erasure-coding: do not panic on 1 validator (#2022)

* erasure-coding: do not panic on 1 validator

* tabify fuzz tests

* remove num_validators length check

* remove unused import

* move erasure_coding_fuzzer to fuzzer

* change the authors to admit (at) parity.io

* Apply suggestions from code review

Co-authored-by: Sergei Shulepov <sergei@parity.io>

Co-authored-by: Sergei Shulepov <sergei@parity.io>

polkadot/erasure-coding/erasure_coding_fuzzer/src/reconstruct.rs

@@ -1,20 +0,0 @@
-use polkadot_erasure_coding::*;
-use primitives::v1::AvailableData;
-use std::sync::Arc;
-use honggfuzz::fuzz;
-
-fn main(){
-    loop {
-        fuzz!(|data: (usize, Vec<(Vec<u8>, usize)>)| {
-            let (num_validators, chunk_input) = data;
-            if num_validators <= 1 || num_validators > 10_000 {
-                return;
-            }
-            let reconstructed: Result<AvailableData, _> = reconstruct_v1(
-                num_validators,
-                chunk_input.iter().map(|t| (&*t.0, t.1)).collect::<Vec<(&[u8], usize)>>()
-            );
-            println!("reconstructed {:?}", reconstructed);
-        });
-    }
-}

polkadot/erasure-coding/erasure_coding_fuzzer/src/round_trip.rs

@@ -1,40 +0,0 @@
-use polkadot_erasure_coding::*;
-use primitives::v1::{AvailableData, BlockData, PoV};
-use std::sync::Arc;
-use honggfuzz::fuzz;
-
-
-fn main(){
-    loop {
-        fuzz!(|data: &[u8]| {
-            let pov_block = PoV {
-                block_data: BlockData(data.iter().cloned().collect()),
-            };
-
-            let available_data = AvailableData {
-                pov: Arc::new(pov_block),
-                validation_data: Default::default(),
-            };
-            let chunks = obtain_chunks_v1(
-                10,
-                &available_data,
-            ).unwrap();
-
-            assert_eq!(chunks.len(), 10);
-
-            // any 4 chunks should work.
-            let reconstructed: AvailableData = reconstruct_v1(
-                10,
-                [
-                    (&*chunks[1], 1),
-                    (&*chunks[4], 4),
-                    (&*chunks[6], 6),
-                    (&*chunks[9], 9),
-                ].iter().cloned(),
-            ).unwrap();
-
-            assert_eq!(reconstructed, available_data);
-            println!("{:?}", reconstructed);
-        });
-    }
-}

polkadot/erasure-coding/fuzzer/Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name = "erasure_coding_fuzzer"
 version = "0.1.0"
-authors = ["Vincent Ulitzsch <vincent@srlabs.de>"]
+authors = ["Parity Technologies <admin@parity.io>"]
 edition = "2018"
 
 [dependencies]

polkadot/erasure-coding/fuzzer/src/reconstruct.rs

@@ -0,0 +1,16 @@
+use polkadot_erasure_coding::*;
+use primitives::v1::AvailableData;
+use honggfuzz::fuzz;
+
+fn main() {
+	loop {
+		fuzz!(|data: (usize, Vec<(Vec<u8>, usize)>)| {
+			let (num_validators, chunk_input) = data;
+			let reconstructed: Result<AvailableData, _> = reconstruct_v1(
+				num_validators,
+				chunk_input.iter().map(|t| (&*t.0, t.1)).collect::<Vec<(&[u8], usize)>>()
+			);
+			println!("reconstructed {:?}", reconstructed);
+		});
+	}
+}

polkadot/erasure-coding/fuzzer/src/round_trip.rs

@@ -0,0 +1,40 @@
+use polkadot_erasure_coding::*;
+use primitives::v1::{AvailableData, BlockData, PoV};
+use std::sync::Arc;
+use honggfuzz::fuzz;
+
+
+fn main() {
+	loop {
+		fuzz!(|data: &[u8]| {
+			let pov_block = PoV {
+				block_data: BlockData(data.iter().cloned().collect()),
+			};
+
+			let available_data = AvailableData {
+				pov: Arc::new(pov_block),
+				validation_data: Default::default(),
+			};
+			let chunks = obtain_chunks_v1(
+				10,
+				&available_data,
+			).unwrap();
+
+			assert_eq!(chunks.len(), 10);
+
+			// any 4 chunks should work.
+			let reconstructed: AvailableData = reconstruct_v1(
+				10,
+				[
+					(&*chunks[1], 1),
+					(&*chunks[4], 4),
+					(&*chunks[6], 6),
+					(&*chunks[9], 9),
+				].iter().cloned(),
+			).unwrap();
+
+			assert_eq!(reconstructed, available_data);
+			println!("{:?}", reconstructed);
+		});
+	}
+}

polkadot/erasure-coding/src/lib.rs

@@ -45,9 +45,9 @@ pub enum Error {
 	/// Returned when there are too many validators.
 	#[error("There are too many validators")]
 	TooManyValidators,
-	/// Cannot encode something for no validators
-	#[error("Validator set is empty")]
-	EmptyValidators,
+	/// Cannot encode something for zero or one validator
+	#[error("Expected at least 2 validators")]
+	NotEnoughValidators,
 	/// Cannot reconstruct: wrong number of validators.
 	#[error("Validator count mismatches between encoding and decoding")]
 	WrongValidatorCount,
@@ -122,7 +122,7 @@ impl CodeParams {
 
 fn code_params(n_validators: usize) -> Result<CodeParams, Error> {
 	if n_validators > MAX_VALIDATORS { return Err(Error::TooManyValidators) }
-	if n_validators == 0 { return Err(Error::EmptyValidators) }
+	if n_validators <= 1 { return Err(Error::NotEnoughValidators) }
 
 	let n_faulty = n_validators.saturating_sub(1) / 3;
 	let n_good = n_validators - n_faulty;
@@ -406,12 +406,9 @@ mod tests {
 
 	#[test]
 	fn test_code_params() {
-		assert_eq!(code_params(0), Err(Error::EmptyValidators));
+		assert_eq!(code_params(0), Err(Error::NotEnoughValidators));
 
-		assert_eq!(code_params(1), Ok(CodeParams {
-			data_shards: 1,
-			parity_shards: 0,
-		}));
+		assert_eq!(code_params(1), Err(Error::NotEnoughValidators));
 
 		assert_eq!(code_params(2), Ok(CodeParams {
 			data_shards: 1,
@@ -487,6 +484,15 @@ mod tests {
 		assert_eq!(reconstructed, available_data);
 	}
 
+	#[test]
+	fn reconstruct_does_not_panic_on_low_validator_count() {
+		let reconstructed = reconstruct_v1(
+			1,
+			[].iter().cloned(),
+		);
+		assert_eq!(reconstructed, Err(Error::NotEnoughValidators));
+	}
+
 	#[test]
 	fn construct_valid_branches() {
 		let pov_block = PoVBlock {