pezkuwi-subxt/substrate/client/network/src/config.rs

// This file is part of Substrate.

// Copyright (C) 2017-2022 Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0

// This program 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.

// This program 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 this program. If not, see <https://www.gnu.org/licenses/>.

//! Configuration of the networking layer.
//!
//! The [`Params`] struct is the struct that must be passed in order to initialize the networking.
//! See the documentation of [`Params`].

pub use sc_network_common::{
	config::ProtocolId,
	request_responses::{
		IncomingRequest, OutgoingResponse, ProtocolConfig as RequestResponseConfig,
	},
	sync::warp::WarpSyncProvider,
};

pub use libp2p::{build_multiaddr, core::PublicKey, identity};

use crate::ExHashT;

use core::{fmt, iter};
use futures::future;
use libp2p::{
	identity::{ed25519, Keypair},
	multiaddr, Multiaddr, PeerId,
};
use prometheus_endpoint::Registry;
use sc_consensus::ImportQueue;
use sc_network_common::sync::ChainSync;
use sp_runtime::traits::Block as BlockT;
use std::{
	borrow::Cow,
	collections::HashMap,
	error::Error,
	fs,
	future::Future,
	io::{self, Write},
	net::Ipv4Addr,
	path::{Path, PathBuf},
	pin::Pin,
	str,
	str::FromStr,
	sync::Arc,
};
use zeroize::Zeroize;

/// Network initialization parameters.
pub struct Params<B, H, Client>
where
	B: BlockT + 'static,
	H: ExHashT,
{
	/// Assigned role for our node (full, light, ...).
	pub role: Role,

	/// How to spawn background tasks. If you pass `None`, then a threads pool will be used by
	/// default.
	pub executor: Option<Box<dyn Fn(Pin<Box<dyn Future<Output = ()> + Send>>) + Send>>,

	/// How to spawn the background task dedicated to the transactions handler.
	pub transactions_handler_executor: Box<dyn Fn(Pin<Box<dyn Future<Output = ()> + Send>>) + Send>,

	/// Network layer configuration.
	pub network_config: NetworkConfiguration,

	/// Client that contains the blockchain.
	pub chain: Arc<Client>,

	/// Pool of transactions.
	///
	/// The network worker will fetch transactions from this object in order to propagate them on
	/// the network.
	pub transaction_pool: Arc<dyn TransactionPool<H, B>>,

	/// Name of the protocol to use on the wire. Should be different for each chain.
	pub protocol_id: ProtocolId,

	/// Import queue to use.
	///
	/// The import queue is the component that verifies that blocks received from other nodes are
	/// valid.
	pub import_queue: Box<dyn ImportQueue<B>>,

	/// Factory function that creates a new instance of chain sync.
	pub create_chain_sync: Box<
		dyn FnOnce(
			sc_network_common::sync::SyncMode,
			Arc<Client>,
			Option<Arc<dyn WarpSyncProvider<B>>>,
		) -> crate::error::Result<Box<dyn ChainSync<B>>>,
	>,

	/// Registry for recording prometheus metrics to.
	pub metrics_registry: Option<Registry>,

	/// Request response configuration for the block request protocol.
	///
	/// [`RequestResponseConfig::name`] is used to tag outgoing block requests with the correct
	/// protocol name. In addition all of [`RequestResponseConfig`] is used to handle incoming
	/// block requests, if enabled.
	///
	/// Can be constructed either via
	/// `sc_network_sync::block_request_handler::generate_protocol_config` allowing outgoing but
	/// not incoming requests, or constructed via `sc_network_sync::block_request_handler::
	/// BlockRequestHandler::new` allowing both outgoing and incoming requests.
	pub block_request_protocol_config: RequestResponseConfig,

	/// Request response configuration for the light client request protocol.
	///
	/// Can be constructed either via
	/// `sc_network_light::light_client_requests::generate_protocol_config` allowing outgoing but
	/// not incoming requests, or constructed via
	/// `sc_network_light::light_client_requests::handler::LightClientRequestHandler::new`
	/// allowing both outgoing and incoming requests.
	pub light_client_request_protocol_config: RequestResponseConfig,

