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app.go
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app.go
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package main
import (
"bufio"
"bytes"
"fmt"
"io"
"io/ioutil"
"log"
"os"
"regexp"
"strings"
"github.com/pkg/errors"
"github.com/robfig/cron/v3"
"github.com/tim-online/insert-cronjob-into-crontab/logger"
)
// Initialize cronjob parser
var (
parser = cron.NewParser(cron.Minute | cron.Hour | cron.Dom | cron.Month | cron.Dow | cron.Descriptor)
assignmentRegexp = regexp.MustCompile(`^\s*\w*\s*=\s*\w*`)
)
type App struct {
log *logger.Logger
Config Config
}
func NewApp() *App {
app := &App{}
logger, err := app.newLogger()
if err != nil {
log.Fatal(err)
}
err = app.initializeConfig()
if err != nil {
log.Fatal(err)
}
// initialize logger again but with config value
logger, err = app.newLogger()
if err != nil {
app.log.Fatal(err)
}
app.setLogger(logger)
return app
}
func (a *App) initializeConfig() error {
return nil
}
func (a *App) newLogger() (*logger.Logger, error) {
log := logger.New(logger.Config{})
return log, nil
}
func (a *App) setLogger(log *logger.Logger) error {
a.log = log
return nil
}
func (a *App) Run(alias string, cronLines []string) error {
for _, cronLine := range cronLines {
err := checkCronLine(cronLine)
if err != nil {
return err
}
}
cronLine := cronLines[0]
// stdin is "just" a file so stat it
stdin := os.Stdin
fi, err := stdin.Stat()
if err != nil {
return err
}
if fi.Mode()&os.ModeNamedPipe == 0 {
// no pipe
return errors.New("Please provide a crontab via stdin")
}
// read all stdin
b, err := ioutil.ReadAll(stdin)
if err != nil {
return err
}
// search for lines matching the comment
r := bytes.NewReader(b)
// check if stdin contains a valid crontab
err = checkCrontab(r)
r.Seek(0, 0)
if err != nil {
return err
}
linesWithComment := findLinesWithAlias(alias, r)
r.Seek(0, 0)
if len(linesWithComment) > 1 {
return errors.Errorf(`Found too many lines matching '%s'. Don't know what to do ¯\_(ツ)_/¯`, alias)
}
// replace existing line
if len(linesWithComment) > 0 {
lineNo := 0
for l, _ := range linesWithComment {
lineNo = l
}
replaceLine(r, lineNo, cronLine, os.Stdout)
return nil
}
entry := fmt.Sprintf(`# %s
%s`, alias, cronLine)
io.Copy(os.Stdout, r)
os.Stdout.Write([]byte(entry))
os.Stdout.Write([]byte(string('\n')))
return err
}
func findLinesWithAlias(alias string, crontab io.Reader) map[int]string {
comment := fmt.Sprintf("# %s", alias)
scanner := bufio.NewScanner(crontab)
i := 0
linesWithComment := map[int]string{}
for scanner.Scan() {
line := scanner.Text()
line = strings.TrimSpace(line)
if line == comment {
linesWithComment[i] = line
}
i = i + 1
}
return linesWithComment
}
func replaceLine(crontab io.Reader, lineNo int, cronLine string, w io.Writer) {
scanner := bufio.NewScanner(crontab)
i := 0
for scanner.Scan() {
if i == lineNo+1 {
w.Write([]byte(cronLine))
w.Write([]byte(string('\n')))
i = i + 1
continue
}
i = i + 1
w.Write(scanner.Bytes())
w.Write([]byte(string('\n')))
}
return
}
func checkCronLine(cronLine string) error {
// Check if cronjob contains enough fields
pieces := strings.Split(cronLine, " ")
if len(pieces) < 6 {
_, err := parser.Parse(cronLine)
return errors.Errorf("%s is not a valid cron expression (%s)", cronLine, err)
}
// Check if cronjob is valid
spec := strings.Join(pieces[0:5], " ")
// cmd := strings.Join(pieces[5:], " ")
_, err := parser.Parse(spec)
if err != nil {
return errors.Errorf("%s is not a valid cron expression (%s)", spec, err)
}
return nil
}
func checkCrontab(crontab io.Reader) error {
scanner := bufio.NewScanner(crontab)
i := 0
for scanner.Scan() {
line := scanner.Text()
if strings.TrimSpace(line) == "" {
i = i + 1
continue
}
if lineIsComment(line) {
i = i + 1
continue
}
if lineIsAssignment(line) {
i = i + 1
continue
}
// not a comment & not an assignment: should be a valid cron expression
err := checkCronLine(line)
if err != nil {
return err
}
}
return nil
}
func lineIsComment(line string) bool {
return strings.HasPrefix(line, "#")
}
func lineIsAssignment(line string) bool {
return assignmentRegexp.MatchString(line)
}