[FAB-3955] Event producer registers nil handlers

This CR fixes a bug where the event producer would allow a nil handler
to be registered. This resulted in a panic whenever the handler was
used to send an event message.

Change-Id: I757945a71a73b3f9a210ca25e1be1e4027ae2fdd
Signed-off-by: Will Lahti <[email protected]>

Author: wlahti

events/producer/events.go

@@ -50,6 +50,10 @@ type chaincodeHandlerList struct {
 }
 
 func (hl *chaincodeHandlerList) add(ie *pb.Interest, h *handler) (bool, error) {
+	if h == nil {
+		return false, fmt.Errorf("cannot add nil chaincode handler")
+	}
+
 	hl.Lock()
 	defer hl.Unlock()
 
@@ -157,6 +161,9 @@ func (hl *chaincodeHandlerList) foreach(e *pb.Event, action func(h *handler)) {
 }
 
 func (hl *genericHandlerList) add(ie *pb.Interest, h *handler) (bool, error) {
+	if h == nil {
+		return false, fmt.Errorf("cannot add nil generic handler")
+	}
 	hl.Lock()
 	if _, ok := hl.handlers[h]; ok {
 		hl.Unlock()

events/producer/events_test.go

@@ -127,6 +127,8 @@ func TestRegister(t *testing.T) {
 
 	// attempt to register handlers (invalid type or nil handlers)
 	assert.Error(t, registerHandler(&peer.Interest{EventType: 100}, nil))
+	assert.Error(t, registerHandler(&peer.Interest{EventType: peer.EventType_BLOCK}, nil))
+	assert.Error(t, registerHandler(&peer.Interest{EventType: peer.EventType_CHAINCODE}, nil))
 
 	// attempt to register valid handler
 	recvChan := make(chan *streamEvent)