golang 大文件分割

package main    import (      "fmt"      "io/ioutil"      "math"      "os"      "strconv"  )    const chunkSize int64 = 4 << 20    func main() {      fileInfo, err := os.Stat("test.zip")      if err != nil {          fmt.Println(err)      }        num := int(math.Ceil(float64(fileInfo.Size()) / float64(chunkSize)))        fi, err := os.OpenFile("test.zip", os.O_RDONLY, os.ModePerm)      if err != nil {          fmt.Println(err)          return      }      b := make([]byte, chunkSize)      var i int64 = 1      for ; i <= int64(num); i++ {            fi.Seek((i-1)*(chunkSize), 0)            if len(b) > int((fileInfo.Size() - (i-1)*chunkSize)) {              b = make([]byte, fileInfo.Size()-(i-1)*chunkSize)          }            fi.Read(b)            f, err := os.OpenFile("./"+strconv.Itoa(int(i))+".db", os.O_CREATE|os.O_WRONLY, os.ModePerm)          if err != nil {              fmt.Println(err)              return          }          f.Write(b)          f.Close()      }      fi.Close()      fii, err := os.OpenFile("test.zip", os.O_CREATE|os.O_WRONLY|os.O_APPEND, os.ModePerm)      if err != nil {          fmt.Println(err)          return      }      for i := 1; i <= num; i++ {          f, err := os.OpenFile("./"+strconv.Itoa(int(i))+".db", os.O_RDONLY, os.ModePerm)          if err != nil {              fmt.Println(err)              return          }          b, err := ioutil.ReadAll(f)          if err != nil {              fmt.Println(err)              return          }          fii.Write(b)          f.Close()      }  }