staging_xcm/v4/traits.rs
1// Copyright (C) Parity Technologies (UK) Ltd.
2// This file is part of Polkadot.
3
4// Polkadot is free software: you can redistribute it and/or modify
5// it under the terms of the GNU General Public License as published by
6// the Free Software Foundation, either version 3 of the License, or
7// (at your option) any later version.
8
9// Polkadot is distributed in the hope that it will be useful,
10// but WITHOUT ANY WARRANTY; without even the implied warranty of
11// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12// GNU General Public License for more details.
13
14// You should have received a copy of the GNU General Public License
15// along with Polkadot. If not, see <http://www.gnu.org/licenses/>.
16
17//! Cross-Consensus Message format data structures.
18
19pub use crate::v3::{Error, Result, SendError, XcmHash};
20use codec::{Decode, Encode};
21use core::result;
22use scale_info::TypeInfo;
23
24pub use sp_weights::Weight;
25
26use super::*;
27
28/// Outcome of an XCM execution.
29#[derive(Clone, Encode, Decode, Eq, PartialEq, Debug, TypeInfo)]
30pub enum Outcome {
31 /// Execution completed successfully; given weight was used.
32 Complete { used: Weight },
33 /// Execution started, but did not complete successfully due to the given error; given weight
34 /// was used.
35 Incomplete { used: Weight, error: Error },
36 /// Execution did not start due to the given error.
37 Error { error: Error },
38}
39
40impl Outcome {
41 pub fn ensure_complete(self) -> Result {
42 match self {
43 Outcome::Complete { .. } => Ok(()),
44 Outcome::Incomplete { error, .. } => Err(error),
45 Outcome::Error { error, .. } => Err(error),
46 }
47 }
48 pub fn ensure_execution(self) -> result::Result<Weight, Error> {
49 match self {
50 Outcome::Complete { used, .. } => Ok(used),
51 Outcome::Incomplete { used, .. } => Ok(used),
52 Outcome::Error { error, .. } => Err(error),
53 }
54 }
55 /// How much weight was used by the XCM execution attempt.
56 pub fn weight_used(&self) -> Weight {
57 match self {
58 Outcome::Complete { used, .. } => *used,
59 Outcome::Incomplete { used, .. } => *used,
60 Outcome::Error { .. } => Weight::zero(),
61 }
62 }
63}
64
65impl From<Error> for Outcome {
66 fn from(error: Error) -> Self {
67 Self::Error { error }
68 }
69}
70
71pub trait PreparedMessage {
72 fn weight_of(&self) -> Weight;
73}
74
75/// Type of XCM message executor.
76pub trait ExecuteXcm<Call> {
77 type Prepared: PreparedMessage;
78 fn prepare(message: Xcm<Call>) -> result::Result<Self::Prepared, Xcm<Call>>;
79 fn execute(
80 origin: impl Into<Location>,
81 pre: Self::Prepared,
82 id: &mut XcmHash,
83 weight_credit: Weight,
84 ) -> Outcome;
85 fn prepare_and_execute(
86 origin: impl Into<Location>,
87 message: Xcm<Call>,
88 id: &mut XcmHash,
89 weight_limit: Weight,
90 weight_credit: Weight,
91 ) -> Outcome {
92 let pre = match Self::prepare(message) {
93 Ok(x) => x,
94 Err(_) => return Outcome::Error { error: Error::WeightNotComputable },
95 };
96 let xcm_weight = pre.weight_of();
97 if xcm_weight.any_gt(weight_limit) {
98 return Outcome::Error { error: Error::WeightLimitReached(xcm_weight) }
99 }
100 Self::execute(origin, pre, id, weight_credit)
101 }
102
103 /// Deduct some `fees` to the sovereign account of the given `location` and place them as per
104 /// the convention for fees.
