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//! Fragments of configuration.
//!
//! There are several crates that provide common fragments of configuration to configure some
//! specific functionality. These fragments are described in terms of the [`Fragment`] trait.
//!
//! # How to use them
//!
//! A [`Fragment`] can be used directly, usually through [`create`] method. The trait has some
//! other methods and associated types, but these are usually used only internally.
//!
//! The other option is to use fragments through [`Pipeline`]s. A pipeline describes how the
//! fragment is extracted from the configuration, how instances of resources it describes are
//! cached and created, how to post-process them and how to install or activate them. Depending on
//! the kind of fragment, less or more tweaking may be needed or desirable.
//!
//! # How pipelines work
//!
//! A [`Pipeline`] manages certain fragment of configuration and creates [`Resource`]s out of it.
//! There are several traits in play there.
//!
//! * A pipeline is triggered whenever new configuration is loaded. It runs its configured
//! [`Extractor`]. This extractor provides an instance of the [`Fragment`].
//! * A [`Driver`] is provided with the extracted fragment. The [`Driver`] decides if the
//! [`Resource`] needs to be recreated or if an old instance need to be destroyed. Each fragment
//! has its default [`Driver`], but the driver of a pipeline can be manually replaced by other
//! one, to for example change caching strategy. Note that the [`Driver`] is allowed to partition
//! the [`Fragment`] into smaller [`Fragment`]s and drive the rest of the pipeline multiple times
//! on the smaller ones (eg. a `Vec<F>` would be split into multiple runs over `F`).
//! * When creating the [`Resource`], there are two stages. First, a [`Seed`] is created with the
//! [`make_seed`] method. Then one or more [`Resource`]s are made out of the [`Seed`] with the
//! [`make_resource`] method. This allows more flexible caching strategies and allows for example
//! to change attached configuration without closing and opening a network socket if the port
//! haven't changed (which would be problematic, as spirit first tries to create the new instance
//! and only if it works gets rid of the old one ‒ but that couldn't be done if we still had the
//! old with the same port). Some [`Fragment`]s don't need this two-stage configuration,
//! therefore they have the [`Seed`] set to `()` and trivial [`make_seed`] method. You can use
//! the [`simple_fragment`](../macro.simple_fragment.html) macro to generate such trait
//! configuration.
//! * Then the resource goes through configured set of [`Transformation`]s. These may be quite
//! arbitrary, but they usually tie the resource with some kind of functionality ‒ a network
//! socket is provided with a function to handle each new connection, a HTTP server is provided
//! with the service it'll serve, etc. A freshly created [`Pipeline`] has no transformations, but
//! they can be added.
//! * Finally, the resulting product is installed using the [`Installer`]. Some fragments come with
//! a default installer, some do not. The [`Installer`] is often set as part of a transformation.
//! Nevertheless, an installer can always be set manually.
//! * The installer returns [`UninstallHandle`]s. These represent the lifetime of the installed
//! resources. The pipeline stores them until the time is right to destroy the resources ‒ then
//! it drops the handles, which results in removal of the resources.
//!
//! # Names
//!
//! Most methods around the mentioned traits take a `name: &'static str` parameter. This is used by
//! them to enrich log messages, as there might be multiple distinct parts of configuration of the
//! same type.
//!
//! The name is provided when creating the [`Pipeline`]. It needs to be a string literal, but as
//! this should correspond to specific functionality in the program, this should not be very
//! limiting.
//!
//! TODO: An example
//!
//! # How to create a fragment
//!
//! First, try to do it manually, without fragments or pipeline ‒ eg. write the code that takes the
//! configuration and creates something out of it and activates it.
//!
//! Then decide how this should be reloaded when new configuration appears, how it can be
//! reinstalled or if and how it should be cached.
//!
//! Then you can have a look at available pieces, like ready-made
//! [drivers][crate::fragment::driver] or installers. Sometimes, they come from another trait ‒ eg.
//! the [`spirit_tokio`] crate comes with an installer for futures. Usually, you need to implement
//! only the [`Fragment`] trait (either in two-stage or single-stage fashion), but sometimes you
//! might need to add some kind of [`Transformation`] to tie the part that comes from the
//! configuration with some actual code.
//!
//! You may also want to implement the [`Stackable`] and possibly [`Comparable`] traits for the
//! fragment.
//!
