blockchain101

Async P2P Blockchain Simulation in Rust

• A fully asynchronous, multi-node blockchain network implementing Proof-of-Work, peer-to-peer gossip, and longest-chain consensus using Rust and Tokio.

Overview

This project implements a miniature blockchain protocol from first principles, designed to mirror real-world blockchain engineering patterns such as:

• Peer-to-peer networking
• Proof-of-Work mining
• Block validation and propagation
• Chain conflict resolution
• Concurrent execution and synchronization

The system simulates a distributed network of nodes, each independently mining, validating, broadcasting, and synchronizing blocks without any central coordinator.

Key Design Goals

• Models real blockchain mechanics, not just data structures
• Mining and networking run asynchronously
• Longest valid chain rule
• All data is revalidated locally
• Easy to reason about and extend

Architecture

High-Level Components

Component	Description
Block	Immutable data unit secured with SHA-256
Blockchain	Ordered block history with validation rules
Node	Independent participant with local state
Network	Fully connected P2P mesh via async channels
Consensus	Longest valid chain wins

Each node maintains its own blockchain and communicates with peers using Tokio MPSC channels, emulating a decentralized gossip network.

Block Structure

Each block cryptographically commits to:

• Block index
• Timestamp
• Transaction data
• Previous block hash
• Nonce (Proof-of-Work)
• Resulting SHA-256 hash

Block {
  index
  timestamp
  data
  previous_hash
  nonce
  hash = SHA256(index || timestamp || data || previous_hash || nonce)
}

Proof of Work (Mining)

Mining is implemented via a hash-based difficulty target:

• A block is valid if its hash starts with N leading zeros
• N is the network difficulty
• Mining runs on a dedicated blocking thread to avoid starving async tasks

spawn_blocking(mine_block)

This closely mirrors real blockchain systems where mining is CPU-bound.

Network Messaging Protocol

Nodes communicate using a small but expressive protocol:

Message	Purpose
Mine(data)	Trigger block mining
NewBlock(block)	Broadcast newly mined block
RequestChain(node_id)	Request full chain on conflict
Chain(Vec<Block>)	Respond with full blockchain

All messages are broadcast-based, enabling decentralized propagation.

Consensus Mechanism

The system uses a Longest Valid Chain Rule:

1. Every received block is independently validated

2. Invalid blocks trigger a full chain request

3. Nodes replace their chain only if:

   • The new chain is longer
   • The entire chain is valid
   • Proof-of-Work is satisfied

This ensures eventual consistency across the network.

Concurrency Model

Task	Execution
Network I/O	Async Tokio tasks
Mining	spawn_blocking threads
Blockchain State	Arc<Mutex<>>
Validation	Synchronous & deterministic

This design prevents:

• Async executor starvation
• Race conditions on shared state
• Invalid state propagation

Simulation Flow

1. Spawn N nodes
2. Fully connect all nodes (P2P mesh)
3. Random nodes mine blocks
4. Blocks propagate through the network
5. Forks resolve automatically
6. Final chains converge