Fix ssz formatting for /light_client/updates beacon API endpoint (#7806)

#7759


  We were incorrectly encoding the full response from `/light_client/updates` instead of only encoding the light client update

common/eth2/src/lib.rs

@@ -981,6 +981,32 @@ impl BeaconNodeHttpClient {
         })
     }
 
+    /// `GET beacon/light_client/updates`
+    ///
+    /// Returns `Ok(None)` on a 404 error.
+    pub async fn get_beacon_light_client_updates_ssz<E: EthSpec>(
+        &self,
+        start_period: u64,
+        count: u64,
+    ) -> Result<Option<Vec<u8>>, Error> {
+        let mut path = self.eth_path(V1)?;
+
+        path.path_segments_mut()
+            .map_err(|()| Error::InvalidUrl(self.server.clone()))?
+            .push("beacon")
+            .push("light_client")
+            .push("updates");
+
+        path.query_pairs_mut()
+            .append_pair("start_period", &start_period.to_string());
+
+        path.query_pairs_mut()
+            .append_pair("count", &count.to_string());
+
+        self.get_bytes_opt_accept_header(path, Accept::Ssz, self.timeouts.default)
+            .await
+    }
+
     /// `GET beacon/light_client/bootstrap`
     ///
     /// Returns `Ok(None)` on a 404 error.

common/eth2/src/types.rs

@@ -11,6 +11,7 @@ use multiaddr::Multiaddr;
 use reqwest::header::HeaderMap;
 use serde::{Deserialize, Deserializer, Serialize};
 use serde_utils::quoted_u64::Quoted;
+use ssz::Encode;
 use ssz::{Decode, DecodeError};
 use ssz_derive::{Decode, Encode};
 use std::fmt::{self, Display};
@@ -823,16 +824,32 @@ pub struct LightClientUpdatesQuery {
     pub count: u64,
 }
 
-#[derive(Encode, Decode)]
-pub struct LightClientUpdateResponseChunk {
+pub struct LightClientUpdateResponseChunk<E: EthSpec> {
     pub response_chunk_len: u64,
-    pub response_chunk: LightClientUpdateResponseChunkInner,
+    pub response_chunk: LightClientUpdateResponseChunkInner<E>,
 }
 
-#[derive(Encode, Decode)]
-pub struct LightClientUpdateResponseChunkInner {
+impl<E: EthSpec> Encode for LightClientUpdateResponseChunk<E> {
+    fn is_ssz_fixed_len() -> bool {
+        false
+    }
+
+    fn ssz_bytes_len(&self) -> usize {
+        0_u64.ssz_bytes_len()
+            + self.response_chunk.context.len()
+            + self.response_chunk.payload.ssz_bytes_len()
+    }
+
+    fn ssz_append(&self, buf: &mut Vec<u8>) {
+        buf.extend_from_slice(&self.response_chunk_len.to_le_bytes());
+        buf.extend_from_slice(&self.response_chunk.context);
+        self.response_chunk.payload.ssz_append(buf);
+    }
+}
+
+pub struct LightClientUpdateResponseChunkInner<E: EthSpec> {
     pub context: [u8; 4],
-    pub payload: Vec<u8>,
+    pub payload: LightClientUpdate<E>,
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize, Hash)]