op_pool: use max cover algorithm, refactor

eth2/operation_pool/src/attestation_id.rs

@@ -0,0 +1,35 @@
+use int_to_bytes::int_to_bytes8;
+use ssz::ssz_encode;
+use types::{AttestationData, BeaconState, ChainSpec, Domain, Epoch, EthSpec};
+
+/// Serialized `AttestationData` augmented with a domain to encode the fork info.
+#[derive(PartialEq, Eq, Clone, Hash, Debug)]
+pub struct AttestationId(Vec<u8>);
+
+/// Number of domain bytes that the end of an attestation ID is padded with.
+const DOMAIN_BYTES_LEN: usize = 8;
+
+impl AttestationId {
+    pub fn from_data<T: EthSpec>(
+        attestation: &AttestationData,
+        state: &BeaconState<T>,
+        spec: &ChainSpec,
+    ) -> Self {
+        let mut bytes = ssz_encode(attestation);
+        let epoch = attestation.target_epoch;
+        bytes.extend_from_slice(&AttestationId::compute_domain_bytes(epoch, state, spec));
+        AttestationId(bytes)
+    }
+
+    pub fn compute_domain_bytes<T: EthSpec>(
+        epoch: Epoch,
+        state: &BeaconState<T>,
+        spec: &ChainSpec,
+    ) -> Vec<u8> {
+        int_to_bytes8(spec.get_domain(epoch, Domain::Attestation, &state.fork))
+    }
+
+    pub fn domain_bytes_match(&self, domain_bytes: &[u8]) -> bool {
+        &self.0[self.0.len() - DOMAIN_BYTES_LEN..] == domain_bytes
+    }
+}