hide CHT internals from header chain

Cargo.lock

@@ -285,6 +285,11 @@ name = "dtoa"
 version = "0.2.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
+name = "either"
+version = "1.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "elastic-array"
 version = "0.6.0"
@@ -515,6 +520,7 @@ dependencies = [
  "ethcore-network 1.6.0",
  "ethcore-util 1.6.0",
  "futures 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)",
+ "itertools 0.5.9 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "rand 0.3.14 (registry+https://github.com/rust-lang/crates.io-index)",
  "rlp 0.1.0",
@@ -943,6 +949,14 @@ name = "itertools"
 version = "0.4.13"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
+name = "itertools"
+version = "0.5.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "either 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "itoa"
 version = "0.1.1"
@@ -2424,6 +2438,7 @@ dependencies = [
 "checksum deque 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)" = "1614659040e711785ed8ea24219140654da1729f3ec8a47a9719d041112fe7bf"
 "checksum docopt 0.6.80 (registry+https://github.com/rust-lang/crates.io-index)" = "4cc0acb4ce0828c6a5a11d47baa432fe885881c27428c3a4e473e454ffe57a76"
 "checksum dtoa 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)" = "0dd841b58510c9618291ffa448da2e4e0f699d984d436122372f446dae62263d"
+"checksum either 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)" = "3d2b503c86dad62aaf414ecf2b8c527439abedb3f8d812537f0b12bfd6f32a91"
 "checksum elastic-array 0.6.0 (git+https://github.com/ethcore/elastic-array)" = "<none>"
 "checksum env_logger 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)" = "aba65b63ffcc17ffacd6cf5aa843da7c5a25e3bd4bbe0b7def8b214e411250e5"
 "checksum eth-secp256k1 0.5.4 (git+https://github.com/ethcore/rust-secp256k1)" = "<none>"
@@ -2445,6 +2460,7 @@ dependencies = [
 "checksum igd 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)" = "c8c12b1795b8b168f577c45fa10379b3814dcb11b7ab702406001f0d63f40484"
 "checksum isatty 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "7408a548dc0e406b7912d9f84c261cc533c1866e047644a811c133c56041ac0c"
 "checksum itertools 0.4.13 (registry+https://github.com/rust-lang/crates.io-index)" = "086e1fa5fe48840b1cfdef3a20c7e3115599f8d5c4c87ef32a794a7cdd184d76"
+"checksum itertools 0.5.9 (registry+https://github.com/rust-lang/crates.io-index)" = "d95557e7ba6b71377b0f2c3b3ae96c53f1b75a926a6901a500f557a370af730a"
 "checksum itoa 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "ae3088ea4baeceb0284ee9eea42f591226e6beaecf65373e41b38d95a1b8e7a1"
 "checksum jsonrpc-core 5.0.0 (git+https://github.com/ethcore/jsonrpc.git)" = "<none>"
 "checksum jsonrpc-http-server 7.0.0 (git+https://github.com/ethcore/jsonrpc.git)" = "<none>"

ethcore/light/Cargo.toml

@@ -22,6 +22,7 @@ time = "0.1"
 smallvec = "0.3.1"
 futures = "0.1"
 rand = "0.3"
+itertools = "0.5"
 
 [features]
 default = []

ethcore/light/src/cht.rs

@@ -34,7 +34,7 @@ macro_rules! val {
 	($hash: expr, $td: expr) => {{
 		let mut stream = RlpStream::new_list(2);
 		stream.append(&$hash).append(&$td);
-		stream.out()
+		stream.drain()
 	}}
 }
 
@@ -116,6 +116,26 @@ pub fn build<F>(cht_num: u64, mut fetcher: F) ->  Option<CHT<MemoryDB>>
 	})
 }
 
+/// Compute a CHT root from an iterator of (hash, td) pairs. Fails if shorter than
+/// SIZE items. The items are assumed to proceed sequentially from `start_number(cht_num)`.
+/// Discards the trie's nodes.
+pub fn compute_root<I>(cht_num: u64, iterable: I) -> Option<H256>
+	where I: IntoIterator<Item=(H256, U256)>
+{
+	let mut v = Vec::with_capacity(SIZE as usize);
+	let start_num = start_number(cht_num) as usize;
+
+	for (i, (h, td)) in iterable.into_iter().take(SIZE as usize).enumerate() {
+		v.push((key!(i + start_num).to_vec(), val!(h, td).to_vec()))
+	}
+
+	if v.len() == SIZE as usize {
+		Some(::util::triehash::trie_root(v))
+	} else {
+		None
+	}
+}
+
 /// Convert a block number to a CHT number.
 /// Returns `None` for `block_num` == 0, `Some` otherwise.
 pub fn block_to_cht_number(block_num: u64) -> Option<u64> {

ethcore/light/src/client/header_chain.rs

@@ -173,26 +173,34 @@ impl HeaderChain {
 			// produce next CHT root if it's time.
 			let earliest_era = *candidates.keys().next().expect("at least one era just created; qed");
 			if earliest_era + HISTORY + cht::SIZE <= number {
-				let mut values = Vec::with_capacity(cht::SIZE as usize);
+				let cht_num = cht::block_to_cht_number(earliest_era)
-				{
+					.expect("fails only for number == 0; genesis never imported; qed");
-					let mut headers = self.headers.write();
+				debug_assert_eq!(cht_num as usize, self.cht_roots.lock().len());
-					for i in (0..cht::SIZE).map(|x| x + earliest_era) {
+
+				let mut headers = self.headers.write();
+
+				let cht_root = {
+					let mut i = earliest_era;
+
+					// iterable function which removes the candidates as it goes
+					// along. this will only be called until the CHT is complete.
+					let iter = || {
 						let era_entry = candidates.remove(&i)
 							.expect("all eras are sequential with no gaps; qed");
+						i += 1;
 
 						for ancient in &era_entry.candidates {
 							headers.remove(&ancient.hash);
 						}
 
-						values.push((
+						let canon = &era_entry.candidates[0];
-							::rlp::encode(&i).to_vec(),
+						(canon.hash, canon.total_difficulty)
-							::rlp::encode(&era_entry.canonical_hash).to_vec(),
+					};
-						));
+					cht::compute_root(cht_num, ::itertools::repeat_call(iter))
-					}
+						.expect("fails only when too few items; this is checked; qed")
-				}
+				};
 
-				let cht_root = ::util::triehash::trie_root(values);
+				debug!(target: "chain", "Produced CHT {} root: {:?}", cht_num, cht_root);
-				debug!(target: "chain", "Produced CHT {} root: {:?}", (earliest_era - 1) % cht::SIZE, cht_root);
 
 				self.cht_roots.lock().push(cht_root);
 			}

ethcore/light/src/lib.rs

@@ -68,6 +68,7 @@ extern crate smallvec;
 extern crate time;
 extern crate futures;
 extern crate rand;
+extern crate itertools;
 
 #[cfg(feature = "ipc")]
 extern crate ethcore_ipc as ipc;

util/src/triehash.rs

@@ -77,7 +77,9 @@ pub fn ordered_trie_root<I>(input: I) -> H256
 /// 	assert_eq!(trie_root(v), H256::from_str(root).unwrap());
 /// }
 /// ```
-pub fn trie_root(input: Vec<(Vec<u8>, Vec<u8>)>) -> H256 {
+pub fn trie_root<I>(input: I) -> H256
+	where I: IntoIterator<Item=(Vec<u8>, Vec<u8>)>
+{
 	let gen_input = input
 		// first put elements into btree to sort them and to remove duplicates
 		.into_iter()