99 lines
1.8 KiB
Go
99 lines
1.8 KiB
Go
package logger
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import (
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"bufio"
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"fmt"
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"io"
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"os"
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)
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func ReadLastNLines(path string, n int) ([]string, error) {
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// Open the file
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file, err := os.Open(fmt.Sprintf("%s/%s", path, accessFilename))
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if err != nil {
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return nil, err
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}
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defer file.Close()
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// Get file size
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fileInfo, err := file.Stat()
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if err != nil {
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return nil, err
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}
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fileSize := fileInfo.Size()
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// If file is empty, return empty slice
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if fileSize == 0 {
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return []string{}, nil
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}
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// Buffer for reading
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bufferSize := int64(4096)
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if bufferSize > fileSize {
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bufferSize = fileSize
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}
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buffer := make([]byte, bufferSize)
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// Start reading from the end
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position := fileSize
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lines := make([]string, 0, n)
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lineCount := 0
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for lineCount < n && position > 0 {
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// How much to read
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readSize := bufferSize
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if position < bufferSize {
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readSize = position
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}
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position -= readSize
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// Read chunk from position
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_, err := file.Seek(position, io.SeekStart)
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if err != nil {
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return nil, err
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}
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_, err = file.Read(buffer[:readSize])
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if err != nil {
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return nil, err
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}
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// Count newlines in reverse
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for i := readSize - 1; i >= 0; i-- {
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if buffer[i] == '\n' {
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lineCount++
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if lineCount > n {
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// We found more than n lines
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// Need to adjust position to read only last n lines
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position += int64(i) + 1
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break
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}
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}
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}
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}
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// If we couldn't find n lines, start from beginning
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if position < 0 {
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position = 0
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}
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// Seek to the position where we want to start reading
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_, err = file.Seek(position, io.SeekStart)
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if err != nil {
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return nil, err
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}
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// Read lines from position to end
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scanner := bufio.NewScanner(file)
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for scanner.Scan() {
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lines = append(lines, scanner.Text())
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}
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// Check if we need to trim
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if len(lines) > n {
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lines = lines[len(lines)-n:]
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}
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return lines, scanner.Err()
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}
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