init: initialize bundle maintenance

Interface through 'crontab' to update the daily maintenance schedule
for all routes. This can be modified in the future to allow both a
--daily and --hourly schedule.

Author: derrickstolee

cmd/git-bundle-server/cron.go

@@ -0,0 +1,54 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"strings"
+
+	"github.com/github/git-bundle-server/internal/core"
+)
+
+func SetCronSchedule() error {
+	pathToExec, err := os.Executable()
+	if err != nil {
+		return fmt.Errorf("failed to get executable: %w", err)
+	}
+
+	dailySchedule := "0 0 * * * \"" + pathToExec + "\" update-all\n"
+
+	scheduleBytes, err := core.LoadExistingSchedule()
+	if err != nil {
+		return fmt.Errorf("failed to get existing cron schedule: %w", err)
+	}
+
+	scheduleStr := string(scheduleBytes)
+
+	// TODO: Use comments to indicate a "region" where our schedule
+	// is set, so we can remove the entire region even if we update
+	// the schedule in the future.
+	if strings.Contains(scheduleStr, dailySchedule) {
+		// We already have this schedule, so skip modifying
+		// the crontab schedule.
+		return nil
+	}
+
+	scheduleBytes = append(scheduleBytes, []byte(dailySchedule)...)
+	scheduleFile := core.CrontabFile()
+
+	err = os.WriteFile(scheduleFile, scheduleBytes, 0o600)
+	if err != nil {
+		return fmt.Errorf("failed to write new cron schedule to temp file: %w", err)
+	}
+
+	err = core.CommitCronSchedule(scheduleFile)
+	if err != nil {
+		return fmt.Errorf("failed to commit new cron schedule: %w", err)
+	}
+
+	err = os.Remove(scheduleFile)
+	if err != nil {
+		return fmt.Errorf("failed to clear schedule file: %w", err)
+	}
+
+	return nil
+}

cmd/git-bundle-server/init.go

@@ -63,5 +63,7 @@ func (Init) run(args []string) error {
 		return fmt.Errorf("failed to write bundle list: %w", listErr)
 	}
 
+	SetCronSchedule()
+
 	return nil
 }

internal/core/cron.go

@@ -0,0 +1,64 @@
+package core
+
+import (
+	"bytes"
+	"fmt"
+	"os/exec"
+)
+
+func GetCrontabCommand(args ...string) (*exec.Cmd, error) {
+	crontab, err := exec.LookPath("crontab")
+	if err != nil {
+		return nil, fmt.Errorf("failed to find 'crontab' on the path: %w", err)
+	}
+
+	cmd := exec.Command(crontab, args...)
+	return cmd, nil
+}
+
+func LoadExistingSchedule() ([]byte, error) {
+	cmd, err := GetCrontabCommand("-l")
+	if err != nil {
+		return nil, err
+	}
+
+	buffer := bytes.Buffer{}
+	cmd.Stdout = &buffer
+
+	errorBuffer := bytes.Buffer{}
+	cmd.Stderr = &errorBuffer
+
+	err = cmd.Start()
+	if err != nil {
+		return nil, fmt.Errorf("crontab failed to start: %w", err)
+	}
+
+	err = cmd.Wait()
+	if err != nil {
+		return nil, fmt.Errorf("crontab returned a failure: %w\nstderr: %s", err, errorBuffer.String())
+	}
+
+	return buffer.Bytes(), nil
+}
+
+func CommitCronSchedule(filename string) error {
+	cmd, err := GetCrontabCommand(filename)
+	if err != nil {
+		return err
+	}
+
+	errorBuffer := bytes.Buffer{}
+	cmd.Stderr = &errorBuffer
+
+	err = cmd.Start()
+	if err != nil {
+		return fmt.Errorf("crontab failed to start: %w", err)
+	}
+
+	err = cmd.Wait()
+	if err != nil {
+		return fmt.Errorf("crontab returned a failure: %w\nstderr: %s", err, errorBuffer.String())
+	}
+
+	return nil
+}

internal/core/paths.go

@@ -19,3 +19,7 @@ func webroot() string {
 func reporoot() string {
 	return bundleroot() + "git/"
 }
+
+func CrontabFile() string {
+	return bundleroot() + "cron-schedule"
+}