add pool & writer

helper/pool.go

@@ -0,0 +1,32 @@
+package helper
+
+import (
+	"bytes"
+	"sync"
+)
+
+// https://github.com/Mrs4s/MiraiGo/blob/master/binary/pool.go
+
+var bufferPool = sync.Pool{
+	New: func() interface{} {
+		return new(Writer)
+	},
+}
+
+// SelectWriter 从池中取出一个 Writer
+func SelectWriter() *Writer {
+	// 因为 bufferPool 定义有 New 函数
+	// 所以 bufferPool.Get() 永不为 nil
+	// 不用判空
+	return bufferPool.Get().(*Writer)
+}
+
+// PutWriter 将 Writer 放回池中
+func PutWriter(w *Writer) {
+	// See https://golang.org/issue/23199
+	const maxSize = 1 << 16
+	if (*bytes.Buffer)(w).Cap() < maxSize { // 对于大Buffer直接丢弃
+		w.Reset()
+		bufferPool.Put(w)
+	}
+}