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/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);
+		});
+	}
+}