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

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)

}