feat: Implement RevertDecoder for transaction revert reason decoding

[Copilot]

変更内容の説明

TransactionDebuggerモジュールに、失敗したトランザクションのRevert ReasonをデコードするRevertDecoderクラスを実装しました。

主な機能:

• Error(string) 形式のデコード (signature: 0x08c379a0)
• Panic codeのデコード (signature: 0x4e487b71) - 8種類の標準コードに対応
• Receipt内のrevertReasonから直接デコード
• eth_callシミュレーションによるフォールバック抽出
• 0xプレフィックスの有無に対応した柔軟な入力処理

使用例:

client = CryptoWalletTool::Client.new(url)
decoder = CryptoWalletTool::TransactionDebugger::RevertDecoder.new(client: client)

# Receiptから直接デコード
receipt = fetcher.fetch_receipt(tx_hash)
reason = decoder.decode_from_receipt(receipt)
# => "Insufficient balance"

# Revert dataを直接デコード
decoder.decode_revert_data('0x08c379a0...')
# => "Error message"

# Panic codeをデコード
decoder.decode_revert_data('0x4e487b71...0011')
# => "Panic: Arithmetic operation underflowed or overflowed (code: 0x11)"

変更の種類

• feat: 新機能の追加
• fix: バグ修正
• docs: ドキュメントのみの変更
• style: コードの動作に影響しない変更（フォーマット、セミコロン等）
• refactor: バグ修正や機能追加を伴わないコードの改善
• perf: パフォーマンス改善
• test: テストの追加や修正
• chore: ビルドプロセスやツールの変更

テスト内容

• テストを追加しました
• 既存のテストを更新しました
• テストは不要です

テスト詳細:

20の新規テストケースを追加し、全機能をカバー:

• Error(string)デコード（複数パターン）
• 8種類のPanic codeデコード
• eth_callシミュレーション（成功・複数エラーパターン）
• エッジケース（nil、空データ、無効データ）
• Clientなし時のエラーハンドリング

全100テスト通過（新規20 + 既存80）

チェックリスト

• テストが追加/更新されている
• ドキュメントが更新されている（必要に応じて）
• RuboCopのチェックを通過している（bundle exec rubocop）
• すべてのテストが通過している（bundle exec rspec）
• 関連Issueがリンクされている（下記参照）
• コミットメッセージがConventional Commitsの形式に従っている

関連Issue

Issue #7 (Transaction receipt and fetcher) に依存

スクリーンショット（該当する場合）

N/A

破壊的変更（該当する場合）

• このPRには破壊的変更が含まれています

追加情報

実装の詳細:

• モジュール化された設計で複雑度を抑制（CyclomaticComplexity: 5以下）
• 完全なエラーハンドリングとフェイルセーフ
• CodeQL: 脆弱性0件
• Clientパラメータはオプション（シミュレーション使用時のみ必須）

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[Feature] Implement Revert Reason decoder</issue_title>
<issue_description># Transaction Debugger - Revert Reason decoder実装

概要

失敗したトランザクションのRevert Reasonをデコードする機能を実装

背景

Solidityのrevert("Error message")は以下の形式でエンコードされる：

• Function signature: Error(string) → 0x08c379a0
• ABI encoded string

実装内容

# lib/transaction_debugger/revert_decoder.rb
module TransactionDebugger
  class RevertDecoder
    ERROR_STRING_SIGNATURE = '0x08c379a0'
    PANIC_SIGNATURE = '0x4e487b71'
    
    PANIC_CODES = {
      0x01 => 'Assertion error',
      0x11 => 'Arithmetic operation underflowed or overflowed',
      0x12 => 'Division or modulo by zero',
      0x21 => 'Enum conversion error',
      0x31 => 'Pop on empty array',
      0x32 => 'Array index out of bounds',
      0x41 => 'Out of memory',
      0x51 => 'Invalid internal function call'
    }.freeze
    
    def initialize(client: nil)
      @client = client || Client.new
    end
    
    def decode_from_receipt(receipt)
      return nil if receipt.success?
      
      if receipt.raw_data['revertReason']
        decode_revert_data(receipt.raw_data['revertReason'])
      else
        decode_from_simulation(receipt)
      end
    end
    
    def decode_revert_data(data)
      return nil if data.nil? || data == '0x'
      
      hex_data = data.start_with?('0x') ? data[2..-1] : data
      signature = "0x#{hex_data[0..7]}"
      
      case signature
      when ERROR_STRING_SIGNATURE
        decode_error_string(hex_data)
      when PANIC_SIGNATURE
        decode_panic(hex_data)
      else
        "Unknown error (signature: #{signature})"
      end
    end
    
    private
    
    def decode_error_string(hex_data)
      begin
        data_hex = hex_data[8..-1]
        data_binary = [data_hex].pack('H*')
        length = data_binary[32..63].unpack1('H*').to_i(16)
        string_data = data_binary[64, length]
        string_data.force_encoding('UTF-8')
      rescue => e
        "Failed to decode error string: #{e.message}"
      end
    end
    
    def decode_panic(hex_data)
      panic_code = hex_data[8..71].to_i(16)
      description = PANIC_CODES[panic_code] || "Unknown panic code"
      "Panic: #{description} (code: 0x#{panic_code.to_s(16)})"
    end
    
    def decode_from_simulation(receipt)
      tx_data = @client.eth_get_transaction_by_hash(receipt.transaction_hash)
      
      call_params = {
        from: tx_data['from'],
        to: tx_data['to'],
        data: tx_data['input'],
        value: tx_data['value']
      }
      
      begin
        @client.eth_call(call_params, receipt.block_number - 1)
        nil
      rescue RPCError => e
        extract_revert_from_error(e.message)
      end
    end
    
    def extract_revert_from_error(error_message)
      if error_message =~ /execution reverted:?\s*(.+)/i
        $1.strip
      elsif error_message =~ /revert\s+(.+)/i
        $1.strip
      else
        error_message
      end
    end
  end
end

