How to build dht in golang-Golang-php.cn

DHT, or distributed hash table, is a distributed protocol used to implement distributed storage and distributed computing. In a peer-to-peer network environment, DHT is particularly important because it can serve as a routing protocol and a key function for organizing data. This article will introduce how to implement DHT using Golang language.

1. Principle of DHT

The core algorithm used by DHT is the hash table algorithm. DHT maps data and nodes into a hash space respectively, and the hash values of nodes and data determine their positions in the hash space. Each node maintains its own hash value and the hash value of its adjacent nodes, thus forming a hash ring.

When a node joins DHT, it needs to contact known nodes, find the position where it should belong on the hash ring, and become the successor node of that position. At this time, the node can receive requests from other nodes, store the data that needs to be stored in its own location, and at the same time send its own hash value and the hash value of the successor node to the known node. When a node leaves the DHT, it needs its successor nodes to reconnect to ensure the normal operation of the DHT network.

The position of a DHT node in the hash ring not only determines its position in the DHT network, but also determines what data it needs to store and which requests it needs to process. For example, when a node needs to look up a value, it can visit nodes that are closer to that value than it is in the hash ring. These nodes forward the request step by step until a node is found that stores the value. Similarly, when a node needs to store a value, it needs to store it on a node that is closer to that value than it is in the hash ring.

2. Implementing DHT in Golang

It is very simple to implement DHT in Golang. First, we need to use a hash function to convert the identity of the node and data into a hash value. Golang provides a variety of hash functions, including MD5, SHA-1, SHA-256, etc. We can choose any of them.

import (

"crypto/sha1"

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)

func hash(data string) []byte {

h := sha1.New()
h.Write([]byte(data))
return h.Sum(nil)

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}

Next, we A node type needs to be defined to store the node's identity, hash value, and hash value of the successor node.

type Node struct {

ID       string
Hash     []byte
Successor []byte

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}

type DHT struct {

Nodes   map[string]*Node

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}

The DHT structure contains a node mapping Table Nodes, stores all known nodes. We can use map to implement this mapping table.

Before implementing the DHT algorithm, we need to implement some auxiliary functions, such as finding the successor node corresponding to a key value in the hash ring, adding a new node, etc.

func (dht *DHT) findSuccessor(key []byte) []byte {

for _, node := range dht.Nodes {
    if bytes.Compare(key, node.Hash) == -1 || bytes.Equal(key, node.Hash) {
        return node.Hash
    }
}
return dht.Nodes[dht.minNode()].Hash

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}

func (dht DHT) addNode(node Node) error {

if _, ok := dht.Nodes[node.ID]; ok {
    return errors.New("Node already exists")
}

dht.Nodes[node.ID] = node
dht.fixSuccessorList()
return nil

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}

In the findSuccessor function, we traverse the node mapping table Nodes to find a successor node closest to the given hash value key. When the key is less than or equal to the hash value of the node or all nodes have been traversed, the function returns the closest successor node. In the addNode function, we first check whether the node already exists in the node mapping table Nodes, and return an error if it exists. Otherwise, we add the new node to Nodes and then call the fixSuccessorList function to adjust the node's successor list.

func (dht *DHT) fixSuccessorList() {

ids := make([]string, 0, len(dht.Nodes))
for id := range dht.Nodes {
    ids = append(ids, id)
}

sort.Slice(ids, func(i, j int) bool {
    return bytes.Compare(dht.Nodes[ids[i]].Hash, dht.Nodes[ids[j]].Hash) == -1
})

for i, id := range ids {
    prev := ids[(i+len(ids)-1)%len(ids)]
    next := ids[(i+1)%len(ids)]
    dht.Nodes[id].Successor = dht.Nodes[next].Hash
    dht.Nodes[id].Predecessor = dht.Nodes[prev].Hash
}

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}

In the fixSuccessorList function, we sort the node mapping table Nodes, and then set the Predecessor node and successor node. The prev node is the node before the current node after sorting, and the next node is the node after the current node after sorting. Please note that we use the % operator to ensure that the connection to the node map is circular.

Finally, we can implement the DHT algorithm. When a node needs to find a value, it sends a request to its successor nodes. If the successor node does not have this value, it forwards the request to its successor node. Likewise, when a node needs to store a value, it will store the value in its own location and send its hash and the hash of the successor node to known nodes. These nodes will forward the request step by step until the node storing the value is found.

func (dht *DHT) findValue(key string) (string, error) {

hash := hash(key)
successor := dht.findSuccessor(hash)

if bytes.Equal(successor, hash) {
    return dht.Nodes[string(successor)].Value, nil
}

addr := dht.getNodeAddr(successor)
conn, err := net.Dial("tcp", addr)
if err != nil {
    return "", err
}
defer conn.Close()

request := &FindValueRequest{Key: key}
response := &FindValueResponse{}
if err := sendRequest(conn, request); err != nil {
    return "", err
}
if err := receiveResponse(conn, response); err != nil {
    return "", err
}

if len(response.Value) == 0 {
    return "", errors.New("Key not found")
}
return response.Value, nil

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}

func (dht *DHT) storeValue(key, value string) error {

hash := hash(key)
successor := dht.findSuccessor(hash)

if bytes.Equal(successor, hash) {
    dht.Nodes[string(hash)].Value = value
    return nil
}

addr := dht.getNodeAddr(successor)
conn, err := net.Dial("tcp", addr)
if err != nil {
    return err
}
defer conn.Close()

request := &StoreValueRequest{Key: key, Value: value}
response := &StoreValueResponse{}
if err := sendRequest(conn, request); err != nil {
    return err
}
if err := receiveResponse(conn, response); err != nil {
    return err
}

return nil

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}

In the findValue function, we first use the hash function to convert the key value into a hash value, and find the successor node corresponding to the hash value. If the successor node is equal to the hash value, we have found the corresponding value and return it. Otherwise, we send a request to the successor node and recursively call the function that handles the request. In the storeValue function, we use the hash function to convert the key value into a hash value, and find the successor node corresponding to the hash value. If the successor node is equal to the hash value, we store the value on that node and return it. Otherwise, we send a request to the successor node and recursively call the function that handles the request.

3. Summary

This article introduces how to implement the DHT algorithm using Golang language. DHT is a hash table-based distributed protocol used to implement distributed storage and distributed computing. This article enables us to better understand the principles and implementation of this protocol by implementing a simple DHT algorithm. DHT is widely used in many fields, such as BitTorrent file sharing, transaction verification of cryptocurrencies such as Bitcoin, etc.

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