dht network implements nodejs

DHT network is a protocol for distributed data storage and lookup. It obtains information from different nodes, allowing these nodes to share resources and form a network. The DHT network is a completely decentralized network that does not rely on any specific central node to provide services. In this article, we will explore how to implement a DHT network using Node.js.

What is DHT network?

DHT network is a network based on distributed hash table (Distributed Hash Table) built on the existing network. The DHT network enables decentralized data storage and search services between nodes, which means that it does not need to rely on a specific central node to provide services to other nodes like traditional networks.

The DHT network has the following characteristics:

1. Completely decentralized: The nodes of the DHT network are connected to each other, and no node has more permissions, which makes the network highly Decentralized properties.
2. Self-organization: The DHT network can automatically reorganize and rebalance when joining or exiting the network.
3. Deduplication: In the DHT network, only one copy of the same file or data is stored, which makes the data in the network highly deduplicated.
4. Distributed: The data of the DHT network is stored on different nodes, which makes the data more distributed.

DHT network is mainly used for P2P file sharing and search, distributed computing and distributed storage.

How to implement DHT network?

Implementing the DHT network requires completing the following tasks:

1. ID generation and node joining: Nodes need to be assigned a unique ID to join the network, and we need to use a hash function to combine the node information Convert to ID.
2. Routing table: Each node needs to maintain a routing table to store the IDs and IP addresses of other nodes.
3. Data storage and search: Nodes can store their own data in the DHT network and search it. We need to implement corresponding algorithms to realize these functions.

Here is an example of implementing a DHT network using Node.js:

1. ID generation and node joining

We can use the crypto module Use the hash function in to generate the ID, such as SHA1:

const crypto = require('crypto');

function generateNodeId() {
  const nodeId = crypto.createHash('sha1')
    .update(`${Date.now()}_${Math.random()}`)
    .digest('hex')
    .substring(0, 20);
  return nodeId;
}

When a node joins the network, it needs to generate the ID first, then send the joining information to other known nodes, and at the same time store the information of other nodes in the routing table middle.

const Node = require('./node');

const bootstrapNodes = [
  { id: 'node1', address: '127.0.0.1:8001' },
  { id: 'node2', address: '127.0.0.1:8002' }
];

const node = new Node(generateNodeId(), '127.0.0.1:8000');
for (const bootstrapNode of bootstrapNodes) {
  node.joinNetwork(bootstrapNode.id, bootstrapNode.address);
}

2. Routing table

We can use an array to implement the routing table, where each element represents a range of IDs, for example:

##[2^160/2^1, 2^160/2^2)[node3, node4]......

ID range	Node list
[0, 2^160/2^1)	[node1, node2]

When looking for a node, you can find the distance to it based on the prefix of the ID The nearest node is then used for the next search step.

Data storage and search

Data storage can be achieved by storing data on the node closest to the data ID, which allows the data to be efficiently stored in the network distributed. When searching for data, you only need to find the node closest to the target ID from the routing table, and the node will search for it on your behalf. If the node does not find the target data, it can forward the search request to neighboring nodes until the target data is found or the number of nodes reached reaches the upper limit.

class Node {
  // ...
  lookup(key, callback) {
    const targetId = getKeyId(key);
    const tableIds = getTableIds(targetId);
    const closestNodes = this.getClosestNodes(tableIds);
    const seenNodes = {};

    const next = () => {
      const node = closestNodes.shift();
      if (!node || seenNodes[node.id]) {
        return callback(null, null);
      }

      seenNodes[node.id] = true;
      if (node.id === this.id) {
        // key found
        return callback(null, this.store[key]);
      } else {
        // find key in next node
        this.findKeyInNode(node.id, targetId, (err, val) => {
          if (err || val) {
            return callback(err, val);
          } else {
            return next();
          }
        });
      }
    };
    
    next();
  }

  findKeyInNode(nodeId, targetId, callback) {
    // send find_key request to node
    // ...
    // callback with result if found
  }
}

Summary

In this article, we introduced the DHT network and its implementation method, and implemented a simple DHT network using Node.js. Because the DHT network is highly decentralized and self-organizing, it is able to play an important role in distributed computing and storage. For developers who need to build distributed applications, it is very useful to become familiar with the DHT network and learn to use Node.js to implement it.

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