Health Endpoints for UI (#3668)

This PR adds some health endpoints for the beacon node and the validator client.

Specifically it adds the endpoint:
`/lighthouse/ui/health`

These are not entirely stable yet. But provide a base for modification for our UI. 

These also may have issues with various platforms and may need modification.

validator_client/src/http_api/mod.rs

@@ -16,6 +16,7 @@ use eth2::lighthouse_vc::{
     types::{self as api_types, GenericResponse, PublicKey, PublicKeyBytes},
 };
 use lighthouse_version::version_with_platform;
+use parking_lot::RwLock;
 use serde::{Deserialize, Serialize};
 use slog::{crit, info, warn, Logger};
 use slot_clock::SlotClock;
@@ -24,6 +25,8 @@ use std::marker::PhantomData;
 use std::net::{IpAddr, Ipv4Addr, SocketAddr};
 use std::path::PathBuf;
 use std::sync::Arc;
+use sysinfo::{System, SystemExt};
+use system_health::observe_system_health_vc;
 use task_executor::TaskExecutor;
 use types::{ChainSpec, ConfigAndPreset, EthSpec};
 use validator_dir::Builder as ValidatorDirBuilder;
@@ -183,6 +186,35 @@ pub fn serve<T: 'static + SlotClock + Clone, E: EthSpec>(
     let api_token_path_inner = api_token_path.clone();
     let api_token_path_filter = warp::any().map(move || api_token_path_inner.clone());
 
+    // Create a `warp` filter that provides access to local system information.
+    let system_info = Arc::new(RwLock::new(sysinfo::System::new()));
+    {
+        // grab write access for initialisation
+        let mut system_info = system_info.write();
+        system_info.refresh_disks_list();
+        system_info.refresh_networks_list();
+    } // end lock
+
+    let system_info_filter =
+        warp::any()
+            .map(move || system_info.clone())
+            .map(|sysinfo: Arc<RwLock<System>>| {
+                {
+                    // refresh stats
+                    let mut sysinfo_lock = sysinfo.write();
+                    sysinfo_lock.refresh_memory();
+                    sysinfo_lock.refresh_cpu_specifics(sysinfo::CpuRefreshKind::everything());
+                    sysinfo_lock.refresh_cpu();
+                    sysinfo_lock.refresh_system();
+                    sysinfo_lock.refresh_networks();
+                    sysinfo_lock.refresh_disks();
+                } // end lock
+                sysinfo
+            });
+
+    let app_start = std::time::Instant::now();
+    let app_start_filter = warp::any().map(move || app_start);
+
     // GET lighthouse/version
     let get_node_version = warp::path("lighthouse")
         .and(warp::path("version"))
@@ -279,6 +311,24 @@ pub fn serve<T: 'static + SlotClock + Clone, E: EthSpec>(
             },
         );
 
+    // GET lighthouse/ui/health
+    let get_lighthouse_ui_health = warp::path("lighthouse")
+        .and(warp::path("ui"))
+        .and(warp::path("health"))
+        .and(warp::path::end())
+        .and(system_info_filter)
+        .and(app_start_filter)
+        .and(validator_dir_filter.clone())
+        .and(signer.clone())
+        .and_then(|sysinfo, app_start: std::time::Instant, val_dir, signer| {
+            blocking_signed_json_task(signer, move || {
+                let app_uptime = app_start.elapsed().as_secs() as u64;
+                Ok(api_types::GenericResponse::from(observe_system_health_vc(
+                    sysinfo, val_dir, app_uptime,
+                )))
+            })
+        });
+
     // POST lighthouse/validators/
     let post_validators = warp::path("lighthouse")
         .and(warp::path("validators"))
@@ -894,6 +944,7 @@ pub fn serve<T: 'static + SlotClock + Clone, E: EthSpec>(
                         .or(get_lighthouse_spec)
                         .or(get_lighthouse_validators)
                         .or(get_lighthouse_validators_pubkey)
+                        .or(get_lighthouse_ui_health)
                         .or(get_fee_recipient)
                         .or(get_gas_limit)
                         .or(get_std_keystores)