Add memo size check

[levonpetrosyan93]

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Summary by CodeRabbit

• Bug Fixes
  • Strengthened memo decoding during coin identification to ensure the decrypted memo data matches the expected format before extracting the memo length.
  • Improved memo validation consistency across both mint and spend identification paths, while preserving the same failure behavior if identification cannot be completed.

Walkthrough

Coin::identify() now centralizes padded memo validation and decoding through DecodeMemoOrThrow. Both mint and spend paths use the helper, which enforces the expected padded memo size and preserves the existing identification failure exception.

Changes

Memo decoding validation

Layer / File(s)	Summary
Shared memo decoder and identification integration src/libspark/coin.cpp	Adds DecodeMemoOrThrow for exact padded-memo size and encoded-length validation, then uses it in both mint and spend identification branches.

Estimated code review effort: 2 (Simple) | ~10 minutes

🚥 Pre-merge checks | ✅ 3 | ❌ 2

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	No PR description was provided, so the required intention and code changes sections are missing.	Add the required PR intention and code changes brief sections, describing the memo size validation change and its purpose.
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title matches the main change: adding a memo size check during coin identification.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch memo_size

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[chatgpt-codex-connector]

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Reviewed commit: 2972c16cbc

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[chatgpt-codex-connector]

Guard empty memo buffers before subtracting

This new bounds check still misses a decrypted recipient payload whose serialized padded_memo is empty: r.padded_memo[0] has already read out of bounds, and r.padded_memo.size() - 1 wraps to a huge value, so the intended Unable to identify coin path is not reached. A sender can craft an authenticated payload with trailing bytes to satisfy the fixed outer ciphertext size while leaving the inner memo string empty, so wallet scanning can still hit undefined behavior instead of rejecting the coin; check empty() before indexing/subtracting in both identify paths.

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🧹 Nitpick comments (1)

src/libspark/coin.cpp (1)

4-25: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

Apply the repository’s C++ formatting rules to the new helper.

The anonymous namespace uses same-line braces, and the helper is tab-indented. Use a newline before the namespace brace and four spaces throughout this added block.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@src/libspark/coin.cpp` around lines 4 - 25, Reformat the DecodeMemoOrThrow
helper block to match repository C++ style: place the anonymous namespace
opening brace on the following line and replace tab indentation with four spaces
throughout the added namespace and helper code. Preserve all logic unchanged.

Source: Coding guidelines

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@src/libspark/coin.cpp`:
- Around line 4-25: Reformat the DecodeMemoOrThrow helper block to match
repository C++ style: place the anonymous namespace opening brace on the
following line and replace tab indentation with four spaces throughout the added
namespace and helper code. Preserve all logic unchanged.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: cf3ad6a8-3d73-4b41-94d5-601821ef5724

📥 Commits

Reviewing files that changed from the base of the PR and between 2972c16 and efb4c57.

📒 Files selected for processing (1)

• src/libspark/coin.cpp