Add API endpoint for fork choice

beacon_node/beacon_chain/src/fork_choice.rs

@@ -29,6 +29,7 @@ pub enum Error {
     UnknownBlockSlot(Hash256),
     UnknownJustifiedBlock(Hash256),
     UnknownJustifiedState(Hash256),
+    UnableToJsonEncode(String),
 }
 
 pub struct ForkChoice<T: BeaconChainTypes> {
@@ -230,6 +231,10 @@ impl<T: BeaconChainTypes> ForkChoice<T> {
         self.backend.maybe_prune(finalized_root).map_err(Into::into)
     }
 
+    pub fn as_json(&self) -> Result<String> {
+        self.backend.as_json().map_err(Error::UnableToJsonEncode)
+    }
+
     /// Returns a `SszForkChoice` which contains the current state of `Self`.
     pub fn as_ssz_container(&self) -> SszForkChoice {
         SszForkChoice {