http.rs

// Copyright 2019 Parity Technologies (UK) Ltd.
// This file is part of Substrate.

// Substrate 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.

// Substrate 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 Substrate.  If not, see <http://www.gnu.org/licenses/>.

//! This module is composed of two structs: [`HttpApi`] and [`HttpWorker`]. Calling the [`http`]
//! function returns a pair of [`HttpApi`] and [`HttpWorker`] that share some state.
//!
//! The [`HttpApi`] is (indirectly) passed to the runtime when calling an offchain worker, while
//! the [`HttpWorker`] must be processed in the background. The [`HttpApi`] mimicks the API of the
//! HTTP-related methods available to offchain workers.
//!
//! The reason for this design is driven by the fact that HTTP requests should continue running
//! (i.e.: the socket should continue being processed) in the background even if the runtime isn't
//! actively calling any function.

use crate::api::timestamp;
use bytes::Buf as _;
use fnv::FnvHashMap;
use futures::{prelude::*, channel::mpsc, compat::Compat01As03};
use log::{warn, error};
use primitives::offchain::{HttpRequestId, Timestamp, HttpRequestStatus, HttpError};
use std::{fmt, io::Read as _, mem, pin::Pin, task::Context, task::Poll};

/// Creates a pair of [`HttpApi`] and [`HttpWorker`].
pub fn http() -> (HttpApi, HttpWorker) {
	let (to_worker, from_api) = mpsc::unbounded();
	let (to_api, from_worker) = mpsc::unbounded();

	let api = HttpApi {
		to_worker,
		from_worker: from_worker.fuse(),
		// We start with a random ID for the first HTTP request, to prevent mischievous people from
		// writing runtime code with hardcoded IDs.
		next_id: HttpRequestId(rand::random::<u16>() % 2000),
		requests: FnvHashMap::default(),
	};

	let engine = HttpWorker {
		to_api,
		from_api,
		// TODO: don't unwrap; we should fall back to the HttpConnector if we fail to create the
		// Https one; there doesn't seem to be any built-in way to do this
		http_client: HyperClient::new(),
		requests: Vec::new(),
	};

	(api, engine)
}

/// Provides HTTP capabilities.
///
/// Since this struct is a helper for offchain workers, its API is mimicking the API provided
/// to offchain workers.
pub struct HttpApi {
	/// Used to sends messages to the worker.
	to_worker: mpsc::UnboundedSender<ApiToWorker>,
	/// Used to receive messages from the worker.
	/// We use a `Fuse` in order to have an extra protection against panicking.
	from_worker: stream::Fuse<mpsc::UnboundedReceiver<WorkerToApi>>,
	/// Id to assign to the next HTTP request that is started.
	next_id: HttpRequestId,
	/// List of HTTP requests in preparation or in progress.
	requests: FnvHashMap<HttpRequestId, HttpApiRequest>,
}

/// One active request within `HttpApi`.
enum HttpApiRequest {
	/// The request object is being constructed locally and not started yet.
	NotDispatched(hyper::Request<hyper::Body>, hyper::body::Sender),
	/// The request has been dispatched and we're in the process of sending out the body (if the
	/// field is `Some`) or waiting for a response (if the field is `None`).
	Dispatched(Option<hyper::body::Sender>),
	/// Received a response.
	Response(HttpApiRequestRp),
	/// A request has been dispatched but the worker notified us of an error. We report this
	/// failure to the user as an `IoError` and remove the request from the list as soon as
	/// possible.
	Fail(hyper::Error),
}

/// A request within `HttpApi` that has received a response.
struct HttpApiRequestRp {
	/// We might still be writing the request's body when the response comes.
	/// This field allows to continue writing that body.
	sending_body: Option<hyper::body::Sender>,
	/// Status code of the response.
	status_code: hyper::StatusCode,
	/// Headers of the response.
	headers: hyper::HeaderMap,
	/// Body of the response, as a channel of `Chunk` objects.
	/// While the code is designed to drop the `Receiver` once it ends, we wrap it within a
	/// `Fuse` in order to be extra precautious about panics.
	/// Elements extracted from the channel are first put into `current_read_chunk`.
	/// If the channel produces an error, then that is translated into an `IoError` and the request
	/// is removed from the list.
	body: stream::Fuse<mpsc::Receiver<Result<hyper::Chunk, hyper::Error>>>,
	/// Chunk that has been extracted from the channel and that is currently being read.
	/// Reading data from the response should read from this field in priority.
	current_read_chunk: Option<bytes::Reader<hyper::Chunk>>,
}