	/// Request response configuration for the state request protocol.
	///
	/// Can be constructed either via
	/// `sc_network_sync::state_request_handler::generate_protocol_config` allowing outgoing but
	/// not incoming requests, or constructed via
	/// `sc_network_sync::state_request_handler::StateRequestHandler::new` allowing
	/// both outgoing and incoming requests.
	pub state_request_protocol_config: RequestResponseConfig,

	/// Optional warp sync protocol support. Include protocol config and sync provider.
	pub warp_sync: Option<(Arc<dyn WarpSyncProvider<B>>, RequestResponseConfig)>,
}

/// Role of the local node.
#[derive(Debug, Clone)]
pub enum Role {
	/// Regular full node.
	Full,
	/// Actual authority.
	Authority,
}

impl Role {
	/// True for [`Role::Authority`].
	pub fn is_authority(&self) -> bool {
		matches!(self, Self::Authority { .. })
	}
}

impl fmt::Display for Role {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
		match self {
			Self::Full => write!(f, "FULL"),
			Self::Authority { .. } => write!(f, "AUTHORITY"),
		}
	}
}

/// Result of the transaction import.
#[derive(Clone, Copy, Debug)]
pub enum TransactionImport {
	/// Transaction is good but already known by the transaction pool.
	KnownGood,
	/// Transaction is good and not yet known.
	NewGood,
	/// Transaction is invalid.
	Bad,
	/// Transaction import was not performed.
	None,
}

/// Future resolving to transaction import result.
pub type TransactionImportFuture = Pin<Box<dyn Future<Output = TransactionImport> + Send>>;

/// Transaction pool interface
pub trait TransactionPool<H: ExHashT, B: BlockT>: Send + Sync {
	/// Get transactions from the pool that are ready to be propagated.
	fn transactions(&self) -> Vec<(H, B::Extrinsic)>;
	/// Get hash of transaction.
	fn hash_of(&self, transaction: &B::Extrinsic) -> H;
	/// Import a transaction into the pool.
	///
	/// This will return future.
	fn import(&self, transaction: B::Extrinsic) -> TransactionImportFuture;
	/// Notify the pool about transactions broadcast.
	fn on_broadcasted(&self, propagations: HashMap<H, Vec<String>>);
	/// Get transaction by hash.
	fn transaction(&self, hash: &H) -> Option<B::Extrinsic>;
}

/// Dummy implementation of the [`TransactionPool`] trait for a transaction pool that is always
/// empty and discards all incoming transactions.
///
/// Requires the "hash" type to implement the `Default` trait.
///
/// Useful for testing purposes.
pub struct EmptyTransactionPool;

impl<H: ExHashT + Default, B: BlockT> TransactionPool<H, B> for EmptyTransactionPool {
	fn transactions(&self) -> Vec<(H, B::Extrinsic)> {
		Vec::new()
	}

	fn hash_of(&self, _transaction: &B::Extrinsic) -> H {
		Default::default()
	}

	fn import(&self, _transaction: B::Extrinsic) -> TransactionImportFuture {
		Box::pin(future::ready(TransactionImport::KnownGood))
	}

	fn on_broadcasted(&self, _: HashMap<H, Vec<String>>) {}

	fn transaction(&self, _h: &H) -> Option<B::Extrinsic> {
		None
	}
}

/// Parses a string address and splits it into Multiaddress and PeerId, if
/// valid.
///
/// # Example
///
/// ```
/// # use sc_network::{Multiaddr, PeerId, config::parse_str_addr};
/// let (peer_id, addr) = parse_str_addr(
/// 	"/ip4/198.51.100.19/tcp/30333/p2p/QmSk5HQbn6LhUwDiNMseVUjuRYhEtYj4aUZ6WfWoGURpdV"
/// ).unwrap();
/// assert_eq!(peer_id, "QmSk5HQbn6LhUwDiNMseVUjuRYhEtYj4aUZ6WfWoGURpdV".parse::<PeerId>().unwrap());
/// assert_eq!(addr, "/ip4/198.51.100.19/tcp/30333".parse::<Multiaddr>().unwrap());
/// ```
pub fn parse_str_addr(addr_str: &str) -> Result<(PeerId, Multiaddr), ParseErr> {
	let addr: Multiaddr = addr_str.parse()?;
	parse_addr(addr)
}

