Log & Event Extraction

Every smart contract interaction emits events — Transfer, Approval, Swap, and hundreds of others. After simulating a transaction, you can extract and decode these events to see exactly what happened, including ERC-20/ERC-721/ERC-1155 token movements.

The StateChangesExtractor goes further: it consolidates all Transfer events into a net balance change per address, giving you a "what changed" summary rather than a raw event list.

Prerequisites

dotnet add package Nethereum.EVM

Decoded Events

After decoding a simulation result (see Call Tree Decoding), all events are available in decoded.DecodedLogs:

var decoder = new ProgramResultDecoder(abiStorage);
var decoded = decoder.Decode(execResult, callInput, chainId);

foreach (var log in decoded.DecodedLogs)
{
    Console.WriteLine($"Event: {log.GetDisplayName()}");
    Console.WriteLine($"  Contract: {log.ContractAddress}");

    if (log.IsDecoded && log.Parameters != null)
    {
        foreach (var param in log.Parameters)
        {
            Console.WriteLine($"  {param.Parameter.Name}: {param.Result}");
        }
    }
}

Each DecodedLog contains:

• Event — the EventABI with signature and parameter types
• Parameters — decoded values for both indexed and non-indexed parameters
• ContractAddress / ContractName — which contract emitted it
• IsDecoded — whether the ABI was found; if false, OriginalLog has the raw data

Decoding a Single Log

You can decode individual logs from any source — not just simulation results:

var decoder = new ProgramResultDecoder(abiStorage);
var decodedLog = decoder.DecodeLog(filterLog, chainId);

if (decodedLog.IsDecoded)
{
    Console.WriteLine($"{decodedLog.GetEventName()}({string.Join(", ",
        decodedLog.Parameters.Select(p => $"{p.Parameter.Name}={p.Result}"))})");
}

This works with any FilterLog from eth_getLogs, eth_getTransactionReceipt, or the simulation trace.

Extracting Balance Changes

While decoded logs show individual events, the StateChangesExtractor consolidates them into net balance changes — the "what is the bottom line" view that wallets display.

using Nethereum.EVM.StateChanges;

var extractor = new StateChangesExtractor();
var stateChanges = extractor.ExtractFromDecodedResult(
    decoded, executionStateService, "0xCurrentUserAddress");

foreach (var change in stateChanges.BalanceChanges)
{
    switch (change.Type)
    {
        case BalanceChangeType.Native:
            Console.WriteLine($"{change.Address}: {Web3.Convert.FromWei(change.Change)} ETH");
            break;
        case BalanceChangeType.ERC20:
            Console.WriteLine($"{change.Address}: {change.Change} {change.TokenSymbol ?? change.TokenAddress}");
            break;
        case BalanceChangeType.ERC721:
            Console.WriteLine($"{change.Address}: NFT #{change.TokenId} ({change.TokenAddress})");
            break;
        case BalanceChangeType.ERC1155:
            Console.WriteLine($"{change.Address}: {change.Change}x token #{change.TokenId}");
            break;
    }
}

The extractor handles:

• ERC-20: Transfer(from, to, value) events
• ERC-721: Transfer(from, to, tokenId) events (detected by indexed tokenId)
• ERC-1155: TransferSingle and TransferBatch events
• Native ETH: value transfers from the call tree (not from events)

Balance Change Types

Each BalanceChange includes a Type that tells you what kind of asset moved:

Type	Source	Key Properties
Native	Call tree value transfers	Change (wei)
ERC20	Transfer events	Change, TokenAddress, TokenSymbol, TokenDecimals
ERC721	Transfer events (indexed tokenId)	TokenId, TokenAddress
ERC1155	TransferSingle/TransferBatch	TokenId, Change, TokenAddress

Validating Token Balances

Fee-on-transfer tokens and rebasing tokens cause the actual balance change to differ from what the Transfer event reports. The extractor can cross-check against actual state:

extractor.ValidateTokenBalances(stateChanges, program, executionStateService);

foreach (var change in stateChanges.BalanceChanges)
{
    if (change.ValidationStatus == BalanceValidationStatus.FeeOnTransfer)
    {
        Console.WriteLine($"Warning: {change.TokenSymbol} charges transfer fees");
    }
    else if (change.ValidationStatus == BalanceValidationStatus.Rebasing)
    {
        Console.WriteLine($"Warning: {change.TokenSymbol} is a rebasing token");
    }
}

Validation statuses:

• NotValidated — not yet checked
• Verified — change matches actual state
• FeeOnTransfer — actual change is less than expected (token takes a fee)
• Rebasing — actual change is more than expected (token rebases)
• OwnerMismatch / Mismatch — unexpected discrepancy

Quick Summary

For a text summary of all balance changes, call tree, and events:

Console.WriteLine(stateChanges.ToSummaryString());

Next Steps

• Revert Decoding — handle failed transactions and decode error reasons
• Transaction Simulation — the full pipeline that produces these results
• Call Tree Decoding — inspect which calls emitted which events