修复热点数据从文件系统转移到内存时可能不完整的Bug/实现部分Partial Content功能

internal/caches/writer_memory.go

@@ -1,6 +1,7 @@
 package caches
 
 import (
+	"errors"
 	"github.com/cespare/xxhash"
 	"sync"
 	"time"
@@ -55,6 +56,13 @@ func (this *MemoryWriter) Write(data []byte) (n int, err error) {
 	return len(data), nil
 }
 
+// WriteAt 在指定位置写入数据
+func (this *MemoryWriter) WriteAt(b []byte, offset int64) error {
+	_ = b
+	_ = offset
+	return errors.New("not supported")
+}
+
 // HeaderSize 数据尺寸
 func (this *MemoryWriter) HeaderSize() int64 {
 	return this.headerSize