refactor: consolidate encoding logic across request types

- Refactored Encode methods in ApiVersionsRequest, DescribeTopicPartitionsRequest, and FetchRequest to utilize a shared encodeRequest function, enhancing code reuse and readability.
- Introduced a new request.go file to centralize the encoding logic, streamlining the encoding process for various request types.

Author: ryan-gang

protocol/api/api_versions_request.go

@@ -30,14 +30,7 @@ type ApiVersionsRequest struct {
 }
 
 func (r ApiVersionsRequest) Encode() []byte {
-	encoder := encoder.Encoder{}
-	encoder.Init(make([]byte, 4096))
-
-	r.Header.Encode(&encoder)
-	r.Body.Encode(&encoder)
-	messageBytes := encoder.PackMessage()
-
-	return messageBytes
+	return encodeRequest(r)
 }
 
 func (r ApiVersionsRequest) GetHeader() builder.RequestHeaderI {

protocol/api/describe_topic_partitions_request.go

@@ -59,15 +59,7 @@ type DescribeTopicPartitionsRequest struct {
 }
 
 func (r DescribeTopicPartitionsRequest) Encode() []byte {
-	encoder := encoder.Encoder{}
-	encoder.Init(make([]byte, 4096))
-
-	r.Header.Encode(&encoder)
-	r.Body.Encode(&encoder)
-	messageBytes := encoder.PackMessage()
-
-	return messageBytes
-
+	return encodeRequest(r)
 }
 
 func (r DescribeTopicPartitionsRequest) GetHeader() builder.RequestHeaderI {

protocol/api/fetch_request.go

@@ -109,14 +109,7 @@ type FetchRequest struct {
 }
 
 func (r FetchRequest) Encode() []byte {
-	encoder := encoder.Encoder{}
-	encoder.Init(make([]byte, 4096))
-
-	r.Header.Encode(&encoder)
-	r.Body.Encode(&encoder)
-	message := encoder.PackMessage()
-
-	return message
+	return encodeRequest(r)
 }
 
 func (r FetchRequest) GetHeader() builder.RequestHeaderI {

protocol/api/request.go

@@ -0,0 +1,16 @@
+package kafkaapi
+
+import (
+	"github.com/codecrafters-io/kafka-tester/protocol/builder"
+	"github.com/codecrafters-io/kafka-tester/protocol/encoder"
+)
+
+func encodeRequest(req builder.RequestI) []byte {
+	encoder := encoder.Encoder{}
+	encoder.Init(make([]byte, 4096))
+
+	req.GetHeader().Encode(&encoder)
+	req.GetBody().Encode(&encoder)
+
+	return encoder.PackMessage()
+}