CHT calculations for full nodes

ethcore/light/src/on_demand/mod.rs

@@ -112,7 +112,7 @@ impl OnDemand {
 	// dispatch the request, completing the request if no peers available.
 	fn dispatch_header_by_number(&self, ctx: &BasicContext, req: request::HeaderByNumber, sender: Sender<encoded::Header>) {
 		let num = req.num;
-		let cht_num = ::client::cht::block_to_cht_number(req.num);
+		let cht_num = ::cht::block_to_cht_number(req.num);
 		let les_req = LesRequest::HeaderProofs(les_request::HeaderProofs {
 			requests: vec![les_request::HeaderProof {
 				cht_number: cht_num,

ethcore/light/src/provider.rs

@@ -226,8 +226,49 @@ impl<T: ProvingBlockChainClient + ?Sized> Provider for T {
 		self.code_by_hash(req.account_key, BlockId::Hash(req.block_hash))
 	}
 
-	fn header_proof(&self, _req: request::HeaderProof) -> Option<(encoded::Header, Vec<Bytes>)> {
-		None
+	fn header_proof(&self, req: request::HeaderProof) -> Option<(encoded::Header, Vec<Bytes>)> {
+		use util::MemoryDB;
+		use util::trie::{Trie, TrieMut, TrieDB, TrieDBMut, Recorder};
+
+		if req.cht_number != ::cht::block_to_cht_number(req.block_number) {
+			debug!(target: "les_provider", "Requested CHT number mismatch with block number.");
+			return None;
+		}
+
+		let mut memdb = MemoryDB::new();
+		let mut root = H256::default();
+		let mut needed_hdr = None;
+		{
+			let mut t = TrieDBMut::new(&mut memdb, &mut root);
+			let start_num = ::cht::start_number(req.cht_number);
+			for i in (0..::cht::SIZE).map(|x| x + start_num) {
+				match self.block_header(BlockId::Number(i)) {
+					None => return None,
+					Some(hdr) => {
+						t.insert(
+							&*::rlp::encode(&i),
+							&*::rlp::encode(&hdr.hash()),
+						).expect("fresh in-memory database is infallible; qed");
+
+						if i == req.block_number { needed_hdr = Some(hdr) }
+					}
+				}
+			}
+		}
+		let needed_hdr = needed_hdr.expect("`needed_hdr` always set in loop, number checked before; qed");
+
+		let mut recorder = Recorder::new();
+		let t = TrieDB::new(&memdb, &root)
+			.expect("Same DB and root as just produced by TrieDBMut; qed");
+
+		if let Err(e) = t.get_with(&*::rlp::encode(&req.block_number), &mut recorder) {
+			debug!(target: "les_provider", "Error looking up number in freshly-created CHT: {}", e);
+			return None;
+		}
+
+		// TODO: cache calculated CHT if possible.
+		let proof = recorder.drain().into_iter().map(|x| x.data).collect();
+		Some((needed_hdr, proof))
 	}
 
 	fn ready_transactions(&self) -> Vec<PendingTransaction> {