durable-objects-cron

CRON scheduling interface for Cloudflare Worker Durable Objects.

Installation

npm install durable-objects-cron
# or
yarn add durable-objects-cron
# or
pnpm add durable-objects-cron

Usage

This package provides a simple interface for scheduling and executing tasks using Cloudflare Worker Durable Objects' alarm capabilities.

Basic Example

import { createCronDurableObject } from 'durable-objects-cron'

// Create a Durable Object class with cron capabilities
export class MyCronDurableObject extends createCronDurableObject({
  defaultHandler: async (task) => {
    console.log(`Executing task ${task.id} with data:`, task.data)
    // Perform your task logic here
  },
}) {}

// In your Worker
export default {
  async fetch(request, env) {
    const id = env.MY_CRON_DURABLE_OBJECT.newUniqueId()
    const obj = env.MY_CRON_DURABLE_OBJECT.get(id)

    // Schedule a task to run every 5 minutes
    if (request.url.includes('/schedule')) {
      return obj.fetch(
        new Request('http://cron/schedule', {
          method: 'POST',
          headers: { 'Content-Type': 'application/json' },
          body: JSON.stringify({
            cron: '*/5 * * * *',
            options: {
              id: 'my-task',
              data: { foo: 'bar' },
            },
          }),
        }),
      )
    }

    // List all scheduled tasks
    if (request.url.includes('/tasks')) {
      return obj.fetch(new Request('http://cron/tasks'))
    }

    // Cancel a task
    if (request.url.includes('/cancel')) {
      return obj.fetch(
        new Request('http://cron/cancel', {
          method: 'POST',
          headers: { 'Content-Type': 'application/json' },
          body: JSON.stringify({ id: 'my-task' }),
        }),
      )
    }

    return new Response('Not found', { status: 404 })
  },
}

// In your wrangler.toml
// [durable_objects]
// bindings = [
//   { name = "MY_CRON_DURABLE_OBJECT", class_name = "MyCronDurableObject" }
// ]

Advanced Usage with Task-Specific Handlers

import { createCronDurableObject } from 'durable-objects-cron'

// Create a Durable Object class with task-specific handlers
export class MyCronDurableObject extends createCronDurableObject({
  handlers: {
    'backup:': async (task) => {
      console.log(`Running backup task ${task.id}`)
      // Backup logic here
    },
    'notification:': async (task) => {
      console.log(`Sending notification ${task.id}`)
      // Notification logic here
    },
  },
  defaultHandler: async (task) => {
    console.log(`Executing default task ${task.id}`)
    // Default task logic here
  },
}) {}

API

createCronDurableObject(options)

Creates a new Durable Object class with cron capabilities.

Options

• defaultHandler: Function that handles all tasks without a specific handler
• handlers: Record mapping task ID prefixes to handler functions

CronDurableObject Methods

schedule(cron, options)

Schedules a task to be executed according to a cron expression.

• cron: Cron expression (e.g., */5 * * * * for every 5 minutes)
• options:
  • id: Optional unique identifier for the task
  • data: Optional data to be passed to the task when it executes

Returns a ScheduleResult with the task ID and next execution time.

cancel(id)

Cancels a scheduled task.

• id: ID of the task to cancel

Returns a boolean indicating whether the task was found and canceled.

getTask(id)

Gets a scheduled task by ID.

• id: ID of the task to get

Returns the task or null if not found.

listTasks()

Lists all scheduled tasks.

Returns an array of scheduled tasks.

License

MIT License

Copyright (c) 2024 AI Primitives

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Error Handling

The library provides built-in error handling for task execution:

1. When a task fails, the error is logged to the console
2. The error details are stored in the Durable Object storage with a key format of error:{taskId}:{timestamp}
3. The task is updated with error information in its data field:
   • _errors: Count of consecutive errors
   • _lastErrorAt: Timestamp of the last error
   • _lastError: String representation of the last error

Error Handling Recommendations

1. Monitor errors: Regularly check for error records in your Durable Object storage

   // List all error records
   const errors = await storage.list({ prefix: 'error:' })

2. Implement custom error handlers: Extend the default error handling for specific tasks

   createCronDurableObject({
     handlers: {
       'critical:': async (task) => {
         try {
           // Task logic
         } catch (error) {
           // Custom error handling
           await notifyAdmin(error)
           throw error // Re-throw to trigger built-in error handling
         }
       }
     }
   })

3. Add retry limits: Check error counts in your handlers to limit retries

   async function myHandler(task) {
     if (task.data._errors && task.data._errors > 3) {
       console.warn(`Task ${task.id} failed too many times, disabling`)
       // Handle permanent failure
       return
     }
     // Normal task execution
   }