Crates.io | lifeline |
lib.rs | lifeline |
version | 0.6.1 |
source | src |
created_at | 2020-08-24 00:26:31.077479 |
updated_at | 2021-02-02 04:13:47.126977 |
description | Lifeline is a dependency injection library for asynchronous message-based applications. |
homepage | https://github.com/austinjones/lifeline-rs |
repository | https://github.com/austinjones/lifeline-rs |
max_upload_size | |
id | 279952 |
size | 160,929 |
Lifeline is a dependency injection library for message-based applications. Lifeline produces applications which are:
In order to achieve these goals, lifeline provides patterns, traits, and implementations:
For a quick introduction, see the hello.rs example. For a full-scale application see tab-rs.
Lifeline can be used with the tokio and async-std runtimes. By default, lifeline uses tokio
.
lifeline = "0.6"
async-std can be enabled with the async-std-executor
feature. And the mpsc
implementation can be enabled with the async-std-channels
feature:
lifeline = { version = "0.6", default-features = false, features = ["dyn-bus", "async-std-executor", "async-std-channels"] }
Lifeline also supports postage channels, a library that provides a portable set of channel implementations (compatible with any executor).
Postage also provides Stream and Sink combinators (similar to futures StreamExt), that are optimized for async channels.
Postage is intended to replace the LifelineSender/LifelineReceiver wrappers that were removed in lifeline v0.6.0.
v0.6.0 contains several breaking changes:
use lifeline::{Sender, Receiver}
.The bus carries channels and resources. When services spawn, they receive a reference to the bus.
Channels can be taken from the bus. If the channel endpoint is clonable, it will remain available for other services. If the channel is not clonable, future calls will receive an Err
value. The Rx/Tx type parameters are type-safe, and will produce a compile error
if you attempt to take a channel for an message type which the bus does not carry.
use lifeline::lifeline_bus;
use lifeline::Message;
use lifeline::Bus;
use myapp::message::MainSend;
use myapp::message::MainRecv;
use tokio::sync::mpsc;
lifeline_bus!(pub struct MainBus);
impl Message<MainBus> for MainSend {
type Channel = mpsc::Sender<Self>;
}
impl Message<MainBus> for MainRecv {
type Channel = mpsc::Sender<Self>;
}
fn use_bus() -> anyhow::Result<()> {
let bus = MainBus::default();
let tx_main = bus.tx::<MainRecv>()?;
tx_main.send(MainRecv {});
Ok(())
}
Carriers provide a way to move messages between busses. Carriers can translate, ignore, or collect information, providing each bus with the messages that it needs.
Large applications have a tree of Busses. This is good, it breaks your app into small chunks.
- MainBus
| ConnectionListenerBus
| | ConnectionBus
| DomainSpecificBus
| | ...
Carriers allow each bus to define messages that minimally represent the information it's services need to function, and prevent an explosion of messages which are copied to all busses.
Carriers centralize the communication between busses, making large applications easier to reason about.
Busses deeper in the tree should implement FromCarrier
for their parents - see the carrier.rs example for more details.
let main_bus = MainBus::default();
let connection_listener_bus = ConnectionListenerBus::default();
let _carrier = connection_listener_bus.carry_from(&main_bus)?;
// you can also use the IntoCarrier trait, which has a blanket implementation
let _carrier = main_bus.carry_into(&main_bus)?;
The Service synchronously takes channels from the Bus, and spawns a tree of async tasks (which send & receive messages). When spawned, the service returns one or more Lifeline values. When a Lifeline is dropped, the associated task is immediately cancelled.
It's common for Service::spawn
to return a Result. Taking channel endpoints is a fallible operation. This is because, depending on the channel type, the endpoint may not be clonable. Lifeline clones endpoints when it can (mpsc::Sender
, broadcast::*
, and watch::Receiver
). Lifeline tries to make this happen as early as possible.
use lifeline::{Service, Task};
pub struct ExampleService {
_greet: Lifeline,
}
impl Service for ExampleService {
type Bus = ExampleBus;
type Lifeline = Lifeline;
fn spawn(bus: &Self::Bus) -> Self::Lifeline {
let mut rx = bus.rx::<ExampleRecv>()?;
let mut tx = bus.tx::<ExampleSend>()?;
let config = bus.resource::<ExampleConfig>()?;
Self::task("greet", async move {
// drive the channels!
})
}
}
The Task executes a Future
, and returns a Lifeline
value when spawned. When the lifeline is dropped, the future is immediately cancelled.
Task
is a trait that is implemented for all types - you can import it and use Self::task
in any type. In lifeline, it's
most commonly used in Service implementations.
Tasks can be infallible:
Self::task("greet", async move {
// do something
})
Or, if you have a fallible task, you can return anyhow::Result<T>
. Anyhow is required to solve type inference issues.
