From 1a8cf8cfb31f585450cc4dea0e2f490d0894d2f8 Mon Sep 17 00:00:00 2001
From: Jamie Holdstock <jholdstock@decred.org>
Date: Tue, 22 Mar 2022 13:46:43 +0000
Subject: [PATCH] Fix assignment to nil map.

Ensure that Tickets loaded from the database are returned with empty maps instead of nil maps.

To be back-ported to 1.1.0 release.
---
 database/helpers.go      | 28 +++++++++++++++
 database/helpers_test.go | 78 ++++++++++++++++++++++++++++++++++++++++
 database/ticket.go       | 28 +++++----------
 3 files changed, 115 insertions(+), 19 deletions(-)
 create mode 100644 database/helpers.go
 create mode 100644 database/helpers_test.go

diff --git a/database/helpers.go b/database/helpers.go
new file mode 100644
index 00000000..099d46e7
--- /dev/null
+++ b/database/helpers.go
@@ -0,0 +1,28 @@
+// Copyright (c) 2022 The Decred developers
+// Use of this source code is governed by an ISC
+// license that can be found in the LICENSE file.
+
+package database
+
+import (
+	"encoding/json"
+)
+
+func bytesToStringMap(bytes []byte) (map[string]string, error) {
+	if bytes == nil {
+		return make(map[string]string), nil
+	}
+
+	var stringMap map[string]string
+	err := json.Unmarshal(bytes, &stringMap)
+	if err != nil {
+		return nil, err
+	}
+
+	// stringMap can still be nil here, eg. if bytes == "null".
+	if stringMap == nil {
+		stringMap = make(map[string]string)
+	}
+
+	return stringMap, nil
+}
diff --git a/database/helpers_test.go b/database/helpers_test.go
new file mode 100644
index 00000000..b12f53dd
--- /dev/null
+++ b/database/helpers_test.go
@@ -0,0 +1,78 @@
+// Copyright (c) 2022 The Decred developers
+// Use of this source code is governed by an ISC
+// license that can be found in the LICENSE file.
+
+package database
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestBytesToStringMap(t *testing.T) {
+	t.Parallel()
+
+	var tests = []struct {
+		name      string
+		input     []byte
+		expect    map[string]string
+		expectErr bool
+	}{
+		{
+			name:      "Empty map on nil bytes",
+			input:     nil,
+			expect:    map[string]string{},
+			expectErr: false,
+		},
+		{
+			name:      "Empty map on empty json map",
+			input:     []byte("{}"),
+			expect:    map[string]string{},
+			expectErr: false,
+		},
+		{
+			name:      "Empty map on null",
+			input:     []byte("null"),
+			expect:    map[string]string{},
+			expectErr: false,
+		},
+		{
+			name:      "Correct values with valid json",
+			input:     []byte("{\"key\":\"value\"}"),
+			expect:    map[string]string{"key": "value"},
+			expectErr: false,
+		},
+		{
+			name:      "Error on no bytes",
+			input:     []byte(""),
+			expect:    nil,
+			expectErr: true,
+		},
+		{
+			name:      "Error on invalid json",
+			input:     []byte("invalid json"),
+			expect:    nil,
+			expectErr: true,
+		},
+		{
+			name:      "Error on non-map json",
+			input:     []byte("[\"not a map\"]"),
+			expect:    nil,
+			expectErr: true,
+		},
+	}
+
+	for _, test := range tests {
+		test := test
+		t.Run(test.name, func(t *testing.T) {
+			t.Parallel()
+			result, err := bytesToStringMap(test.input)
+			if !reflect.DeepEqual(test.expect, result) {
+				t.Fatalf("expected %v, got %v", test.expect, result)
+			}
+			if test.expectErr != (err != nil) {
+				t.Fatalf("expected err=%t, got %v", test.expectErr, err)
+			}
+		})
+	}
+}
diff --git a/database/ticket.go b/database/ticket.go
index 18c7443b..e3df2d83 100644
--- a/database/ticket.go
+++ b/database/ticket.go
@@ -223,29 +223,19 @@ func getTicketFromBkt(bkt *bolt.Bucket) (Ticket, error) {
 	ticket.Confirmed = bytesToBool(bkt.Get(confirmedK))
 
 	var err error
-
-	voteChoicesB := bkt.Get(voteChoicesK)
-	if voteChoicesB != nil {
-		err = json.Unmarshal(voteChoicesB, &ticket.VoteChoices)
-		if err != nil {
-			return ticket, fmt.Errorf("unmarshal VoteChoices err: %w", err)
-		}
+	ticket.VoteChoices, err = bytesToStringMap(bkt.Get(voteChoicesK))
+	if err != nil {
+		return ticket, fmt.Errorf("unmarshal VoteChoices err: %w", err)
 	}
 
-	tSpendPolicyB := bkt.Get(tSpendPolicyK)
-	if tSpendPolicyB != nil {
-		err = json.Unmarshal(tSpendPolicyB, &ticket.TSpendPolicy)
-		if err != nil {
-			return ticket, fmt.Errorf("unmarshal TSpendPolicy err: %w", err)
-		}
+	ticket.TSpendPolicy, err = bytesToStringMap(bkt.Get(tSpendPolicyK))
+	if err != nil {
+		return ticket, fmt.Errorf("unmarshal TSpendPolicy err: %w", err)
 	}
 
-	treasuryPolicyB := bkt.Get(treasuryPolicyK)
-	if treasuryPolicyB != nil {
-		err = json.Unmarshal(treasuryPolicyB, &ticket.TreasuryPolicy)
-		if err != nil {
-			return ticket, fmt.Errorf("unmarshal TreasuryPolicy err: %w", err)
-		}
+	ticket.TreasuryPolicy, err = bytesToStringMap(bkt.Get(treasuryPolicyK))
+	if err != nil {
+		return ticket, fmt.Errorf("unmarshal TreasuryPolicy err: %w", err)
 	}
 
 	return ticket, nil