extend bytes.Buffer: WriteNextBegin/WriteNextEnd (#73)

* extend bytes.Buffer: WriteNextBegin/WriteNextEnd

* format

* release large buffer

bytes/buffer_test.go

+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package gxbytes
+
+import (
+	"testing"
+)
+
+import (
+	"github.com/stretchr/testify/assert"
+)
+
+func TestBufferWithPeek(t *testing.T) {
+	var b Buffer
+	b.WriteString("hello")
+
+	b1 := b
+	b1.WriteNextBegin(100)
+	assert.True(t, b.off == b1.off)
+	assert.True(t, b.lastRead == b1.lastRead)
+	assert.True(t, len(b.buf) == len(b1.buf))
+	assert.True(t, cap(b.buf) < cap(b1.buf))
+
+	// out of range
+	//l, err := b1.WriteNextEnd(101)
+	//assert.Zero(t, l)
+	//assert.NotNil(t, err)
+
+	l, err := b1.WriteNextEnd(99)
+	assert.Nil(t, err)
+	assert.True(t, l == 99)
+	assert.NotNil(t, b1.buf)
+}