impl HttpApi {
	/// Mimicks the corresponding method in the offchain API.
	pub fn request_start(
		&mut self,
		method: &str,
		uri: &str
	) -> Result<HttpRequestId, ()> {
		// Start by building the prototype of the request.
		// We do this first so that we don't touch anything in `self` if building the prototype
		// fails.
		let (body_sender, body) = hyper::Body::channel();
		let mut request = hyper::Request::new(body);
		*request.method_mut() = hyper::Method::from_bytes(method.as_bytes()).map_err(|_| ())?;
		*request.uri_mut() = hyper::Uri::from_shared(From::from(uri)).map_err(|_| ())?;

		let new_id = self.next_id;
		debug_assert!(!self.requests.contains_key(&new_id));
		match self.next_id.0.checked_add(1) {
			Some(new_id) => self.next_id.0 = new_id,
			None => {
				error!("Overflow in offchain worker HTTP request ID assignment");
				return Err(());
			}
		};
		self.requests.insert(new_id, HttpApiRequest::NotDispatched(request, body_sender));

		Ok(new_id)
	}

	/// Mimicks the corresponding method in the offchain API.
	pub fn request_add_header(
		&mut self,
		request_id: HttpRequestId,
		name: &str,
		value: &str
	) -> Result<(), ()> {
		let request = match self.requests.get_mut(&request_id) {
			Some(&mut HttpApiRequest::NotDispatched(ref mut rq, _)) => rq,
			_ => return Err(())
		};

		let name = hyper::header::HeaderName::from_bytes(name.as_bytes()).map_err(|_| ())?;
		let value = hyper::header::HeaderValue::from_str(value).map_err(|_| ())?;
		// Note that we're always appending headers and never replacing old values.
		// We assume here that the user knows what they're doing.
		request.headers_mut().append(name, value);
		Ok(())
	}

	/// Mimicks the corresponding method in the offchain API.
	pub fn request_write_body(
		&mut self,
		request_id: HttpRequestId,
		chunk: &[u8],
		deadline: Option<Timestamp>
	) -> Result<(), HttpError> {
		// Extract the request from the list.
		// Don't forget to add it back if necessary when returning.
		let mut request = match self.requests.remove(&request_id) {
			None => return Err(HttpError::Invalid),
			Some(r) => r,
		};

		let mut deadline = timestamp::deadline_to_future(deadline);
		// Closure that writes data to a sender, taking the deadline into account. Can return `Ok`
		// (if the body has been written), or `DeadlineReached`, or `IoError`.
		// If `IoError` is returned, don't forget to remove the request from the list.
		let mut poll_sender = move |sender: &mut hyper::body::Sender| -> Result<(), HttpError> {
			let mut when_ready = future::maybe_done(Compat01As03::new(
				futures01::future::poll_fn(|| sender.poll_ready())
			));
			futures::executor::block_on(future::select(&mut when_ready, &mut deadline));
			match when_ready {
				future::MaybeDone::Done(Ok(())) => {}
				future::MaybeDone::Done(Err(_)) => return Err(HttpError::IoError),
				future::MaybeDone::Future(_) |
				future::MaybeDone::Gone => {
					debug_assert!(if let future::MaybeDone::Done(_) = deadline { true } else { false });
					return Err(HttpError::DeadlineReached)
				}
			};

			match sender.send_data(hyper::Chunk::from(chunk.to_owned())) {
				Ok(()) => Ok(()),
				Err(_chunk) => {
					error!("HTTP sender refused data despite being ready");
					Err(HttpError::IoError)
				},
			}
		};

		loop {
			request = match request {
				HttpApiRequest::NotDispatched(request, sender) => {
					// If the request is not dispatched yet, dispatch it and loop again.
					let _ = self.to_worker.unbounded_send(ApiToWorker::Dispatch {
						id: request_id,
						request
					});
					HttpApiRequest::Dispatched(Some(sender))
				}

				HttpApiRequest::Dispatched(Some(mut sender)) =>
					if !chunk.is_empty() {
						match poll_sender(&mut sender) {
							Err(HttpError::IoError) => return Err(HttpError::IoError),
							other => {
								self.requests.insert(
									request_id,
									HttpApiRequest::Dispatched(Some(sender))
								);
								return other
							}
						}
					} else {
						// Writing an empty body is a hint that we should stop writing. Dropping
						// the sender.
						self.requests.insert(request_id, HttpApiRequest::Dispatched(None));
						return Ok(())
					}

