reassign requests indefinitely

ethcore/light/src/on_demand/mod.rs

@@ -128,6 +128,8 @@ impl OnDemand {
 			}],
 		});
 
+		let pending = Pending::HeaderByNumber(req, sender);
+
 		// we're looking for a peer with serveHeaders who's far enough along in the
 		// chain.
 		for (id, peer) in self.peers.read().iter() {
@@ -137,7 +139,7 @@ impl OnDemand {
 						trace!(target: "on_demand", "Assigning request to peer {}", id);
 						self.pending_requests.write().insert(
 							req_id,
-							Pending::HeaderByNumber(req, sender)
+							pending,
 						);
 						return
 					},
@@ -147,9 +149,8 @@ impl OnDemand {
 			}
 		}
 
-		// TODO: retrying
 		trace!(target: "on_demand", "No suitable peer for request");
-		sender.complete(Err(Error::NoPeersAvailable));
+		self.orphaned_requests.write().push(pending)
 	}
 
 	/// Request a header by hash. This is less accurate than by-number because we don't know
@@ -177,16 +178,17 @@ impl OnDemand {
 			.collect::<Vec<_>>();
 
 		let mut rng = ::rand::thread_rng();
-
 		::rand::Rng::shuffle(&mut rng, &mut potential_peers);
 
+		let pending = Pending::HeaderByHash(req, sender);
+
 		for id in potential_peers {
 			match ctx.request_from(id, les_req.clone()) {
 				Ok(req_id) => {
 					trace!(target: "on_demand", "Assigning request to peer {}", id);
 					self.pending_requests.write().insert(
 						req_id,
-						Pending::HeaderByHash(req, sender),
+						pending,
 					);
 					return
 				}
@@ -195,9 +197,8 @@ impl OnDemand {
 			}
 		}
 
-		// TODO: retrying
 		trace!(target: "on_demand", "No suitable peer for request");
-		sender.complete(Err(Error::NoPeersAvailable));
+		self.orphaned_requests.write().push(pending)
 	}
 
 	/// Request a block, given its header. Block bodies are requestable by hash only,
@@ -225,6 +226,7 @@ impl OnDemand {
 		let les_req = LesRequest::Bodies(les_request::Bodies {
 			block_hashes: vec![req.hash],
 		});
+		let pending = Pending::Block(req, sender);
 
 		// we're looking for a peer with serveChainSince(num)
 		for (id, peer) in self.peers.read().iter() {
@@ -234,7 +236,7 @@ impl OnDemand {
 						trace!(target: "on_demand", "Assigning request to peer {}", id);
 						self.pending_requests.write().insert(
 							req_id,
-							Pending::Block(req, sender)
+							pending,
 						);
 						return
 					}
@@ -244,9 +246,8 @@ impl OnDemand {
 			}
 		}
 
-		// TODO: retrying
 		trace!(target: "on_demand", "No suitable peer for request");
-		sender.complete(Err(Error::NoPeersAvailable));
+		self.orphaned_requests.write().push(pending)
 	}
 
 	/// Request the receipts for a block. The header serves two purposes:
@@ -269,6 +270,7 @@ impl OnDemand {
 		let les_req = LesRequest::Receipts(les_request::Receipts {
 			block_hashes: vec![req.0.hash()],
 		});
+		let pending = Pending::BlockReceipts(req, sender);
 
 		// we're looking for a peer with serveChainSince(num)
 		for (id, peer) in self.peers.read().iter() {
@@ -278,7 +280,7 @@ impl OnDemand {
 						trace!(target: "on_demand", "Assigning request to peer {}", id);
 						self.pending_requests.write().insert(
 							req_id,
-							Pending::BlockReceipts(req, sender)
+							pending,
 						);
 						return
 					}
@@ -288,9 +290,8 @@ impl OnDemand {
 			}
 		}
 
-		// TODO: retrying
 		trace!(target: "on_demand", "No suitable peer for request");
-		sender.complete(Err(Error::NoPeersAvailable));
+		self.orphaned_requests.write().push(pending)
 	}
 
 	/// Request an account by address and block header -- which gives a hash to query and a state root
@@ -311,6 +312,7 @@ impl OnDemand {
 				from_level: 0,
 			}],
 		});
+		let pending = Pending::Account(req, sender);
 
 		// we're looking for a peer with serveStateSince(num)
 		for (id, peer) in self.peers.read().iter() {
@@ -320,7 +322,7 @@ impl OnDemand {
 						trace!(target: "on_demand", "Assigning request to peer {}", id);
 						self.pending_requests.write().insert(
 							req_id,
-							Pending::Account(req, sender)
+							pending,
 						);
 						return
 					}
@@ -330,9 +332,8 @@ impl OnDemand {
 			}
 		}
 
-		// TODO: retrying
 		trace!(target: "on_demand", "No suitable peer for request");
-		sender.complete(Err(Error::NoPeersAvailable));
+		self.orphaned_requests.write().push(pending)
 	}
 
 	/// Request code by address, known code hash, and block header.
@@ -357,6 +358,7 @@ impl OnDemand {
 				account_key: ::util::Hashable::sha3(&req.address),
 			}]
 		});
+		let pending = Pending::Code(req, sender);
 