完了条件

• Error(string)形式のデコードができる
• Panic codeのデコードができる
• eth_callシミュレーションが動作する
• テストが全てパスする

Phase

Phase 1 - 基礎実装

Dependencies

• Issue [Feature] Implement transaction receipt and transaction fetcher #7: [Feature] Implement transaction receipt and transaction fetcher</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [Feature] Implement Revert Reason decoder #8

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[coderabbitai]

Important

Review skipped

Bot user detected.

To trigger a single review, invoke the @coderabbitai review command.

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[codecov-commenter]

⚠️ Please install the to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (1b02e17) to head (5181f4e).
❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #50   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            7         8    +1     
  Lines          166       215   +49     
=========================================
+ Hits           166       215   +49     

Files with missing lines	Coverage Δ
lib/crypto_wallet_tool.rb	100.00% <100.00%> (ø)
...wallet_tool/transaction_debugger/revert_decoder.rb	100.00% <100.00%> (ø)

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[claude]

Code Review: RevertDecoder Implementation

Great work on implementing the RevertDecoder feature! The implementation is solid overall, with comprehensive test coverage and clean code structure. Here are my findings:

✅ Strengths

Code Quality

• Excellent modularization: Breaking down complex logic into small, focused private methods keeps cyclomatic complexity low
• Consistent style: Follows the project's RuboCop conventions
• Clear naming: Method and variable names are descriptive and self-documenting
• Proper error handling: Graceful degradation with rescue blocks

Test Coverage

• Comprehensive testing: 20 new test cases covering all major code paths
• Edge cases covered: nil values, empty data, invalid data, missing client scenarios
• All 8 panic codes tested: Complete coverage of the PANIC_CODES hash

Architecture

• Follows existing patterns: Consistent with Fetcher and Receipt classes
• Optional client dependency: Smart design allowing decode_revert_data to work without a client
• Flexible input handling: Accepts data with or without 0x prefix

🔍 Issues Found

1. Bug: Incorrect block parameter type in eth_call (line 93)

Severity: High

The eth_call method expects a hex string or tag, but you are passing an integer. This will cause the RPC call to fail.

Current code:

@client.eth_call(call_params, receipt.block_number - 1)

Fix:

block_hex = "0x#{(receipt.block_number - 1).to_s(16)}"
@client.eth_call(call_params, block_hex)

2. Potential issue: Array slicing (lines 47, 75)

Severity: Medium

If data is very short, this could produce unexpected results. Add validation:

return nil if hex_data.length < 8

3. Magic number: Block offset (line 93)

Severity: Low

Add a comment or constant to explain the -1 offset.

4. Inconsistent client initialization (line 21)

Severity: Low

Consider adding a comment explaining why client is optional, unlike in Fetcher class.

🚀 Performance Considerations

Efficient

• No unnecessary network calls
• Early returns for success cases
• Minimal string processing

🔒 Security Concerns

Good Practices

• No eval or unsafe operations
• Length validation present
• Proper error handling

Minor Concerns

1. Binary data handling could validate UTF-8:

string_data.force_encoding('UTF-8')
return "Invalid UTF-8 in error string" unless string_data.valid_encoding?
string_data

📚 Documentation

Missing

• No YARD/RDoc comments on public methods
• PANIC_CODES hash could include references to Solidity docs

Suggestion:

# Decodes revert reason from a transaction receipt
# @param receipt [Receipt] The transaction receipt
# @return [String, nil] Decoded revert reason or nil if transaction succeeded
def decode_from_receipt(receipt)

🧪 Test Coverage Analysis

Well Covered

• All panic codes
• Error string decoding
• Client simulation paths
• Edge cases

Could Be Improved

• No integration tests with real node
• Missing test for extremely long error strings
• Missing test for malformed panic data
• Missing test for block_number 0

📋 Recommendations

Critical (Must Fix)

1. Fix the eth_call block parameter type conversion

High Priority (Should Fix)

2. Add validation for minimum hex data length
3. Validate UTF-8 encoding after force_encoding

Nice to Have

4. Add YARD documentation for public methods
5. Extract magic number for block offset
6. Add test for edge cases
7. Add explanatory comment about optional client

Summary

This is a well-implemented feature with excellent test coverage and clean architecture. The main issue is the block parameter type bug in eth_call, which will prevent the simulation fallback from working correctly. Once that's fixed, this will be production-ready.

Overall Rating: 8/10

• Code Quality: 9/10
• Test Coverage: 9/10
• Security: 8/10
• Documentation: 6/10

Great job on this implementation!