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std::unique_ptr implementation backed by Ethereum NFTs

Hacker News - Sun Apr 11 21:32

C++ std::unique_ptr that represents each object as an NFT on the Ethereum blockchain.

Build nft_ptr Follow us: worthdoingbadly.com | @zhuowei | @[email protected]

  auto ptr1 = make_nft<Cow>();
  nft_ptr<Animal> ptr2;

  ptr2 = std::move(ptr1);

This transfers the Non-Fungible Token 0x7faa4bc09c90, representing the Cow's memory address, from ptr1 (OpenSea, Etherscan) to ptr2 (OpenSea, Etherscan).

screenshot of OpenSea Trading History showing token transfer

[2021-04-09T01:59:48Z INFO  nft_ptr_lib] Transferring 0x7faa4bc09c90 (Cow) to 0x7ffee35a7890 (0x1564b0a7c258fc88a96aa9fe1c513101883abb13) from 0x7ffee35a78a8 (0x9ed6006c6f3bb20737bdbe88cc6aa0de00597fef) at PC=0x10c65a946 (main (example.cpp:33))
[2021-04-09T02:00:15Z INFO  nft_ptr_lib] Transaction: 0xcbe06fdd54bd9d221993c875022fe2960128874811a25075d692cc638a28f290
[2021-04-09T02:00:15Z INFO  nft_ptr_lib] https://testnets.opensea.io/assets/goerli/0x90eaf0ab2c6455a9b794f9dcf97839fa25b4ce2d/0x7faa4bc09c90

After the transfer, ptr1 is set to null, and ptr2 contains the new object, just like std::unique_ptr:

  std::cout << "Moved: ptr1 = " << ptr1.get() << " ptr2 = " << ptr2.get()
            << std::endl;
  Moved: ptr1 = 0x0 ptr2 = 0x7faa4bc09c90
  auto ptr1 = make_nft<Cow>();


  • initializes the nft_ptr runtime
  • creates the first nft_ptr<Cow>
  • transfers ownership of the newly created Cow* to the nft_ptr

First, it creates an ERC-721 smart contract that represents each memory address as a Non-Fungible Token.

[2021-04-09T01:57:48Z INFO  nft_ptr_lib] Connected to network id 5
[2021-04-09T01:57:48Z INFO  nft_ptr_lib] Account: 0xd54b39c6bb7774aba2be4b49dc2667332b737909
[2021-04-09T01:57:48Z INFO  nft_ptr_lib] https://goerli.etherscan.io/address/0xd54b39c6bb7774aba2be4b49dc2667332b737909
[2021-04-09T01:57:48Z INFO  nft_ptr_lib] Deploying NFT contract!
[2021-04-09T01:58:18Z INFO  nft_ptr_lib] Token contract deployed at 0x90eaf0ab2c6455a9b794f9dcf97839fa25b4ce2d
[2021-04-09T01:58:18Z INFO  nft_ptr_lib] https://goerli.etherscan.io/token/0x90eaf0ab2c6455a9b794f9dcf97839fa25b4ce2d

Next, it creates another smart contract, that represents the nft_ptr<Cow> instance which can own NftPtr tokens:

[2021-04-09T01:58:18Z INFO  nft_ptr_lib] Deploying contract for nft_ptr 7ffee35a78a8 Cow main (example.cpp:25)
[2021-04-09T01:58:48Z INFO  nft_ptr_lib] Deployed contract for nft_ptr 7ffee35a78a8 Cow main (example.cpp:25) at 0x9ed6006c6f3bb20737bdbe88cc6aa0de00597fef
[2021-04-09T01:58:48Z INFO  nft_ptr_lib] https://goerli.etherscan.io/token/0x9ed6006c6f3bb20737bdbe88cc6aa0de00597fef

Finally, it calls new Cow(), and mints an NFT for this memory address, owned by the new nft_ptr<Cow>.

[2021-04-09T01:58:48Z INFO  nft_ptr_lib] Transferring 0x7faa4bc09c90 (Cow) to 0x7ffee35a78a8 (0x9ed6006c6f3bb20737bdbe88cc6aa0de00597fef) from 0x0 (0xd54b39c6bb7774aba2be4b49dc2667332b737909) at PC=0x10c65a76f (main (example.cpp:25))
[2021-04-09T01:59:18Z INFO  nft_ptr_lib] Transaction: 0x0a148cee1abe8d4b5721996ea3a107c87b526ded155dc2e3895f1f42983bd2e8
[2021-04-09T01:59:18Z INFO  nft_ptr_lib] https://testnets.opensea.io/assets/goerli/0x90eaf0ab2c6455a9b794f9dcf97839fa25b4ce2d/0x7faa4bc09c90

A full example program can be found at example/example.cpp, along with a sample of its output when run.

A longer example, which shows using nft_ptr with function calls and STL containers, can be found at example/long_example.cpp along with its output.

