[NOD-30] move wire.RandomUint64() and binarySerializer to util (#204)

* [NOD-30] move wire.RandomUint64() and binarySerializer to util

* [NOD-30] change const style

util/binaryserializer/binaryserializer_test.go

@@ -0,0 +1,58 @@
+package binaryserializer
+
+import (
+	"reflect"
+	"testing"
+	"unsafe"
+)
+
+func TestBinaryFreeList(t *testing.T) {
+
+	expectedCapacity := 8
+	expectedLength := 8
+
+	first := Borrow()
+	if cap(first) != expectedCapacity {
+		t.Errorf("MsgTx.TestBinaryFreeList: Expected capacity for first %d, but got %d",
+			expectedCapacity, cap(first))
+	}
+	if len(first) != expectedLength {
+		t.Errorf("MsgTx.TestBinaryFreeList: Expected length for first %d, but got %d",
+			expectedLength, len(first))
+	}
+	Return(first)
+
+	// Borrow again, and check that the underlying array is re-used for second
+	second := Borrow()
+	if cap(second) != expectedCapacity {
+		t.Errorf("TestBinaryFreeList: Expected capacity for second %d, but got %d",
+			expectedCapacity, cap(second))
+	}
+	if len(second) != expectedLength {
+		t.Errorf("TestBinaryFreeList: Expected length for second %d, but got %d",
+			expectedLength, len(second))
+	}
+
+	firstArrayAddress := underlyingArrayAddress(first)
+	secondArrayAddress := underlyingArrayAddress(second)
+
+	if firstArrayAddress != secondArrayAddress {
+		t.Errorf("First underlying array is at address %d and second at address %d, "+
+			"which means memory was not re-used", firstArrayAddress, secondArrayAddress)
+	}
+
+	Return(second)
+
+	// test there's no crash when channel is full because borrowed too much
+	buffers := make([][]byte, maxItems+1)
+	for i := 0; i < maxItems+1; i++ {
+		buffers[i] = Borrow()
+	}
+	for i := 0; i < maxItems+1; i++ {
+		Return(buffers[i])
+	}
+}
+
+func underlyingArrayAddress(buf []byte) uint64 {
+	return uint64((*reflect.SliceHeader)(unsafe.Pointer(&buf)).Data)
+}