Claim funds on Substrate chain by providing proof of funds locking on PoA chain (#91)

* ethereum exchange module

* continue

* continue

* added tests for exchange module

* moved

* remove println

* move again

* fixes

* removed redundant deps

* cargo fmt

* fund_locks_transaction_decode_works

* cargo fmt --all

* fix error processing

* added some tracing to bridge modules

* more tests

* more tests

* cargo fmt --all

* kovan.rs -> exchange.rs

* Update bin/node/runtime/src/exchange.rs

Co-authored-by: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* added assumption doc

* Airdrop -> DepositInto

* AsIs -> Identity

* OnTransactionSubmitted

* Transfers::Key = Id

* typo

* Update bin/node/runtime/src/exchange.rs

Co-authored-by: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* block+tx+proof -> proof { block, tx, proof }

* cargo fmt --all

* docs

* check <-> verify

* parse hex

* extracted exchange primitives to separate crate

* added docs to runtime::exchange module

* Update bin/node/runtime/src/exchange.rs

Co-authored-by: Hernando Castano <HCastano@users.noreply.github.com>

* typo

* Update modules/currency-exchange/Cargo.toml

Co-authored-by: Hernando Castano <HCastano@users.noreply.github.com>

* add docs to currency-exchange module

* change tests names

* cargo fmt --all

* Update bin/node/runtime/src/exchange.rs

Co-authored-by: Hernando Castano <HCastano@users.noreply.github.com>

* Update bin/node/runtime/src/exchange.rs

Co-authored-by: Hernando Castano <HCastano@users.noreply.github.com>

* Update bin/node/runtime/src/exchange.rs

Co-authored-by: Hernando Castano <HCastano@users.noreply.github.com>

* Update bin/node/runtime/src/exchange.rs

Co-authored-by: Hernando Castano <HCastano@users.noreply.github.com>

* Update bin/node/runtime/src/exchange.rs

Co-authored-by: Hernando Castano <HCastano@users.noreply.github.com>

* fixed verify_transaction_finalized for siblings of finalized blocks

* cargo fmt --all

* added double spend note

* cargo fmt --all

Co-authored-by: Tomasz Drwięga <tomusdrw@users.noreply.github.com>
Co-authored-by: Hernando Castano <HCastano@users.noreply.github.com>

bridges/primitives/currency-exchange/src/lib.rs

@@ -0,0 +1,127 @@
+// Copyright 2019-2020 Parity Technologies (UK) Ltd.
+// This file is part of Parity Bridges Common.
+
+// Parity Bridges Common 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 Bridges Common 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 Bridges Common.  If not, see <http://www.gnu.org/licenses/>.
+
+#![cfg_attr(not(feature = "std"), no_std)]
+
+use codec::{Decode, Encode, EncodeLike};
+use frame_support::RuntimeDebug;
+use sp_std::marker::PhantomData;
+
+/// All errors that may happen during exchange.
+#[derive(RuntimeDebug, PartialEq)]
+pub enum Error {
+	/// Invalid peer blockchain transaction provided.
+	InvalidTransaction,
+	/// Peer transaction has invalid amount.
+	InvalidAmount,
+	/// Peer transaction has invalid recipient.
+	InvalidRecipient,
+	/// Cannot map from peer recipient to this blockchain recipient.
+	FailedToMapRecipients,
+	/// Failed to convert from peer blockchain currency to this blockhain currency.
+	FailedToConvertCurrency,
+	/// Deposit has failed.
+	DepositFailed,
+}
+
+/// Result of all exchange operations.
+pub type Result<T> = sp_std::result::Result<T, Error>;
+
+/// Peer blockchain lock funds transaction.
+#[derive(Encode, Decode, Clone, RuntimeDebug, PartialEq, Eq)]
+pub struct LockFundsTransaction<TransferId, Recipient, Amount> {
+	/// Something that uniquely identifies this transfer.
+	pub id: TransferId,
+	/// Funds recipient on the peer chain.
+	pub recipient: Recipient,
+	/// Amount of the locked funds.
+	pub amount: Amount,
+}
+
+/// Peer blockchain transaction that may represent lock funds transaction.
+pub trait MaybeLockFundsTransaction {
+	/// Transaction type.
+	type Transaction;
+	/// Identifier that uniquely identifies this transfer.
+	type Id: Decode + Encode + EncodeLike;
+	/// Peer recipient type.
+	type Recipient;
+	/// Peer currency amount type.
+	type Amount;
+
+	/// Parse lock funds transaction of the peer blockchain. Returns None if
+	/// transaction format is unknown, or it isn't a lock funds transaction.
+	fn parse(tx: &Self::Transaction) -> Result<LockFundsTransaction<Self::Id, Self::Recipient, Self::Amount>>;
+}
+
+/// Map that maps recipients from peer blockchain to this blockchain recipients.
+pub trait RecipientsMap {
+	/// Peer blockchain recipient type.
+	type PeerRecipient;
+	/// Current blockchain recipient type.
+	type Recipient;
+
+	/// Lookup current blockchain recipient by peer blockchain recipient.
+	fn map(peer_recipient: Self::PeerRecipient) -> Result<Self::Recipient>;
+}
+
+/// Conversion between two currencies.
+pub trait CurrencyConverter {
+	/// Type of the source currency amount.
+	type SourceAmount;
+	/// Type of the target currency amount.
+	type TargetAmount;
+
+	/// Covert from source to target currency.
+	fn convert(amount: Self::SourceAmount) -> Result<Self::TargetAmount>;
+}
+
+/// Currency deposit.
+pub trait DepositInto {
+	/// Recipient type.
+	type Recipient;
+	/// Currency amount type.
+	type Amount;
+
+	/// Grant some money to given account.
+	fn deposit_into(recipient: Self::Recipient, amount: Self::Amount) -> Result<()>;
+}
+
+/// Recipients map which is used when accounts ids are the same on both chains.
+#[derive(Debug)]
+pub struct IdentityRecipients<AccountId>(PhantomData<AccountId>);
+
+impl<AccountId> RecipientsMap for IdentityRecipients<AccountId> {
+	type PeerRecipient = AccountId;
+	type Recipient = AccountId;
+
+	fn map(peer_recipient: Self::PeerRecipient) -> Result<Self::Recipient> {
+		Ok(peer_recipient)
+	}
+}
+
+/// Currency converter which is used when currency is the same on both chains.
+#[derive(Debug)]
+pub struct IdentityCurrencyConverter<Amount>(PhantomData<Amount>);
+
+impl<Amount> CurrencyConverter for IdentityCurrencyConverter<Amount> {
+	type SourceAmount = Amount;
+	type TargetAmount = Amount;
+
+	fn convert(currency: Self::SourceAmount) -> Result<Self::TargetAmount> {
+		Ok(currency)
+	}
+}