  • Biggest issue facing $125 billion security industry: Memory safety.

  • The world's largest codebases are written in C++

    • Browsers, operating systems, databases, financial systems
  • C++ memory management is hard to understand, opaque, and not secure

  • As we all know, adding blockchain to a problem automatically makes it simple, transparent, and cryptographically secure.

  • Thus, we extend std::unique_ptr, the most popular C++ smart pointer used for memory management, with blockchain support

  • Non-Fungible Tokens and std::unique_ptr have the exact same semantics:

    • each token/object is unique, not fungible with other tokens/objects
    • each token/object is owned by one owner/unique_ptr
    • others may view the NFT/use the object, but only the owner can transfer/destroy the NFT/object.
    • absolutely no protection against just pirating the image represented by the NFT/copying the pointer out of the unique_ptr
  • Written in Rust for the hipster cred.

  • Made with 💖 by a Blockchain Expert who wrote like 100 lines of Solidity in 2017 (which didn't work)

For more information, please read our white paper.

nft_ptr has negligible performance overhead compared to std::unique_ptr, as shown by this benchmark on our example program:

Implementation Runtime
std::unique_ptr 0.005 seconds
nft_ptr 3 minutes
  • Deploying ERC-721 smart contract on program start
  • Create smart contract for each nft_ptr instance
  • Call smart contract to create token when a pointer is transferred into an nft_ptr
  • Transfer token when pointer moved between nft_ptrs

nft_ptr instances are themselves ERC-20 tokens with 0 supply, for forward compatibility with our next library, nft_shared_ptr.

nft_shared_ptr will implement reference counting with security by selling shares to the owned object until the SEC complains.

How we call from C++ to Rust to Solidity:

+-----+              +------+              +--------+        +---------------+
|     |  extern "C"  |      |  rust-web3   |        |        |               |
| C++ +------------->| Rust +------------->| Wallet +------->| NFT Contracts |
|     |              |      |              |        |        |               |
+-----+              +------+              +--------+        +---------------+

How the NftPtrToken contract and the NftPtrOwner contracts interact:

+-------------+          +-------------------+
| NftPtrToken |          | NftPtrOwner       |
|             | Owns     |                   |
| 0x41414141<--+---------+ nft_ptr<Animal>   |
|             |          +-------------------+
|             |
|             | Owns     +-------------------+
| 0x42424242<--+---------+ NftPtrOwner       |
|             |          |                   |
|             |          | nft_ptr<Animal>   |
| (1 instance |          +-------------------+
| per program)|          ...
|             |
+-------------+       (1 instance per nft_ptr)

For a limited time, you can buy any Git commit from this repository as a Non-Fungible Token on my Content-First Multimedia Proof-of-Authority revision-controlled realtime collaborative private enterprise blockchain (a shared Google Doc).

You can also help by going full r/roastme on my code: this is only my second Rust project, and I would appreciate guidance on my journey to carcinization.

  • how C++ smart pointers are implemented
  • how to implement a Non-Fungible Token
  • how the Ethereum ecosystem has evolved since I wrote my last smart contract in 2017
  • how to integrate my previous Solidity, Truffle, and Ganache workflow with new tools such as OpenZeppelin and hosted wallets
  • how to write a (trivial) program in Rust without fighting the borrow checker once
  • how to use rust-web3, serde_json, and the openssl crates
  • how to call Rust from C

All instructions tested on macOS 11.2.1.

You need:

cd contracts
npm install
truffle compile
cd ../impl
rustup override set nightly
cargo build
cd ../example

Download and run Ganache to setup a private local blockchain. Then, run

cd example
RUST_BACKTRACE=1 RUST_LOG=info ./example

To run this against a public test blockchain, the easiest way is to use a hosted node.

Create a new keystore file on MyEtherWallet and get some Görli test ethers from the Görli faucet.

Do not use an existing wallet or password! nft_ptr is very insecure; do not re-use a wallet or a password you care about, even for these worthless fake test ethers.

Run the example using your new keystore and a hosted node:

RUST_BACKTRACE=1 RUST_LOG=info NFT_PTR_HTTP="https://nodes.mewapi.io/rpc/goerli" \
NFT_PTR_KEYSTORE="/path/to/your/MewWallet.keystore" \
NFT_PTR_PASSWORD="sample password" \
exec ./example

You can also run the example against a local lite node.

Download Geth and start a lite node connected to the Görli testnet:

./geth --goerli --syncmode light

Stop Geth and import your testnet wallet:

cp ~/Downloads/MewWallet.keystore ~/Library/Ethereum/goerli/keystore/

Restart Geth and unlock your testnet wallet: This is insecure!

./geth --goerli --syncmode light --unlock 0x<address> --http --allow-insecure-unlock

Enter your password, then hit Enter. It should say

Unlocked account                         address=0x<address>

Finally run with local HTTP transport:

cd example