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
// Copyright 2015-2017 Parity Technologies (UK) Ltd.
// This file is part of Parity.

// Parity 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 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.  If not, see <http://www.gnu.org/licenses/>.

//! Helpers for decoding and verifying responses for headers.

use std::fmt;

use ethcore::header::Header;
use light::request::{HashOrNumber, Headers as HeadersRequest};
use rlp::{DecoderError, UntrustedRlp, View};
use util::{Bytes, H256};

/// Errors found when decoding headers and verifying with basic constraints.
#[derive(Debug, PartialEq)]
pub enum BasicError {
	/// Wrong skip value: expected, found (if any).
	WrongSkip(u64, Option<u64>),
	/// Wrong start number.
	WrongStartNumber(u64, u64),
	/// Wrong start hash.
	WrongStartHash(H256, H256),
	/// Too many headers.
	TooManyHeaders(usize, usize),
	/// Decoder error.
	Decoder(DecoderError),
}

impl From<DecoderError> for BasicError {
	fn from(err: DecoderError) -> Self {
		BasicError::Decoder(err)
	}
}

impl fmt::Display for BasicError {
	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
		try!(write!(f, "Header response verification error: "));

		match *self {
			BasicError::WrongSkip(ref exp, ref got)
				=> write!(f, "wrong skip (expected {}, got {:?})", exp, got),
			BasicError::WrongStartNumber(ref exp, ref got)
				=> write!(f, "wrong start number (expected {}, got {})", exp, got),
			BasicError::WrongStartHash(ref exp, ref got)
				=> write!(f, "wrong start hash (expected {}, got {})", exp, got),
			BasicError::TooManyHeaders(ref max, ref got)
				=> write!(f, "too many headers (max {}, got {})", max, got),
			BasicError::Decoder(ref err)
				=> write!(f, "{}", err),
		}
	}
}

/// Request verification constraint.
pub trait Constraint {
	type Error;

	/// Verify headers against this.
	fn verify(&self, headers: &[Header], reverse: bool) -> Result<(), Self::Error>;
}

/// Decode a response and do basic verification against a request.
pub fn decode_and_verify(headers: &[Bytes], request: &HeadersRequest) -> Result<Vec<Header>, BasicError> {
	let headers: Vec<_> = try!(headers.iter().map(|x| UntrustedRlp::new(&x).as_val()).collect());

	let reverse = request.reverse;

	try!(Max(request.max).verify(&headers, reverse));
	match request.start {
		HashOrNumber::Number(ref num) => try!(StartsAtNumber(*num).verify(&headers, reverse)),
		HashOrNumber::Hash(ref hash) => try!(StartsAtHash(*hash).verify(&headers, reverse)),
	}

	try!(SkipsBetween(request.skip).verify(&headers, reverse));

	Ok(headers)
}

struct StartsAtNumber(u64);
struct StartsAtHash(H256);
struct SkipsBetween(u64);
struct Max(usize);

impl Constraint for StartsAtNumber {
	type Error = BasicError;

	fn verify(&self, headers: &[Header], _reverse: bool) -> Result<(), BasicError> {
		headers.first().map_or(Ok(()), |h| {
			if h.number() == self.0 {
				Ok(())
			} else {
				Err(BasicError::WrongStartNumber(self.0, h.number()))
			}
		})
	}
}

impl Constraint for StartsAtHash {
	type Error = BasicError;

	fn verify(&self, headers: &[Header], _reverse: bool) -> Result<(), BasicError> {
		headers.first().map_or(Ok(()), |h| {
			if h.hash() == self.0 {
				Ok(())
			} else {
				Err(BasicError::WrongStartHash(self.0, h.hash()))
			}
		})
	}
}

impl Constraint for SkipsBetween {
	type Error = BasicError;

	fn verify(&self, headers: &[Header], reverse: bool) -> Result<(), BasicError> {
		for pair in headers.windows(2) {
			let (low, high) = if reverse { (&pair[1], &pair[0]) } else { (&pair[0], &pair[1]) };
			if low.number() >= high.number() { return Err(BasicError::WrongSkip(self.0, None)) }

			let skip = (high.number() - low.number()) - 1;
			if skip != self.0 { return Err(BasicError::WrongSkip(self.0, Some(skip))) }
		}

		Ok(())
	}
}

impl Constraint for Max {
	type Error = BasicError;

	fn verify(&self, headers: &[Header], _reverse: bool) -> Result<(), BasicError> {
		match headers.len() > self.0 {
			true => Err(BasicError::TooManyHeaders(self.0, headers.len())),
			false => Ok(())
		}
	}
}

#[cfg(test)]
mod tests {
	use ethcore::header::Header;
	use light::request::Headers as HeadersRequest;

	use super::*;

	#[test]
	fn sequential_forward() {
		let request = HeadersRequest {
			start: 10.into(),
			max: 30,
			skip: 0,
			reverse: false,
		};

		let mut parent_hash = None;
		let headers: Vec<_> = (0..25).map(|x| x + 10).map(|x| {
			let mut header = Header::default();
			header.set_number(x);

			if let Some(parent_hash) = parent_hash {
				header.set_parent_hash(parent_hash);
			}

			parent_hash = Some(header.hash());

			::rlp::encode(&header).to_vec()
		}).collect();

		assert!(decode_and_verify(&headers, &request).is_ok());
	}

	#[test]
	fn sequential_backward() {
		let request = HeadersRequest {
			start: 34.into(),
			max: 30,
			skip: 0,
			reverse: true,
		};

		let mut parent_hash = None;
		let headers: Vec<_> = (0..25).map(|x| x + 10).rev().map(|x| {
			let mut header = Header::default();
			header.set_number(x);

			if let Some(parent_hash) = parent_hash {
				header.set_parent_hash(parent_hash);
			}

			parent_hash = Some(header.hash());

			::rlp::encode(&header).to_vec()
		}).collect();

		assert!(decode_and_verify(&headers, &request).is_ok());
	}

	#[test]
	fn too_many() {
		let request = HeadersRequest {
			start: 10.into(),
			max: 20,
			skip: 0,
			reverse: false,
		};

		let mut parent_hash = None;
		let headers: Vec<_> = (0..25).map(|x| x + 10).map(|x| {
			let mut header = Header::default();
			header.set_number(x);

			if let Some(parent_hash) = parent_hash {
				header.set_parent_hash(parent_hash);
			}

			parent_hash = Some(header.hash());

			::rlp::encode(&header).to_vec()
		}).collect();

		assert_eq!(decode_and_verify(&headers, &request), Err(BasicError::TooManyHeaders(20, 25)));
	}

	#[test]
	fn wrong_skip() {
		let request = HeadersRequest {
			start: 10.into(),
			max: 30,
			skip: 5,
			reverse: false,
		};

		let headers: Vec<_> = (0..25).map(|x| x * 3).map(|x| x + 10).map(|x| {
			let mut header = Header::default();
			header.set_number(x);

			::rlp::encode(&header).to_vec()
		}).collect();

		assert_eq!(decode_and_verify(&headers, &request), Err(BasicError::WrongSkip(5, Some(2))));
	}
}