From 0d9ca2b4c761df52873615087aaa8f84fd761c8a Mon Sep 17 00:00:00 2001
From: David Florness <david@florness.com>
Date: Thu, 31 Mar 2022 19:46:04 -0400
Subject: [PATCH] Check for nil pointer

We've been seeing nil pointer panics in this function.
---
 election/msg.go | 33 ++++++++++++++++++++-------------
 1 file changed, 20 insertions(+), 13 deletions(-)

diff --git a/election/msg.go b/election/msg.go
index c7e4684..9e5b839 100644
--- a/election/msg.go
+++ b/election/msg.go
@@ -598,10 +598,17 @@ func (elections *ElectionsMap) onEvalsMessage(evt *event.Event) (success bool) {
 		return
 	}
 
+	// here to find bugs
+	if el.FinalJoinIDs == nil {
+		errorf("FinalJoinIDs is nil")
+		return
+	}
+	FinalJoinIDs := *el.FinalJoinIDs
+
 	// KeysIDs
-	if len(content.KeysIDs) != len(*el.FinalJoinIDs) {
+	if len(content.KeysIDs) != len(FinalJoinIDs) {
 		warnf("the number of keys IDs is wrong (%s instead of %s)",
-			len(content.KeysIDs), len(*el.FinalJoinIDs))
+			len(content.KeysIDs), len(FinalJoinIDs))
 		return
 	}
 	for i, keysID := range content.KeysIDs {
@@ -610,17 +617,17 @@ func (elections *ElectionsMap) onEvalsMessage(evt *event.Event) (success bool) {
 			debugf("we couldn't get the keys event, %s", keysID)
 			return
 		}
-		if keysEvent.JoinID != (*el.FinalJoinIDs)[i] {
+		if keysEvent.JoinID != FinalJoinIDs[i] {
 			warnf("the join ID (%s) of a key (%s) does not match the start event's join ID (%s)",
-				keysEvent.JoinID, keysID, (*el.FinalJoinIDs)[i])
+				keysEvent.JoinID, keysID, FinalJoinIDs[i])
 			return
 		}
 		contents = append(contents, keysEvent.Content)
 	}
 
-	if len(content.Evals) != len(*el.FinalJoinIDs) {
+	if len(content.Evals) != len(FinalJoinIDs) {
 		warnf("the number of evals is wrong (%s instead of %s)",
-			len(content.Evals), len(*el.FinalJoinIDs))
+			len(content.Evals), len(FinalJoinIDs))
 		return
 	}
 
@@ -705,7 +712,7 @@ func (elections *ElectionsMap) onEvalsMessage(evt *event.Event) (success bool) {
 		}
 	}
 
-	outputHashes := make([][]byte, len(*el.FinalJoinIDs))
+	outputHashes := make([][]byte, len(FinalJoinIDs))
 	for i, eval := range content.Evals {
 		var err error
 		outputHashes[i], err = base64.StdEncoding.DecodeString(eval.OutputHash)
@@ -721,18 +728,18 @@ func (elections *ElectionsMap) onEvalsMessage(evt *event.Event) (success bool) {
 
 		// public
 		publicCircuit.HashSeed = el.GetHashSeed()
-		publicCircuit.Inputs = make([]frontend.Variable, len(*el.FinalJoinIDs))
-		for i, joinID := range *el.FinalJoinIDs {
+		publicCircuit.Inputs = make([]frontend.Variable, len(FinalJoinIDs))
+		for i, joinID := range FinalJoinIDs {
 			publicCircuit.Inputs[i].Assign(&el.Joins[joinID].Input)
 		}
-		publicCircuit.OutputHashes = make([]frontend.Variable, len(*el.FinalJoinIDs))
+		publicCircuit.OutputHashes = make([]frontend.Variable, len(FinalJoinIDs))
 		for i, outputHash := range outputHashes {
 			publicCircuit.OutputHashes[i].Assign(outputHash)
 		}
 
 		// private
 		publicCircuit.BallotBits = make([]frontend.Variable, len(el.Candidates)*len(el.Candidates))
-		publicCircuit.Coeffs = make([]frontend.Variable, len(*el.FinalJoinIDs)-1)
+		publicCircuit.Coeffs = make([]frontend.Variable, len(FinalJoinIDs)-1)
 
 		if el.LocalVoter.EvalVerifyingKey == nil {
 			// should never happen because we processed all keys
@@ -766,13 +773,13 @@ func (elections *ElectionsMap) onEvalsMessage(evt *event.Event) (success bool) {
 	voter.OutputHashes = &outputHashes
 
 	// calculate our sum if we have everyone's outputs
-	for _, voterID := range *el.FinalJoinIDs {
+	for _, voterID := range FinalJoinIDs {
 		if el.Joins[voterID].Output == nil {
 			return true
 		}
 	}
 	sum := new(fr.Element).SetZero()
-	for _, voterID := range *el.FinalJoinIDs {
+	for _, voterID := range FinalJoinIDs {
 		sum.Add(sum, el.Joins[voterID].Output)
 	}
 	el.LocalVoter.Sum = sum
-- 
2.38.4