//! [`Fragment`]: crate::fragment::Fragment
//! [`Driver`]: crate::fragment::driver::Driver
//! [`create`]: crate::fragment::Fragment::create
//! [`Pipeline`]: crate::fragment::pipeline::Pipeline
//! [`Extractor`]: crate::fragment::Extractor
//! [`Resource`]: crate::fragment::Fragment::Resource
//! [`Seed`]: crate::fragment::Fragment::Seed
//! [`make_seed`]: crate::fragment::Fragment::make_seed
//! [`make_resource`]: crate::fragment::Fragment::make_resource
//! [`simple_fragment`]: crate::simple_fragment
//! [`Transformation`]: crate::fragment::Transformation
//! [`Installer`]: crate::fragment::Installer
//! [`UninstallHandle`]: crate::fragment::Installer::UninstallHandle
//! [`Stackable`]: crate::fragment::Stackable
//! [`Comparable`]: crate::fragment::driver::Comparable
//! [`spirit_tokio`]: https://docs.rs/spirit-tokio
use std::collections::{BTreeSet, BinaryHeap, HashSet, LinkedList};
use std::hash::{BuildHasher, Hash};
use log::trace;
use serde::de::DeserializeOwned;
use structopt::StructOpt;
use self::driver::{Driver, RefDriver, SeqDriver};
use crate::extension::Extensible;
use crate::AnyError;
pub mod driver;
pub mod pipeline;
/// An entity that is able to install a resource.
///
/// At the end of a [`Pipeline`][crate::fragment::pipeline::Pipeline] there's an installer. It
/// takes the (transformed) resource and somehow makes it active in the program.
///
/// An installer can be even a storage provided by a user where the resource is stored ‒ eg. a
/// proxy object to the resource where it can be switched.
///
/// Note that installation of the resource must not fail.
pub trait Installer<Resource, O, C> {
/// A handle representing lifetime of the resource.
///
/// Some resources or installers are for a single instance. In that case a new resource simply
/// replaces the old one and the `UninstallHandle` serves no role and can be set to `()`.
///
/// In other cases it is possible to have multiple instances of the `Resource` active at the
/// same time (eg. futures in the tokio runtime). Then the installer returns a handle for each
/// resource installed. The [`Pipeline`] uses the handle as a proxy to the installed resource.
/// When the time comes for the resource to go away, the [`Pipeline`] drops the respective
/// handle and that should take care of removing the resource.
///
/// # See also
///
/// The [`Stackable`] marker trait describes if it makes sense to have multiple instances of
/// the resource, therefore if using collections of the [`Fragment`] in the configuration makes
/// sense and is allowed.
///
/// [`Pipeline`]: crate::fragment::pipeline::Pipeline
type UninstallHandle: Send + 'static;
/// Installs another instance of the resource.
///
/// This is the main method of the trait.
///
/// The installation must not fail. Depending on the resource semantics, this should either
/// replace the previous instance or return relevant
/// [`UninstallHandle`][Installer::UninstallHandle].
fn install(&mut self, resource: Resource, name: &'static str) -> Self::UninstallHandle;
/// Initialize the installer.
///
/// The pipeline will run this method exactly once, upon being inserted into a
/// [`Builder`][crate::Builder] or [`Spirit`][crate::Spirit]. This happens before any resources
/// are installed.
///
/// The installer may set up the [`Extensible`][crate::Extensible] in a suitable way.
///
/// It is not mandatory to implement this method. The default installation does nothing (as
/// many installers simply don't need any special setup).
fn init<B: Extensible<Opts = O, Config = C, Ok = B>>(
&mut self,
builder: B,
_name: &'static str,
) -> Result<B, AnyError>
where
B::Config: DeserializeOwned + Send + Sync + 'static,
B::Opts: StructOpt + Send + Sync + 'static,
{
Ok(builder)
}
}
/// A sequence installer.
///
/// This is an auxiliary installer wrapper, to install instances from a collection of fragments.
///
/// Usually, this is used behind the scenes in things like `Vec<F: Fragment>` and shouldn't have to
/// be used by user directly.
#[derive(Debug, Default)]
pub struct SeqInstaller<Slave> {
slave: Slave,
}
impl<Resource, O, C, Slave> Installer<Resource, O, C> for SeqInstaller<Slave>
where
Resource: IntoIterator,
Slave: Installer<Resource::Item, O, C>,
{
type UninstallHandle = Vec<Slave::UninstallHandle>;
fn install(&mut self, resource: Resource, name: &'static str) -> Self::UninstallHandle {
resource
.into_iter()
.map(|r| self.slave.install(r, name))
.collect()
}
fn init<B: Extensible<Opts = O, Config = C, Ok = B>>(
&mut self,
builder: B,
name: &'static str,
) -> Result<B, AnyError>
where
B::Config: DeserializeOwned + Send + Sync + 'static,
B::Opts: StructOpt + Send + Sync + 'static,
{
self.slave.init(builder, name)
}
}
/// A trait to mark [`Fragment`]s that can form collections.