				HttpApiRequest::Response(mut response @ HttpApiRequestRp { sending_body: Some(_), .. }) =>
					if !chunk.is_empty() {
						match poll_sender(response.sending_body.as_mut()
							.expect("Can only enter this match branch if Some; qed")) {
							Err(HttpError::IoError) => return Err(HttpError::IoError),
							other => {
								self.requests.insert(request_id, HttpApiRequest::Response(response));
								return other
							}
						}

					} else {
						// Writing an empty body is a hint that we should stop writing. Dropping
						// the sender.
						self.requests.insert(request_id, HttpApiRequest::Response(HttpApiRequestRp {
							sending_body: None,
							..response
						}));
						return Ok(())
					}

				HttpApiRequest::Fail(_) =>
					// If the request has already failed, return without putting back the request
					// in the list.
					return Err(HttpError::IoError),

				v @ HttpApiRequest::Dispatched(None) |
				v @ HttpApiRequest::Response(HttpApiRequestRp { sending_body: None, .. }) => {
					// We have already finished sending this body.
					self.requests.insert(request_id, v);
					return Err(HttpError::Invalid)
				}
			}
		}
	}

	/// Mimicks the corresponding method in the offchain API.
	pub fn response_wait(
		&mut self,
		ids: &[HttpRequestId],
		deadline: Option<Timestamp>
	) -> Vec<HttpRequestStatus> {
		// First of all, dispatch all the non-dispatched requests and drop all senders so that the
		// user can't write anymore data.
		for id in ids {
			match self.requests.get_mut(id) {
				Some(HttpApiRequest::NotDispatched(_, _)) => {}
				Some(HttpApiRequest::Dispatched(sending_body)) |
				Some(HttpApiRequest::Response(HttpApiRequestRp { sending_body, .. })) => {
					let _ = sending_body.take();
					continue
				}
				_ => continue
			};

			let (request, _sender) = match self.requests.remove(id) {
				Some(HttpApiRequest::NotDispatched(rq, s)) => (rq, s),
				_ => unreachable!("we checked for NotDispatched above; qed")
			};

			let _ = self.to_worker.unbounded_send(ApiToWorker::Dispatch {
				id: *id,
				request
			});

			// We also destroy the sender in order to forbid writing more data.
			self.requests.insert(*id, HttpApiRequest::Dispatched(None));
		}

		let mut deadline = timestamp::deadline_to_future(deadline);

		loop {
			// Within that loop, first try to see if we have all the elements for a response.
			// This includes the situation where the deadline is reached.
			{
				let mut output = Vec::with_capacity(ids.len());
				let mut must_wait_more = false;
				for id in ids {
					output.push(match self.requests.get_mut(id) {
						None => HttpRequestStatus::Invalid,
						Some(HttpApiRequest::NotDispatched(_, _)) =>
							unreachable!("we replaced all the NotDispatched with Dispatched earlier; qed"),
						Some(HttpApiRequest::Dispatched(_)) => {
							must_wait_more = true;
							HttpRequestStatus::DeadlineReached
						},
						Some(HttpApiRequest::Fail(_)) => HttpRequestStatus::IoError,
						Some(HttpApiRequest::Response(HttpApiRequestRp { status_code, .. })) =>
							HttpRequestStatus::Finished(status_code.as_u16()),
					});
				}
				debug_assert_eq!(output.len(), ids.len());

				// Are we ready to call `return`?
				let is_done = if let future::MaybeDone::Done(_) = deadline {
					true
				} else if !must_wait_more {
					true
				} else {
					false
				};

				if is_done {
					// Requests in "fail" mode are purged before returning.
					debug_assert_eq!(output.len(), ids.len());
					for n in (0..ids.len()).rev() {
						if let HttpRequestStatus::IoError = output[n] {
							self.requests.remove(&ids[n]);
						}
					}
					return output
				}
			}

			// Grab next message from the worker. We call `continue` if deadline is reached so that
			// we loop back and `return`.
			let next_message = {
				let mut next_msg = future::maybe_done(self.from_worker.next());
				futures::executor::block_on(future::select(&mut next_msg, &mut deadline));
				if let future::MaybeDone::Done(msg) = next_msg {
					msg
				} else {
					debug_assert!(if let future::MaybeDone::Done(_) = deadline { true } else { false });
					continue
				}
			};

			// Update internal state based on received message.
			match next_message {
				Some(WorkerToApi::Response { id, status_code, headers, body }) =>
					match self.requests.remove(&id) {
						Some(HttpApiRequest::Dispatched(sending_body)) => {
							self.requests.insert(id, HttpApiRequest::Response(HttpApiRequestRp {
								sending_body,
								status_code,
								headers,
								body: body.fuse(),
								current_read_chunk: None,
							}));
						}
						None => {}	// can happen if we detected an IO error when sending the body
						_ => error!("State mismatch between the API and worker"),
					}

