From 4f4e81cf739632b83e303fea965b62f65de052d4 Mon Sep 17 00:00:00 2001
From: Jim Posen <jim.posen@gmail.com>
Date: Tue, 19 Nov 2019 17:47:17 +0100
Subject: [PATCH 1/2] Introduce Rlp::at_with_offset.

---
 rlp/src/rlpin.rs   | 14 ++++++++++++--
 rlp/tests/tests.rs | 29 +++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/rlp/src/rlpin.rs b/rlp/src/rlpin.rs
index dd2ee9826..960af6a7a 100644
--- a/rlp/src/rlpin.rs
+++ b/rlp/src/rlpin.rs
@@ -189,6 +189,15 @@ impl<'a> Rlp<'a> {
 	pub fn at<'view>(&'view self, index: usize) -> Result<Rlp<'a>, DecoderError>
 	where
 		'a: 'view,
+	{
+		let (rlp, _offset) = self.at_with_offset(index)?;
+		Ok(rlp)
+	}
+
+	pub fn at_with_offset<'view>(&'view self, index: usize)
+		-> Result<(Rlp<'a>, usize), DecoderError>
+		where
+			'a: 'view,
 	{
 		if !self.is_list() {
 			return Err(DecoderError::RlpExpectedToBeList);
@@ -211,11 +220,12 @@ impl<'a> Rlp<'a> {
 		let (bytes, consumed) = Rlp::consume_items(bytes, indexes_to_skip)?;
 
 		// update the cache
-		self.offset_cache.set(Some(OffsetCache::new(index, bytes_consumed + consumed)));
+		let offset = bytes_consumed + consumed;
+		self.offset_cache.set(Some(OffsetCache::new(index, offset)));
 
 		// construct new rlp
 		let found = BasicDecoder::payload_info(bytes)?;
-		Ok(Rlp::new(&bytes[0..found.header_len + found.value_len]))
+		Ok((Rlp::new(&bytes[0..found.header_len + found.value_len]), offset))
 	}
 
 	pub fn is_null(&self) -> bool {
diff --git a/rlp/tests/tests.rs b/rlp/tests/tests.rs
index 84a090e09..6f51b9bd3 100644
--- a/rlp/tests/tests.rs
+++ b/rlp/tests/tests.rs
@@ -53,6 +53,35 @@ fn rlp_at() {
 	}
 }
 
+#[test]
+fn rlp_at_with_offset() {
+	let data = vec![0xc8, 0x83, b'c', b'a', b't', 0x83, b'd', b'o', b'g'];
+	{
+		let rlp = Rlp::new(&data);
+		assert!(rlp.is_list());
+		let animals: Vec<String> = rlp.as_list().unwrap();
+		assert_eq!(animals, vec!["cat".to_owned(), "dog".to_owned()]);
+
+		let (cat, cat_offset) = rlp.at_with_offset(0).unwrap();
+		assert!(cat.is_data());
+		assert_eq!(cat_offset, 1);
+		assert_eq!(cat.as_raw(), &[0x83, b'c', b'a', b't']);
+		assert_eq!(cat.as_val::<String>().unwrap(), "cat".to_owned());
+
+		let (dog, dog_offset) = rlp.at_with_offset(1).unwrap();
+		assert!(dog.is_data());
+		assert_eq!(dog_offset, 5);
+		assert_eq!(dog.as_raw(), &[0x83, b'd', b'o', b'g']);
+		assert_eq!(dog.as_val::<String>().unwrap(), "dog".to_owned());
+
+		let (cat_again, cat_offset) = rlp.at_with_offset(0).unwrap();
+		assert!(cat_again.is_data());
+		assert_eq!(cat_offset, 1);
+		assert_eq!(cat_again.as_raw(), &[0x83, b'c', b'a', b't']);
+		assert_eq!(cat_again.as_val::<String>().unwrap(), "cat".to_owned());
+	}
+}
+
 #[test]
 fn rlp_at_err() {
 	let data = vec![0xc8, 0x83, b'c', b'a', b't', 0x83, b'd', b'o'];

From 46b7272113c87158dfdfe1f6f4113dd1becd3cc2 Mon Sep 17 00:00:00 2001
From: Jim Posen <jim.posen@gmail.com>
Date: Wed, 20 Nov 2019 13:24:07 +0100
Subject: [PATCH 2/2] Method docs for Rlp::at and Rlp::at_with_offset.

---
 rlp/src/rlpin.rs | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/rlp/src/rlpin.rs b/rlp/src/rlpin.rs
index 960af6a7a..5dd3730b6 100644
--- a/rlp/src/rlpin.rs
+++ b/rlp/src/rlpin.rs
@@ -186,6 +186,9 @@ impl<'a> Rlp<'a> {
 		}
 	}
 
+	/// Returns an Rlp item in a list at the given index.
+	///
+	/// Returns an error if this Rlp is not a list or if the index is out of range.
 	pub fn at<'view>(&'view self, index: usize) -> Result<Rlp<'a>, DecoderError>
 	where
 		'a: 'view,
@@ -194,6 +197,10 @@ impl<'a> Rlp<'a> {
 		Ok(rlp)
 	}
 
+	/// Returns an Rlp item in a list at the given index along with the byte offset into the
+	/// raw data slice.
+	///
+	/// Returns an error if this Rlp is not a list or if the index is out of range.
 	pub fn at_with_offset<'view>(&'view self, index: usize)
 		-> Result<(Rlp<'a>, usize), DecoderError>
 		where