diff --git a/Cargo.lock b/Cargo.lock
index 80c8810fe..43f6c7af2 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -509,6 +509,7 @@ dependencies = [
"ethcore-ipc-codegen 1.5.0",
"ethcore-network 1.5.0",
"ethcore-util 1.5.0",
+ "futures 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)",
"log 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
"rlp 0.1.0",
"smallvec 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)",
diff --git a/ethcore/light/Cargo.toml b/ethcore/light/Cargo.toml
index 67ae166dc..20f5f93bd 100644
--- a/ethcore/light/Cargo.toml
+++ b/ethcore/light/Cargo.toml
@@ -20,6 +20,7 @@ ethcore-ipc = { path = "../../ipc/rpc", optional = true }
rlp = { path = "../../util/rlp" }
time = "0.1"
smallvec = "0.3.1"
+futures = "0.1"
[features]
default = []
diff --git a/ethcore/light/src/lib.rs b/ethcore/light/src/lib.rs
index 5cdc3addc..60984d9c2 100644
--- a/ethcore/light/src/lib.rs
+++ b/ethcore/light/src/lib.rs
@@ -34,6 +34,7 @@
pub mod client;
pub mod net;
+pub mod on_demand;
#[cfg(not(feature = "ipc"))]
pub mod provider;
@@ -64,6 +65,7 @@ extern crate ethcore_io as io;
extern crate rlp;
extern crate smallvec;
extern crate time;
+extern crate futures;
#[cfg(feature = "ipc")]
extern crate ethcore_ipc as ipc;
diff --git a/ethcore/light/src/on_demand/mod.rs b/ethcore/light/src/on_demand/mod.rs
new file mode 100644
index 000000000..0bf25d68b
--- /dev/null
+++ b/ethcore/light/src/on_demand/mod.rs
@@ -0,0 +1,125 @@
+// Copyright 2015, 2016 Parity Technologies (UK) Ltd.
+// This file is part of Parity.
+
+// Parity is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Parity is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Parity. If not, see .
+
+//! On-demand chain requests over LES. This is a major building block for RPCs.
+//! The request service is implemented using Futures. Higher level request handlers
+//! will take the raw data received here and extract meaningful results from it.
+
+use std::collections::HashMap;
+
+use ethcore::ids::BlockId;
+use ethcore::block::Block;
+use ethcore::header::Header;
+use ethcore::receipt::Receipt;
+
+use futures::Future;
+use futures::sync::oneshot::{self, Sender, Receiver};
+use network::PeerId;
+
+use client::Client;
+use net::{Handler, Status, Capabilities, Announcement, EventContext, BasicContext, ReqId};
+use util::{Address, H256, RwLock};
+
+struct Account;
+
+// relevant peer info.
+struct Peer {
+ status: Status,
+ capabilities: Capabilities,
+}
+
+// request info and where to send the result.
+enum Request {
+ HeaderByNumber(u64, H256, Sender), // num + CHT root
+ HeaderByHash(H256, Sender),
+ Block(Header, Sender),
+ BlockReceipts(Header, Sender>),
+ Account(Header, Address, Sender),
+ Storage(Header, Address, H256, Sender),
+}
+
+/// On demand request service. See module docs for more details.
+/// Accumulates info about all peers' capabilities and dispatches
+/// requests to them accordingly.
+pub struct OnDemand {
+ peers: RwLock>,
+ pending_requests: RwLock>,
+}
+
+impl Handler for OnDemand {
+ fn on_connect(&self, ctx: &EventContext, status: &Status, capabilities: &Capabilities) {
+ self.peers.write().insert(ctx.peer(), Peer { status: status.clone(), capabilities: capabilities.clone() })
+ }
+
+ fn on_disconnect(&self, ctx: &EventContext, unfulfilled: &[ReqId]) {
+ self.peers.write().remove(&ctx.peer());
+ }
+}
+
+impl OnDemand {
+ /// Request a header by block number and CHT root hash.
+ pub fn header_by_number(&self, ctx: &BasicContext, num: u64, cht_root: H256) -> Receiver {
+ let (sender, receiver) = oneshot::channel();
+ self.dispatch_request(ctx, Request::HeaderByNumber(num, cht_root, sender));
+ receiver
+ }
+
+ /// Request a header by hash. This is less accurate than by-number because we don't know
+ /// where in the chain this header lies, and therefore can't find a peer who is supposed to have
+ /// it as easily.
+ pub fn header_by_hash(&self, ctx: &BasicContext, hash: H256) -> Receiver {
+ let (sender, receiver) = oneshot::channel();
+ self.dispatch_request(ctx, Request::HeaderByHash(hash, sender));
+ receiver
+ }
+
+ /// Request a block, given its header. Block bodies are requestable by hash only,
+ /// and the header is required anyway to verify and complete the block body
+ /// -- this just doesn't obscure the network query.
+ pub fn block(&self, ctx: &BasicContext, header: Header) -> Receiver {
+ let (sender, receiver) = oneshot::channel();
+ self.dispatch_request(ctx, Request::Block(header, sender));
+ receiver
+ }
+
+ /// Request the receipts for a block. The header serves two purposes:
+ /// provide the block hash to fetch receipts for, and for verification of the receipts root.
+ pub fn block_receipts(&self, ctx: &BasicContext, header: Header) -> Receiver> {
+ let (sender, receiver) = oneshot::channel();
+ self.dispatch_request(ctx, Request::BlockReceipts(header, sender));
+ receiver
+ }
+
+ /// Request an account by address and block header -- which gives a hash to query and a state root
+ /// to verify against.
+ pub fn account(&self, ctx: &BasicContext, header: Header, address: Address) -> Receiver {
+ let (sender, receiver) = oneshot::channel();
+ self.dispatch_request(ctx, Request::Account(header, address, sender));
+ receiver
+ }
+
+ /// Request account storage value by block header, address, and key.
+ pub fn storage(&self, ctx: &BasicContext, header: Header, address: Address, key: H256) -> Receiver {
+ let (sender, receiver) = oneshot::channel();
+ self.dispatch_request(ctx, Request::Storage(header, address, key, sender));
+ receiver
+ }
+
+ // dispatch a request to a suitable peer.
+ fn dispatch_request(&self, ctx: &BasicContext, request: Request) {
+ unimplemented!()
+ }
+}