Foundry NFT — Learning Project

A hands-on Solidity / Foundry learning project for building and deploying ERC-721 NFTs. It walks through the full lifecycle — writing the contract, embedding an image fully on-chain, storing metadata on IPFS, deploying to a local Anvil node or Sepolia testnet, and minting/viewing the result in MetaMask.

This is a learning repo, not production code. The contract and tests are deliberately kept small and heavily commented so each concept is easy to follow. See Concepts covered for the study notes.

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What this project does

It implements two NFT contracts and the scripts + tests to drive them:

Contract	Description
BasicNft.sol	A minimal ERC-721 where mintNft(tokenUri) stores an arbitrary URI (usually an IPFS URI) per token.
MoodNft.sol	A "dynamic" / fully-on-chain SVG NFT. The artwork is encoded in the contract itself and can be flipped between Happy and Sad states by the owner.

Both inherit OpenZeppelin's ERC721 — so most of the heavy lifting (transfer, approval, safeMint, balanceOf, ownerOf) comes for free.

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Project structure

├── src/
│   ├── BasicNft.sol          # Minimal ERC-721 with per-token URI
│   └── MoodNft.sol           # On-chain SVG NFT with flipMood()
├── script/
│   ├── DeployBasicNft.s.sol  # Deploys BasicNft
│   ├── DeployMoodNft.s.sol   # Reads img/*.svg, base64-encodes them, deploys MoodNft
│   └── Interactions.s.sol    # MintBasicNft / MintMoodNft (uses DevOpsTools to find latest deployment)
├── test/
│   ├── unit/                 # Isolated unit tests (DeployMoodNftTest, MoodNftTest)
│   └── interactions/         # Integration tests (BasicNftTest, MoodNftIntegrationTest)
├── img/                      # Source SVG art + example metadata JSONs for IPFS
├── lib/                      # Submodules: forge-std, openzeppelin-contracts, foundry-devops
├── foundry.toml              # Foundry config (build, remappings, rpc/etherscan)
├── Makefile                  # Convenience targets (deploy, mint, test, anvil...)
├── sample1-deploy.txt        # Reference log: Sepolia deploy of BasicNft
└── sample2-mint.txt          # Reference log: Sepolia mint of BasicNft

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Getting started

1. Install Foundry

curl -L https://foundry.paradigm.xyz | bash
foundryup

2. Install dependencies (git submodules)

git submodule update --init --recursive

3. Build & test

forge build
forge test

The test suite runs 6 tests across 4 suites and should pass green.

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Run against a local Anvil node

# Terminal 1 — start a local EVM
make anvil

# Terminal 2 — deploy and mint
make deploy
make mint

make anvil starts anvil with a known test mnemonic and 1-second block time. The default deployer key is Anvil's first account (0xac09...), already configured in the Makefile.

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Deploy to Sepolia testnet

Set up your .env (ignored by git):

SEPOLIA_RPC_URL=https://eth-sepolia.g.alchemy.com/v2/<YOUR_KEY>
ETHERSCAN_API_KEY=<YOUR_KEY>
SEPOLIA_PRIVATE_KEY=<YOUR_PRIVATE_KEY>

Then:

make deploy ARGS="--network sepolia"
make mint ARGS="--network sepolia"

The make deploy/make mint targets auto-switch to the Sepolia RPC + auto-verify on Etherscan when --network sepolia is passed. See sample1-deploy.txt and sample2-mint.txt for what a successful run looks like.

Viewing the NFT in MetaMask: add the deployed contract + token ID (starts at 0) as a collectible. For BasicNft you'll see the IPFS image; for MoodNft the artwork is rendered from the on-chain base64 SVG.

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Concepts covered

1. ERC-721 essentials (OpenZeppelin)

• Inheriting ERC721 gives you the full token standard (ERC-165, transfers, approvals, metadata).
• _safeMint(to, tokenId) — guarantees the recipient can actually receive ERC-721s (reverts for plain EOAs that would lose the token).
• Custom errors (error BasicNft__TokenUriNotFound();) — modern, gas-cheaper alternative to require with string messages.

2. tokenURI and metadata

• tokenURI(tokenId) returns the location of the token's metadata JSON — not necessarily the raw image.
• The standard metadata shape:

  {
    "name": "...",
    "description": "...",
    "image": "<ipfs or data: URI>",
    "attributes": [ { "trait_type": "...", "value": "..." } ]
  }
  

  Store this JSON on IPFS, then point the contract at its ipfs:// CID. Example metadata JSONs live in img/*.json.

3. Fully on-chain SVG (MoodNft)

• Instead of hosting art on IPFS, the SVG is base64-encoded and embedded in the contract:

  data:image/svg+xml;base64,<encoded>
  

• DeployMoodNft uses vm.readFile("img/smile.svg") + Base64.encode(...) (OpenZeppelin) to build these image URIs at deploy time.
• tokenURI then builds a JSON data:application/json;base64,... URI on the fly, so the entire NFT is self-contained on-chain.
• flipMood(tokenId) mutates on-chain state (s_tokenIdToMood), so the NFT "changes expression" — a gentle intro to dynamic NFTs.

4. Foundry testing patterns

• Unit tests (test/unit/) instantiate contracts directly with fixed inputs.
• Integration tests (test/interactions/) run the actual deploy scripts (deployer.run()) to exercise the full path.
• vm.prank(USER) — impersonate an address for the next call.
• makeAddr("HOELEE") — deterministic fake address from a label.
• String comparison gotcha: you can't == two strings in Solidity. Compare their hashes instead:

  keccak256(abi.encodePacked(a)) == keccak256(abi.encodePacked(b))
  

5. DevOpsTools (foundry-devops)

DevOpsTools.get_most_recent_deployment("BasicNft", block.chainid) reads the broadcast/ logs to find the latest deployed contract — so the mint script automatically targets the last deployment on the current chain instead of a hardcoded address.

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Notes & gotchas

• Line endings / SVG: the deploy script base64-encodes whatever bytes vm.readFile returns. The repo pins img/*.svg to LF via .gitattributes so the on-chain bytes are deterministic regardless of platform (Windows/core.autocrlf would otherwise inject CRLF and silently change the encoded art).
• remappings in foundry.toml maps @openzeppelin/contracts/... → lib/openzeppelin-contracts/contracts.
• IPFS pinning: Interactions.s.sol contains both IPFS CIDs and Pinata gateway URLs as examples. Prefer the raw ipfs://<CID> form in production so the asset resolves independent of any single gateway.

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Reference

• ERC-721 standard (EIP-721)
• Foundry book
• OpenZeppelin Contracts