Global Sync access (#994)

* Connect sync logic to network globals

* Add further sync info to sync status

* Build new syncing HTTP API methods

* Fix bug in updating sync state

* Highest slot is current slot

* Update book for syncing API

eth2/utils/rest_types/src/lib.rs

@@ -4,6 +4,7 @@
 
 mod beacon;
 mod consensus;
+mod node;
 mod validator;
 
 pub use beacon::{
@@ -16,3 +17,5 @@ pub use validator::{
 };
 
 pub use consensus::{IndividualVote, IndividualVotesRequest, IndividualVotesResponse};
+
+pub use node::{SyncingResponse, SyncingStatus};

eth2/utils/rest_types/src/node.rs

@@ -0,0 +1,32 @@
+//! Collection of types for the /node HTTP
+use serde::{Deserialize, Serialize};
+use ssz_derive::{Decode, Encode};
+use types::Slot;
+
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize, Encode, Decode)]
+/// The current syncing status of the node.
+pub struct SyncingStatus {
+    /// The starting slot of sync.
+    ///
+    /// For a finalized sync, this is the start slot of the current finalized syncing
+    /// chain.
+    ///
+    /// For head sync this is the last finalized slot.
+    pub starting_slot: Slot,
+    /// The current slot.
+    pub current_slot: Slot,
+    /// The highest known slot. For the current syncing chain.
+    ///
+    /// For a finalized sync, the target finalized slot.
+    /// For head sync, this is the highest known slot of all head chains.
+    pub highest_slot: Slot,
+}
+
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize, Encode, Decode)]
+/// The response for the /node/syncing HTTP GET.
+pub struct SyncingResponse {
+    /// Is the node syncing.
+    pub is_syncing: bool,
+    /// The current sync status.
+    pub sync_status: SyncingStatus,
+}