 		// we're looking for a peer with serveStateSince(num)
 		for (id, peer) in self.peers.read().iter() {
@@ -366,7 +368,7 @@ impl OnDemand {
 						trace!(target: "on_demand", "Assigning request to peer {}", id);
 						self.pending_requests.write().insert(
 							req_id,
-							Pending::Code(req, sender)
+							pending
 						);
 						return
 					}
@@ -376,40 +378,79 @@ impl OnDemand {
 			}
 		}
 
-		// TODO: retrying.
 		trace!(target: "on_demand", "No suitable peer for request");
-		sender.complete(Err(Error::NoPeersAvailable));
+		self.orphaned_requests.write().push(pending)
+	}
+
+	// dispatch orphaned requests, and discard those for which the corresponding
+	// receiver has been dropped.
+	fn dispatch_orphaned(&self, ctx: &BasicContext) {
+		// wrapper future for calling `poll_cancel` on our `Senders` to preserve
+		// the invariant that it's always within a task.
+		struct CheckHangup<'a, T: 'a>(&'a mut Sender<T>);
+
+		impl<'a, T: 'a> Future for CheckHangup<'a, T> {
+			type Item = bool;
+			type Error = ();
+
+			fn poll(&mut self) -> Poll<bool, ()> {
+				Ok(Async::Ready(match self.0.poll_cancel() {
+					Ok(Async::NotReady) => false, // hasn't hung up.
+					_ => true, // has hung up.
+				}))
+			}
+		}
+
+		// check whether a sender's hung up (using `wait` to preserve the task invariant)
+		// returns true if has hung up, false otherwise.
+		fn check_hangup<T>(send: &mut Sender<T>) -> bool {
+			CheckHangup(send).wait().expect("CheckHangup always returns ok; qed")
+		}
+
+		if self.orphaned_requests.read().is_empty() { return }
+
+		let to_dispatch = ::std::mem::replace(&mut *self.orphaned_requests.write(), Vec::new());
+
+		for orphaned in to_dispatch {
+			match orphaned {
+				Pending::HeaderByNumber(req, mut sender) =>
+					if !check_hangup(&mut sender) { self.dispatch_header_by_number(ctx, req, sender) },
+				Pending::HeaderByHash(req, mut sender) =>
+					if !check_hangup(&mut sender) {	self.dispatch_header_by_hash(ctx, req, sender) },
+				Pending::Block(req, mut sender) =>
+					if !check_hangup(&mut sender) { self.dispatch_block(ctx, req, sender) },
+				Pending::BlockReceipts(req, mut sender) =>
+					if !check_hangup(&mut sender) { self.dispatch_block_receipts(ctx, req, sender) },
+				Pending::Account(req, mut sender) =>
+					if !check_hangup(&mut sender) { self.dispatch_account(ctx, req, sender) },
+				Pending::Code(req, mut sender) =>
+					if !check_hangup(&mut sender) { self.dispatch_code(ctx, req, sender) },
+			}
+		}
 	}
 }
 
 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() });
+		self.dispatch_orphaned(ctx.as_basic());
 	}
 
 	fn on_disconnect(&self, ctx: &EventContext, unfulfilled: &[ReqId]) {
 		self.peers.write().remove(&ctx.peer());
 		let ctx = ctx.as_basic();
 
-		for unfulfilled in unfulfilled {
-			if let Some(pending) = self.pending_requests.write().remove(unfulfilled) {
-				trace!(target: "on_demand", "Attempting to reassign dropped request");
-				match pending {
-					Pending::HeaderByNumber(req, sender)
-						=> self.dispatch_header_by_number(ctx, req, sender),
-					Pending::HeaderByHash(req, sender)
-						=> self.dispatch_header_by_hash(ctx, req, sender),
-					Pending::Block(req, sender)
-						=> self.dispatch_block(ctx, req, sender),
-					Pending::BlockReceipts(req, sender)
-						=> self.dispatch_block_receipts(ctx, req, sender),
-					Pending::Account(req, sender)
-						=> self.dispatch_account(ctx, req, sender),
-					Pending::Code(req, sender)
-						=> self.dispatch_code(ctx, req, sender),
+		{
+			let mut orphaned = self.orphaned_requests.write();
+			for unfulfilled in unfulfilled {
+				if let Some(pending) = self.pending_requests.write().remove(unfulfilled) {
+					trace!(target: "on_demand", "Attempting to reassign dropped request");
+					orphaned.push(pending);
 				}
 			}
 		}
+
+		self.dispatch_orphaned(ctx);
 	}
 
 	fn on_announcement(&self, ctx: &EventContext, announcement: &Announcement) {
@@ -418,6 +459,8 @@ impl Handler for OnDemand {
 			peer.status.update_from(&announcement);
 			peer.capabilities.update_from(&announcement);
 		}
+
+		self.dispatch_orphaned(ctx.as_basic());
 	}
 
 	fn on_header_proofs(&self, ctx: &EventContext, req_id: ReqId, proofs: &[(Bytes, Vec<Bytes>)]) {
@@ -587,6 +630,10 @@ impl Handler for OnDemand {
 			_ => panic!("Only code request fetches code; qed"),
 		}
 	}
+
+	fn tick(&self, ctx: &BasicContext) {
+		self.dispatch_orphaned(ctx)
+	}
 }
 
 #[cfg(test)]