[Good First Issue]: use `stringToByteVector` utility in `extractSignatureBytes`

[rwalworth]

🆕🐥 First-Time Friendly

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👾 Description of the Issue

The extractSignatureBytes helper function in Transaction.cc manually converts a std::string to std::vector<std::byte> using std::transform, but the codebase already has a utility function that does exactly the same thing: internal::Utilities::stringToByteVector().

The current implementation:

std::vector<std::byte> sigBytes(sigStr->size());
std::transform(sigStr->begin(), sigStr->end(), sigBytes.begin(), [](char c) { return static_cast<std::byte>(c); });
return sigBytes;

The rest of the file uses stringToByteVector for the same conversion (e.g., in getSignaturesInternal), so this helper should too.

Additionally, the test file TransactionUnitTests.cc is missing a trailing newline at the end of the file, which should be added for POSIX compliance and consistency with the other files in the repository.

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💡 Proposed Solution

1. Refactor extractSignatureBytes to use the existing internal::Utilities::stringToByteVector() utility, which simplifies the function and makes it consistent with the rest of the codebase.
2. Add a trailing newline to the end of TransactionUnitTests.cc.

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👩‍💻 Implementation Steps

Part 1: Refactor extractSignatureBytes

1. Open src/sdk/main/src/Transaction.cc
2. Locate the extractSignatureBytes function in the anonymous namespace near the top of the file (around line 84)
3. Replace the current implementation:

namespace
{
/**
 * Helper function - Extract the raw signature bytes from a protobuf SignaturePair.
 */
std::vector<std::byte> extractSignatureBytes(const proto::SignaturePair& pair)
{
  const std::string* sigStr = nullptr;
  if (pair.has_ed25519())
  {
    sigStr = &pair.ed25519();
  }
  else if (pair.has_ecdsa_secp256k1())
  {
    sigStr = &pair.ecdsa_secp256k1();
  }
  else
  {
    throw IllegalStateException("Unknown signature type");
  }

  std::vector<std::byte> sigBytes(sigStr->size());
  std::transform(sigStr->begin(), sigStr->end(), sigBytes.begin(), [](char c) { return static_cast<std::byte>(c); });
  return sigBytes;
}
} // anonymous namespace

with:

namespace
{
/**
 * Extract the raw signature bytes from a protobuf SignaturePair.
 */
std::vector<std::byte> extractSignatureBytes(const proto::SignaturePair& pair)
{
  if (pair.has_ed25519())
  {
    return internal::Utilities::stringToByteVector(pair.ed25519());
  }

  if (pair.has_ecdsa_secp256k1())
  {
    return internal::Utilities::stringToByteVector(pair.ecdsa_secp256k1());
  }

  throw IllegalStateException("Unknown signature type");
}
} // anonymous namespace

Part 2: Fix trailing newline

1. Open src/sdk/tests/unit/TransactionUnitTests.cc
2. Go to the very end of the file
3. Ensure there is a newline character after the final closing } brace

Most editors will show this as "no newline at end of file" — simply press Enter after the last } to add one.

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✅ Acceptance Criteria

To merge a pull request for this issue:

• Scope: Changes are limited to the two files listed below
• Behavior: No SDK behavior or public API changes (the refactored function produces identical output)
• Tests: Existing CI checks pass
• Review: All code review feedback addressed

---

📋 Step-by-Step Contribution Guide

• Comment /assign to request the issue
• Wait for assignment
• Fork the repository and create a branch
• Set up the project by following the instructions in README.md
• Make the requested changes
• Sign each commit using -s -S
• Push your branch and open a pull request

Read Workflow Guide for step-by-step workflow guidance.
Read README.md for setup instructions.

❗ Pull requests cannot be merged without S and s signed commits.
See the Signing Guide.

---

🤔 Additional Information

This issue was identified during the review of #1218 (which added the removeSignature and removeAllSignatures methods).

Files to Change

File	Change
src/sdk/main/src/Transaction.cc	Refactor extractSignatureBytes to use stringToByteVector
src/sdk/tests/unit/TransactionUnitTests.cc	Add trailing newline at end of file

Reference

The existing usage of stringToByteVector in the same file can be seen in the getSignaturesInternal method, which does the same string-to-byte-vector conversion for signature data.

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[ak004]

/assign

[github-actions]

👋 Hi @ak004, welcome to the Hiero C++ SDK community! Thank you for choosing to contribute — we're thrilled to have you here! 🎉

You've been assigned this Good First Issue, and the Good First Issue Support Team (@hiero-ledger/hiero-sdk-good-first-issue-support) is ready to help you succeed.

The issue description above has everything you need: implementation steps, contribution workflow, and links to guides. If anything is unclear, just ask — we're happy to help.

Good luck, and welcome aboard! 🚀