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// Copyright (C) Parity Technologies (UK) Ltd.
// This file is part of Polkadot.
// Polkadot 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.
// Polkadot 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 Polkadot. If not, see <http://www.gnu.org/licenses/>.
//! Cross-Consensus Message format data structures.
use crate::v2::Error as OldError;
use codec::{Decode, Encode, MaxEncodedLen};
use core::result;
use scale_info::TypeInfo;
pub use sp_weights::Weight;
use super::*;
// A simple trait to get the weight of some object.
pub trait GetWeight<W> {
fn weight(&self) -> sp_weights::Weight;
}
/// Error codes used in XCM. The first errors codes have explicit indices and are part of the XCM
/// format. Those trailing are merely part of the XCM implementation; there is no expectation that
/// they will retain the same index over time.
#[derive(Copy, Clone, Encode, Decode, Eq, PartialEq, Debug, TypeInfo)]
#[scale_info(replace_segment("staging_xcm", "xcm"))]
#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
pub enum Error {
// Errors that happen due to instructions being executed. These alone are defined in the
// XCM specification.
/// An arithmetic overflow happened.
#[codec(index = 0)]
Overflow,
/// The instruction is intentionally unsupported.
#[codec(index = 1)]
Unimplemented,
/// Origin Register does not contain a value value for a reserve transfer notification.
#[codec(index = 2)]
UntrustedReserveLocation,
/// Origin Register does not contain a value value for a teleport notification.
#[codec(index = 3)]
UntrustedTeleportLocation,
/// `MultiLocation` value too large to descend further.
#[codec(index = 4)]
LocationFull,
/// `MultiLocation` value ascend more parents than known ancestors of local location.
#[codec(index = 5)]
LocationNotInvertible,
/// The Origin Register does not contain a valid value for instruction.
#[codec(index = 6)]
BadOrigin,
/// The location parameter is not a valid value for the instruction.
#[codec(index = 7)]
InvalidLocation,
/// The given asset is not handled.
#[codec(index = 8)]
AssetNotFound,
/// An asset transaction (like withdraw or deposit) failed (typically due to type conversions).
#[codec(index = 9)]
FailedToTransactAsset(#[codec(skip)] &'static str),
/// An asset cannot be withdrawn, potentially due to lack of ownership, availability or rights.
#[codec(index = 10)]
NotWithdrawable,
/// An asset cannot be deposited under the ownership of a particular location.
#[codec(index = 11)]
LocationCannotHold,
/// Attempt to send a message greater than the maximum supported by the transport protocol.
#[codec(index = 12)]
ExceedsMaxMessageSize,
/// The given message cannot be translated into a format supported by the destination.
#[codec(index = 13)]
DestinationUnsupported,
/// Destination is routable, but there is some issue with the transport mechanism.
#[codec(index = 14)]
Transport(#[codec(skip)] &'static str),
/// Destination is known to be unroutable.
#[codec(index = 15)]
Unroutable,
/// Used by `ClaimAsset` when the given claim could not be recognized/found.
#[codec(index = 16)]
UnknownClaim,
/// Used by `Transact` when the functor cannot be decoded.
#[codec(index = 17)]
FailedToDecode,
/// Used by `Transact` to indicate that the given weight limit could be breached by the
/// functor.
#[codec(index = 18)]
MaxWeightInvalid,
/// Used by `BuyExecution` when the Holding Register does not contain payable fees.
#[codec(index = 19)]
NotHoldingFees,
/// Used by `BuyExecution` when the fees declared to purchase weight are insufficient.
#[codec(index = 20)]
TooExpensive,
/// Used by the `Trap` instruction to force an error intentionally. Its code is included.
#[codec(index = 21)]
Trap(u64),
/// Used by `ExpectAsset`, `ExpectError` and `ExpectOrigin` when the expectation was not true.
#[codec(index = 22)]
ExpectationFalse,
/// The provided pallet index was not found.
#[codec(index = 23)]
PalletNotFound,
/// The given pallet's name is different to that expected.
#[codec(index = 24)]
NameMismatch,
/// The given pallet's version has an incompatible version to that expected.
