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
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
// This file is part of Substrate.

// Copyright (C) Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// 	http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! Traits for dealing with validation and validators.

use crate::{dispatch::Parameter, weights::Weight};
use alloc::{vec, vec::Vec};
use codec::{Codec, Decode, MaxEncodedLen};
use sp_runtime::{
	traits::{Convert, Zero},
	BoundToRuntimeAppPublic, ConsensusEngineId, Permill, RuntimeAppPublic,
};
use sp_staking::SessionIndex;

/// A trait for online node inspection in a session.
///
/// Something that can give information about the current validator set.
pub trait ValidatorSet<AccountId> {
	/// Type for representing validator id in a session.
	type ValidatorId: Parameter + MaxEncodedLen;
	/// A type for converting `AccountId` to `ValidatorId`.
	type ValidatorIdOf: Convert<AccountId, Option<Self::ValidatorId>>;

	/// Returns current session index.
	fn session_index() -> SessionIndex;

	/// Returns the active set of validators.
	fn validators() -> Vec<Self::ValidatorId>;
}

/// [`ValidatorSet`] combined with an identification.
pub trait ValidatorSetWithIdentification<AccountId>: ValidatorSet<AccountId> {
	/// Full identification of `ValidatorId`.
	type Identification: Parameter;
	/// A type for converting `ValidatorId` to `Identification`.
	type IdentificationOf: Convert<Self::ValidatorId, Option<Self::Identification>>;
}

/// A trait for finding the author of a block header based on the `PreRuntime` digests contained
/// within it.
pub trait FindAuthor<Author> {
	/// Find the author of a block based on the pre-runtime digests.
	fn find_author<'a, I>(digests: I) -> Option<Author>
	where
		I: 'a + IntoIterator<Item = (ConsensusEngineId, &'a [u8])>;
}

impl<A> FindAuthor<A> for () {
	fn find_author<'a, I>(_: I) -> Option<A>
	where
		I: 'a + IntoIterator<Item = (ConsensusEngineId, &'a [u8])>,
	{
		None
	}
}

/// A trait for verifying the seal of a header and returning the author.
pub trait VerifySeal<Header, Author> {
	/// Verify a header and return the author, if any.
	fn verify_seal(header: &Header) -> Result<Option<Author>, &'static str>;
}

/// A session handler for specific key type.
pub trait OneSessionHandler<ValidatorId>: BoundToRuntimeAppPublic {
	/// The key type expected.
	type Key: Decode + RuntimeAppPublic;

	/// The given validator set will be used for the genesis session.
	/// It is guaranteed that the given validator set will also be used
	/// for the second session, therefore the first call to `on_new_session`
	/// should provide the same validator set.
	fn on_genesis_session<'a, I: 'a>(validators: I)
	where
		I: Iterator<Item = (&'a ValidatorId, Self::Key)>,
		ValidatorId: 'a;

	/// Session set has changed; act appropriately. Note that this can be called
	/// before initialization of your module.
	///
	/// `changed` is true when at least one of the session keys
	/// or the underlying economic identities/distribution behind one the
	/// session keys has changed, false otherwise.
	///
	/// The `validators` are the validators of the incoming session, and `queued_validators`
	/// will follow.
	fn on_new_session<'a, I: 'a>(changed: bool, validators: I, queued_validators: I)
	where
		I: Iterator<Item = (&'a ValidatorId, Self::Key)>,
		ValidatorId: 'a;

	/// A notification for end of the session.
	///
	/// Note it is triggered before any `SessionManager::end_session` handlers,
	/// so we can still affect the validator set.
	fn on_before_session_ending() {}

	/// A validator got disabled. Act accordingly until a new session begins.
	fn on_disabled(_validator_index: u32);
}

/// Something that can estimate at which block the next session rotation will happen (i.e. a new
/// session starts).
///
/// The accuracy of the estimates is dependent on the specific implementation, but in order to get
/// the best estimate possible these methods should be called throughout the duration of the session
/// (rather than calling once and storing the result).
///
/// This should be the same logical unit that dictates `ShouldEndSession` to the session module. No
/// assumptions are made about the scheduling of the sessions.
pub trait EstimateNextSessionRotation<BlockNumber> {
	/// Return the average length of a session.
	///
	/// This may or may not be accurate.
	fn average_session_length() -> BlockNumber;

	/// Return an estimate of the current session progress.
	///
	/// None should be returned if the estimation fails to come to an answer.
	fn estimate_current_session_progress(now: BlockNumber) -> (Option<Permill>, Weight);

