Refactor API key ownership

It is now owned by the appropriate object (ie metadataRequest owns the fact that
the metadataRequest key is 3).

api.go

@@ -0,0 +1,11 @@
+package kafka
+
+type api interface {
+	key() int16
+	version() int16
+}
+
+type apiEncoder interface {
+	encoder
+	api
+}

broker.go

@@ -164,21 +164,11 @@ func (b *broker) rcvResponseLoop() {
 	}
 }
 
-func (b *broker) sendRequest(clientID *string, body encoder, expectResponse bool) (*responsePromise, error) {
+func (b *broker) sendRequest(clientID *string, body apiEncoder, expectResponse bool) (*responsePromise, error) {
 	var prepEnc prepEncoder
 	var realEnc realEncoder
-	var api API
-
-	switch body.(type) {
-	case *metadataRequest:
-		api = REQUEST_METADATA
-	case *produceRequest:
-		api = REQUEST_PRODUCE
-	default:
-		return nil, EncodingError{"Unknown API."}
-	}
 
-	req := request{api, b.correlation_id, clientID, body}
+	req := request{b.correlation_id, clientID, body}
 
 	req.encode(&prepEnc)
 	if prepEnc.err != nil {
@@ -197,7 +187,7 @@ func (b *broker) sendRequest(clientID *string, body encoder, expectResponse bool
 	return &request.response, nil
 }
 
-func (b *broker) sendAndReceive(clientID *string, req encoder, res decoder) error {
+func (b *broker) sendAndReceive(clientID *string, req apiEncoder, res decoder) error {
 	responseChan, err := b.sendRequest(clientID, req, res != nil)
 	if err != nil {
 		return err

broker_manager.go

@@ -104,7 +104,7 @@ func (bm *brokerManager) choosePartition(topic string, p partitionChooser) (int3
 	return p.choosePartition(partitions), nil
 }
 
-func (bm *brokerManager) sendToPartition(topic string, partition int32, req encoder, res decoder) error {
+func (bm *brokerManager) sendToPartition(topic string, partition int32, req apiEncoder, res decoder) error {
 	b, err := bm.getValidLeader(topic, partition)
 	if err != nil {
 		return err
@@ -151,7 +151,7 @@ func (bm *brokerManager) getDefault() *broker {
 	return bm.defaultBroker
 }
 
-func (bm *brokerManager) sendToAny(req encoder, res decoder) error {
+func (bm *brokerManager) sendToAny(req apiEncoder, res decoder) error {
 	for b := bm.getDefault(); b != nil; b = bm.getDefault() {
 		err := b.sendAndReceive(bm.client.id, req, res)
 		switch err.(type) {

metadata_request.go

@@ -27,3 +27,11 @@ func (mr *metadataRequest) decode(pd packetDecoder) (err error) {
 
 	return nil
 }
+
+func (mr *metadataRequest) key() int16 {
+	return 3
+}
+
+func (mr *metadataRequest) version() int16 {
+	return 0
+}

produce_request.go

@@ -48,3 +48,11 @@ func newSingletonProduceRequest(topic string, partition int32, set *messageSet)
 	req.topics[0].partitions[0].msgSet = set
 	return req
 }
+
+func (p *produceRequest) key() int16 {
+	return 0
+}
+
+func (p *produceRequest) version() int16 {
+	return 0
+}

request.go

@@ -1,31 +1,14 @@
 package kafka
 
-type API struct {
-	key     int16
-	version int16
-}
-
-var (
-	REQUEST_PRODUCE        = API{0, 0}
-	REQUEST_FETCH          = API{1, 0}
-	REQUEST_OFFSET         = API{2, 0}
-	REQUEST_METADATA       = API{3, 0}
-	REQUEST_LEADER_AND_ISR = API{4, 0}
-	REQUEST_STOP_REPLICA   = API{5, 0}
-	REQUEST_OFFSET_COMMIT  = API{6, 0}
-	REQUEST_OFFSET_FETCH   = API{7, 0}
-)
-
 type request struct {
-	api            API
 	correlation_id int32
 	id             *string
-	body           encoder
+	body           apiEncoder
 }
 
 func (r *request) encode(pe packetEncoder) {
-	pe.putInt16(r.api.key)
-	pe.putInt16(r.api.version)
+	pe.putInt16(r.body.key())
+	pe.putInt16(r.body.version())
 	pe.putInt32(r.correlation_id)
 	pe.putString(r.id)
 	r.body.encode(pe)