pool: simplify code

dispatcher/pkg/pool/allocator.go

@@ -33,7 +33,7 @@ const intSize = 32 << (^uint(0) >> 63)
 var defaultBufPool = NewAllocator(intSize - 1)
 
 // GetBuf returns a *Buffer from pool with most appropriate cap.
-// It panics if size <= 0.
+// It panics if size < 0.
 func GetBuf(size int) *Buffer {
 	return defaultBufPool.Get(size)
 }
@@ -77,7 +77,7 @@ func NewAllocator(maxPoolBitsLen int) *Allocator {
 
 // Get returns a []byte from pool with most appropriate cap
 func (alloc *Allocator) Get(size int) *Buffer {
-	if size <= 0 {
+	if size < 0 {
 		panic(fmt.Sprintf("invalid slice size %d", size))
 	}
 

dispatcher/pkg/pool/allocator_test.go

@@ -31,7 +31,9 @@ func TestAllocator_Get(t *testing.T) {
 		wantPanic bool
 	}{
 		{-1, 0, true}, // invalid
-		{0, 0, true},  // invalid
+		{0, 1, false},
+		{1, 1, false},
+		{2, 2, false},
 		{12, 16, false},
 		{256, 256, false},
 		{257, 0, true}, // invalid, too large

dispatcher/pkg/pool/msg_buf.go

@@ -18,28 +18,18 @@
 package pool
 
 import (
-	"fmt"
 	"github.com/miekg/dns"
 )
 
+// There is no such way to give dns.Msg.PackBuffer() a buffer
+// with a proper size.
+// Just give it a big buf and hope the buf will be reused in most scenes.
+const packBufSize = 4096
+
 // PackBuffer packs the dns msg m to wire format.
 // Callers should release the buf after they have done with the wire []byte.
 func PackBuffer(m *dns.Msg) (wire []byte, buf *Buffer, err error) {
-	l := m.Len()
-	if l > dns.MaxMsgSize || l <= 0 {
-		return nil, nil, fmt.Errorf("msg length %d is invalid", l)
-	}
-
-	// dns.Msg.PackBuffer() needs one more bit than its msg length.
-	// It also needs a much larger buffer if the msg is compressed.
-	// It is tedious to force dns.Msg.PackBuffer() to use the buffer.
-	// Just give it a big buf and hope the buf will be reused in most scenes.
-	if l > 4095 {
-		buf = GetBuf(l + 1)
-	} else {
-		buf = GetBuf(4096)
-	}
-
+	buf = GetBuf(packBufSize)
 	wire, err = m.PackBuffer(buf.Bytes())
 	if err != nil {
 		buf.Release()