				Some(WorkerToApi::Fail { id, error }) =>
					match self.requests.remove(&id) {
						Some(HttpApiRequest::Dispatched(_)) => {
							self.requests.insert(id, HttpApiRequest::Fail(error));
						}
						None => {}	// can happen if we detected an IO error when sending the body
						_ => error!("State mismatch between the API and worker"),
					}

				None => {
					error!("Worker has crashed");
					return ids.iter().map(|_| HttpRequestStatus::IoError).collect()
				}
			}

		}
	}

	/// Mimicks the corresponding method in the offchain API.
	pub fn response_headers(
		&mut self,
		request_id: HttpRequestId
	) -> Vec<(Vec<u8>, Vec<u8>)> {
		// Do an implicit non-blocking wait on the request.
		let _ = self.response_wait(&[request_id], Some(timestamp::now()));

		let headers = match self.requests.get(&request_id) {
			Some(HttpApiRequest::Response(HttpApiRequestRp { headers, .. })) => headers,
			_ => return Vec::new()
		};

		headers
			.iter()
			.map(|(name, value)| (name.as_str().as_bytes().to_owned(), value.as_bytes().to_owned()))
			.collect()
	}

	/// Mimicks the corresponding method in the offchain API.
	pub fn response_read_body(
		&mut self,
		request_id: HttpRequestId,
		buffer: &mut [u8],
		deadline: Option<Timestamp>
	) -> Result<usize, HttpError> {
		// Do an implicit wait on the request.
		let _ = self.response_wait(&[request_id], deadline);

		// Remove the request from the list and handle situations where the request is invalid or
		// in the wrong state.
		let mut response = match self.requests.remove(&request_id) {
			Some(HttpApiRequest::Response(r)) => r,
			// Because we called `response_wait` above, we know that the deadline has been reached
			// and we still haven't received a response.
			Some(rq @ HttpApiRequest::Dispatched(_)) => {
				self.requests.insert(request_id, rq);
				return Err(HttpError::DeadlineReached)
			},
			// The request has failed.
			Some(HttpApiRequest::Fail { .. }) =>
				return Err(HttpError::IoError),
			// Request hasn't been dispatched yet; reading the body is invalid.
			Some(rq @ HttpApiRequest::NotDispatched(_, _)) => {
				self.requests.insert(request_id, rq);
				return Err(HttpError::Invalid)
			}
			None => return Err(HttpError::Invalid)
		};

		// Convert the deadline into a `Future` that resolves when the deadline is reached.
		let mut deadline = timestamp::deadline_to_future(deadline);

		loop {
			// First read from `current_read_chunk`.
			if let Some(mut current_read_chunk) = response.current_read_chunk.take() {
				match current_read_chunk.read(buffer) {
					Ok(0) => {}
					Ok(n) => {
						self.requests.insert(request_id, HttpApiRequest::Response(HttpApiRequestRp {
							current_read_chunk: Some(current_read_chunk),
							.. response
						}));
						return Ok(n)
					},
					Err(err) => {
						// This code should never be reached unless there's a logic error somewhere.
						error!("Failed to read from current read chunk: {:?}", err);
						return Err(HttpError::IoError)
					}
				}
			}

			// If we reach here, that means the `current_read_chunk` is empty and needs to be
			// filled with a new chunk from `body`. We block on either the next body or the
			// deadline.
			let mut next_body = future::maybe_done(response.body.next());
			futures::executor::block_on(future::select(&mut next_body, &mut deadline));

			if let future::MaybeDone::Done(next_body) = next_body {
				match next_body {
					Some(Ok(chunk)) => response.current_read_chunk = Some(chunk.reader()),
					Some(Err(_)) => return Err(HttpError::IoError),
					None => return Ok(0),  // eof
				}
			}

			if let future::MaybeDone::Done(_) = deadline {
				self.requests.insert(request_id, HttpApiRequest::Response(response));
				return Err(HttpError::DeadlineReached)
			}
		}
	}
}

impl fmt::Debug for HttpApi {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
		f.debug_list()
			.entries(self.requests.iter())
			.finish()
	}
}

impl fmt::Debug for HttpApiRequest {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
		match self {
			HttpApiRequest::NotDispatched(_, _) =>
				f.debug_tuple("HttpApiRequest::NotDispatched").finish(),
			HttpApiRequest::Dispatched(_) =>
				f.debug_tuple("HttpApiRequest::Dispatched").finish(),
			HttpApiRequest::Response(HttpApiRequestRp { status_code, headers, .. }) =>
				f.debug_tuple("HttpApiRequest::Response").field(status_code).field(headers).finish(),
			HttpApiRequest::Fail(err) =>
				f.debug_tuple("HttpApiRequest::Fail").field(err).finish(),
		}
	}
}