#[codec(index = 25)]
VersionIncompatible,
/// The given operation would lead to an overflow of the Holding Register.
#[codec(index = 26)]
HoldingWouldOverflow,
/// The message was unable to be exported.
#[codec(index = 27)]
ExportError,
/// `MultiLocation` value failed to be reanchored.
#[codec(index = 28)]
ReanchorFailed,
/// No deal is possible under the given constraints.
#[codec(index = 29)]
NoDeal,
/// Fees were required which the origin could not pay.
#[codec(index = 30)]
FeesNotMet,
/// Some other error with locking.
#[codec(index = 31)]
LockError,
/// The state was not in a condition where the operation was valid to make.
#[codec(index = 32)]
NoPermission,
/// The universal location of the local consensus is improper.
#[codec(index = 33)]
Unanchored,
/// An asset cannot be deposited, probably because (too much of) it already exists.
#[codec(index = 34)]
NotDepositable,
// Errors that happen prior to instructions being executed. These fall outside of the XCM
// spec.
/// XCM version not able to be handled.
UnhandledXcmVersion,
/// Execution of the XCM would potentially result in a greater weight used than weight limit.
WeightLimitReached(Weight),
/// The XCM did not pass the barrier condition for execution.
///
/// The barrier condition differs on different chains and in different circumstances, but
/// generally it means that the conditions surrounding the message were not such that the chain
/// considers the message worth spending time executing. Since most chains lift the barrier to
/// execution on appropriate payment, presentation of an NFT voucher, or based on the message
/// origin, it means that none of those were the case.
Barrier,
/// The weight of an XCM message is not computable ahead of execution.
WeightNotComputable,
/// Recursion stack limit reached
ExceedsStackLimit,
}
impl MaxEncodedLen for Error {
fn max_encoded_len() -> usize {
// TODO: max_encoded_len doesn't quite work here as it tries to take notice of the fields
// marked `codec(skip)`. We can hard-code it with the right answer for now.
1
}
}
impl TryFrom<OldError> for Error {
type Error = ();
fn try_from(old_error: OldError) -> result::Result<Error, ()> {
use OldError::*;
Ok(match old_error {
Overflow => Self::Overflow,
Unimplemented => Self::Unimplemented,
UntrustedReserveLocation => Self::UntrustedReserveLocation,
UntrustedTeleportLocation => Self::UntrustedTeleportLocation,
MultiLocationFull => Self::LocationFull,
MultiLocationNotInvertible => Self::LocationNotInvertible,
BadOrigin => Self::BadOrigin,
InvalidLocation => Self::InvalidLocation,
AssetNotFound => Self::AssetNotFound,
FailedToTransactAsset(s) => Self::FailedToTransactAsset(s),
NotWithdrawable => Self::NotWithdrawable,
LocationCannotHold => Self::LocationCannotHold,
ExceedsMaxMessageSize => Self::ExceedsMaxMessageSize,
DestinationUnsupported => Self::DestinationUnsupported,
Transport(s) => Self::Transport(s),
Unroutable => Self::Unroutable,
UnknownClaim => Self::UnknownClaim,
FailedToDecode => Self::FailedToDecode,
MaxWeightInvalid => Self::MaxWeightInvalid,
NotHoldingFees => Self::NotHoldingFees,
TooExpensive => Self::TooExpensive,
Trap(i) => Self::Trap(i),
_ => return Err(()),
})
}
}
impl From<SendError> for Error {
fn from(e: SendError) -> Self {
match e {
SendError::NotApplicable | SendError::Unroutable | SendError::MissingArgument =>
Error::Unroutable,
SendError::Transport(s) => Error::Transport(s),
SendError::DestinationUnsupported => Error::DestinationUnsupported,
SendError::ExceedsMaxMessageSize => Error::ExceedsMaxMessageSize,
SendError::Fees => Error::FeesNotMet,
}
}
}
pub type Result = result::Result<(), Error>;
/// Outcome of an XCM execution.
