Filter content by date range or read only last N lines of a file.

logfilter.go

package main

import (
	"bufio"
	"bytes"
	"flag"
	"fmt"
	"io"
	"os"
	"regexp"
	"time"
)

var (
	logFile    string
	afterLines int
	startDate  string
	endDate    string
	mode       string
	lineNum    int
)

const (
	modeDate = "date"
	modeLine = "line"
)

type DateRange struct {
	Start int64
	End   int64
}

func (dr *DateRange) MatchDate(b []byte) bool {
	ly := "2006-01-02"
	f := time.Unix(dr.Start, 0)
	ts := time.Unix(dr.End, 0).Format(ly)
	for {
		fs := f.Format(ly)
		r := regexp.MustCompile(fmt.Sprintf(".*%s.*", fs))
		if r.Match(b) {
			return true
		}
		if fs == ts {
			return false
		}
		f = f.AddDate(0, 0, 1)
	}
}

func GetLogByLine(r io.Reader, n int) []byte {
	buf := bufio.NewReader(r)
	lines := make([][]byte, 0)
	var pre bool
	for {
		line, isPrefix, err := buf.ReadLine()
		if err != nil {
			break
		}
		if !pre {
			lines = append(lines, line)
		} else if len(lines) > 0 {
			lines[len(lines)-1] = append(lines[len(lines)-1], line...)
		}
		if !isPrefix && len(lines) > n {
			lines = lines[1:]
		}
		pre = isPrefix
	}
	result := bytes.Join(lines, []byte("\r\n"))
	return result
}

// param `al` means "After Lines"
func GetLogByDateRange(r io.Reader, dr *DateRange, al int) []byte {
	buf := bufio.NewReader(r)
	lines := make([][]byte, 0)
	var pre bool
	var c int
	for {
		line, isPrefix, err := buf.ReadLine()
		if err != nil {
			break
		}
		m := dr.MatchDate(line)
		if m || (c > 0 && c <= al) {
			if pre {
				lines[len(lines)-1] = append(lines[len(lines)-1], line...)
			} else {
				lines = append(lines, line)
				// Reset c if line matched, or increase c
				if m {
					c = 1
				} else {
					c++
				}
			}
		} else if c != 0 {
			c = 0
		}
		pre = isPrefix
	}
	return bytes.Join(lines, []byte("\r\n"))
}

func main() {
	flag.Usage = func() {
		fmt.Fprintf(flag.CommandLine.Output(), "Filter content by date range or read only last N lines of a file.\n")
		fmt.Fprintf(flag.CommandLine.Output(), "Created by K8sCat <[email protected]>\n\n")
		fmt.Fprintf(flag.CommandLine.Output(), "Usage of %s:\n", os.Args[0])
		flag.PrintDefaults()
	}
	flag.StringVar(&logFile, "f", "", "Log file")
	flag.StringVar(&startDate, "start-date", "", "Start date, layout `2006-01-02`")
	flag.StringVar(&endDate, "end-date", "", "End date, layout `2006-01-02`")
	flag.IntVar(&afterLines, "a", 0, "After lines")
	flag.IntVar(&lineNum, "n", 10, "Line count")
	flag.StringVar(&mode, "m", modeLine, "Mode, date or line")
	flag.Parse()

	f, _ := time.Parse("2006-01-02", startDate)
	t, _ := time.Parse("2006-01-02", endDate)
	dr := &DateRange{
		Start: f.Unix(),
		End:   t.Unix(),
	}
	file, err := os.Open(logFile)
	if err != nil {
		panic(err)
	}

	var result []byte
	switch mode {
	case modeLine:
		result = GetLogByLine(file, lineNum)
	case modeDate:
		result = GetLogByDateRange(file, dr, afterLines)
	default:
		panic("mode not support")
	}
	fmt.Println(string(result))
}