/// Message send from the API to the worker.
enum ApiToWorker {
	/// Dispatches a new HTTP request.
	Dispatch {
		/// ID to send back when the response comes back.
		id: HttpRequestId,
		/// Request to start executing.
		request: hyper::Request<hyper::Body>,
	}
}

/// Message send from the API to the worker.
enum WorkerToApi {
	/// A request has succeeded.
	Response {
		/// The ID that was passed to the worker.
		id: HttpRequestId,
		/// Status code of the response.
		status_code: hyper::StatusCode,
		/// Headers of the response.
		headers: hyper::HeaderMap,
		/// Body of the response, as a channel of `Chunk` objects.
		/// We send the body back through a channel instead of returning the hyper `Body` object
		/// because we don't want the `HttpApi` to have to drive the reading.
		/// Instead, reading an item from the channel will notify the worker task, which will push
		/// the next item.
		/// Can also be used to send an error, in case an error happend on the HTTP socket. After
		/// an error is sent, the channel will close.
		body: mpsc::Receiver<Result<hyper::Chunk, hyper::Error>>,
	},
	/// A request has failed because of an error. The request is then no longer valid.
	Fail {
		/// The ID that was passed to the worker.
		id: HttpRequestId,
		/// Error that happened.
		error: hyper::Error,
	},
}

/// Wraps around a `hyper::Client` with either TLS enabled or disabled.
enum HyperClient {
	/// Everything is ok and HTTPS is available.
	Https(hyper::Client<hyper_tls::HttpsConnector<hyper::client::HttpConnector>, hyper::Body>),
	/// We failed to initialize HTTPS and therefore only allow HTTP.
	Http(hyper::Client<hyper::client::HttpConnector, hyper::Body>),
}

impl HyperClient {
	/// Creates new hyper client.
	///
	/// By default we will try to initialize the `HttpsConnector`,
	/// If that's not possible we'll fall back to `HttpConnector`.
	pub fn new() -> Self {
		match hyper_tls::HttpsConnector::new(1) {
			Ok(tls) => HyperClient::Https(hyper::Client::builder().build(tls)),
			Err(e) => {
				warn!("Unable to initialize TLS client. Falling back to HTTP-only: {:?}", e);
				HyperClient::Http(hyper::Client::new())
			},
		}
	}
}

/// Must be continuously polled for the [`HttpApi`] to properly work.
pub struct HttpWorker {
	/// Used to sends messages to the `HttpApi`.
	to_api: mpsc::UnboundedSender<WorkerToApi>,
	/// Used to receive messages from the `HttpApi`.
	from_api: mpsc::UnboundedReceiver<ApiToWorker>,
	/// The engine that runs HTTP requests.
	http_client: HyperClient,
	/// HTTP requests that are being worked on by the engine.
	requests: Vec<(HttpRequestId, HttpWorkerRequest)>,
}

/// HTTP request being processed by the worker.
enum HttpWorkerRequest {
	/// Request has been dispatched and is waiting for a response from the Internet.
	Dispatched(Compat01As03<hyper::client::ResponseFuture>),
	/// Progressively reading the body of the response and sending it to the channel.
	ReadBody {
		/// Body to read `Chunk`s from. Only used if the channel is ready to accept data.
		body: Compat01As03<hyper::Body>,
		/// Channel to the [`HttpApi`] where we send the chunks to.
		tx: mpsc::Sender<Result<hyper::Chunk, hyper::Error>>,
	},
}

impl Future for HttpWorker {
	type Output = ();

	fn poll(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output> {
		// Reminder: this is continuously run in the background.

		// We use a `me` variable because the compiler isn't smart enough to allow borrowing
		// multiple fields at once through a `Deref`.
		let me = &mut *self;

		// We remove each element from `requests` one by one and add them back only if necessary.
		for n in (0..me.requests.len()).rev() {
			let (id, request) = me.requests.swap_remove(n);
			match request {
				HttpWorkerRequest::Dispatched(mut future) => {
					// Check for an HTTP response from the Internet.
					let mut response = match Future::poll(Pin::new(&mut future), cx) {
						Poll::Pending => {
							me.requests.push((id, HttpWorkerRequest::Dispatched(future)));
							continue
						},
						Poll::Ready(Ok(response)) => response,
						Poll::Ready(Err(err)) => {
							let _ = me.to_api.unbounded_send(WorkerToApi::Fail {
								id,
								error: err,
							});
							continue;		// don't insert the request back
						}
					};