#[derive(Clone, Encode, Decode, Eq, PartialEq, Debug, TypeInfo)]
#[scale_info(replace_segment("staging_xcm", "xcm"))]
pub enum Outcome {
/// Execution completed successfully; given weight was used.
Complete(Weight),
/// Execution started, but did not complete successfully due to the given error; given weight
/// was used.
Incomplete(Weight, Error),
/// Execution did not start due to the given error.
Error(Error),
}
impl Outcome {
pub fn ensure_complete(self) -> result::Result<Weight, Error> {
match self {
Outcome::Complete(weight) => Ok(weight),
Outcome::Incomplete(_, e) => Err(e),
Outcome::Error(e) => Err(e),
}
}
pub fn ensure_execution(self) -> result::Result<Weight, Error> {
match self {
Outcome::Complete(w) => Ok(w),
Outcome::Incomplete(w, _) => Ok(w),
Outcome::Error(e) => Err(e),
}
}
/// How much weight was used by the XCM execution attempt.
pub fn weight_used(&self) -> Weight {
match self {
Outcome::Complete(w) => *w,
Outcome::Incomplete(w, _) => *w,
Outcome::Error(_) => Weight::zero(),
}
}
}
pub trait PreparedMessage {
fn weight_of(&self) -> Weight;
}
/// Type of XCM message executor.
pub trait ExecuteXcm<Call> {
type Prepared: PreparedMessage;
fn prepare(message: Xcm<Call>) -> result::Result<Self::Prepared, Xcm<Call>>;
fn execute(
origin: impl Into<MultiLocation>,
pre: Self::Prepared,
id: &mut XcmHash,
weight_credit: Weight,
) -> Outcome;
fn prepare_and_execute(
origin: impl Into<MultiLocation>,
message: Xcm<Call>,
id: &mut XcmHash,
weight_limit: Weight,
weight_credit: Weight,
) -> Outcome {
let pre = match Self::prepare(message) {
Ok(x) => x,
Err(_) => return Outcome::Error(Error::WeightNotComputable),
};
let xcm_weight = pre.weight_of();
if xcm_weight.any_gt(weight_limit) {
return Outcome::Error(Error::WeightLimitReached(xcm_weight))
}
Self::execute(origin, pre, id, weight_credit)
}
/// Execute some XCM `message` with the message `hash` from `origin` using no more than
/// `weight_limit` weight.
///
/// The weight limit is a basic hard-limit and the implementation may place further
/// restrictions or requirements on weight and other aspects.
fn execute_xcm(
origin: impl Into<MultiLocation>,
message: Xcm<Call>,
hash: XcmHash,
weight_limit: Weight,
) -> Outcome {
let origin = origin.into();
log::debug!(
target: "xcm::execute_xcm",
"origin: {:?}, message: {:?}, weight_limit: {:?}",
origin,
message,
weight_limit,
);
Self::execute_xcm_in_credit(origin, message, hash, weight_limit, Weight::zero())
}
/// Execute some XCM `message` with the message `hash` from `origin` using no more than
/// `weight_limit` weight.
///
/// Some amount of `weight_credit` may be provided which, depending on the implementation, may
/// allow execution without associated payment.
fn execute_xcm_in_credit(
origin: impl Into<MultiLocation>,
message: Xcm<Call>,
mut hash: XcmHash,
weight_limit: Weight,
weight_credit: Weight,
) -> Outcome {
let pre = match Self::prepare(message) {
Ok(x) => x,
Err(_) => return Outcome::Error(Error::WeightNotComputable),
};
let xcm_weight = pre.weight_of();
if xcm_weight.any_gt(weight_limit) {
return Outcome::Error(Error::WeightLimitReached(xcm_weight))
}
Self::execute(origin, pre, &mut hash, weight_credit)
}
/// Deduct some `fees` to the sovereign account of the given `location` and place them as per
/// the convention for fees.
fn charge_fees(location: impl Into<MultiLocation>, fees: MultiAssets) -> Result;
}
pub enum Weightless {}
impl PreparedMessage for Weightless {
fn weight_of(&self) -> Weight {
unreachable!()
}
}
impl<C> ExecuteXcm<C> for () {
type Prepared = Weightless;
fn prepare(message: Xcm<C>) -> result::Result<Self::Prepared, Xcm<C>> {
Err(message)
}
fn execute(
_: impl Into<MultiLocation>,
_: Self::Prepared,
_: &mut XcmHash,
_: Weight,
) -> Outcome {
unreachable!()
}
fn charge_fees(_location: impl Into<MultiLocation>, _fees: MultiAssets) -> Result {
Err(Error::Unimplemented)
}
}
/// Error result value when attempting to send an XCM message.