/// Splits a Multiaddress into a Multiaddress and PeerId.
pub fn parse_addr(mut addr: Multiaddr) -> Result<(PeerId, Multiaddr), ParseErr> {
	let who = match addr.pop() {
		Some(multiaddr::Protocol::P2p(key)) =>
			PeerId::from_multihash(key).map_err(|_| ParseErr::InvalidPeerId)?,
		_ => return Err(ParseErr::PeerIdMissing),
	};

	Ok((who, addr))
}

/// Address of a node, including its identity.
///
/// This struct represents a decoded version of a multiaddress that ends with `/p2p/<peerid>`.
///
/// # Example
///
/// ```
/// # use sc_network::{Multiaddr, PeerId, config::MultiaddrWithPeerId};
/// let addr: MultiaddrWithPeerId =
/// 	"/ip4/198.51.100.19/tcp/30333/p2p/QmSk5HQbn6LhUwDiNMseVUjuRYhEtYj4aUZ6WfWoGURpdV".parse().unwrap();
/// assert_eq!(addr.peer_id.to_base58(), "QmSk5HQbn6LhUwDiNMseVUjuRYhEtYj4aUZ6WfWoGURpdV");
/// assert_eq!(addr.multiaddr.to_string(), "/ip4/198.51.100.19/tcp/30333");
/// ```
#[derive(Debug, Clone, serde::Serialize, serde::Deserialize, PartialEq)]
#[serde(try_from = "String", into = "String")]
pub struct MultiaddrWithPeerId {
	/// Address of the node.
	pub multiaddr: Multiaddr,
	/// Its identity.
	pub peer_id: PeerId,
}

impl MultiaddrWithPeerId {
	/// Concatenates the multiaddress and peer ID into one multiaddress containing both.
	pub fn concat(&self) -> Multiaddr {
		let proto = multiaddr::Protocol::P2p(From::from(self.peer_id));
		self.multiaddr.clone().with(proto)
	}
}

impl fmt::Display for MultiaddrWithPeerId {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
		fmt::Display::fmt(&self.concat(), f)
	}
}

impl FromStr for MultiaddrWithPeerId {
	type Err = ParseErr;

	fn from_str(s: &str) -> Result<Self, Self::Err> {
		let (peer_id, multiaddr) = parse_str_addr(s)?;
		Ok(Self { peer_id, multiaddr })
	}
}

impl From<MultiaddrWithPeerId> for String {
	fn from(ma: MultiaddrWithPeerId) -> String {
		format!("{}", ma)
	}
}

impl TryFrom<String> for MultiaddrWithPeerId {
	type Error = ParseErr;
	fn try_from(string: String) -> Result<Self, Self::Error> {
		string.parse()
	}
}

/// Error that can be generated by `parse_str_addr`.
#[derive(Debug)]
pub enum ParseErr {
	/// Error while parsing the multiaddress.
	MultiaddrParse(multiaddr::Error),
	/// Multihash of the peer ID is invalid.
	InvalidPeerId,
	/// The peer ID is missing from the address.
	PeerIdMissing,
}

impl fmt::Display for ParseErr {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
		match self {
			Self::MultiaddrParse(err) => write!(f, "{}", err),
			Self::InvalidPeerId => write!(f, "Peer id at the end of the address is invalid"),
			Self::PeerIdMissing => write!(f, "Peer id is missing from the address"),
		}
	}
}

impl std::error::Error for ParseErr {
	fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
		match self {
			Self::MultiaddrParse(err) => Some(err),
			Self::InvalidPeerId => None,
			Self::PeerIdMissing => None,
		}
	}
}

impl From<multiaddr::Error> for ParseErr {
	fn from(err: multiaddr::Error) -> ParseErr {
		Self::MultiaddrParse(err)
	}
}

/// Sync operation mode.
#[derive(Clone, Debug, Eq, PartialEq)]
pub enum SyncMode {
	/// Full block download and verification.
	Full,
	/// Download blocks and the latest state.
	Fast {
		/// Skip state proof download and verification.
		skip_proofs: bool,
		/// Download indexed transactions for recent blocks.
		storage_chain_mode: bool,
	},
	/// Warp sync - verify authority set transitions and the latest state.
	Warp,
}

impl SyncMode {
	/// Returns if `self` is [`Self::Warp`].
	pub fn is_warp(&self) -> bool {
		matches!(self, Self::Warp)
	}

