App Frame

App Frame is a compile-time dependency-injected application framework with a service orchestrator.

At compile-time, the framework guarantees that all necessary dependencies will be injected upon application startup. You can define dependency relationships using the provided macros or with custom implementations. At runtime, the framework triggers initialization code, then runs services, monitors their health, and reports that health to any external http health checks.

This trivial example illustrates the bare minimum boilerplate to use the framework, but doesn't actually run anything useful.

use app_frame::{application, service_manager::Application, Never};

async fn tokio_main() -> anyhow::Result<Never> {
    MyApp.run(3600).await
}

pub struct MyApp;

application!(self: MyApp);

This example defines and injects various types of components to illustrate the various features provided by the framework:

use std::sync::Arc;

use async_trait::async_trait;

use app_frame::{
    application,
    dependency_injection::Provides,
    inject,
    service::{Job, LoopConfig, LoopingJobService, SelfConfiguredLoop, Service},
    service_manager::{Heartbeat, Application},
    Never,
};

async fn tokio_main() -> anyhow::Result<Never> {
    MyApp::new(()).run(3600).await
}

pub struct MyApp {
    db_singleton: Arc<DatabaseConnectionPoolSingleton>,
}

impl MyApp {
    pub fn new(database_config: ()) -> Self {
        Self {
            db_singleton: Arc::new(DatabaseConnectionPoolSingleton {
                state: database_config,
            }),
        }
    }
}

// Including a type here implements Provides<ThatType> for MyApp.
//
// Struct definitions wrapped in the `inject!` macro get a From<T>
// implementation where T: Provides<U> for each field of type U in the struct.
// When those structs are provided as a component here, they will be constructed
// with the assumption that MyApp impl Provides<U> for each of those U's
//
// All the types provided here are instantiated separately each time they are
// needed. If you want to support a singleton pattern, you need to construct the
// singletons in the constructor for this type and wrap them in an Arc. Then you
// can provide them in the "provided" section by cloning the Arc.
application! {
    self: MyApp

    // init jobs are types implementing `Job` with a `run_once` function that
    // needs to run once during startup.
    // - constructed the same way as a component
    // - made available as a dependency, like a component
    // - wrap in curly braces for custom construction of an iterable of jobs.
    init [
        InitJob
    ]

    // Services are types with a `run_forever` function that needs to run for
    // the entire lifetime of the application.
    // - constructed the same way as a component
    // - made available as a dependency, like a component
    // - registered as a service and spawned on startup.
    // - wrap in curly braces for custom construction of an iterable of
    //   services.
    // - Use 'as WrapperType' if it needs to be wrapped in order to get
    //   something that implements `Service`. wrapping uses WrapperType::from().
    services [
        MyService,
        JobToLoopForever as LoopingJobService,
    ]

    // Components are items that will be provided as dependencies to anything
    // that needs it. This is similar to the types provided in the "provides"
    // section, except that components can be built exclusively from other
    // components and provided types, whereas "provides" items depend on other
    // state or logic.
    // - constructed via Type::from(MyApp). Use the inject! macro on the
    //   type to make this possible.
    // - Use `as dyn SomeTrait` if you also want to provide the type as the
    //   implementation for Arc<dyn SomeTrait>
    components [
        Component1,
        Component2,
        DatabaseRepository as dyn Repository,
    ]

    // Use this when you want to provide a value of some type that needs to either:
    // - be constructed by some custom code you want to write here.
    // - depend on some state that was initialized in MyApp.
    //
    // Syntax: Provide a list of the types you want to provide, followed by the
    // expression that can be used to instantiate any of those types.
    // ```
    // TypeToProvide: { let x = self.get_x(); TypeToProvide::new(x) },
    // Arc<dyn Trait>, Arc<ConcreteType>: Arc::new(ConcreteType::default()),
    // ```
    provided {
        Arc<DatabaseConnectionPoolSingleton>: self.db_singleton.clone(),
    }
}

inject!(
    pub struct InitJob {
        repo: Arc<dyn Repository>,
    }
);

#[async_trait]
impl Job for InitJob {
    async fn run_once(&self) -> anyhow::Result<()> {
        Ok(())
    }
}

inject!(
    pub struct JobToLoopForever {
        c1: Component1,
        c2: Component2,
    }
);

#[async_trait]
impl Job for JobToLoopForever {
    async fn run_once(&self) -> anyhow::Result<()> {
        Ok(())
    }
}

impl SelfConfiguredLoop for JobToLoopForever {
    fn loop_config(&self) -> LoopConfig {
        LoopConfig {
            delay_secs: 10,
            max_iteration_secs: 20,
        }
    }
}

inject!(
    pub struct Component1 {}
);

inject!(
    pub struct Component2 {
        repo: Arc<dyn Repository>,
    }
);

pub trait Repository: Send + Sync {}

pub struct MyService {
    repository: Arc<dyn Repository>,
    heartbeat: Arc<dyn Heartbeat + 'static>,
    my_health_metric: bool,
}

/// This is how you provide a custom alternative to the `inject!` macro, it is
/// practical here since only one item needs to be injected, and the others can
/// be set to default values.
impl<T> From<&T> for MyService
where
    T: Provides<Arc<dyn Repository>>,
{
    fn from(p: &T) -> Self {
        Self {
            repository: p.provide(),
            heartbeat: Arc::new(()),
            my_health_metric: true,
        }
    }
}

#[async_trait]
impl Service for MyService {
    async fn run_forever(&self) -> Never {
        loop {
            self.heartbeat.beat();
        }
    }

    fn heartbeat_ttl(&self) -> i32 {
        60
    }

    fn set_heartbeat(&mut self, heartbeat: Arc<dyn Heartbeat + 'static>) {
        self.heartbeat = heartbeat;
    }

    fn is_healthy(&self) -> bool {
        self.my_health_metric
    }
}

inject!(
    pub struct DatabaseRepository {
        connection: Arc<DatabaseConnectionPoolSingleton>,
    }
);

impl Repository for DatabaseRepository {}

pub struct DatabaseConnectionPoolSingleton {
    state: (),
}