Add fork choice JSON dumping

eth2/proto_array_fork_choice/src/proto_array.rs

@@ -1,9 +1,10 @@
 use crate::error::Error;
+use serde_derive::{Deserialize, Serialize};
 use ssz_derive::{Decode, Encode};
 use std::collections::HashMap;
 use types::{Epoch, Hash256, Slot};
 
-#[derive(Clone, PartialEq, Debug, Encode, Decode)]
+#[derive(Clone, PartialEq, Debug, Encode, Decode, Serialize, Deserialize)]
 pub struct ProtoNode {
     /// The `slot` is not necessary for `ProtoArray`, it just exists so external components can
     /// easily query the block slot. This is useful for upstream fork choice logic.
@@ -17,7 +18,7 @@ pub struct ProtoNode {
     best_descendant: Option<usize>,
 }
 
-#[derive(PartialEq)]
+#[derive(PartialEq, Serialize, Deserialize)]
 pub struct ProtoArray {
     /// Do not attempt to prune the tree unless it has at least this many nodes. Small prunes
     /// simply waste time.

eth2/proto_array_fork_choice/src/proto_array_fork_choice.rs

@@ -2,6 +2,7 @@ use crate::error::Error;
 use crate::proto_array::ProtoArray;
 use crate::ssz_container::SszContainer;
 use parking_lot::RwLock;
+use serde_json;
 use ssz::{Decode, Encode};
 use ssz_derive::{Decode, Encode};
 use std::collections::HashMap;
@@ -220,6 +221,11 @@ impl ProtoArrayForkChoice {
             .map(Into::into)
             .map_err(|e| format!("Failed to decode ProtoArrayForkChoice: {:?}", e))
     }
+
+    pub fn as_json(&self) -> Result<String, String> {
+        serde_json::to_string(&*self.proto_array.read())
+            .map_err(|e| format!("Failed to JSON encode proto_array: {:?}", e))
+    }
 }
 
 /// Returns a list of `deltas`, where there is one delta for each of the indices in