	/// Returns if `self` is [`Self::Fast`].
	pub fn is_fast(&self) -> bool {
		matches!(self, Self::Fast { .. })
	}
}

impl Default for SyncMode {
	fn default() -> Self {
		Self::Full
	}
}

/// Network service configuration.
#[derive(Clone, Debug)]
pub struct NetworkConfiguration {
	/// Directory path to store network-specific configuration. None means nothing will be saved.
	pub net_config_path: Option<PathBuf>,
	/// Multiaddresses to listen for incoming connections.
	pub listen_addresses: Vec<Multiaddr>,
	/// Multiaddresses to advertise. Detected automatically if empty.
	pub public_addresses: Vec<Multiaddr>,
	/// List of initial node addresses
	pub boot_nodes: Vec<MultiaddrWithPeerId>,
	/// The node key configuration, which determines the node's network identity keypair.
	pub node_key: NodeKeyConfig,
	/// List of request-response protocols that the node supports.
	pub request_response_protocols: Vec<RequestResponseConfig>,
	/// Configuration for the default set of nodes used for block syncing and transactions.
	pub default_peers_set: SetConfig,
	/// Number of substreams to reserve for full nodes for block syncing and transactions.
	/// Any other slot will be dedicated to light nodes.
	///
	/// This value is implicitly capped to `default_set.out_peers + default_set.in_peers`.
	pub default_peers_set_num_full: u32,
	/// Configuration for extra sets of nodes.
	pub extra_sets: Vec<NonDefaultSetConfig>,
	/// Client identifier. Sent over the wire for debugging purposes.
	pub client_version: String,
	/// Name of the node. Sent over the wire for debugging purposes.
	pub node_name: String,
	/// Configuration for the transport layer.
	pub transport: TransportConfig,
	/// Maximum number of peers to ask the same blocks in parallel.
	pub max_parallel_downloads: u32,
	/// Initial syncing mode.
	pub sync_mode: SyncMode,

	/// True if Kademlia random discovery should be enabled.
	///
	/// If true, the node will automatically randomly walk the DHT in order to find new peers.
	pub enable_dht_random_walk: bool,

	/// Should we insert non-global addresses into the DHT?
	pub allow_non_globals_in_dht: bool,

	/// Require iterative Kademlia DHT queries to use disjoint paths for increased resiliency in
	/// the presence of potentially adversarial nodes.
	pub kademlia_disjoint_query_paths: bool,
	/// Enable serving block data over IPFS bitswap.
	pub ipfs_server: bool,

	/// Size of Yamux receive window of all substreams. `None` for the default (256kiB).
	/// Any value less than 256kiB is invalid.
	///
	/// # Context
	///
	/// By design, notifications substreams on top of Yamux connections only allow up to `N` bytes
	/// to be transferred at a time, where `N` is the Yamux receive window size configurable here.
	/// This means, in practice, that every `N` bytes must be acknowledged by the receiver before
	/// the sender can send more data. The maximum bandwidth of each notifications substream is
	/// therefore `N / round_trip_time`.
	///
	/// It is recommended to leave this to `None`, and use a request-response protocol instead if
	/// a large amount of data must be transferred. The reason why the value is configurable is
	/// that some Substrate users mis-use notification protocols to send large amounts of data.
	/// As such, this option isn't designed to stay and will likely get removed in the future.
	///
	/// Note that configuring a value here isn't a modification of the Yamux protocol, but rather
	/// a modification of the way the implementation works. Different nodes with different
	/// configured values remain compatible with each other.
	pub yamux_window_size: Option<u32>,
}

impl NetworkConfiguration {
	/// Create new default configuration
	pub fn new<SN: Into<String>, SV: Into<String>>(
		node_name: SN,
		client_version: SV,
		node_key: NodeKeyConfig,
		net_config_path: Option<PathBuf>,
	) -> Self {
		let default_peers_set = SetConfig::default();
		Self {
			net_config_path,
			listen_addresses: Vec::new(),
			public_addresses: Vec::new(),
			boot_nodes: Vec::new(),
			node_key,
			request_response_protocols: Vec::new(),
			default_peers_set_num_full: default_peers_set.in_peers + default_peers_set.out_peers,
			default_peers_set,
			extra_sets: Vec::new(),
			client_version: client_version.into(),
			node_name: node_name.into(),
			transport: TransportConfig::Normal { enable_mdns: false, allow_private_ipv4: true },
			max_parallel_downloads: 5,
			sync_mode: SyncMode::Full,
			enable_dht_random_walk: true,
			allow_non_globals_in_dht: false,
			kademlia_disjoint_query_paths: false,
			yamux_window_size: None,
			ipfs_server: false,
		}
	}

