chain: Verify the solutionSize field in block headers

Verify the value of the equihash solution size field in block headers.

This field isn't stored in the BlockHeader struct, so we need to verify
it at parse time.

Part of #477.

zebra-chain/src/equihash_solution.rs

@@ -60,7 +60,12 @@ impl ZcashSerialize for EquihashSolution {
 
 impl ZcashDeserialize for EquihashSolution {
     fn zcash_deserialize<R: io::Read>(mut reader: R) -> Result<Self, SerializationError> {
-        reader.read_compactsize()?;
+        let solution_size = reader.read_compactsize()?;
+        if solution_size != (EQUIHASH_SOLUTION_SIZE as u64) {
+            return Err(SerializationError::Parse(
+                "incorrect equihash solution size",
+            ));
+        }
         let mut bytes = [0; EQUIHASH_SOLUTION_SIZE];
         reader.read_exact(&mut bytes[..])?;
         Ok(Self(bytes))
@@ -96,7 +101,7 @@ mod tests {
 
             let mut data = Vec::new();
 
-            solution.zcash_serialize(&mut data).expect("EquihashSolution should serialize");
+            solution.zcash_serialize(&mut data).expect("randomized EquihashSolution should serialize");
 
             let solution2 = EquihashSolution::zcash_deserialize(&data[..])
                 .expect("randomized EquihashSolution should deserialize");
@@ -105,4 +110,48 @@ mod tests {
         }
 
     }
+
+    const EQUIHASH_SOLUTION_BLOCK_OFFSET: usize = 4 + 32 * 3 + 4 * 2 + 32;
+
+    #[test]
+    fn equihash_solution_test_vector() {
+        let solution_bytes =
+            &zebra_test_vectors::HEADER_MAINNET_415000_BYTES[EQUIHASH_SOLUTION_BLOCK_OFFSET..];
+        let solution = EquihashSolution::zcash_deserialize(solution_bytes)
+            .expect("Test vector EquihashSolution should deserialize");
+
+        let mut data = Vec::new();
+        solution
+            .zcash_serialize(&mut data)
+            .expect("Test vector EquihashSolution should serialize");
+
+        assert_eq!(solution_bytes, data.as_slice());
+    }
+
+    static EQUIHASH_SIZE_TESTS: &[u64] = &[
+        0,
+        1,
+        (EQUIHASH_SOLUTION_SIZE - 1) as u64,
+        EQUIHASH_SOLUTION_SIZE as u64,
+        (EQUIHASH_SOLUTION_SIZE + 1) as u64,
+        u64::MAX - 1,
+        u64::MAX,
+    ];
+
+    #[test]
+    fn equihash_solution_size_field() {
+        for size in EQUIHASH_SIZE_TESTS {
+            let mut data = Vec::new();
+            data.write_compactsize(*size as u64)
+                .expect("Compact size should serialize");
+            data.resize(data.len() + EQUIHASH_SOLUTION_SIZE, 0);
+            let result = EquihashSolution::zcash_deserialize(data.as_slice());
+            if *size == (EQUIHASH_SOLUTION_SIZE as u64) {
+                result.expect("Correct size field in EquihashSolution should deserialize");
+            } else {
+                result
+                    .expect_err("Wrong size field in EquihashSolution should fail on deserialize");
+            }
+        }
+    }
 }