first commit

pkg/file/file.go

@@ -0,0 +1,189 @@
+package file
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+)
+
+var (
+	buffSize = 1 << 20
+)
+
+// ReadLineFromEnd --
+type ReadLineFromEnd struct {
+	f *os.File
+
+	fileSize int
+	bwr      *bytes.Buffer
+	lineBuff []byte
+	swapBuff []byte
+
+	isFirst bool
+}
+
+// Exists
+func IsExists(path string) (os.FileInfo, bool) {
+	f, err := os.Stat(path)
+	return f, err == nil || os.IsExist(err)
+}
+
+// NewReadLineFromEnd
+func NewReadLineFromEnd(filename string) (rd *ReadLineFromEnd, err error) {
+	f, err := os.Open(filename)
+	if err != nil {
+		return nil, err
+	}
+
+	info, err := f.Stat()
+	if err != nil {
+		return nil, err
+	}
+
+	if info.IsDir() {
+		return nil, fmt.Errorf("not file")
+	}
+
+	fileSize := int(info.Size())
+
+	rd = &ReadLineFromEnd{
+		f:        f,
+		fileSize: fileSize,
+		bwr:      bytes.NewBuffer([]byte{}),
+		lineBuff: make([]byte, 0),
+		swapBuff: make([]byte, buffSize),
+		isFirst:  true,
+	}
+	return rd, nil
+}
+
+// ReadLine 结尾包含'\n'
+func (c *ReadLineFromEnd) ReadLine() (line []byte, err error) {
+	var ok bool
+	for {
+		ok, err = c.buff()
+		if err != nil {
+			return nil, err
+		}
+		if ok {
+			break
+		}
+	}
+	line, err = c.bwr.ReadBytes('\n')
+	if err == io.EOF && c.fileSize > 0 {
+		err = nil
+	}
+	return line, err
+}
+
+// Close --
+func (c *ReadLineFromEnd) Close() (err error) {
+	return c.f.Close()
+}
+
+func (c *ReadLineFromEnd) buff() (ok bool, err error) {
+	if c.fileSize == 0 {
+		return true, nil
+	}
+
+	if c.bwr.Len() >= buffSize {
+		return true, nil
+	}
+
+	offset := 0
+	if c.fileSize > buffSize {
+		offset = c.fileSize - buffSize
+	}
+	_, err = c.f.Seek(int64(offset), 0)
+	if err != nil {
+		return false, err
+	}
+
+	n, err := c.f.Read(c.swapBuff)
+	if err != nil && err != io.EOF {
+		return false, err
+	}
+	if c.fileSize < n {
+		n = c.fileSize
+	}
+	if n == 0 {
+		return true, nil
+	}
+
+	for {
+		m := bytes.LastIndex(c.swapBuff[:n], []byte{'\n'})
+		if m == -1 {
+			break
+		}
+		if m < n-1 {
+			err = c.writeLine(c.swapBuff[m+1 : n])
+			if err != nil {
+				return false, err
+			}
+			ok = true
+		} else if m == n-1 && !c.isFirst {
+			err = c.writeLine(nil)
+			if err != nil {
+				return false, err
+			}
+			ok = true
+		}
+		n = m
+		if n == 0 {
+			break
+		}
+	}
+	if n > 0 {
+		reverseBytes(c.swapBuff[:n])
+		c.lineBuff = append(c.lineBuff, c.swapBuff[:n]...)
+	}
+	if offset == 0 {
+		err = c.writeLine(nil)
+		if err != nil {
+			return false, err
+		}
+		ok = true
+	}
+	c.fileSize = offset
+	if c.isFirst {
+		c.isFirst = false
+	}
+	return ok, nil
+}
+
+func (c *ReadLineFromEnd) writeLine(b []byte) (err error) {
+	if len(b) > 0 {
+		_, err = c.bwr.Write(b)
+		if err != nil {
+			return err
+		}
+	}
+	if len(c.lineBuff) > 0 {
+		reverseBytes(c.lineBuff)
+		_, err = c.bwr.Write(c.lineBuff)
+		if err != nil {
+			return err
+		}
+		c.lineBuff = c.lineBuff[:0]
+	}
+	_, err = c.bwr.Write([]byte{'\n'})
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+func reverseBytes(b []byte) {
+	n := len(b)
+	if n <= 1 {
+		return
+	}
+	for i := 0; i < n; i++ {
+		k := n - 1
+		if k != i {
+			b[i], b[k] = b[k], b[i]
+		}
+		n--
+	}
+}