Beacon state diffs!

beacon_node/store/src/state_diff.rs

@@ -0,0 +1,49 @@
+use crate::{metrics, DBColumn, Error, StoreItem};
+use flate2::bufread::{ZlibDecoder, ZlibEncoder};
+use ssz::{Decode, Encode};
+use std::io::Read;
+use types::{beacon_state::BeaconStateDiff, EthSpec};
+
+impl<E: EthSpec> StoreItem for BeaconStateDiff<E> {
+    fn db_column() -> DBColumn {
+        DBColumn::BeaconStateDiff
+    }
+
+    fn as_store_bytes(&self) -> Result<Vec<u8>, Error> {
+        let encode_timer = metrics::start_timer(&metrics::BEACON_STATE_DIFF_ENCODE_TIME);
+        let value = self.as_ssz_bytes();
+        drop(encode_timer);
+
+        // FIXME(sproul): try vec with capacity
+        let compression_timer = metrics::start_timer(&metrics::BEACON_STATE_DIFF_COMPRESSION_TIME);
+        let mut encoder = ZlibEncoder::new(&value[..], flate2::Compression::fast());
+        let mut compressed_value = vec![];
+        encoder
+            .read_to_end(&mut compressed_value)
+            .map_err(Error::FlateCompression)?;
+        drop(compression_timer);
+
+        let compression_ratio = value.len() as f64 / compressed_value.len() as f64;
+        metrics::set_float_gauge(
+            &metrics::BEACON_STATE_DIFF_COMPRESSION_RATIO,
+            compression_ratio,
+        );
+
+        metrics::inc_counter_by(
+            &metrics::BEACON_STATE_DIFF_WRITE_BYTES,
+            compressed_value.len() as u64,
+        );
+        metrics::inc_counter(&metrics::BEACON_STATE_DIFF_WRITE_COUNT);
+
+        Ok(compressed_value)
+    }
+
+    fn from_store_bytes(bytes: &[u8]) -> Result<Self, Error> {
+        let mut ssz_bytes = vec![];
+        let mut decoder = ZlibDecoder::new(bytes);
+        decoder
+            .read_to_end(&mut ssz_bytes)
+            .map_err(Error::FlateCompression)?;
+        Ok(Self::from_ssz_bytes(&ssz_bytes)?)
+    }
+}