Deep Dive: ABI Encoding

Status: Planned — outline only.

Summary

A standalone deep dive into how Solidity encodes and decodes data at the ABI level. Covers the full encoding family, calldata layout, and how to read raw bytes.

Planned Sections

1. What is ABI encoding? — The contract-to-contract communication protocol. How function calls become raw bytes and how return data becomes values again.

2. Calldata layout — The 4-byte selector, head/tail encoding, static vs dynamic types, padding rules. Visual byte-by-byte breakdowns.

3. The abi.encode* family — When and why to use each:

   • abi.encode — general-purpose encoding (hashing, storage, cross-chain payloads)
   • abi.encodePacked — tightly packed, no padding (hashing, but beware collision risks)
   • abi.encodeWithSelector — function call encoding without type safety
   • abi.encodeWithSignature — same, from a string signature
   • abi.encodeCall — type-safe function call encoding

4. Decoding — abi.decode, how to decode return data, how to decode revert data (connects to the Errors deep dive).

5. Selector computation — bytes4(keccak256("transfer(address,uint256)")), function selector clashes, and why they matter for proxies.

6. Common patterns and pitfalls — encodePacked collision bugs, dynamic type encoding surprises, nested tuple encoding.

Exercise (planned)

An ABI encoding toolkit exercise: encode/decode function calls manually, verify against abi.encodeCall output, decode raw revert data, and detect selector clashes.