#[derive(Clone, Encode, Decode, Eq, PartialEq, Debug, scale_info::TypeInfo)]
#[scale_info(replace_segment("staging_xcm", "xcm"))]
pub enum SendError {
/// The message and destination combination was not recognized as being reachable.
///
/// This is not considered fatal: if there are alternative transport routes available, then
/// they may be attempted.
NotApplicable,
/// Destination is routable, but there is some issue with the transport mechanism. This is
/// considered fatal.
/// A human-readable explanation of the specific issue is provided.
Transport(#[codec(skip)] &'static str),
/// Destination is known to be unroutable. This is considered fatal.
Unroutable,
/// The given message cannot be translated into a format that the destination can be expected
/// to interpret.
DestinationUnsupported,
/// Message could not be sent due to its size exceeding the maximum allowed by the transport
/// layer.
ExceedsMaxMessageSize,
/// A needed argument is `None` when it should be `Some`.
MissingArgument,
/// Fees needed to be paid in order to send the message and they were unavailable.
Fees,
}
/// A hash type for identifying messages.
pub type XcmHash = [u8; 32];
/// Result value when attempting to send an XCM message.
pub type SendResult<T> = result::Result<(T, MultiAssets), SendError>;
/// Utility for sending an XCM message to a given location.
///
/// These can be amalgamated in tuples to form sophisticated routing systems. In tuple format, each
/// router might return `NotApplicable` to pass the execution to the next sender item. Note that
/// each `NotApplicable` might alter the destination and the XCM message for to the next router.
///
/// # Example
/// ```rust
/// # use codec::Encode;
/// # use staging_xcm::v3::{prelude::*, Weight};
/// # use staging_xcm::VersionedXcm;
/// # use std::convert::Infallible;
///
/// /// A sender that only passes the message through and does nothing.
/// struct Sender1;
/// impl SendXcm for Sender1 {
/// type Ticket = Infallible;
/// fn validate(_: &mut Option<MultiLocation>, _: &mut Option<Xcm<()>>) -> SendResult<Infallible> {
/// Err(SendError::NotApplicable)
/// }
/// fn deliver(_: Infallible) -> Result<XcmHash, SendError> {
/// unreachable!()
/// }
/// }
///
/// /// A sender that accepts a message that has an X2 junction, otherwise stops the routing.
/// struct Sender2;
/// impl SendXcm for Sender2 {
/// type Ticket = ();
/// fn validate(destination: &mut Option<MultiLocation>, message: &mut Option<Xcm<()>>) -> SendResult<()> {
/// match destination.as_ref().ok_or(SendError::MissingArgument)? {
/// MultiLocation { parents: 0, interior: X2(j1, j2) } => Ok(((), MultiAssets::new())),
/// _ => Err(SendError::Unroutable),
/// }
/// }
/// fn deliver(_: ()) -> Result<XcmHash, SendError> {
/// Ok([0; 32])
/// }
/// }
///
/// /// A sender that accepts a message from a parent, passing through otherwise.
/// struct Sender3;
/// impl SendXcm for Sender3 {
/// type Ticket = ();
/// fn validate(destination: &mut Option<MultiLocation>, message: &mut Option<Xcm<()>>) -> SendResult<()> {
/// match destination.as_ref().ok_or(SendError::MissingArgument)? {
/// MultiLocation { parents: 1, interior: Here } => Ok(((), MultiAssets::new())),
/// _ => Err(SendError::NotApplicable),
/// }
/// }
/// fn deliver(_: ()) -> Result<XcmHash, SendError> {
/// Ok([0; 32])
/// }
/// }
///
/// // A call to send via XCM. We don't really care about this.
