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Bitcoin File System (BFS)

Let's build the Bitcoin File System (BFS), a decentralized, open, and permissionless file storage on Bitcoin.
  • write a file to Bitcoin
  • read a file from Bitcoin
  • support large files

Write the BFS smart contract

It turns out that writing the Bitcoin File System smart contract is very simple. Here is a basic contract to provide decentralized file storage on Bitcoinevm.
​
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
​
import "@openzeppelin/contracts/utils/Counters.sol";
​
error FileExists();
​
contract BFS {
using Counters for Counters.Counter;
Counters.Counter private idCounter;
mapping(address => mapping(string => mapping(uint256 => bytes))) public dataStorage;
mapping(address => mapping(string => uint256)) public chunks; // max chunk index
mapping(address => mapping(string => uint256)) public bfsId;
​
constructor () {
idCounter.increment(); // start from 1
}
​
function store(string memory filename, uint256 chunkIndex, bytes memory _data) external {
if (dataStorage[msg.sender][filename][chunkIndex].length > 0) {
revert FileExists();
}
dataStorage[msg.sender][filename][chunkIndex] = _data;
if (chunks[msg.sender][filename] < chunkIndex) {
chunks[msg.sender][filename] = chunkIndex;
}
bfsId[msg.sender][filename] = idCounter.current();
idCounter.increment();
}
​
function load(address addr, string memory filename, uint256 chunkIndex) public view returns (bytes memory, int256) {
uint256 temp = chunkIndex + 1;
int256 nextChunk = (temp > chunks[addr][filename]) ? -1 : int256(temp);
return (dataStorage[addr][filename][chunkIndex], nextChunk);
}
​
function count(address addr, string memory filename) public view returns (uint256) {
return chunks[addr][filename];
}
​
function getId(address addr, string memory filename) public view returns (uint256) {
return bfsId[addr][filename];
}
}
The store() function saves a chunk of a file. The load() function returns the data of a specific chunk. And the getId() function returns the ID of the file.
You can save a large file onto Bitcoin by splitting it into smaller chunks, committing them to Bitcoin, and retrieving & merging them back as needed.
BFS files are immutable.

Clone the smart contract examples

We've prepared a few different examples for you to get started. The BNS example is located at smart-contract-examples/contracts/BNS.sol.
git clone https://github.com/bitcoinevm/smart-contract-examples.git

Compile the contracts

To compile your contracts, use the built-in hardhat compile task.
cd smart-contract-examples
npm install
npx hardhat compile

Deploy the contracts

Review config file hardhat.config.ts. The network configs should look like this.
networks: {
mynw: {
url: "http://localhost:10002",
accounts: {
mnemonic: "<your mnemonic with funds>"
},
timeout: 100_000,
},
blockscoutVerify: {
blockscoutURL: "http://localhost:4000", // your explorer URL
...
}
}
Run the deploy scripts using hardhat-deploy.
Make sure the accounts in hardhat.config.ts have some BTC.

Interact with the contracts

Once the contracts are deployed, you can interact with them. We've prepared a few hardhat tasks to make it easy for you to interact with the contracts.
# store data
echo "this is some text" > data.txt
npx hardhat write-storage --filename ./data.txt
npx hardhat read-storage --filename ./data.txt # read data, print it as readable text