105 fn charge_fees(location: impl Into<Location>, fees: Assets) -> Result;
106}
107
108pub enum Weightless {}
109impl PreparedMessage for Weightless {
110 fn weight_of(&self) -> Weight {
111 unreachable!()
112 }
113}
114
115impl<C> ExecuteXcm<C> for () {
116 type Prepared = Weightless;
117 fn prepare(message: Xcm<C>) -> result::Result<Self::Prepared, Xcm<C>> {
118 Err(message)
119 }
120 fn execute(_: impl Into<Location>, _: Self::Prepared, _: &mut XcmHash, _: Weight) -> Outcome {
121 unreachable!()
122 }
123 fn charge_fees(_location: impl Into<Location>, _fees: Assets) -> Result {
124 Err(Error::Unimplemented)
125 }
126}
127
128pub trait Reanchorable: Sized {
129 /// Type to return in case of an error.
130 type Error: Debug;
131
132 /// Mutate `self` so that it represents the same location from the point of view of `target`.
133 /// The context of `self` is provided as `context`.
134 ///
135 /// Does not modify `self` in case of overflow.
136 fn reanchor(
137 &mut self,
138 target: &Location,
139 context: &InteriorLocation,
140 ) -> core::result::Result<(), ()>;
141
142 /// Consume `self` and return a new value representing the same location from the point of view
143 /// of `target`. The context of `self` is provided as `context`.
144 ///
145 /// Returns the original `self` in case of overflow.
146 fn reanchored(
147 self,
148 target: &Location,
149 context: &InteriorLocation,
150 ) -> core::result::Result<Self, Self::Error>;
151}
152
153/// Result value when attempting to send an XCM message.
154pub type SendResult<T> = result::Result<(T, Assets), SendError>;
155
156/// Utility for sending an XCM message to a given location.
157///
158/// These can be amalgamated in tuples to form sophisticated routing systems. In tuple format, each
159/// router might return `NotApplicable` to pass the execution to the next sender item. Note that
160/// each `NotApplicable` might alter the destination and the XCM message for to the next router.
161///
162/// # Example
163/// ```rust
164/// # use codec::Encode;
165/// # use staging_xcm::v4::{prelude::*, Weight};
166/// # use staging_xcm::VersionedXcm;
167/// # use std::convert::Infallible;
168///
169/// /// A sender that only passes the message through and does nothing.
170/// struct Sender1;
171/// impl SendXcm for Sender1 {
172/// type Ticket = Infallible;
173/// fn validate(_: &mut Option<Location>, _: &mut Option<Xcm<()>>) -> SendResult<Infallible> {
174/// Err(SendError::NotApplicable)
175/// }
176/// fn deliver(_: Infallible) -> Result<XcmHash, SendError> {
177/// unreachable!()
178/// }
179/// }
180///
181/// /// A sender that accepts a message that has two junctions, otherwise stops the routing.
182/// struct Sender2;
183/// impl SendXcm for Sender2 {
184/// type Ticket = ();
185/// fn validate(destination: &mut Option<Location>, message: &mut Option<Xcm<()>>) -> SendResult<()> {
186/// match destination.as_ref().ok_or(SendError::MissingArgument)?.unpack() {
187/// (0, [j1, j2]) => Ok(((), Assets::new())),
188/// _ => Err(SendError::Unroutable),
189/// }
190/// }
191/// fn deliver(_: ()) -> Result<XcmHash, SendError> {
192/// Ok([0; 32])
193/// }
194/// }
195///
196/// /// A sender that accepts a message from a parent, passing through otherwise.
197/// struct Sender3;
198/// impl SendXcm for Sender3 {
199/// type Ticket = ();
200/// fn validate(destination: &mut Option<Location>, message: &mut Option<Xcm<()>>) -> SendResult<()> {
201/// match destination.as_ref().ok_or(SendError::MissingArgument)?.unpack() {
202/// (1, []) => Ok(((), Assets::new())),
203/// _ => Err(SendError::NotApplicable),
204/// }
205/// }
206/// fn deliver(_: ()) -> Result<XcmHash, SendError> {
207/// Ok([0; 32])
208/// }
209/// }
210///
211/// // A call to send via XCM. We don't really care about this.