					// We received a response! Decompose it into its parts.
					let status_code = response.status();
					let headers = mem::replace(response.headers_mut(), hyper::HeaderMap::new());
					let body = Compat01As03::new(response.into_body());

					let (body_tx, body_rx) = mpsc::channel(3);
					let _ = me.to_api.unbounded_send(WorkerToApi::Response {
						id,
						status_code,
						headers,
						body: body_rx,
					});

					me.requests.push((id, HttpWorkerRequest::ReadBody { body, tx: body_tx }));
					cx.waker().wake_by_ref();	// reschedule in order to poll the new future
					continue
				}

				HttpWorkerRequest::ReadBody { mut body, mut tx } => {
					// Before reading from the HTTP response, check that `tx` is ready to accept
					// a new chunk.
					match tx.poll_ready(cx) {
						Poll::Ready(Ok(())) => {}
						Poll::Ready(Err(_)) => continue,  // don't insert the request back
						Poll::Pending => {
							me.requests.push((id, HttpWorkerRequest::ReadBody { body, tx }));
							continue
						}
					}

					// `tx` is ready. Read a chunk from the socket and send it to the channel.
					match Stream::poll_next(Pin::new(&mut body), cx) {
						Poll::Ready(Some(Ok(chunk))) => {
							let _ = tx.start_send(Ok(chunk));
							me.requests.push((id, HttpWorkerRequest::ReadBody { body, tx }));
							cx.waker().wake_by_ref();	// reschedule in order to continue reading
						}
						Poll::Ready(Some(Err(err))) => {
							let _ = tx.start_send(Err(err));
							// don't insert the request back
						},
						Poll::Ready(None) => {}		// EOF; don't insert the request back
						Poll::Pending => {
							me.requests.push((id, HttpWorkerRequest::ReadBody { body, tx }));
						},
					}
				}
			}
		}

		// Check for messages coming from the [`HttpApi`].
		match Stream::poll_next(Pin::new(&mut me.from_api), cx) {
			Poll::Pending => {},
			Poll::Ready(None) => return Poll::Ready(()),	// stops the worker
			Poll::Ready(Some(ApiToWorker::Dispatch { id, request })) => {
				let future = Compat01As03::new(match me.http_client {
					HyperClient::Http(ref mut c) => c.request(request),
					HyperClient::Https(ref mut c) => c.request(request),
				});
				debug_assert!(me.requests.iter().all(|(i, _)| *i != id));
				me.requests.push((id, HttpWorkerRequest::Dispatched(future)));
				cx.waker().wake_by_ref();	// reschedule the task to poll the request
			}
		}

		Poll::Pending
	}
}

impl fmt::Debug for HttpWorker {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
		f.debug_list()
			.entries(self.requests.iter())
			.finish()
	}
}

impl fmt::Debug for HttpWorkerRequest {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
		match self {
			HttpWorkerRequest::Dispatched(_) =>
				f.debug_tuple("HttpWorkerRequest::Dispatched").finish(),
			HttpWorkerRequest::ReadBody { .. } =>
				f.debug_tuple("HttpWorkerRequest::Response").finish(),
		}
	}
}

#[cfg(test)]
mod tests {
	use crate::api::timestamp;
	use super::http;
	use futures::prelude::*;
	use futures01::Future as _;
	use primitives::offchain::{HttpError, HttpRequestId, HttpRequestStatus, Duration};

	// Returns an `HttpApi` whose worker is ran in the background, and a `SocketAddr` to an HTTP
	// server that runs in the background as well.
	macro_rules! build_api_server {
		() => {{
			let (api, worker) = http();
			// Note: we have to use tokio because hyper still uses old futures.
			std::thread::spawn(move || {
				tokio::run(futures::compat::Compat::new(worker.map(|()| Ok::<(), ()>(()))))
			});
			let (addr_tx, addr_rx) = std::sync::mpsc::channel();
			std::thread::spawn(move || {
				let server = hyper::Server::bind(&"127.0.0.1:0".parse().unwrap())
					.serve(|| {
						hyper::service::service_fn_ok(move |_: hyper::Request<hyper::Body>| {
							hyper::Response::new(hyper::Body::from("Hello World!"))
						})
					});
				let _ = addr_tx.send(server.local_addr());
				hyper::rt::run(server.map_err(|e| panic!("{:?}", e)));
			});
			(api, addr_rx.recv().unwrap())
		}};
	}

	#[test]
	fn basic_localhost() {
		let deadline = timestamp::now().add(Duration::from_millis(10_000));