	/// Create new default configuration for localhost-only connection with random port (useful for
	/// testing)
	pub fn new_local() -> NetworkConfiguration {
		let mut config =
			NetworkConfiguration::new("test-node", "test-client", Default::default(), None);

		config.listen_addresses =
			vec![iter::once(multiaddr::Protocol::Ip4(Ipv4Addr::new(127, 0, 0, 1)))
				.chain(iter::once(multiaddr::Protocol::Tcp(0)))
				.collect()];

		config.allow_non_globals_in_dht = true;
		config
	}

	/// Create new default configuration for localhost-only connection with random port (useful for
	/// testing)
	pub fn new_memory() -> NetworkConfiguration {
		let mut config =
			NetworkConfiguration::new("test-node", "test-client", Default::default(), None);

		config.listen_addresses =
			vec![iter::once(multiaddr::Protocol::Ip4(Ipv4Addr::new(127, 0, 0, 1)))
				.chain(iter::once(multiaddr::Protocol::Tcp(0)))
				.collect()];

		config.allow_non_globals_in_dht = true;
		config
	}
}

/// Configuration for a set of nodes.
#[derive(Clone, Debug)]
pub struct SetConfig {
	/// Maximum allowed number of incoming substreams related to this set.
	pub in_peers: u32,
	/// Number of outgoing substreams related to this set that we're trying to maintain.
	pub out_peers: u32,
	/// List of reserved node addresses.
	pub reserved_nodes: Vec<MultiaddrWithPeerId>,
	/// Whether nodes that aren't in [`SetConfig::reserved_nodes`] are accepted or automatically
	/// refused.
	pub non_reserved_mode: NonReservedPeerMode,
}

impl Default for SetConfig {
	fn default() -> Self {
		Self {
			in_peers: 25,
			out_peers: 75,
			reserved_nodes: Vec::new(),
			non_reserved_mode: NonReservedPeerMode::Accept,
		}
	}
}

/// Extension to [`SetConfig`] for sets that aren't the default set.
///
/// > **Note**: As new fields might be added in the future, please consider using the `new` method
/// >			and modifiers instead of creating this struct manually.
#[derive(Clone, Debug)]
pub struct NonDefaultSetConfig {
	/// Name of the notifications protocols of this set. A substream on this set will be
	/// considered established once this protocol is open.
	///
	/// > **Note**: This field isn't present for the default set, as this is handled internally
	/// > by the networking code.
	pub notifications_protocol: Cow<'static, str>,
	/// If the remote reports that it doesn't support the protocol indicated in the
	/// `notifications_protocol` field, then each of these fallback names will be tried one by
	/// one.
	///
	/// If a fallback is used, it will be reported in
	/// [`crate::Event::NotificationStreamOpened::negotiated_fallback`].
	pub fallback_names: Vec<Cow<'static, str>>,
	/// Maximum allowed size of single notifications.
	pub max_notification_size: u64,
	/// Base configuration.
	pub set_config: SetConfig,
}

impl NonDefaultSetConfig {
	/// Creates a new [`NonDefaultSetConfig`]. Zero slots and accepts only reserved nodes.
	pub fn new(notifications_protocol: Cow<'static, str>, max_notification_size: u64) -> Self {
		Self {
			notifications_protocol,
			max_notification_size,
			fallback_names: Vec::new(),
			set_config: SetConfig {
				in_peers: 0,
				out_peers: 0,
				reserved_nodes: Vec::new(),
				non_reserved_mode: NonReservedPeerMode::Deny,
			},
		}
	}

	/// Modifies the configuration to allow non-reserved nodes.
	pub fn allow_non_reserved(&mut self, in_peers: u32, out_peers: u32) {
		self.set_config.in_peers = in_peers;
		self.set_config.out_peers = out_peers;
		self.set_config.non_reserved_mode = NonReservedPeerMode::Accept;
	}

