Add getHealth RPC method

core/src/rpc.rs

@@ -1760,6 +1760,9 @@ pub trait RpcSol {
     #[rpc(meta, name = "getGenesisHash")]
     fn get_genesis_hash(&self, meta: Self::Metadata) -> Result<String>;
 
+    #[rpc(meta, name = "getHealth")]
+    fn get_health(&self, meta: Self::Metadata) -> Result<String>;
+
     #[rpc(meta, name = "getLeaderSchedule")]
     fn get_leader_schedule(
         &self,
@@ -2247,6 +2250,15 @@ impl RpcSol for RpcSolImpl {
         Ok(meta.genesis_hash.to_string())
     }
 
+    fn get_health(&self, meta: Self::Metadata) -> Result<String> {
+        match meta.health.check() {
+            RpcHealthStatus::Ok => Ok("ok".to_string()),
+            RpcHealthStatus::Behind {
+                num_slots: num_slots_behind,
+            } => Err(RpcCustomError::RpcNodeUnhealthy { num_slots_behind }.into()),
+        }
+    }
+
     fn get_leader_schedule(
         &self,
         meta: Self::Metadata,
@@ -2486,9 +2498,15 @@ impl RpcSol for RpcSolImpl {
                 return Err(e);
             }
 
-            if meta.health.check() != RpcHealthStatus::Ok {
-                return Err(RpcCustomError::RpcNodeUnhealthy.into());
+            match meta.health.check() {
+                RpcHealthStatus::Ok => (),
+                RpcHealthStatus::Behind {
+                    num_slots: num_slots_behind,
+                } => {
+                    return Err(RpcCustomError::RpcNodeUnhealthy { num_slots_behind }.into());
+                }
             }
+
             if let (Err(err), logs) = preflight_bank.simulate_transaction(transaction.clone()) {
                 return Err(RpcCustomError::SendTransactionPreflightFailure {
                     message: format!("Transaction simulation failed: {}", err),
@@ -4518,7 +4536,7 @@ pub mod tests {
         );
 
         // sendTransaction will fail due to poor node health
-        health.stub_set_health_status(Some(RpcHealthStatus::Behind));
+        health.stub_set_health_status(Some(RpcHealthStatus::Behind { num_slots: 42 }));
         let req = format!(
             r#"{{"jsonrpc":"2.0","id":1,"method":"sendTransaction","params":["{}"]}}"#,
             bs58::encode(serialize(&bad_transaction).unwrap()).into_string()
@@ -4527,7 +4545,7 @@ pub mod tests {
         assert_eq!(
             res,
             Some(
-                r#"{"jsonrpc":"2.0","error":{"code":-32005,"message":"RPC node is unhealthy"},"id":1}"#.to_string(),
+                r#"{"jsonrpc":"2.0","error":{"code":-32005,"message":"RPC node is behind by 42 slots","data":{"numSlotsBehind":42}},"id":1}"#.to_string(),
             )
         );
         health.stub_set_health_status(None);

core/src/rpc_health.rs

@@ -1,15 +1,17 @@
-use crate::cluster_info::ClusterInfo;
-use solana_sdk::pubkey::Pubkey;
-use std::{
-    collections::HashSet,
-    sync::atomic::{AtomicBool, Ordering},
-    sync::Arc,
+use {
+    crate::cluster_info::ClusterInfo,
+    solana_sdk::{clock::Slot, pubkey::Pubkey},
+    std::{
+        collections::HashSet,
+        sync::atomic::{AtomicBool, Ordering},
+        sync::Arc,
+    },
 };
 
 #[derive(PartialEq, Clone, Copy)]
 pub enum RpcHealthStatus {
     Ok,
-    Behind, // Validator is behind its trusted validators
+    Behind { num_slots: Slot }, // Validator is behind its trusted validators
 }
 
 pub struct RpcHealth {
@@ -88,11 +90,13 @@ impl RpcHealth {
             {
                 RpcHealthStatus::Ok
             } else {
+                let num_slots = latest_trusted_validator_account_hash_slot
+                    .saturating_sub(latest_account_hash_slot);
                 warn!(
-                    "health check: me={}, latest trusted_validator={}",
-                    latest_account_hash_slot, latest_trusted_validator_account_hash_slot
+                    "health check: behind by {} slots: me={}, latest trusted_validator={}",
+                    num_slots, latest_account_hash_slot, latest_trusted_validator_account_hash_slot
                 );
-                RpcHealthStatus::Behind
+                RpcHealthStatus::Behind { num_slots }
             }
         } else {
             // No trusted validator point of reference available, so this validator is healthy

core/src/rpc_service.rs

@@ -159,7 +159,7 @@ impl RpcRequestMiddleware {
     fn health_check(&self) -> &'static str {
         let response = match self.health.check() {
             RpcHealthStatus::Ok => "ok",
-            RpcHealthStatus::Behind => "behind",
+            RpcHealthStatus::Behind { num_slots: _ } => "behind",
         };
         info!("health check: {}", response);
         response