# DHT Search

This is a Mainline DHT crawler and BitTorrent client which also provides an
HTTP interface to query the indexed data.

Distributed Hash Table (DHT) is a distributed system storing key/value pairs,
in this case it is specifically Mainline DHT, the type used by BitTorrent
clients. The crawler also implements a number of extensions which enable it to
get the metadata for the torrent enabling indexing and later searching.

The crawler joins the DHT network and listens to the conversations between
nodes, keeping track of interesting packets. The most interesting packets are
those where another node announces they have a torrent available.

This BitTorrent client only downloads the torrent metadata. The actual files
hosted by the remote nodes are not retrieved.

## Tagging

As torrent metadata is fetched the torrent is tagged using a set of regular
expressions matched against the torrent name and the files in the torrent. By
default all files tagged 'adult' are not indexed.

## Installation

All dependencies have been vendored using the
[dep](https://github.com/golang/dep) tool so installation with a recent Go
version should be as simple as:

```shell
$ go build
```

## Usage

You will need to create a PostgreSQL database using the `schema.sql` file
provided. You are going to need to sort out any port forwarding if you are
behind NAT so remote nodes can get to yours.

The following options are available:

    Usage of ./dht-search:
      -debug
            provide debug output
      -dsn string
            DB DSN (default "postgres://dht:dht@localhost/dht?sslmode=disable")
      -http string
            HTTP listen address:port (default "localhost:6880")
      -no-http
            no HTTP service
      -nodes int
            number of nodes to start (default 1)
      -port int
            listen port (and first of multiple ports) (default 6881)

These options enable you to start a number of DHT nodes thus implementing a
small scale [Sybil attack](https://en.wikipedia.org/wiki/Sybil_attack). The
first DHT node will take the port specified and each subsequent port is for the
following nodes.

## TODO

- Manage downloading threads to reduce memory consumption.
- Add tests!
- Enable rate limiting.
- Enable configuration of tags and reject patterns.
- Enable FTS on database queries.
- Improve our manners on the DHT network (replies etc.).
- Improve the routing table implementation.
- Improve tagging by checking the torrent name against Unicode sections.
- Improve the interface.
- Add results pagination.