	/// Add a node to the list of reserved nodes.
	pub fn add_reserved(&mut self, peer: MultiaddrWithPeerId) {
		self.set_config.reserved_nodes.push(peer);
	}

	/// Add a list of protocol names used for backward compatibility.
	///
	/// See the explanations in [`NonDefaultSetConfig::fallback_names`].
	pub fn add_fallback_names(&mut self, fallback_names: Vec<Cow<'static, str>>) {
		self.fallback_names.extend(fallback_names);
	}
}

/// Configuration for the transport layer.
#[derive(Clone, Debug)]
pub enum TransportConfig {
	/// Normal transport mode.
	Normal {
		/// If true, the network will use mDNS to discover other libp2p nodes on the local network
		/// and connect to them if they support the same chain.
		enable_mdns: bool,

		/// If true, allow connecting to private IPv4 addresses (as defined in
		/// [RFC1918](https://tools.ietf.org/html/rfc1918)). Irrelevant for addresses that have
		/// been passed in [`NetworkConfiguration::boot_nodes`].
		allow_private_ipv4: bool,
	},

	/// Only allow connections within the same process.
	/// Only addresses of the form `/memory/...` will be supported.
	MemoryOnly,
}

/// The policy for connections to non-reserved peers.
#[derive(Clone, Debug, PartialEq, Eq)]
pub enum NonReservedPeerMode {
	/// Accept them. This is the default.
	Accept,
	/// Deny them.
	Deny,
}

impl NonReservedPeerMode {
	/// Attempt to parse the peer mode from a string.
	pub fn parse(s: &str) -> Option<Self> {
		match s {
			"accept" => Some(Self::Accept),
			"deny" => Some(Self::Deny),
			_ => None,
		}
	}
}

/// The configuration of a node's secret key, describing the type of key
/// and how it is obtained. A node's identity keypair is the result of
/// the evaluation of the node key configuration.
#[derive(Clone, Debug)]
pub enum NodeKeyConfig {
	/// A Ed25519 secret key configuration.
	Ed25519(Secret<ed25519::SecretKey>),
}

impl Default for NodeKeyConfig {
	fn default() -> NodeKeyConfig {
		Self::Ed25519(Secret::New)
	}
}

/// The options for obtaining a Ed25519 secret key.
pub type Ed25519Secret = Secret<ed25519::SecretKey>;

/// The configuration options for obtaining a secret key `K`.
#[derive(Clone)]
pub enum Secret<K> {
	/// Use the given secret key `K`.
	Input(K),
	/// Read the secret key from a file. If the file does not exist,
	/// it is created with a newly generated secret key `K`. The format
	/// of the file is determined by `K`:
	///
	///   * `ed25519::SecretKey`: An unencoded 32 bytes Ed25519 secret key.
	File(PathBuf),
	/// Always generate a new secret key `K`.
	New,
}

impl<K> fmt::Debug for Secret<K> {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
		match self {
			Self::Input(_) => f.debug_tuple("Secret::Input").finish(),
			Self::File(path) => f.debug_tuple("Secret::File").field(path).finish(),
			Self::New => f.debug_tuple("Secret::New").finish(),
		}
	}
}

impl NodeKeyConfig {
	/// Evaluate a `NodeKeyConfig` to obtain an identity `Keypair`:
	///
	///  * If the secret is configured as input, the corresponding keypair is returned.
	///
	///  * If the secret is configured as a file, it is read from that file, if it exists. Otherwise
	///    a new secret is generated and stored. In either case, the keypair obtained from the
	///    secret is returned.
	///
	///  * If the secret is configured to be new, it is generated and the corresponding keypair is
	///    returned.
	pub fn into_keypair(self) -> io::Result<Keypair> {
		use NodeKeyConfig::*;
		match self {
			Ed25519(Secret::New) => Ok(Keypair::generate_ed25519()),

			Ed25519(Secret::Input(k)) => Ok(Keypair::Ed25519(k.into())),

			Ed25519(Secret::File(f)) => get_secret(
				f,
				|mut b| match String::from_utf8(b.to_vec()).ok().and_then(|s| {
					if s.len() == 64 {
						hex::decode(&s).ok()
					} else {
						None
					}
				}) {
					Some(s) => ed25519::SecretKey::from_bytes(s),
					_ => ed25519::SecretKey::from_bytes(&mut b),
				},
				ed25519::SecretKey::generate,
				|b| b.as_ref().to_vec(),
			)
			.map(ed25519::Keypair::from)
			.map(Keypair::Ed25519),
		}
	}
}