/// # fn main() {
/// let call: Vec<u8> = ().encode();
/// let message = Xcm(vec![Instruction::Transact {
/// origin_kind: OriginKind::Superuser,
/// require_weight_at_most: Weight::zero(),
/// call: call.into(),
/// }]);
/// let message_hash = message.using_encoded(sp_io::hashing::blake2_256);
///
/// // Sender2 will block this.
/// assert!(send_xcm::<(Sender1, Sender2, Sender3)>(Parent.into(), message.clone()).is_err());
///
/// // Sender3 will catch this.
/// assert!(send_xcm::<(Sender1, Sender3)>(Parent.into(), message.clone()).is_ok());
/// # }
/// ```
pub trait SendXcm {
/// Intermediate value which connects the two phases of the send operation.
type Ticket;
/// Check whether the given `message` is deliverable to the given `destination` and if so
/// determine the cost which will be paid by this chain to do so, returning a `Validated` token
/// which can be used to enact delivery.
///
/// The `destination` and `message` must be `Some` (or else an error will be returned) and they
/// may only be consumed if the `Err` is not `NotApplicable`.
///
/// If it is not a destination which can be reached with this type but possibly could by others,
/// then this *MUST* return `NotApplicable`. Any other error will cause the tuple
/// implementation to exit early without trying other type fields.
fn validate(
destination: &mut Option<MultiLocation>,
message: &mut Option<Xcm<()>>,
) -> SendResult<Self::Ticket>;
/// Actually carry out the delivery operation for a previously validated message sending.
fn deliver(ticket: Self::Ticket) -> result::Result<XcmHash, SendError>;
}
#[impl_trait_for_tuples::impl_for_tuples(30)]
impl SendXcm for Tuple {
for_tuples! { type Ticket = (#( Option<Tuple::Ticket> ),* ); }
fn validate(
destination: &mut Option<MultiLocation>,
message: &mut Option<Xcm<()>>,
) -> SendResult<Self::Ticket> {
let mut maybe_cost: Option<MultiAssets> = None;
let one_ticket: Self::Ticket = (for_tuples! { #(
if maybe_cost.is_some() {
None
} else {
match Tuple::validate(destination, message) {
Err(SendError::NotApplicable) => None,
Err(e) => { return Err(e) },
Ok((v, c)) => {
maybe_cost = Some(c);
Some(v)
},
}
}
),* });
if let Some(cost) = maybe_cost {
Ok((one_ticket, cost))
} else {
Err(SendError::NotApplicable)
}
}
fn deliver(one_ticket: Self::Ticket) -> result::Result<XcmHash, SendError> {
for_tuples!( #(
if let Some(validated) = one_ticket.Tuple {
return Tuple::deliver(validated);
}
)* );
Err(SendError::Unroutable)
}
}
/// Convenience function for using a `SendXcm` implementation. Just interprets the `dest` and wraps
/// both in `Some` before passing them as as mutable references into `T::send_xcm`.
pub fn validate_send<T: SendXcm>(dest: MultiLocation, msg: Xcm<()>) -> SendResult<T::Ticket> {
T::validate(&mut Some(dest), &mut Some(msg))
}
/// Convenience function for using a `SendXcm` implementation. Just interprets the `dest` and wraps
/// both in `Some` before passing them as as mutable references into `T::send_xcm`.
///
/// Returns either `Ok` with the price of the delivery, or `Err` with the reason why the message
/// could not be sent.
///
/// Generally you'll want to validate and get the price first to ensure that the sender can pay it
/// before actually doing the delivery.
pub fn send_xcm<T: SendXcm>(
dest: MultiLocation,
msg: Xcm<()>,
) -> result::Result<(XcmHash, MultiAssets), SendError> {
let (ticket, price) = T::validate(&mut Some(dest), &mut Some(msg))?;
let hash = T::deliver(ticket)?;
Ok((hash, price))
}