Skip serializing blob_schedule before Fulu (#7779)

Alternative to:

- https://github.com/sigp/lighthouse/pull/7758


  Serve the `blob_schedule` field on `/eth/v1/config/spec` _only_ when Fulu is enabled. If the blob schedule is empty, we will still serve it as `[]`, so long as Fulu is enabled.

consensus/types/src/chain_spec.rs

@@ -2,6 +2,7 @@ use crate::application_domain::{ApplicationDomain, APPLICATION_DOMAIN_BUILDER};
 use crate::blob_sidecar::BlobIdentifier;
 use crate::data_column_sidecar::DataColumnsByRootIdentifier;
 use crate::*;
+use derivative::Derivative;
 use ethereum_hashing::hash;
 use int_to_bytes::int_to_bytes4;
 use safe_arith::{ArithError, SafeArith};
@@ -1472,8 +1473,17 @@ pub struct BlobParameters {
 // A wrapper around a vector of BlobParameters to ensure that the vector is reverse
 // sorted by epoch.
 #[cfg_attr(feature = "arbitrary", derive(arbitrary::Arbitrary))]
-#[derive(Debug, PartialEq, Clone)]
+#[derive(Debug, Derivative, Clone)]
-pub struct BlobSchedule(Vec<BlobParameters>);
+#[derivative(PartialEq)]
+pub struct BlobSchedule {
+    schedule: Vec<BlobParameters>,
+    // This is a hack to prevent the blob schedule being serialized on the /eth/v1/config/spec
+    // endpoint prior to the Fulu fork being scheduled.
+    //
+    // We can remove this once Fulu is live on mainnet.
+    #[derivative(PartialEq = "ignore")]
+    skip_serializing: bool,
+}
 
 impl<'de> Deserialize<'de> for BlobSchedule {
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
@@ -1489,30 +1499,48 @@ impl BlobSchedule {
     pub fn new(mut vec: Vec<BlobParameters>) -> Self {
         // reverse sort by epoch
         vec.sort_by(|a, b| b.epoch.cmp(&a.epoch));
-        Self(vec)
+        Self {
+            schedule: vec,
+            skip_serializing: false,
+        }
     }
 
     pub fn is_empty(&self) -> bool {
-        self.0.is_empty()
+        self.schedule.is_empty()
+    }
+
+    pub fn skip_serializing(&self) -> bool {
+        self.skip_serializing
+    }
+
+    pub fn set_skip_serializing(&mut self) {
+        self.skip_serializing = true;
     }
 
     pub fn max_blobs_for_epoch(&self, epoch: Epoch) -> Option<u64> {
-        self.0
+        self.schedule
             .iter()
             .find(|entry| epoch >= entry.epoch)
             .map(|entry| entry.max_blobs_per_block)
     }
 
     pub fn blob_parameters_for_epoch(&self, epoch: Epoch) -> Option<BlobParameters> {
-        self.0.iter().find(|entry| epoch >= entry.epoch).cloned()
+        self.schedule
+            .iter()
+            .find(|entry| epoch >= entry.epoch)
+            .cloned()
     }
 
     pub const fn default() -> Self {
-        Self(vec![])
+        // TODO(EIP-7892): think about what the default should be
+        Self {
+            schedule: vec![],
+            skip_serializing: false,
+        }
     }
 
     pub fn as_vec(&self) -> &Vec<BlobParameters> {
-        &self.0
+        &self.schedule
     }
 }
 
@@ -1521,7 +1549,7 @@ impl Serialize for BlobSchedule {
     where
         S: Serializer,
     {
-        let mut schedule = self.0.clone();
+        let mut schedule = self.schedule.clone();
         // reversing the list to get an ascending order
         schedule.reverse();
         schedule.serialize(serializer)
@@ -1533,7 +1561,7 @@ impl<'a> IntoIterator for &'a BlobSchedule {
     type IntoIter = std::slice::Iter<'a, BlobParameters>;
 
     fn into_iter(self) -> Self::IntoIter {
-        self.0.iter()
+        self.schedule.iter()
     }
 }
 
@@ -1542,7 +1570,7 @@ impl IntoIterator for BlobSchedule {
     type IntoIter = std::vec::IntoIter<BlobParameters>;
 
     fn into_iter(self) -> Self::IntoIter {
-        self.0.into_iter()
+        self.schedule.into_iter()
     }
 }
 
@@ -1747,8 +1775,8 @@ pub struct Config {
     #[serde(with = "serde_utils::quoted_u64")]
     custody_requirement: u64,
     #[serde(default = "BlobSchedule::default")]
-    #[serde(skip_serializing_if = "BlobSchedule::is_empty")]
+    #[serde(skip_serializing_if = "BlobSchedule::skip_serializing")]
-    blob_schedule: BlobSchedule,
+    pub blob_schedule: BlobSchedule,
     #[serde(default = "default_validator_custody_requirement")]
     #[serde(with = "serde_utils::quoted_u64")]
     validator_custody_requirement: u64,

consensus/types/src/config_and_preset.rs

@@ -43,9 +43,8 @@ pub struct ConfigAndPreset {
 }
 
 impl ConfigAndPreset {
-    // DEPRECATED: the `fork_name` argument is never used, we should remove it.
     pub fn from_chain_spec<E: EthSpec>(spec: &ChainSpec, fork_name: Option<ForkName>) -> Self {
-        let config = Config::from_chain_spec::<E>(spec);
+        let mut config = Config::from_chain_spec::<E>(spec);
         let base_preset = BasePreset::from_chain_spec::<E>(spec);
         let altair_preset = AltairPreset::from_chain_spec::<E>(spec);
         let bellatrix_preset = BellatrixPreset::from_chain_spec::<E>(spec);
@@ -53,6 +52,11 @@ impl ConfigAndPreset {
         let deneb_preset = DenebPreset::from_chain_spec::<E>(spec);
         let extra_fields = get_extra_fields(spec);
 
+        // Remove blob schedule for backwards-compatibility.
+        if spec.fulu_fork_epoch.is_none() {
+            config.blob_schedule.set_skip_serializing();
+        }
+
         if spec.fulu_fork_epoch.is_some()
             || fork_name.is_none()
             || fork_name == Some(ForkName::Fulu)
@@ -140,7 +144,7 @@ pub fn get_extra_fields(spec: &ChainSpec) -> HashMap<String, Value> {
 #[cfg(test)]
 mod test {
     use super::*;
-    use crate::MainnetEthSpec;
+    use crate::{Epoch, MainnetEthSpec};
     use std::fs::File;
     use tempfile::NamedTempFile;
 
@@ -152,7 +156,9 @@ mod test {
             .write(true)
             .open(tmp_file.as_ref())
             .expect("error opening file");
-        let mainnet_spec = ChainSpec::mainnet();
+        let mut mainnet_spec = ChainSpec::mainnet();
+        // setting fulu_fork_epoch because we are roundtripping a fulu config
+        mainnet_spec.fulu_fork_epoch = Some(Epoch::new(42));
         let mut yamlconfig =
             ConfigAndPreset::from_chain_spec::<MainnetEthSpec>(&mainnet_spec, None);
         let (k1, v1) = ("SAMPLE_HARDFORK_KEY1", "123456789");