I haven't even looked at this code in years. I just found it sitting on an old hard drive and figured I'd put it up. I don't even know if it still compiles...

A toy implementation of a custom torrent implementation. Contains code for the tracker and a client.

• Run make to build the executables minitorrent and minitracker.
• make clean will remove all binaries
• make cleant will remove all .torrent files

minitracker will start the tracker.

minitorrent --create-torrent tracker file(s) will create .torrent files to be tracked by the tracker specified by 'tracker' for each file in 'file(s).' minitorrent --dump-torrent .torrent_file(s) will display the .torrent file(s) in a human readable form.

minitorrent --upload .torrent_file(s) will tell the tracker specified in the .torrent file that we are uploading the file described by the .torrent file.

minitorrent --download .torrent_file download's the file described by the .torrent file.

minitorrent --tracker-dump tracker will dump the tracker's hash table of files being tracked, and the peers tracking those files. But it does not send them to the client. The information is displayed on whatever screen 'minitracker' was run on.

A torrent file has the following format: The name of the tracker (HOST_MAX [64] bytes) The sha1 hash of the file (SHA1_SIZE [20] bytes) The number of chunks as a 32-bit integer (4 bytes) The sha1 hash of each of the 256kb chunks of the file (SHA1_SIZE * num_chunks bytes) The friendly name of the file (up to PATH_MAX bytes)

Example from torrent.c:

write(tfd, (void*)host_buf, HOST_MAX);
write(tfd, (void*)file_hash, SHA1_SIZE);
write(tfd, (void*)&num_chunks, sizeof(num_chunks)); 
for(i=0; i<num_chunks; i++) {
    write(tfd, (void*)chunks[i], SHA1_SIZE);
    free(chunks[i]);
}
write(tfd, (void*)stripped_path, strlen(stripped_path));

The minitracker runs on port 20000. Clients talk to the tracker on that port. Clients talk to eachother on port 30000. (May add support to have user-specified ports later).

There are currently three commands that the client can send to the tracker:

#define TRACKER_CMD_UPLOAD 1
#define TRACKER_CMD_DOWNLOAD 2
#define TRACKER_CMD_DUMP 3

They are sent to the tracker in the following struct:

typedef struct tracker_request {
    int cmd;
    unsigned char hash[SHA1_SIZE];
} tracker_request;

Example from tracker.c:

int tracker_cmd(int cmd, char *host, unsigned char *fh) {
    int sfd;
    tracker_request rq;
    sfd = tracker_connect(host);
    rq.cmd = cmd;
    if (fh != NULL)
        memcpy(rq.hash, fh, SHA1_SIZE);
    write(sfd, (void *)&rq, sizeof(rq));
    return sfd;
}

The client sends this command to let the tracker know that it is uploading a file. tracker_request.fh should be the sha1 hash of the file to be uploaded

The client sends this command to let the tracker know that it wants to download a file. tracker_request.fh should be the sha1 hashof the file to be downloaded.

This is a debugging command, and will be removed from the final version. It causes the tracker to dump it's list of hashed files and the peers downloading those files

After the tracker receives a TRACKER_CMD_DOWNLOAD command, it sends the following information to the client: The number of peers uploading the file as a 32-bit int (4 bytes) For each peer, it sends the host-name of that peer (HOST_MAX bytes)

Example from tracker.c:

write(cfd, (void*)&npeers, sizeof(npeers));
for(i=0; plist != NULL; plist = plist->next, i++) {
    write(cfd, (void*)plist->host, HOST_MAX);
}
assert(i==npeers);

A download request is sent in the following struct:

typedef struct download_request {
    unsigned char hash[SHA1_SIZE];
    int chunk;
} download_request;

hash is the sha1 hash of the file you want to download, chunk is the 0 indexed chunk.

The response will be the CHUNK_SIZE chunk of the file.

MIT