1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141

// 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/>.

//! Various implementations for `SendXcm`.

use frame_system::unique;
use parity_scale_codec::Encode;
use sp_std::{marker::PhantomData, result::Result};
use xcm::prelude::*;
use xcm_executor::{traits::FeeReason, FeesMode};

/// Wrapper router which, if the message does not already end with a `SetTopic` instruction,
/// appends one to the message filled with a universally unique ID. This ID is returned from a
/// successful `deliver`.
///
/// If the message does already end with a `SetTopic` instruction, then it is the responsibility
/// of the code author to ensure that the ID supplied to `SetTopic` is universally unique. Due to
/// this property, consumers of the topic ID must be aware that a user-supplied ID may not be
/// unique.
///
/// This is designed to be at the top-level of any routers, since it will always mutate the
/// passed `message` reference into a `None`. Don't try to combine it within a tuple except as the
/// last element.
pub struct WithUniqueTopic<Inner>(PhantomData<Inner>);
impl<Inner: SendXcm> SendXcm for WithUniqueTopic<Inner> {
	type Ticket = (Inner::Ticket, [u8; 32]);

	fn validate(
		destination: &mut Option<Location>,
		message: &mut Option<Xcm<()>>,
	) -> SendResult<Self::Ticket> {
		let mut message = message.take().ok_or(SendError::MissingArgument)?;
		let unique_id = if let Some(SetTopic(id)) = message.last() {
			*id
		} else {
			let unique_id = unique(&message);
			message.0.push(SetTopic(unique_id));
			unique_id
		};
		let (ticket, assets) = Inner::validate(destination, &mut Some(message))?;
		Ok(((ticket, unique_id), assets))
	}

	fn deliver(ticket: Self::Ticket) -> Result<XcmHash, SendError> {
		let (ticket, unique_id) = ticket;
		Inner::deliver(ticket)?;
		Ok(unique_id)
	}
}

pub trait SourceTopic {
	fn source_topic(entropy: impl Encode) -> XcmHash;
}

impl SourceTopic for () {
	fn source_topic(_: impl Encode) -> XcmHash {
		[0u8; 32]
	}
}

/// Wrapper router which, if the message does not already end with a `SetTopic` instruction,
/// prepends one to the message filled with an ID from `TopicSource`. This ID is returned from a
/// successful `deliver`.
///
/// This is designed to be at the top-level of any routers, since it will always mutate the
/// passed `message` reference into a `None`. Don't try to combine it within a tuple except as the
/// last element.
pub struct WithTopicSource<Inner, TopicSource>(PhantomData<(Inner, TopicSource)>);
impl<Inner: SendXcm, TopicSource: SourceTopic> SendXcm for WithTopicSource<Inner, TopicSource> {
	type Ticket = (Inner::Ticket, [u8; 32]);

	fn validate(
		destination: &mut Option<Location>,
		message: &mut Option<Xcm<()>>,
	) -> SendResult<Self::Ticket> {
		let mut message = message.take().ok_or(SendError::MissingArgument)?;
		let unique_id = if let Some(SetTopic(id)) = message.last() {
			*id
		} else {
			let unique_id = TopicSource::source_topic(&message);
			message.0.push(SetTopic(unique_id));
			unique_id
		};
		let (ticket, assets) = Inner::validate(destination, &mut Some(message))
			.map_err(|_| SendError::NotApplicable)?;
		Ok(((ticket, unique_id), assets))
	}

	fn deliver(ticket: Self::Ticket) -> Result<XcmHash, SendError> {
		let (ticket, unique_id) = ticket;
		Inner::deliver(ticket)?;
		Ok(unique_id)
	}
}

/// Trait for a type which ensures all requirements for successful delivery with XCM transport
/// layers.
pub trait EnsureDelivery {
	/// Prepare all requirements for successful `XcmSender: SendXcm` passing (accounts, balances,
	/// channels ...). Returns:
	/// - possible `FeesMode` which is expected to be set to executor
	/// - possible `Assets` which are expected to be subsume to the Holding Register
	fn ensure_successful_delivery(
		origin_ref: &Location,
		dest: &Location,
		fee_reason: FeeReason,
	) -> (Option<FeesMode>, Option<Assets>);
}

/// Tuple implementation for `EnsureDelivery`.
#[impl_trait_for_tuples::impl_for_tuples(30)]
impl EnsureDelivery for Tuple {
	fn ensure_successful_delivery(
		origin_ref: &Location,
		dest: &Location,
		fee_reason: FeeReason,
	) -> (Option<FeesMode>, Option<Assets>) {
		for_tuples!( #(
			// If the implementation returns something, we're done; if not, let others try.
			match Tuple::ensure_successful_delivery(origin_ref, dest, fee_reason.clone()) {
				r @ (Some(_), Some(_)) | r @ (Some(_), None) | r @ (None, Some(_)) => return r,
				(None, None) => (),
			}
		)* );
		// doing nothing
		(None, None)
	}
}