		// Performs an HTTP query to a background HTTP server.

		let (mut api, addr) = build_api_server!();

		let id = api.request_start("POST", &format!("http://{}", addr)).unwrap();
		api.request_write_body(id, &[], Some(deadline)).unwrap();

		match api.response_wait(&[id], Some(deadline))[0] {
			HttpRequestStatus::Finished(200) => {},
			v => panic!("Connecting to localhost failed: {:?}", v)
		}

		let headers = api.response_headers(id);
		assert!(headers.iter().any(|(h, _)| h.eq_ignore_ascii_case(b"Date")));

		let mut buf = vec![0; 2048];
		let n = api.response_read_body(id, &mut buf, Some(deadline)).unwrap();
		assert_eq!(&buf[..n], b"Hello World!");
	}

	#[test]
	fn request_start_invalid_call() {
		let (mut api, addr) = build_api_server!();

		match api.request_start("\0", &format!("http://{}", addr)) {
			Err(()) => {}
			Ok(_) => panic!()
		};

		match api.request_start("GET", "http://\0localhost") {
			Err(()) => {}
			Ok(_) => panic!()
		};
	}

	#[test]
	fn request_add_header_invalid_call() {
		let (mut api, addr) = build_api_server!();

		match api.request_add_header(HttpRequestId(0xdead), "Foo", "bar") {
			Err(()) => {}
			Ok(_) => panic!()
		};

		let id = api.request_start("GET", &format!("http://{}", addr)).unwrap();
		match api.request_add_header(id, "\0", "bar") {
			Err(()) => {}
			Ok(_) => panic!()
		};

		let id = api.request_start("POST", &format!("http://{}", addr)).unwrap();
		match api.request_add_header(id, "Foo", "\0") {
			Err(()) => {}
			Ok(_) => panic!()
		};

		let id = api.request_start("POST", &format!("http://{}", addr)).unwrap();
		api.request_add_header(id, "Foo", "Bar").unwrap();
		api.request_write_body(id, &[1, 2, 3, 4], None).unwrap();
		match api.request_add_header(id, "Foo2", "Bar") {
			Err(()) => {}
			Ok(_) => panic!()
		};

		let id = api.request_start("GET", &format!("http://{}", addr)).unwrap();
		api.response_headers(id);
		match api.request_add_header(id, "Foo2", "Bar") {
			Err(()) => {}
			Ok(_) => panic!()
		};

		let id = api.request_start("GET", &format!("http://{}", addr)).unwrap();
		api.response_read_body(id, &mut [], None).unwrap();
		match api.request_add_header(id, "Foo2", "Bar") {
			Err(()) => {}
			Ok(_) => panic!()
		};
	}

	#[test]
	fn request_write_body_invalid_call() {
		let (mut api, addr) = build_api_server!();

		match api.request_write_body(HttpRequestId(0xdead), &[1, 2, 3], None) {
			Err(HttpError::Invalid) => {}
			_ => panic!()
		};

		match api.request_write_body(HttpRequestId(0xdead), &[], None) {
			Err(HttpError::Invalid) => {}
			_ => panic!()
		};

		let id = api.request_start("POST", &format!("http://{}", addr)).unwrap();
		api.request_write_body(id, &[1, 2, 3, 4], None).unwrap();
		api.request_write_body(id, &[1, 2, 3, 4], None).unwrap();
		api.request_write_body(id, &[], None).unwrap();
		match api.request_write_body(id, &[], None) {
			Err(HttpError::Invalid) => {}
			_ => panic!()
		};

		let id = api.request_start("POST", &format!("http://{}", addr)).unwrap();
		api.request_write_body(id, &[1, 2, 3, 4], None).unwrap();
		api.request_write_body(id, &[1, 2, 3, 4], None).unwrap();
		api.request_write_body(id, &[], None).unwrap();
		match api.request_write_body(id, &[1, 2, 3, 4], None) {
			Err(HttpError::Invalid) => {}
			_ => panic!()
		};

		let id = api.request_start("POST", &format!("http://{}", addr)).unwrap();
		api.request_write_body(id, &[1, 2, 3, 4], None).unwrap();
		api.response_wait(&[id], None);
		match api.request_write_body(id, &[], None) {
			Err(HttpError::Invalid) => {}
			_ => panic!()
		};

		let id = api.request_start("POST", &format!("http://{}", addr)).unwrap();
		api.request_write_body(id, &[1, 2, 3, 4], None).unwrap();
		api.response_wait(&[id], None);
		match api.request_write_body(id, &[1, 2, 3, 4], None) {
			Err(HttpError::Invalid) => {}
			_ => panic!()
		};

