Add trusted peers (#1640)

## Issue Addressed

Closes #1581 

## Proposed Changes

Adds a new cli option for trusted peers who always have the maximum possible score.

beacon_node/eth2_libp2p/src/peer_manager/peer_info.rs

@@ -1,5 +1,5 @@
 use super::client::Client;
-use super::score::Score;
+use super::score::{PeerAction, Score, ScoreState};
 use super::PeerSyncStatus;
 use crate::rpc::MetaData;
 use crate::Multiaddr;
@@ -19,7 +19,7 @@ pub struct PeerInfo<T: EthSpec> {
     /// The connection status of the peer
     _status: PeerStatus,
     /// The peers reputation
-    pub score: Score,
+    score: Score,
     /// Client managing this peer
     pub client: Client,
     /// Connection status of this peer
@@ -36,6 +36,8 @@ pub struct PeerInfo<T: EthSpec> {
     /// necessary.
     #[serde(skip)]
     pub min_ttl: Option<Instant>,
+    /// Is the peer a trusted peer.
+    pub is_trusted: bool,
 }
 
 impl<TSpec: EthSpec> Default for PeerInfo<TSpec> {
@@ -49,11 +51,21 @@ impl<TSpec: EthSpec> Default for PeerInfo<TSpec> {
             sync_status: PeerSyncStatus::Unknown,
             meta_data: None,
             min_ttl: None,
+            is_trusted: false,
         }
     }
 }
 
 impl<T: EthSpec> PeerInfo<T> {
+    /// Return a PeerInfo struct for a trusted peer.
+    pub fn trusted_peer_info() -> Self {
+        PeerInfo {
+            score: Score::max_score(),
+            is_trusted: true,
+            ..Default::default()
+        }
+    }
+
     /// Returns if the peer is subscribed to a given `SubnetId`
     pub fn on_subnet(&self, subnet_id: SubnetId) -> bool {
         if let Some(meta_data) = &self.meta_data {
@@ -69,6 +81,38 @@ impl<T: EthSpec> PeerInfo<T> {
     pub fn has_future_duty(&self) -> bool {
         self.min_ttl.map_or(false, |i| i >= Instant::now())
     }
+
+    /// Returns score of the peer.
+    pub fn score(&self) -> Score {
+        self.score
+    }
+
+    /// Returns the state of the peer based on the score.
+    pub(crate) fn score_state(&self) -> ScoreState {
+        self.score.state()
+    }
+
+    /// Applies decay rates to a non-trusted peer's score.
+    pub fn score_update(&mut self) {
+        if !self.is_trusted {
+            self.score.update()
+        }
+    }
+
+    /// Apply peer action to a non-trusted peer's score.
+    pub fn apply_peer_action_to_score(&mut self, peer_action: PeerAction) {
+        if !self.is_trusted {
+            self.score.apply_peer_action(peer_action)
+        }
+    }
+
+    #[cfg(test)]
+    /// Add an f64 to a non-trusted peer's score abiding by the limits.
+    pub fn add_to_score(&mut self, score: f64) {
+        if !self.is_trusted {
+            self.score.add(score)
+        }
+    }
 }
 
 #[derive(Clone, Debug, Serialize)]