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# Backie

Background task processing library for Rust. It uses Postgres DB as a task queue.

## Key Features

 Here are some of the fang's key features:

 - Async and threaded workers.
   Workers can be started in threads (threaded workers) or `tokio` tasks (async workers)
 - Scheduled tasks.
   Tasks can be scheduled at any time in the future
 - Periodic (CRON) tasks.
   Tasks can be scheduled using cron expressions
 - Unique tasks.
   Tasks are not duplicated in the queue if they are unique
 - Single-purpose workers.
   Tasks are stored in a single table but workers can be configured to execute only tasks of a specific type
 - Retries.
   Tasks can be retried with a custom backoff mode

## Differences from original fang

- Supports only async processing
- Supports graceful shutdown
- The connection pool for the queue is provided by the user

## Installation

1. Add this to your Cargo.toml


#### the Blocking feature
```toml
[dependencies]
fang = { version = "0.10" , features = ["blocking"], default-features = false }
```

#### the Asynk feature
```toml
[dependencies]
fang = { version = "0.10" , features = ["asynk"], default-features = false }
```

#### Both features
```toml
fang = { version = "0.10" }
```

*Supports rustc 1.67+*

2. Create the `fang_tasks` table in the Postgres database. The migration can be found in [the migrations directory](https://github.com/ayrat555/fang/blob/master/migrations/2022-08-20-151615_create_fang_tasks/up.sql).

## Usage

### Defining a task

#### Blocking feature
Every task should implement the `fang::Runnable` trait which is used by `fang` to execute it.

```rust
use fang::Error;
use fang::Runnable;
use fang::typetag;
use fang::PgConnection;
use fang::serde::{Deserialize, Serialize};

#[derive(Serialize, Deserialize)]
#[serde(crate = "fang::serde")]
struct MyTask {
    pub number: u16,
}

#[typetag::serde]
impl Runnable for MyTask {
    fn run(&self, _queue: &dyn Queueable) -> Result<(), Error> {
        println!("the number is {}", self.number);

        Ok(())
    }

    // If `uniq` is set to true and the task is already in the storage, it won't be inserted again
    // The existing record will be returned for for any insertions operaiton
    fn uniq(&self) -> bool {
      true
    }

    // This will be useful if you want to filter tasks.
    // the default value is `common`
    fn task_type(&self) -> String {
      "my_task".to_string()
    }

    // This will be useful if you would like to schedule tasks.
    // default value is None (the task is not scheduled, it's just executed as soon as it's inserted)
    fn cron(&self) -> Option<Scheduled> {
        let expression = "0/20 * * * Aug-Sep * 2022/1";
        Some(Scheduled::CronPattern(expression.to_string()))
    }

    // the maximum number of retries. Set it to 0 to make it not retriable
    // the default value is 20
    fn max_retries(&self) -> i32 {
      20
    }

    // backoff mode for retries
    fn backoff(&self, attempt: u32) -> u32 {
      u32::pow(2, attempt)
    }
}
```

As you can see from the example above, the trait implementation has `#[typetag::serde]` attribute which is used to deserialize the task.

The second parameter of the `run` function is a struct that implements `fang::Queueable`. You can re-use it to manipulate the task queue, for example, to add a new job during the current job's execution. If you don't need it, just ignore it.


#### Asynk feature
Every task should implement `fang::AsyncRunnable` trait which is used by `fang` to execute it.

Be careful not to call two implementations of the AsyncRunnable trait with the same name, because it will cause a failure in the `typetag` crate.
```rust
use fang::AsyncRunnable;
use fang::asynk::async_queue::AsyncQueueable;
use fang::serde::{Deserialize, Serialize};
use fang::async_trait;

#[derive(Serialize, Deserialize)]
#[serde(crate = "fang::serde")]
struct AsyncTask {
  pub number: u16,
}

#[typetag::serde]
#[async_trait]
impl AsyncRunnable for AsyncTask {
    async fn run(&self, _queueable: &mut dyn AsyncQueueable) -> Result<(), Error> {
        Ok(())
    }
    // this func is optional
    // Default task_type is common
    fn task_type(&self) -> String {
        "my-task-type".to_string()
    }


    // If `uniq` is set to true and the task is already in the storage, it won't be inserted again
    // The existing record will be returned for for any insertions operaiton
    fn uniq(&self) -> bool {
      true
    }

    // This will be useful if you would like to schedule tasks.
    // default value is None (the task is not scheduled, it's just executed as soon as it's inserted)
    fn cron(&self) -> Option<Scheduled> {
        let expression = "0/20 * * * Aug-Sep * 2022/1";
        Some(Scheduled::CronPattern(expression.to_string()))
    }

    // the maximum number of retries. Set it to 0 to make it not retriable
    // the default value is 20
    fn max_retries(&self) -> i32 {
      20
    }

    // backoff mode for retries
    fn backoff(&self, attempt: u32) -> u32 {
      u32::pow(2, attempt)
    }
}
```

In both modules, tasks can be scheduled to be executed once. Use `Scheduled::ScheduleOnce` enum variant.

Datetimes and cron patterns are interpreted in the UTC timezone. So you should introduce the offset to schedule in a different timezone.

