From b3dfe07c2f687779097454b8eaeb6c67e35cb3e9 Mon Sep 17 00:00:00 2001
From: chriseth <c@ethdev.com>
Date: Thu, 2 Jul 2015 17:37:15 +0200
Subject: [PATCH] Helper to find the length of an RLP item.

---
 libdevcore/RLP.cpp | 10 +++++-----
 libdevcore/RLP.h   |  5 ++++-
 2 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/libdevcore/RLP.cpp b/libdevcore/RLP.cpp
index cf4218050..960843f4c 100644
--- a/libdevcore/RLP.cpp
+++ b/libdevcore/RLP.cpp
@@ -50,7 +50,7 @@ RLP::iterator& RLP::iterator::operator++()
 	if (m_remaining)
 	{
 		m_currentItem.retarget(m_currentItem.next().data(), m_remaining);
-		m_currentItem = m_currentItem.cropped(0, RLP(m_currentItem, ThrowOnFail | FailIfTooSmall).actualSize());
+		m_currentItem = m_currentItem.cropped(0, actualSizeOfPrefix(m_currentItem));
 		m_remaining -= std::min<size_t>(m_remaining, m_currentItem.size());
 	}
 	else
@@ -63,7 +63,7 @@ RLP::iterator::iterator(RLP const& _parent, bool _begin)
 	if (_begin && _parent.isList())
 	{
 		auto pl = _parent.payload();
-		m_currentItem = pl.cropped(0, RLP(pl, ThrowOnFail | FailIfTooSmall).actualSize());
+		m_currentItem = pl.cropped(0, actualSizeOfPrefix(pl));
 		m_remaining = pl.size() - m_currentItem.size();
 	}
 	else
@@ -77,14 +77,14 @@ RLP RLP::operator[](size_t _i) const
 {
 	if (_i < m_lastIndex)
 	{
-		m_lastEnd = RLP(payload(), ThrowOnFail | FailIfTooSmall).actualSize();
+		m_lastEnd = actualSizeOfPrefix(payload());
 		m_lastItem = payload().cropped(0, m_lastEnd);
 		m_lastIndex = 0;
 	}
 	for (; m_lastIndex < _i && m_lastItem.size(); ++m_lastIndex)
 	{
 		m_lastItem = payload().cropped(m_lastEnd);
-		m_lastItem = m_lastItem.cropped(0, RLP(m_lastItem, ThrowOnFail | FailIfTooSmall).actualSize());
+		m_lastItem = m_lastItem.cropped(0, actualSizeOfPrefix(m_lastItem));
 		m_lastEnd += m_lastItem.size();
 	}
 	return RLP(m_lastItem, ThrowOnFail | FailIfTooSmall);
@@ -204,7 +204,7 @@ size_t RLP::items() const
 		bytesConstRef d = payload().cropped(0, length());
 		size_t i = 0;
 		for (; d.size(); ++i)
-			d = d.cropped(RLP(d, ThrowOnFail | FailIfTooSmall).actualSize());
+			d = d.cropped(actualSizeOfPrefix(d));
 		return i;
 	}
 	return 0;
diff --git a/libdevcore/RLP.h b/libdevcore/RLP.h
index 1586616d8..e124ea2b6 100644
--- a/libdevcore/RLP.h
+++ b/libdevcore/RLP.h
@@ -301,7 +301,7 @@ public:
 	/// @returns the data payload. Valid for all types.
 	bytesConstRef payload() const { auto l = length(); if (l > m_data.size()) BOOST_THROW_EXCEPTION(BadRLP()); return m_data.cropped(payloadOffset(), l); }
 
-	/// @returns the theoretical size of this item.
+	/// @returns the theoretical size of this item as encoded in the data.
 	/// @note Under normal circumstances, is equivalent to m_data.size() - use that unless you know it won't work.
 	size_t actualSize() const;
 
@@ -327,6 +327,9 @@ private:
 	/// @returns the number of data items.
 	size_t items() const;
 
+	/// @returns the "actualSize" of the RLP encoded in the largest prefix of @a _data and throws on error.
+	static size_t actualSizeOfPrefix(bytesConstRef _data) { return RLP(_data, ThrowOnFail | FailIfTooSmall).actualSize(); }
+
 	/// Our byte data.
 	bytesConstRef m_data;