad96bb45b67c2d133be99 < \download\ubuntu-10.10-desktop-i386.iso && echo good
+(These are for Windows; use forward slashes in Unix/Linux)
+
+Automation and scripting
+------------------------
+Torrentcheck returns 0 in the Unix $? return code or Windows errorlevel
+if it successfully verifies a torrent, or nonzero return codes if it fails.
+
+If you have your torrents in \torrents and the downloaded files in \share,
+make a "bad" directory under \torrents, cd to \torrents, and run:
+
+(Windows)
+for %i in (*.torrent) do torrentcheck -t "%i" -p \share || move "%i" bad
+(Linux)
+for i in *.torrent; do torrentcheck -t "$i" -p /share || mv "$i" bad ; done
+
+This will check all the torrents, and move any that are not fully
+downloaded and correct into \torrents\bad.
+
+Run this command to generate a master list file with the contents of all your
+torrents. This file can be searched to find a particular file and which torrent
+it comes from.
+
+(Windows)
+for %i in (*.torrent) do torrentcheck -t "%i" >> masterlist.txt & echo. >> masterlist.txt
+(Linux)
+for i in *.torrent; do torrentcheck -t "$i" >> masterlist.txt ; echo >> masterlist.txt ; done
+
+Detailed description
+--------------------
+BitTorrent is a file sharing system which uses a metadata file, usually with
+the .torrent extension, to identify a data file or group of files. Given the
+metadata file, a BitTorrent client can download and share the data files.
+It can also verify the integrity of the files.
+
+The metadata file uses an encoding scheme called "bencode" which can store
+integers, strings, lists, and key-value pairs. It can represent binary values
+without any escaping, so a bencoded string can be loaded into memory and parsed
+in place, without any decoding. Torrent metadata contains the names and sizes
+of all the files in the torrent, and also contains a series of SHA1 hashes on
+each piece of the data file or files. The piece size is specified in the
+metadata, ranging from 32KiB (32768) to 4MiB (4194304) in a sample of torrents.
+
+SHA1 is a complex error-checking code designed by the National Security Agency
+for the military Defense Messaging System. It inputs an arbitrarily long byte
+string and outputs a 20-byte check code. If any bit in the input changes, the
+check code will change. SHA1 is complex enough so that even by deliberate
+effort it is very difficult to find two strings with the same check code. The
+chance of this happening by accident is small enough to ignore.
+
+To check a single-file torrent, allocate a buffer equal to the "piece size"
+string in the metadata, open the input file identified by the "name" string
+or specified on the command line, and read in pieces one at a time. The last
+piece will likely be short; keep track of the number of bytes actually read.
+Hash each piece, and compare the hash code against the corresponding hash code
+in the metadata. Any mismatch is an error.
+
+To check a multiple-file torrent, allocate a buffer as above. Read files in
+order from the "files" list in the metadata and reconstruct the paths, where
+the "name" string may be the base directory. Read from each file in sequence
+into the buffer until the buffer is full or the last file has been read, then
+hash it and check against the list in the metadata. Any mismatch is an error.
+
+Hash pieces span multiple files, so a missing or corrupt file can cause the
+previous or next file to fail as well. In particular, a missing file usually
+causes the previous and next files to fail verification. This is an artifact of
+the torrent format, and there is no way to avoid it. Torrents often contain a
+large media file and a small descriptive text file. If the text file is
+missing, the media file usually cannot be verified.
+
+Torrentcheck also verifies the length of each file, and flags an error if the
+length is wrong even if the hash codes match. It is designed to handle files
+over 4GB on a 32-bit machine.
+
+The SHA1 implementation used by torrentcheck was written by David Ireland,
+AM Kuchling, and Peter Gutmann. The source code does not contain a copyright
+notice, and this file is widely used on the Internet.
+
+Compiling
+---------
+There is no makefile. The required gcc lines are at the top of the
+torrentcheck.c source file. The major catch in compiling is making 64-bit file
+I/O work. It is tested on Windows, Linux, and Solaris, but you may have to
+experiment with compiler options to get 64-bit ftell and fseek working.