Example:

If your timezone is UTC + 2 and you want to schedule at 11:00:

```rust
 let expression = "0 0 9 * * * *";
```


### Enqueuing a task

#### the Blocking feature
To enqueue a task use `Queue::enqueue_task`

```rust
use fang::Queue;

// create a r2d2 pool

// create a fang queue

 let queue = Queue::builder().connection_pool(pool).build();

 let task_inserted = queue.insert_task(&MyTask::new(1)).unwrap();

```

#### the Asynk feature
To enqueue a task use `AsyncQueueable::insert_task`.

For Postgres backend.
```rust
use fang::asynk::async_queue::AsyncQueue;
use fang::NoTls;
use fang::AsyncRunnable;

// Create an AsyncQueue
let max_pool_size: u32 = 2;

let mut queue = AsyncQueue::builder()
    // Postgres database url
    .uri("postgres://postgres:postgres@localhost/fang")
    // Max number of connections that are allowed
    .max_pool_size(max_pool_size)
    .build();

// Always connect first in order to perform any operation
queue.connect(NoTls).await.unwrap();

```
As an easy example, we are using NoTls type. If for some reason you would like to encrypt Postgres requests, you can use [openssl](https://docs.rs/postgres-openssl/latest/postgres_openssl/)  or [native-tls](https://docs.rs/postgres-native-tls/latest/postgres_native_tls/).

```rust
// AsyncTask from the first example
let task = AsyncTask { 8 };
let task_returned = queue
  .insert_task(&task as &dyn AsyncRunnable)
  .await
  .unwrap();
```

### Starting workers

#### the Blocking feature
Every worker runs in a separate thread. In case of panic, they are always restarted.

Use `WorkerPool` to start workers. Use `WorkerPool::builder` to create your worker pool and run tasks.


```rust
use fang::WorkerPool;
use fang::Queue;

// create a Queue

let mut worker_pool = WorkerPool::<Queue>::builder()
    .queue(queue)
    .number_of_workers(3_u32)
     // if you want to run tasks of the specific kind
    .task_type("my_task_type")
    .build();

worker_pool.start();
```

#### the Asynk feature
Every worker runs in a separate `tokio` task. In case of panic, they are always restarted.
Use `AsyncWorkerPool` to start workers.

```rust
use fang::asynk::async_worker_pool::AsyncWorkerPool;

// Need to create a queue
// Also insert some tasks

let mut pool: AsyncWorkerPool<AsyncQueue<NoTls>> = AsyncWorkerPool::builder()
        .number_of_workers(max_pool_size)
        .queue(queue.clone())
         // if you want to run tasks of the specific kind
        .task_type("my_task_type")
        .build();

pool.start().await;
```


Check out:

- [Simple Worker Example](https://github.com/ayrat555/fang/tree/master/fang_examples/blocking/simple_worker) - simple worker example
- [Simple Cron Worker Example](https://github.com/ayrat555/fang/tree/master/fang_examples/blocking/simple_cron_worker) - simple worker example
- [Simple Async Worker Example](https://github.com/ayrat555/fang/tree/master/fang_examples/asynk/simple_async_worker) - simple async worker example
- [Simple Cron Async Worker Example](https://github.com/ayrat555/fang/tree/master/fang_examples/asynk/simple_cron_async_worker) - simple async worker example
- [El Monitorro](https://github.com/ayrat555/el_monitorro) - telegram feed reader. It uses the Fang's blocking module to synchronize feeds and deliver updates to users.
- [weather_bot_rust](https://github.com/pxp9/weather_bot_rust) - A bot that provides weather info. It uses the Fang's asynk module to process updates from Telegram users and schedule weather info.

### Configuration

#### Blocking feature

Just use `TypeBuilder` for `WorkerPool`.

#### Asynk feature

Just use `TypeBuilder` for `AsyncWorkerPool`.

### Configuring the type of workers

### Configuring retention mode

By default, all successfully finished tasks are removed from the DB, failed tasks aren't.

There are three retention modes you can use:

```rust
pub enum RetentionMode {
    KeepAll,        // doesn't remove tasks
    RemoveAll,      // removes all tasks
    RemoveFinished, // default value
}
```

Set retention mode with worker pools `TypeBuilder` in both modules.

### Configuring sleep values

#### Blocking feature

You can use use `SleepParams` to configure sleep values:

```rust
pub struct SleepParams {
    pub sleep_period: Duration,     // default value is 5 seconds
    pub max_sleep_period: Duration, // default value is 15 seconds
    pub min_sleep_period: Duration, // default value is 5 seconds
    pub sleep_step: Duration,       // default value is 5 seconds
}
```

If there are no tasks in the DB, a worker sleeps for `sleep_period` and each time this value increases by `sleep_step` until it reaches `max_sleep_period`. `min_sleep_period` is the initial value for `sleep_period`. All values are in seconds.


Use `set_sleep_params` to set it:
```rust
let sleep_params = SleepParams {
    sleep_period: Duration::from_secs(2),
    max_sleep_period: Duration::from_secs(6),
    min_sleep_period: Duration::from_secs(2),
    sleep_step: Duration::from_secs(1),
};
```

Set sleep params with worker pools `TypeBuilder` in both modules.

## Contributing

1. [Fork it!](https://github.com/ayrat555/fang/fork)
2. Create your feature branch (`git checkout -b my-new-feature`)
3. Commit your changes (`git commit -am 'Add some feature'`)
4. Push to the branch (`git push origin my-new-feature`)
5. Create a new Pull Request

### Running tests locally
- Install diesel_cli.
```
cargo install diesel_cli
```
- Install docker on your machine.

- Run a Postgres docker container. (See in Makefile.)
```
make db
```

- Run the migrations
```
make diesel
```

- Run tests
```
make tests
```

- Run dirty//long tests, DB must be recreated afterwards.
```
make ignored
```

- Kill the docker container
```
make stop
```

## Authors

- Ayrat Badykov (@ayrat555)

- Pepe Márquez (@pxp9)


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