add stronger protections for nil pointers in server join merge

command/agent/config.go

@@ -381,19 +381,31 @@ type ServerJoin struct {
 	RetryInterval time.Duration `mapstructure:"retry_interval"`
 }
 
-func (s *ServerJoin) Merge(b *ServerJoin) {
+func (s *ServerJoin) Merge(b *ServerJoin) *ServerJoin {
+	if s == nil {
+		return b
+	}
+
+	result := *s
+
+	if b == nil {
+		return &result
+	}
+
 	if len(b.StartJoin) != 0 {
-		s.StartJoin = b.StartJoin
+		result.StartJoin = b.StartJoin
 	}
 	if len(b.RetryJoin) != 0 {
-		s.RetryJoin = b.RetryJoin
+		result.RetryJoin = b.RetryJoin
 	}
 	if b.RetryMaxAttempts != 0 {
-		s.RetryMaxAttempts = b.RetryMaxAttempts
+		result.RetryMaxAttempts = b.RetryMaxAttempts
 	}
 	if b.RetryInterval != 0 {
-		s.RetryInterval = b.RetryInterval
+		result.RetryInterval = b.RetryInterval
 	}
+
+	return &result
 }
 
 // EncryptBytes returns the encryption key configured.
@@ -1104,7 +1116,7 @@ func (a *ServerConfig) Merge(b *ServerConfig) *ServerConfig {
 		result.EncryptKey = b.EncryptKey
 	}
 	if b.ServerJoin != nil {
-		result.ServerJoin.Merge(b.ServerJoin)
+		result.ServerJoin = result.ServerJoin.Merge(b.ServerJoin)
 	}
 
 	// Add the schedulers

command/agent/config_test.go

@@ -926,11 +926,11 @@ func TestMergeServerJoin(t *testing.T) {
 		}
 		b := &ServerJoin{}
 
-		a.Merge(b)
-		require.Equal(a.RetryJoin, retryJoin)
-		require.Equal(a.StartJoin, startJoin)
-		require.Equal(a.RetryMaxAttempts, retryMaxAttempts)
-		require.Equal(a.RetryInterval, retryInterval)
+		result := a.Merge(b)
+		require.Equal(result.RetryJoin, retryJoin)
+		require.Equal(result.StartJoin, startJoin)
+		require.Equal(result.RetryMaxAttempts, retryMaxAttempts)
+		require.Equal(result.RetryInterval, retryInterval)
 	}
 	{
 		retryJoin := []string{"127.0.0.1", "127.0.0.2"}
@@ -946,11 +946,51 @@ func TestMergeServerJoin(t *testing.T) {
 			RetryInterval:    time.Duration(retryInterval),
 		}
 
-		a.Merge(b)
-		require.Equal(a.RetryJoin, retryJoin)
-		require.Equal(a.StartJoin, startJoin)
-		require.Equal(a.RetryMaxAttempts, retryMaxAttempts)
-		require.Equal(a.RetryInterval, retryInterval)
+		result := a.Merge(b)
+		require.Equal(result.RetryJoin, retryJoin)
+		require.Equal(result.StartJoin, startJoin)
+		require.Equal(result.RetryMaxAttempts, retryMaxAttempts)
+		require.Equal(result.RetryInterval, retryInterval)
+	}
+	{
+		retryJoin := []string{"127.0.0.1", "127.0.0.2"}
+		startJoin := []string{"127.0.0.1", "127.0.0.2"}
+		retryMaxAttempts := 1
+		retryInterval := time.Duration(0)
+
+		var a *ServerJoin
+		b := &ServerJoin{
+			RetryJoin:        retryJoin,
+			StartJoin:        startJoin,
+			RetryMaxAttempts: retryMaxAttempts,
+			RetryInterval:    time.Duration(retryInterval),
+		}
+
+		result := a.Merge(b)
+		require.Equal(result.RetryJoin, retryJoin)
+		require.Equal(result.StartJoin, startJoin)
+		require.Equal(result.RetryMaxAttempts, retryMaxAttempts)
+		require.Equal(result.RetryInterval, retryInterval)
+	}
+	{
+		retryJoin := []string{"127.0.0.1", "127.0.0.2"}
+		startJoin := []string{"127.0.0.1", "127.0.0.2"}
+		retryMaxAttempts := 1
+		retryInterval := time.Duration(0)
+
+		a := &ServerJoin{
+			RetryJoin:        retryJoin,
+			StartJoin:        startJoin,
+			RetryMaxAttempts: retryMaxAttempts,
+			RetryInterval:    time.Duration(retryInterval),
+		}
+		var b *ServerJoin
+
+		result := a.Merge(b)
+		require.Equal(result.RetryJoin, retryJoin)
+		require.Equal(result.StartJoin, startJoin)
+		require.Equal(result.RetryMaxAttempts, retryMaxAttempts)
+		require.Equal(result.RetryInterval, retryInterval)
 	}
 	{
 		retryJoin := []string{"127.0.0.1", "127.0.0.2"}
@@ -967,10 +1007,10 @@ func TestMergeServerJoin(t *testing.T) {
 			RetryInterval:    time.Duration(retryInterval),
 		}
 
-		a.Merge(b)
-		require.Equal(a.RetryJoin, retryJoin)
-		require.Equal(a.StartJoin, startJoin)
-		require.Equal(a.RetryMaxAttempts, retryMaxAttempts)
-		require.Equal(a.RetryInterval, retryInterval)
+		result := a.Merge(b)
+		require.Equal(result.RetryJoin, retryJoin)
+		require.Equal(result.StartJoin, startJoin)
+		require.Equal(result.RetryMaxAttempts, retryMaxAttempts)
+		require.Equal(result.RetryInterval, retryInterval)
 	}
 }