212/// # fn main() {
213/// let call: Vec<u8> = ().encode();
214/// let message = Xcm(vec![Instruction::Transact {
215/// origin_kind: OriginKind::Superuser,
216/// require_weight_at_most: Weight::zero(),
217/// call: call.into(),
218/// }]);
219/// let message_hash = message.using_encoded(sp_io::hashing::blake2_256);
220///
221/// // Sender2 will block this.
222/// assert!(send_xcm::<(Sender1, Sender2, Sender3)>(Parent.into(), message.clone()).is_err());
223///
224/// // Sender3 will catch this.
225/// assert!(send_xcm::<(Sender1, Sender3)>(Parent.into(), message.clone()).is_ok());
226/// # }
227/// ```
228pub trait SendXcm {
229 /// Intermediate value which connects the two phases of the send operation.
230 type Ticket;
231
232 /// Check whether the given `_message` is deliverable to the given `_destination` and if so
233 /// determine the cost which will be paid by this chain to do so, returning a `Validated` token
234 /// which can be used to enact delivery.
235 ///
236 /// The `destination` and `message` must be `Some` (or else an error will be returned) and they
237 /// may only be consumed if the `Err` is not `NotApplicable`.
238 ///
239 /// If it is not a destination which can be reached with this type but possibly could by others,
240 /// then this *MUST* return `NotApplicable`. Any other error will cause the tuple
241 /// implementation to exit early without trying other type fields.
242 fn validate(
243 destination: &mut Option<Location>,
244 message: &mut Option<Xcm<()>>,
245 ) -> SendResult<Self::Ticket>;
246
247 /// Actually carry out the delivery operation for a previously validated message sending.
248 fn deliver(ticket: Self::Ticket) -> result::Result<XcmHash, SendError>;
249}
250
251#[impl_trait_for_tuples::impl_for_tuples(30)]
252impl SendXcm for Tuple {
253 for_tuples! { type Ticket = (#( Option<Tuple::Ticket> ),* ); }
254
255 fn validate(
256 destination: &mut Option<Location>,
257 message: &mut Option<Xcm<()>>,
258 ) -> SendResult<Self::Ticket> {
259 let mut maybe_cost: Option<Assets> = None;
260 let one_ticket: Self::Ticket = (for_tuples! { #(
261 if maybe_cost.is_some() {
262 None
263 } else {
264 match Tuple::validate(destination, message) {
265 Err(SendError::NotApplicable) => None,
266 Err(e) => { return Err(e) },
267 Ok((v, c)) => {
268 maybe_cost = Some(c);
269 Some(v)
270 },
271 }
272 }
273 ),* });
274 if let Some(cost) = maybe_cost {
275 Ok((one_ticket, cost))
276 } else {
277 Err(SendError::NotApplicable)
278 }
279 }
280
281 fn deliver(one_ticket: Self::Ticket) -> result::Result<XcmHash, SendError> {
282 for_tuples!( #(
283 if let Some(validated) = one_ticket.Tuple {
284 return Tuple::deliver(validated);
285 }
286 )* );
287 Err(SendError::Unroutable)
288 }
289}
290
291/// Convenience function for using a `SendXcm` implementation. Just interprets the `dest` and wraps
292/// both in `Some` before passing them as mutable references into `T::send_xcm`.
293pub fn validate_send<T: SendXcm>(dest: Location, msg: Xcm<()>) -> SendResult<T::Ticket> {
294 T::validate(&mut Some(dest), &mut Some(msg))
295}
296
297/// Convenience function for using a `SendXcm` implementation. Just interprets the `dest` and wraps
298/// both in `Some` before passing them as mutable references into `T::send_xcm`.
299///
300/// Returns either `Ok` with the price of the delivery, or `Err` with the reason why the message
301/// could not be sent.
302///
303/// Generally you'll want to validate and get the price first to ensure that the sender can pay it
304/// before actually doing the delivery.
305pub fn send_xcm<T: SendXcm>(
306 dest: Location,
307 msg: Xcm<()>,
308) -> result::Result<(XcmHash, Assets), SendError> {
309 let (ticket, price) = T::validate(&mut Some(dest), &mut Some(msg))?;
310 let hash = T::deliver(ticket)?;
311 Ok((hash, price))
312}