		let id = api.request_start("POST", &format!("http://{}", addr)).unwrap();
		api.response_headers(id);
		match api.request_write_body(id, &[1, 2, 3, 4], None) {
			Err(HttpError::Invalid) => {}
			_ => panic!()
		};

		let id = api.request_start("GET", &format!("http://{}", addr)).unwrap();
		api.response_headers(id);
		match api.request_write_body(id, &[], None) {
			Err(HttpError::Invalid) => {}
			_ => panic!()
		};

		let id = api.request_start("POST", &format!("http://{}", addr)).unwrap();
		api.response_read_body(id, &mut [], None).unwrap();
		match api.request_write_body(id, &[1, 2, 3, 4], None) {
			Err(HttpError::Invalid) => {}
			_ => panic!()
		};

		let id = api.request_start("POST", &format!("http://{}", addr)).unwrap();
		api.response_read_body(id, &mut [], None).unwrap();
		match api.request_write_body(id, &[], None) {
			Err(HttpError::Invalid) => {}
			_ => panic!()
		};
	}

	#[test]
	fn response_headers_invalid_call() {
		let (mut api, addr) = build_api_server!();
		assert!(api.response_headers(HttpRequestId(0xdead)).is_empty());

		let id = api.request_start("POST", &format!("http://{}", addr)).unwrap();
		assert!(api.response_headers(id).is_empty());

		let id = api.request_start("POST", &format!("http://{}", addr)).unwrap();
		api.request_write_body(id, &[], None).unwrap();
		while api.response_headers(id).is_empty() {
			std::thread::sleep(std::time::Duration::from_millis(100));
		}

		let id = api.request_start("GET", &format!("http://{}", addr)).unwrap();
		api.response_wait(&[id], None);
		assert!(!api.response_headers(id).is_empty());

		let id = api.request_start("GET", &format!("http://{}", addr)).unwrap();
		let mut buf = [0; 128];
		while api.response_read_body(id, &mut buf, None).unwrap() != 0 {}
		assert!(api.response_headers(id).is_empty());
	}

	#[test]
	fn response_header_invalid_call() {
		let (mut api, addr) = build_api_server!();

		let id = api.request_start("POST", &format!("http://{}", addr)).unwrap();
		assert!(api.response_headers(id).is_empty());

		let id = api.request_start("POST", &format!("http://{}", addr)).unwrap();
		api.request_add_header(id, "Foo", "Bar").unwrap();
		assert!(api.response_headers(id).is_empty());

		let id = api.request_start("GET", &format!("http://{}", addr)).unwrap();
		api.request_add_header(id, "Foo", "Bar").unwrap();
		api.request_write_body(id, &[], None).unwrap();
		// Note: this test actually sends out the request, and is supposed to test a situation
		// where we haven't received any response yet. This test can theoretically fail if the
		// HTTP response comes back faster than the kernel schedules our thread, but that is highly
		// unlikely.
		assert!(api.response_headers(id).is_empty());
	}

	#[test]
	fn response_read_body_invalid_call() {
		let (mut api, addr) = build_api_server!();
		let mut buf = [0; 512];

		match api.response_read_body(HttpRequestId(0xdead), &mut buf, None) {
			Err(HttpError::Invalid) => {}
			_ => panic!()
		}

		let id = api.request_start("GET", &format!("http://{}", addr)).unwrap();
		while api.response_read_body(id, &mut buf, None).unwrap() != 0 {}
		match api.response_read_body(id, &mut buf, None) {
			Err(HttpError::Invalid) => {}
			_ => panic!()
		}
	}

	#[test]
	fn fuzzing() {
		// Uses the API in random ways to try to trigger panicks.
		// Doesn't test some paths, such as waiting for multiple requests. Also doesn't test what
		// happens if the server force-closes our socket.

		let (mut api, addr) = build_api_server!();

		for _ in 0..50 {
			let id = api.request_start("POST", &format!("http://{}", addr)).unwrap();

			for _ in 0..250 {
				match rand::random::<u8>() % 6 {
					0 => { let _ = api.request_add_header(id, "Foo", "Bar"); }
					1 => { let _ = api.request_write_body(id, &[1, 2, 3, 4], None); }
					2 => { let _ = api.request_write_body(id, &[], None); }
					3 => { let _ = api.response_wait(&[id], None); }
					4 => { let _ = api.response_headers(id); }
					5 => {
						let mut buf = [0; 512];
						let _ = api.response_read_body(id, &mut buf, None);
					}
					6 ..= 255 => unreachable!()
				}
			}
		}
	}
}