如何从后往前按行读取文件,有什么思路?
7楼 <a href="/user/victorl" title="@victorl">@victorl</a> 前面我改的那个是复杂了,我改了下
```golang
c.fileSize = offset
if offset == 0 {
_, err = c.bwr.Write([]byte{'\n'})
if err != nil {
return err
}
} else {
if c.fileSize > buffSize {
c.fileSize = offset + n - 1
} else {
c.fileSize = offset + n - 1
c.swapBuff = make([]byte, c.fileSize)
}
}
```
#11
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临时写了一个,测试了一下可以,如用于生产环境的话还需要严格测试。
```go
package file
import (
"bytes"
"fmt"
"io"
"os"
)
var (
buffSize = 1 << 20
)
// ReadLineFromEnd --
type ReadLineFromEnd struct {
f *os.File
fileSize int
bwr *bytes.Buffer
swapBuff []byte
}
// NewReadLineFromEnd --
func NewReadLineFromEnd(name string) (rd *ReadLineFromEnd, err error) {
f, err := os.Open(name)
if err != nil {
return nil, err
}
info, err := f.Stat()
if info.IsDir() {
return nil, fmt.Errorf("not file")
}
fileSize := int(info.Size())
rd = &ReadLineFromEnd{
f: f,
fileSize: fileSize,
bwr: bytes.NewBuffer([]byte{}),
swapBuff: make([]byte, buffSize),
}
return rd, nil
}
// Read --
func (c *ReadLineFromEnd) Read(p []byte) (n int, err error) {
err = c.buff()
if err != nil {
return n, err
}
return c.bwr.Read(p)
}
// ReadLine 结尾包含'\n'
func (c *ReadLineFromEnd) ReadLine() (line []byte, err error) {
err = c.buff()
if err != nil {
return nil, err
}
return c.bwr.ReadBytes('\n')
}
// Close --
func (c *ReadLineFromEnd) Close() (err error) {
return c.f.Close()
}
func (c *ReadLineFromEnd) buff() (err error) {
if c.fileSize == 0 {
return nil
}
if c.bwr.Len() >= buffSize {
return nil
}
offset := 0
if c.fileSize > buffSize {
offset = c.fileSize - buffSize
}
_, err = c.f.Seek(int64(offset), 0)
if err != nil {
return err
}
n, err := c.f.Read(c.swapBuff)
if err != nil && err != io.EOF {
return err
}
if n == 0 {
return nil
}
for {
m := bytes.LastIndex(c.swapBuff[:n], []byte{'\n'})
if m == -1 {
break
}
if m < n-1 {
_, err = c.bwr.Write(c.swapBuff[m+1 : n])
if err != nil {
return err
}
_, err = c.bwr.Write([]byte{'\n'})
if err != nil {
return err
}
}
n = m
if n == 0 {
break
}
}
if n > 0 {
_, err := c.bwr.Write(c.swapBuff[:n])
if err != nil {
return err
}
}
c.fileSize = offset
return nil
}
```
测试代码
```go
func TestNewReadLineFromEnd(t *testing.T) {
rd, err := NewReadLineFromEnd("./123.log")
if err != nil {
t.Fatal(err)
}
defer rd.Close()
for {
data, err := rd.ReadLine()
if err != nil {
if err != io.EOF {
t.Fatal(err)
}
break
}
fmt.Print(string(data))
}
}
```
#2