CCNext ABI Encoding

A Rust library for encoding Ethereum transactions and receipts into ABI format, specifically designed for the CCNext project. This library provides efficient encoding that respects Solidity's stack limitations through a sophisticated chunking mechanism.

Overview

The CCNext ABI encoding library transforms Ethereum transactions and their corresponding receipts into a standardized ABI-encoded format. The primary innovation of this library is its chunked encoding approach, which is specifically designed to work around Solidity's stack depth limitations.

Why Chunked Encoding?

The Solidity Stack Problem

Solidity has a strict stack depth limit of 1024 slots. When dealing with complex Ethereum transactions (especially Type 3 and Type 4 transactions), encoding all transaction data as a single large tuple can easily exceed this limit, causing smart contract calls to fail with stack overflow errors.

Consider a Type 3 (EIP-4844) transaction with:

• Multiple access list entries
• Large blob versioned hashes arrays
• Complex authorization lists
• Extensive log data in receipts

Encoding all this data in one tuple could require 1500+ stack slots, exceeding Solidity's limit.

The Chunking Solution

Our chunking strategy divides transaction data into logical, smaller chunks that can be processed independently:

// Instead of one massive tuple:
// (nonce, gasLimit, from, to, value, input, accessList, blobHashes, ..., logs, receipts)

// We use multiple smaller chunks:
// Chunk 1: Common fields (nonce, gasLimit, from, to, value, input)
// Chunk 2: Transaction-specific fields (gasPrice, accessList, signatures)  
// Chunk 3: Receipt data (status, gasUsed, logs, blooms)
// Chunk 4: Additional data for complex transaction types

This approach ensures that:

• Each chunk stays well below the 1024 stack limit
• Smart contracts can process chunks sequentially
• Memory usage is optimized
• Encoding remains deterministic and verifiable

Supported Transaction Types

The library supports all current Ethereum transaction types with optimized chunking:

Chunk Structure

Chunk 1: Common Transaction Fields

(
    nonce: uint64,
    gasLimit: uint64, 
    from: address,
    isToNull: bool,        // true for contract creation
    to: address,
    value: uint256,
    input: bytes           // transaction data
)

Chunk 2: Transaction Type Specific Fields

Varies by transaction type, but includes signatures, gas pricing, and type-specific data.

Chunk 3: Extended Data (Types 3 & 4)

Additional authorization lists, blob data, or other complex structures.

Chunk 3/4: Receipt Data

(
    status: uint8,         // success/failure
    gasUsed: uint64,
    logs: Log[],          // event logs
    logsBloom: bytes      // bloom filter
)

Usage

use ccnext_abi_encoding::{abi_encode, EncodingVersion};
use alloy::rpc::types::{Transaction, TransactionReceipt};

// Encode a transaction and receipt
let result = abi_encode(transaction, receipt, EncodingVersion::V1)?;

// Get the encoded bytes
let encoded_bytes = result.abi();

// Verify the encoding version
assert_eq!(result.version(), EncodingVersion::V1);

Encoding Format

The final encoded output follows this structure:

(
    transactionType: uint8,    // 0, 1, 2, 3, or 4
    chunks: bytes[]           // Array of ABI-encoded chunks
)

Each chunk in the array is independently ABI-encoded, allowing for:

• Efficient on-chain processing
• Reduced stack usage
• Parallel verification
• Modular decoding

Technical Details

Stack Optimization

The chunking strategy ensures that no single operation exceeds ~800 stack items, leaving a safety margin below Solidity's 1024 limit. This is achieved by:

1. Logical grouping: Related fields are grouped together
2. Size monitoring: Each chunk's complexity is tracked
3. Dynamic splitting: Large arrays are distributed across chunks
4. Sequential processing: Chunks can be processed one at a time

Memory Efficiency

• Chunks are encoded lazily during the encoding process
• No unnecessary data duplication
• Optimal byte packing within each chunk
• Minimal metadata overhead

Deterministic Encoding

The encoding is completely deterministic:

• Same transaction + receipt = same encoded output
• Field ordering is standardized
• No random elements or timestamps
• Suitable for cryptographic verification

Integration with Smart Contracts

Smart contracts can efficiently process the chunked encoding:

function processTransaction(bytes memory encodedData) external {
    (uint8 txType, bytes[] memory chunks) = abi.decode(encodedData, (uint8, bytes[]));
    
    // Process each chunk individually - no stack overflow!
    for (uint i = 0; i < chunks.length; i++) {
        processChunk(txType, i, chunks[i]);
    }
}