Add unit tests for Kafka dissector (#807)

* Add unit tests for Kafka dissector

* Return `io.EOF` if request or response header size is zero

* Sort the slice in `representMapAsTable`

* Remove the dead code

* Remove more dead code

* Remove more dead code

* Fix `dissector.Analyze` call

Co-authored-by: gadotroee <55343099+gadotroee@users.noreply.github.com>

tap/extensions/kafka/decode.go

@@ -1,7 +1,6 @@
 package kafka
 
 import (
-	"bytes"
 	"encoding/binary"
 	"fmt"
 	"hash/crc32"
@@ -9,8 +8,6 @@ import (
 	"io/ioutil"
 	"reflect"
 	"strings"
-	"sync"
-	"sync/atomic"
 )
 
 type discarder interface {
@@ -26,15 +23,6 @@ type decoder struct {
 	crc32  uint32
 }
 
-func (d *decoder) Reset(r io.Reader, n int) {
-	d.reader = r
-	d.remain = n
-	d.buffer = [8]byte{}
-	d.err = nil
-	d.table = nil
-	d.crc32 = 0
-}
-
 func (d *decoder) Read(b []byte) (int, error) {
 	if d.err != nil {
 		return 0, d.err
@@ -483,52 +471,3 @@ func decodeReadInt32(b []byte) int32 {
 func decodeReadInt64(b []byte) int64 {
 	return int64(binary.BigEndian.Uint64(b))
 }
-
-func Unmarshal(data []byte, version int16, value interface{}) error {
-	typ := elemTypeOf(value)
-	cache, _ := unmarshalers.Load().(map[versionedType]decodeFunc)
-	key := versionedType{typ: typ, version: version}
-	decode := cache[key]
-
-	if decode == nil {
-		decode = decodeFuncOf(reflect.TypeOf(value).Elem(), version, false, structTag{
-			MinVersion: -1,
-			MaxVersion: -1,
-			TagID:      -2,
-			Compact:    true,
-			Nullable:   true,
-		})
-
-		newCache := make(map[versionedType]decodeFunc, len(cache)+1)
-		newCache[key] = decode
-
-		for typ, fun := range cache {
-			newCache[typ] = fun
-		}
-
-		unmarshalers.Store(newCache)
-	}
-
-	d, _ := decoders.Get().(*decoder)
-	if d == nil {
-		d = &decoder{reader: bytes.NewReader(nil)}
-	}
-
-	d.remain = len(data)
-	r, _ := d.reader.(*bytes.Reader)
-	r.Reset(data)
-
-	defer func() {
-		r.Reset(nil)
-		d.Reset(r, 0)
-		decoders.Put(d)
-	}()
-
-	decode(d, valueOf(value))
-	return dontExpectEOF(d.err)
-}
-
-var (
-	decoders     sync.Pool    // *decoder
-	unmarshalers atomic.Value // map[versionedType]decodeFunc
-)