Add getEpochInfo() and getLeaderSchedule() RPC methods (#5189)

* Add getLeaderSchedule() RPC method

* Add getEpochInfo() RPC method

* Add JSON RPC docs

book/src/jsonrpc-api.md

@@ -25,6 +25,8 @@ Methods
 * [getAccountInfo](#getaccountinfo)
 * [getBalance](#getbalance)
 * [getClusterNodes](#getclusternodes)
+* [getEpochInfo](#getepochinfo)
+* [getLeaderSchedule](#getleaderschedule)
 * [getProgramAccounts](#getprogramaccounts)
 * [getRecentBlockhash](#getrecentblockhash)
 * [getSignatureStatus](#getsignaturestatus)
@@ -172,6 +174,50 @@ curl -X POST -H "Content-Type: application/json" -d '{"jsonrpc":"2.0", "id":1, "
 
 ---
 
+### getEpochInfo
+Returns information about the current epoch
+
+##### Parameters:
+None
+
+##### Results:
+The result field will be an object with the following fields:
+* `epoch`, the current epoch
+* `slotIndex`, the current slot relative to the start of the current epoch
+* `slotsInEpoch`, the number of slots in this epoch
+
+##### Example:
+```bash
+// Request
+curl -X POST -H "Content-Type: application/json" -d '{"jsonrpc":"2.0","id":1, "method":"getEpochInfo"}' http://localhost:8899
+
+// Result
+{"jsonrpc":"2.0","result":{"epoch":3,"slotIndex":126,"slotsInEpoch":256},"id":1}
+```
+
+---
+
+### getLeaderSchedule
+Returns the leader schedule for the current epoch
+
+##### Parameters:
+None
+
+##### Results:
+The result field will be an array of leader public keys (as base-58 encoded
+strings) for each slot in the current epoch
+
+##### Example:
+```bash
+// Request
+curl -X POST -H "Content-Type: application/json" -d '{"jsonrpc":"2.0","id":1, "method":"getLeaderSchedule"}' http://localhost:8899
+
+// Result
+{"jsonrpc":"2.0","result":[...],"id":1}
+```
+
+---
+
 ### getProgramAccounts
 Returns all accounts owned by the provided program Pubkey
 

core/src/leader_schedule.rs

@@ -29,6 +29,10 @@ impl LeaderSchedule {
             .collect();
         Self { slot_leaders }
     }
+
+    pub(crate) fn get_slot_leaders(&self) -> &[Pubkey] {
+        &self.slot_leaders
+    }
 }
 
 impl Index<u64> for LeaderSchedule {

core/src/leader_schedule_utils.rs

@@ -5,16 +5,16 @@ use solana_sdk::pubkey::Pubkey;
 use solana_sdk::timing::NUM_CONSECUTIVE_LEADER_SLOTS;
 
 /// Return the leader schedule for the given epoch.
-pub fn leader_schedule(epoch_height: u64, bank: &Bank) -> Option<LeaderSchedule> {
-    staking_utils::staked_nodes_at_epoch(bank, epoch_height).map(|stakes| {
+pub fn leader_schedule(epoch: u64, bank: &Bank) -> Option<LeaderSchedule> {
+    staking_utils::staked_nodes_at_epoch(bank, epoch).map(|stakes| {
         let mut seed = [0u8; 32];
-        seed[0..8].copy_from_slice(&epoch_height.to_le_bytes());
+        seed[0..8].copy_from_slice(&epoch.to_le_bytes());
         let mut stakes: Vec<_> = stakes.into_iter().collect();
         sort_stakes(&mut stakes);
         LeaderSchedule::new(
             &stakes,
             seed,
-            bank.get_slots_in_epoch(epoch_height),
+            bank.get_slots_in_epoch(epoch),
             NUM_CONSECUTIVE_LEADER_SLOTS,
         )
     })

core/src/rpc.rs

@@ -220,6 +220,19 @@ pub struct RpcVoteAccountInfo {
     pub commission: u8,
 }
 
+#[derive(Serialize, Deserialize, Clone, Debug)]
+#[serde(rename_all = "camelCase")]
+pub struct RpcEpochInfo {
+    /// The current epoch
+    pub epoch: u64,
+
+    /// The number of slots in this epoch
+    pub slots_in_epoch: u64,
+
+    /// The current slot, relative to the start of the current epoch
+    pub slot_index: u64,
+}
+
 #[rpc(server)]
 pub trait RpcSol {
     type Metadata;
@@ -239,6 +252,12 @@ pub trait RpcSol {
     #[rpc(meta, name = "getClusterNodes")]
     fn get_cluster_nodes(&self, _: Self::Metadata) -> Result<Vec<RpcContactInfo>>;
 
+    #[rpc(meta, name = "getEpochInfo")]
+    fn get_epoch_info(&self, _: Self::Metadata) -> Result<RpcEpochInfo>;
+
+    #[rpc(meta, name = "getLeaderSchedule")]
+    fn get_leader_schedule(&self, _: Self::Metadata) -> Result<Option<Vec<String>>>;
+
     #[rpc(meta, name = "getRecentBlockhash")]
     fn get_recent_blockhash(&self, _: Self::Metadata) -> Result<(String, FeeCalculator)>;
 
@@ -369,6 +388,32 @@ impl RpcSol for RpcSolImpl {
             .collect())
     }
 
+    fn get_epoch_info(&self, meta: Self::Metadata) -> Result<RpcEpochInfo> {
+        let bank = meta.request_processor.read().unwrap().bank();
+        let epoch_schedule = bank.epoch_schedule();
+        let (epoch, slot_index) = epoch_schedule.get_epoch_and_slot_index(bank.slot());
+        Ok(RpcEpochInfo {
+            epoch,
+            slots_in_epoch: epoch_schedule.get_slots_in_epoch(epoch),
+            slot_index,
+        })
+    }
+
+    fn get_leader_schedule(&self, meta: Self::Metadata) -> Result<Option<Vec<String>>> {
+        let bank = meta.request_processor.read().unwrap().bank();
+        Ok(
+            crate::leader_schedule_utils::leader_schedule(bank.epoch(), &bank).map(
+                |leader_schedule| {
+                    leader_schedule
+                        .get_slot_leaders()
+                        .iter()
+                        .map(|pubkey| pubkey.to_string())
+                        .collect()
+                },
+            ),
+        )
+    }
+
     fn get_recent_blockhash(&self, meta: Self::Metadata) -> Result<(String, FeeCalculator)> {
         debug!("get_recent_blockhash rpc request received");
         Ok(meta