fix issue 971 (#973)

* fix issue 971

* fix int => int32

* fix TestMakeBrokersOneMissing

* update documentation

conn.go

@@ -1017,11 +1017,17 @@ func (c *Conn) ReadPartitions(topics ...string) (partitions []Partition, err err
 }
 
 func makeBrokers(brokers map[int32]Broker, ids ...int32) []Broker {
-	b := make([]Broker, 0, len(ids))
-	for _, id := range ids {
-		if br, ok := brokers[id]; ok {
-			b = append(b, br)
+	b := make([]Broker, len(ids))
+	for i, id := range ids {
+		br, ok := brokers[id]
+		if !ok {
+			// When the broker id isn't found in the current list of known
+			// brokers, use a placeholder to report that the cluster has
+			// logical knowledge of the broker but no information about the
+			// physical host where it is running.
+			br.ID = int(id)
 		}
+		b[i] = br
 	}
 	return b
 }

conn_test.go

@@ -1353,16 +1353,19 @@ func TestMakeBrokersAllPresent(t *testing.T) {
 func TestMakeBrokersOneMissing(t *testing.T) {
 	brokers := make(map[int32]Broker)
 	brokers[1] = Broker{ID: 1, Host: "203.0.113.101", Port: 9092}
-	brokers[3] = Broker{ID: 1, Host: "203.0.113.103", Port: 9092}
+	brokers[3] = Broker{ID: 3, Host: "203.0.113.103", Port: 9092}
 
 	b := makeBrokers(brokers, 1, 2, 3)
-	if len(b) != 2 {
-		t.Errorf("Expected 2 brokers, got %d", len(b))
+	if len(b) != 3 {
+		t.Errorf("Expected 3 brokers, got %d", len(b))
 	}
 	if b[0] != brokers[1] {
 		t.Errorf("Expected broker 1 at index 0, got %d", b[0].ID)
 	}
-	if b[1] != brokers[3] {
-		t.Errorf("Expected broker 3 at index 1, got %d", b[1].ID)
+	if b[1] != (Broker{ID: 2}) {
+		t.Errorf("Expected broker 2 at index 1, got %d", b[1].ID)
+	}
+	if b[2] != brokers[3] {
+		t.Errorf("Expected broker 3 at index 1, got %d", b[2].ID)
 	}
 }

kafka.go

@@ -38,6 +38,11 @@ type Partition struct {
 	ID    int
 
 	// Leader, replicas, and ISR for the partition.
+	//
+	// When no physical host is known to be running a broker, the Host and Port
+	// fields will be set to the zero values. The logical broker ID is always
+	// set to the value known to the kafka cluster, even if the broker is not
+	// currently backed by a physical host.
 	Leader   Broker
 	Replicas []Broker
 	Isr      []Broker