feat: add initial scheduled task implementation

This functionality enables users to manage a global crontab for the Dokku user that contains all scheduled tasks across all apps. Alternative schedulers can implement cron tasks as desired.

plugins/cron/functions.go

@@ -0,0 +1,152 @@
+package cron
+
+import (
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+	"html/template"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strings"
+
+	appjson "github.com/dokku/dokku/plugins/app-json"
+	"github.com/dokku/dokku/plugins/common"
+
+	cronparser "github.com/robfig/cron/v3"
+)
+
+type templateCommand struct {
+	ID       string
+	App      string
+	Command  string
+	Schedule string
+}
+
+func fetchCronEntries(appName string) ([]templateCommand, error) {
+	commands := []templateCommand{}
+	scheduler := common.GetAppScheduler(appName)
+	if scheduler != "docker-local" {
+		return commands, nil
+	}
+
+	appjsonPath := appjson.GetAppjsonPath(appName)
+	if !common.FileExists(appjsonPath) {
+		return commands, nil
+	}
+
+	b, err := ioutil.ReadFile(appjsonPath)
+	if err != nil {
+		return commands, fmt.Errorf("Cannot read app.json file for %s: %v", appName, err)
+	}
+
+	if strings.TrimSpace(string(b)) == "" {
+		return commands, nil
+	}
+
+	var appJSON appjson.AppJSON
+	if err = json.Unmarshal(b, &appJSON); err != nil {
+		return commands, fmt.Errorf("Cannot parse app.json for %s: %v", appName, err)
+	}
+
+	for _, c := range appJSON.Cron {
+		parser := cronparser.NewParser(cronparser.Minute | cronparser.Hour | cronparser.Dom | cronparser.Month | cronparser.Dow | cronparser.Descriptor)
+		_, err := parser.Parse(c.Schedule)
+		if err != nil {
+			return commands, err
+		}
+
+		commands = append(commands, templateCommand{
+			App:      appName,
+			Command:  c.Command,
+			Schedule: c.Schedule,
+			ID:       generateCommandID(appName, c),
+		})
+	}
+
+	return commands, nil
+}
+
+func writeCronEntries() error {
+	apps, err := common.DokkuApps()
+	if err != nil {
+		return nil
+	}
+
+	commands := []templateCommand{}
+	for _, appName := range apps {
+		scheduler := common.GetAppScheduler(appName)
+		if scheduler != "docker-local" {
+			continue
+		}
+
+		c, err := fetchCronEntries(appName)
+		if err != nil {
+			return err
+		}
+
+		commands = append(commands, c...)
+	}
+
+	if len(commands) == 0 {
+		if !common.FileExists("/var/spool/cron/crontabs/dokku") {
+			return nil
+		}
+
+		command := common.NewShellCmd("crontab -r -u dokku")
+		command.ShowOutput = false
+		out, err := command.CombinedOutput()
+		if err != nil {
+			return fmt.Errorf("Unable to remove schedule file: %v", out)
+		}
+	}
+
+	data := map[string]interface{}{
+		"Commands": commands,
+	}
+
+	t, err := getCronTemplate()
+	if err != nil {
+		return err
+	}
+
+	tmpFile, err := ioutil.TempFile(os.TempDir(), fmt.Sprintf("dokku-%s-%s", common.MustGetEnv("DOKKU_PID"), "CopyFromImage"))
+	if err != nil {
+		return fmt.Errorf("Cannot create temporary schedule file: %v", err)
+	}
+
+	defer tmpFile.Close()
+	defer os.Remove(tmpFile.Name())
+
+	if err := t.Execute(tmpFile, data); err != nil {
+		return fmt.Errorf("Unable to template out schedule file: %v", err)
+	}
+
+	command := common.NewShellCmd(fmt.Sprintf("crontab -u dokku %s", tmpFile.Name()))
+	command.ShowOutput = false
+	out, err := command.CombinedOutput()
+	if err != nil {
+		return fmt.Errorf("Unable to update schedule file: %v", out)
+	}
+
+	common.LogInfo1("Updated schedule file")
+
+	return nil
+}
+
+func getCronTemplate() (*template.Template, error) {
+	t := template.New("cron")
+
+	templatePath := filepath.Join(common.MustGetEnv("PLUGIN_ENABLED_PATH"), "cron", "templates", "cron.tmpl")
+	b, err := ioutil.ReadFile(templatePath)
+	if err != nil {
+		return t, fmt.Errorf("Cannot read template file: %v", err)
+	}
+
+	s := strings.TrimSpace(string(b))
+	return t.Parse(s)
+}
+
+func generateCommandID(appName string, c appjson.CronCommand) string {
+	return base64.StdEncoding.EncodeToString([]byte(appName + "===" + c.Command + "===" + c.Schedule))
+}