/// Load a secret key from a file, if it exists, or generate a
/// new secret key and write it to that file. In either case,
/// the secret key is returned.
fn get_secret<P, F, G, E, W, K>(file: P, parse: F, generate: G, serialize: W) -> io::Result<K>
where
	P: AsRef<Path>,
	F: for<'r> FnOnce(&'r mut [u8]) -> Result<K, E>,
	G: FnOnce() -> K,
	E: Error + Send + Sync + 'static,
	W: Fn(&K) -> Vec<u8>,
{
	std::fs::read(&file)
		.and_then(|mut sk_bytes| {
			parse(&mut sk_bytes).map_err(|e| io::Error::new(io::ErrorKind::InvalidData, e))
		})
		.or_else(|e| {
			if e.kind() == io::ErrorKind::NotFound {
				file.as_ref().parent().map_or(Ok(()), fs::create_dir_all)?;
				let sk = generate();
				let mut sk_vec = serialize(&sk);
				write_secret_file(file, &sk_vec)?;
				sk_vec.zeroize();
				Ok(sk)
			} else {
				Err(e)
			}
		})
}

/// Write secret bytes to a file.
fn write_secret_file<P>(path: P, sk_bytes: &[u8]) -> io::Result<()>
where
	P: AsRef<Path>,
{
	let mut file = open_secret_file(&path)?;
	file.write_all(sk_bytes)
}

/// Opens a file containing a secret key in write mode.
#[cfg(unix)]
fn open_secret_file<P>(path: P) -> io::Result<fs::File>
where
	P: AsRef<Path>,
{
	use std::os::unix::fs::OpenOptionsExt;
	fs::OpenOptions::new().write(true).create_new(true).mode(0o600).open(path)
}

/// Opens a file containing a secret key in write mode.
#[cfg(not(unix))]
fn open_secret_file<P>(path: P) -> Result<fs::File, io::Error>
where
	P: AsRef<Path>,
{
	fs::OpenOptions::new().write(true).create_new(true).open(path)
}

#[cfg(test)]
mod tests {
	use super::*;
	use tempfile::TempDir;

	fn tempdir_with_prefix(prefix: &str) -> TempDir {
		tempfile::Builder::new().prefix(prefix).tempdir().unwrap()
	}

	fn secret_bytes(kp: &Keypair) -> Vec<u8> {
		match kp {
			Keypair::Ed25519(p) => p.secret().as_ref().iter().cloned().collect(),
			Keypair::Secp256k1(p) => p.secret().to_bytes().to_vec(),
			_ => panic!("Unexpected keypair."),
		}
	}

	#[test]
	fn test_secret_file() {
		let tmp = tempdir_with_prefix("x");
		std::fs::remove_dir(tmp.path()).unwrap(); // should be recreated
		let file = tmp.path().join("x").to_path_buf();
		let kp1 = NodeKeyConfig::Ed25519(Secret::File(file.clone())).into_keypair().unwrap();
		let kp2 = NodeKeyConfig::Ed25519(Secret::File(file.clone())).into_keypair().unwrap();
		assert!(file.is_file() && secret_bytes(&kp1) == secret_bytes(&kp2))
	}

	#[test]
	fn test_secret_input() {
		let sk = ed25519::SecretKey::generate();
		let kp1 = NodeKeyConfig::Ed25519(Secret::Input(sk.clone())).into_keypair().unwrap();
		let kp2 = NodeKeyConfig::Ed25519(Secret::Input(sk)).into_keypair().unwrap();
		assert!(secret_bytes(&kp1) == secret_bytes(&kp2));
	}

	#[test]
	fn test_secret_new() {
		let kp1 = NodeKeyConfig::Ed25519(Secret::New).into_keypair().unwrap();
		let kp2 = NodeKeyConfig::Ed25519(Secret::New).into_keypair().unwrap();
		assert!(secret_bytes(&kp1) != secret_bytes(&kp2));
	}
}