Self::try_task("greet", async move {
// do something
let something = do_something()?;
Ok(())
})
One of the goals of Lifeline is to provide interfaces that are very easy to test. Lifeline runtimes are easy to construct in tests:
#[tokio::test]
async fn test() -> anyhow::Result<()> {
// this is zero-cost. channel construction is lazy.
let bus = MainBus::default();
let service = MainService::spawn(&bus)?;
// the service took `bus.rx::<MainRecv>()`
// + `bus.tx::<MainSend>()`
// let's communicate using channels we take.
let tx = bus.tx::<MainRecv>()?;
let rx = bus.rx::<MainSend>()?;
// drop the bus, so that any 'channel closed' errors will occur during our test.
// this would likely happen in practice during the long lifetime of the program
drop(bus);
tx.send(MainRecv::MyMessage)?;
// wait up to 200ms for the message to arrive
// if we remove the 200 at the end, the default is 50ms
lifeline::assert_completes!(async move {
let response = rx.recv().await;
assert_eq!(MainSend::MyResponse, response);
}, 200);
Ok(())
}
Tasks (via log) provide debug logs when the are started, ended, or cancelled.
If the task returns a value, it is also printed to the debug log using Debug
.
2020-08-23 16:45:10,422 DEBUG [lifeline::spawn] START ExampleService/ok_task
2020-08-23 16:45:10,422 DEBUG [lifeline::spawn] END ExampleService/ok_task
2020-08-23 16:45:10,422 DEBUG [lifeline::spawn] START ExampleService/valued_task
2020-08-23 16:45:10,422 DEBUG [lifeline::spawn] END ExampleService/valued_task: MyStruct {}
If the task is cancelled (because it's lifeline is dropped), that is also printed.
2020-08-23 16:45:10,422 DEBUG [lifeline::spawn] START ExampleService/cancelled_task
2020-08-23 16:45:10,422 DEBUG [lifeline::spawn] CANCEL ExampleService/cancelled_task
If the task is started using Task::try_task
, the Ok
/Err
value will be printed with Display
.
2020-08-23 16:45:10,422 DEBUG [lifeline::spawn] START ExampleService/ok_task
2020-08-23 16:45:10,422 DEBUG [lifeline::spawn] OK ExampleService/ok_task
2020-08-23 16:45:10,422 DEBUG [lifeline::spawn] END ExampleService/ok_task
2020-08-23 16:45:10,422 DEBUG [lifeline::spawn] START ExampleService/err_task
2020-08-23 16:45:10,422 ERROR [lifeline::service] ERR: ExampleService/err_task: my error
2020-08-23 16:45:10,422 DEBUG [lifeline::spawn] END ExampleService/err_task
rust-analyzer
does not currently support auto-import for structs defined in macros. Lifeline really needs the
struct defined in the macro, as it injects magic fields which store the channels at runtime.
There is a workaround: define a prelude.rs
file in your crate root that exports pub use
for all your bus implementations.
pub use lifeline::*;
pub use crate::bus::MainBus;
pub use crate::other::OtherBus;
...
Then in all your modules:
use crate::prelude::*
Resources can be stored on the bus. This is very useful for configuration (e.g MainConfig
), or connections (e.g. a TcpStream
).
Resources implement the Storage
trait, which is easy with the impl_storage_clone!
and impl_storage_take!
macros.
use lifeline::{lifeline_bus, impl_storage_clone};
lifeline_bus!(MainBus);
pub struct MainConfig {
pub port: u16
}
impl_storage_clone!(MainConfig);
fn main() {
let bus = MainBus::default()
bus.store_resource::<MainConfig>(MainConfig { port: 12345 });
// from here
}
Lifeline does not provide Resource
implementations for Channel endpoints - use bus.rx()
and bus.tx()
.
Channel senders must implement the Channel
trait to be usable in an impl Message
binding.
In most cases, the Channel
endpoints just implement Storage
, which determines whether to 'take or clone' the endpoint on a bus.rx()
or bus.tx()
call.
Here is an example implem
use lifeline::Channel;
use crate::{impl_channel_clone, impl_channel_take};
use tokio::sync::{broadcast, mpsc, oneshot, watch};
impl<T: Send + 'static> Channel for mpsc::Sender<T> {
type Tx = Self;
type Rx = mpsc::Receiver<T>;
fn channel(capacity: usize) -> (Self::Tx, Self::Rx) {
mpsc::channel(capacity)
}
fn default_capacity() -> usize {
16
}
}
impl_channel_clone!(mpsc::Sender<T>);
impl_channel_take!(mpsc::Receiver<T>);
Broadcast senders should implement the trait with the clone_rx
method overriden, to take from Rx
, then subscribe to Tx
.