	/// Return the block number at which the next session rotation is estimated to happen.
	///
	/// None should be returned if the estimation fails to come to an answer.
	fn estimate_next_session_rotation(now: BlockNumber) -> (Option<BlockNumber>, Weight);
}

impl<BlockNumber: Zero> EstimateNextSessionRotation<BlockNumber> for () {
	fn average_session_length() -> BlockNumber {
		Zero::zero()
	}

	fn estimate_current_session_progress(_: BlockNumber) -> (Option<Permill>, Weight) {
		(None, Zero::zero())
	}

	fn estimate_next_session_rotation(_: BlockNumber) -> (Option<BlockNumber>, Weight) {
		(None, Zero::zero())
	}
}

/// Something that can estimate at which block scheduling of the next session will happen (i.e when
/// we will try to fetch new validators).
///
/// This only refers to the point when we fetch the next session details and not when we enact them
/// (for enactment there's `EstimateNextSessionRotation`). With `pallet-session` this should be
/// triggered whenever `SessionManager::new_session` is called.
///
/// For example, if we are using a staking module this would be the block when the session module
/// would ask staking what the next validator set will be, as such this must always be implemented
/// by the session module.
pub trait EstimateNextNewSession<BlockNumber> {
	/// Return the average length of a session.
	///
	/// This may or may not be accurate.
	fn average_session_length() -> BlockNumber;

	/// Return the block number at which the next new session is estimated to happen.
	///
	/// None should be returned if the estimation fails to come to an answer.
	fn estimate_next_new_session(_: BlockNumber) -> (Option<BlockNumber>, Weight);
}

impl<BlockNumber: Zero> EstimateNextNewSession<BlockNumber> for () {
	fn average_session_length() -> BlockNumber {
		Zero::zero()
	}

	fn estimate_next_new_session(_: BlockNumber) -> (Option<BlockNumber>, Weight) {
		(None, Zero::zero())
	}
}

/// Something which can compute and check proofs of
/// a historical key owner and return full identification data of that
/// key owner.
pub trait KeyOwnerProofSystem<Key> {
	/// The proof of membership itself.
	type Proof: Codec;
	/// The full identification of a key owner and the stash account.
	type IdentificationTuple: Codec;

	/// Prove membership of a key owner in the current block-state.
	///
	/// This should typically only be called off-chain, since it may be
	/// computationally heavy.
	///
	/// Returns `Some` iff the key owner referred to by the given `key` is a
	/// member of the current set.
	fn prove(key: Key) -> Option<Self::Proof>;

	/// Check a proof of membership on-chain. Return `Some` iff the proof is
	/// valid and recent enough to check.
	fn check_proof(key: Key, proof: Self::Proof) -> Option<Self::IdentificationTuple>;
}

impl<Key> KeyOwnerProofSystem<Key> for () {
	// The proof and identification tuples is any bottom type to guarantee that the methods of this
	// implementation can never be called or return anything other than `None`.
	type Proof = sp_core::Void;
	type IdentificationTuple = sp_core::Void;

	fn prove(_key: Key) -> Option<Self::Proof> {
		None
	}

	fn check_proof(_key: Key, _proof: Self::Proof) -> Option<Self::IdentificationTuple> {
		None
	}
}

/// Trait to be used by block producing consensus engine modules to determine
/// how late the current block is (e.g. in a slot-based proposal mechanism how
/// many slots were skipped since the previous block).
pub trait Lateness<N> {
	/// Returns a generic measure of how late the current block is compared to
	/// its parent.
	fn lateness(&self) -> N;
}

impl<N: Zero> Lateness<N> for () {
	fn lateness(&self) -> N {
		Zero::zero()
	}
}

/// Implementors of this trait provide information about whether or not some validator has
/// been registered with them. The [Session module](../../pallet_session/index.html) is an
/// implementor.
pub trait ValidatorRegistration<ValidatorId> {
	/// Returns true if the provided validator ID has been registered with the implementing runtime
	/// module
	fn is_registered(id: &ValidatorId) -> bool;
}

/// Trait used to check whether a given validator is currently disabled and should not be
/// participating in consensus (e.g. because they equivocated).
pub trait DisabledValidators {
	/// Returns true if the given validator is disabled.
	fn is_disabled(index: u32) -> bool;

	/// Returns all disabled validators
	fn disabled_validators() -> Vec<u32>;
}

impl DisabledValidators for () {
	fn is_disabled(_index: u32) -> bool {
		false
	}

	fn disabled_validators() -> Vec<u32> {
		vec![]
	}
}