golang 读取文件内容，清空文件内容，把读取的内容写入到文件里

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package main   import (     "encoding/json"     "fmt"     "io"     "log"     "os" )   type PvRelationList struct {     Item []PvRelationInfo `json:"item"` } type PvRelationInfo struct {     PodName string `json:"pod_name"`     PodUid  string `json:"pod_uid"` }   func readFile(f *os.File) ([]byte, error) {     var size int     if info, err := f.Stat(); err == nil {         size64 := info.Size()         if int64(int(size64)) == size64 {             size = int(size64)         }     }     size++ // one byte for final read at EOF       if size < 512 {         size = 512     }       data := make([]byte, 0, size)     for {         if len(data) >= cap(data) {             d := append(data[:cap(data)], 0)             data = d[:len(data)]         }         n, err := f.Read(data[len(data):cap(data)])         data = data[:len(data)+n]         if err != nil {             if err == io.EOF {                 err = nil             }             return data, err         }     } } func isFileEmpty(filePath string) (bool, error) {     fileInfo, err := os.Stat(filePath)     if err != nil {         return false, err     }       return fileInfo.Size() == 0, nil } func main() {     filename := "1.log"     f, err := os.OpenFile(filename, os.O_RDWR|os.O_CREATE, 0666)     if err != nil {         panic(err.Error())     }     defer f.Close()       readInfo, err := readFile(f)     if err != nil {         fmt.Println(err.Error())     }     fmt.Printf("read data %v \n", string(readInfo))     //write     pvRelationList := make([]PvRelationInfo, 0)     res, err := isFileEmpty(filename)     if err != nil {         panic(err.Error())     }     if !res {         err = json.Unmarshal(readInfo, &pvRelationList)         if err != nil {             panic(err.Error())         }     }     pvRelationInfo := PvRelationInfo{         PodName: "ioioiuo",         PodUid:  "97492uwoer8u",     }     pvRelationList = append(pvRelationList, pvRelationInfo)     pvRelationListByte, err := json.Marshal(pvRelationList)     if err != nil {         panic(err.Error())     }     err = f.Truncate(0)     if err != nil {         panic(err.Error())     }     // 将文件指针移动到文件的开始位置     _, err = f.Seek(0, 0)     if err != nil {         log.Fatalf("failed to seek file: %s", err)     }       fmt.Printf("write data %v \n", string(pvRelationListByte))     writeRes, err := f.Write(pvRelationListByte)     if err != nil {         panic(err.Error())     }     fmt.Println(writeRes)   }