///
/// If it makes sense to use collections of the fragment (eg. `Vec<F>` or `HashSet<F>`) in the
/// configuration, in addition to implementing the [`Fragment`] trait, mark the fragment by this
/// trait. Then a default implementation of [`Fragment`] will be provided for the common
/// collections.
pub trait Stackable {}
/// A trait similar to [`Stackable`], but marking the ability to be optional.
///
/// This allows using the [`Fragment`] as `Option<F>`. This is automatically implemented for all
/// [`Stackable`] fragments.
pub trait Optional {}
impl<F: Stackable> Optional for F {}
/// A fragment of configuration.
///
/// The fragment is the part of configuration [`Pipeline`][pipeline::Pipeline]s work with. It
/// usually comes directly from the configuration, but it also may be constructed by the
/// [`Extractor`] (maybe by combining parts of the configuration, or combining data from
/// configuration and command line options).
///
/// See the details of how [pipelines work](index.html#how-pipelines-work).
///
/// Note that fragments as described by this trait create their resources in two stages ‒ first a
/// [`Seed`] is created, then turned into [`Resource`]. The [`Driver`] controls this. Note that one
/// [`Seed`] may be used to create multiple instances of the [`Resource`] (depending on the driver
/// either in parallel or sequentially, replacing the previous ones). However, if fragment doesn't
/// want to have this two-phase creation, it can set the [`Seed`] to `()`.
///
/// [`Seed`]: Fragment::Seed
/// [`Resource`]: Fragment::Resource
pub trait Fragment: Sized {
/// The default driver to be used by the fragment.
///
/// If a pipeline is created with this fragment, this is the driver that will be used by
/// default, unless the user overrides it. There's a list of [drivers][driver] to pick from if
/// you don't want to write your own (the most common caching and creation needs should be
/// covered).
type Driver: Driver<Self> + Default;
/// The default installer to be used unless a transformation or the user doesn't provide one.
///
/// This is the type the pipeline will use for installation of resources created by this
/// fragment. Note that some fragments don't have a default installer (because they either need
/// to be put into a user-provided storage or need to be transformed first). They can have the
/// `Installer` set to `()` ‒ but the pipeline will not be usable unless an installer is
/// provided by some means later on.
type Installer: Default;
/// The intermediate product if the fragment supports two-stage creation of
/// [`Resource`][Fragment::Resource]s. If not, it can be set to `()`.
type Seed;
/// The actual product this [`Fragment`] creates.
type Resource;
/// Configuration if the pipeline should be run once even before the config is loaded.
///
/// If this is set to true, the pipeline will be run once immediately after loading the command
/// line options, even before the initial configuration is ready (therefore the fragment will
/// come from within the default configuration).
///
/// This does not stop the pipeline to run again once the configuration is loaded, but it may
/// be used to provide some early intermediate setup.
///
/// This is used with for example logging, as it:
///
/// * Initializes very basic logging directly from the [`Installer::init`] method.
/// * Initializes logging based on the command line only once that becomes available.
/// * Switches to logging based on the configuration once that is available.
///
/// However, most „normal“ fragments don't need to worry about this and can wait for real
/// configuration to become available.
const RUN_BEFORE_CONFIG: bool = false;
/// Runs the first stage of creation.
///
/// This creates the [`Seed`][Fragment::Seed]. If the two-stage creation is not needed for this
/// fragment, this should simply return `Ok(())`.
///
/// This method should be provided by an implementation, but wouldn't usually be called
/// directly by the user. This is used either by the [`Pipeline`][pipeline::Pipeline] or
/// internally by the higher-level [`create`][Fragment::create] method.
fn make_seed(&self, name: &'static str) -> Result<Self::Seed, AnyError>;
/// Runs the second stage of creation.
///
/// This turns the seed into the actual resource. If the two-stage configuration is not
/// supported by this fragment, the real work should happen in this method.
///
/// This method needs to be provided by the implementation, but it wouldn't usually be called
/// directly by the user. It is used internally by [`Pipeline`][pipeline::Pipeline] and the
/// [`create`][Fragment::create] method.
fn make_resource(
&self,
seed: &mut Self::Seed,
name: &'static str,
) -> Result<Self::Resource, AnyError>;
/// Runs both stages of creation at once.
///
/// This runs both [`make_seed`][Fragment::make_seed] and
/// [`make_resource`][Fragment::make_resource]. It should *not* be overridden by an
/// implementation.
///
/// This is meant to be used by the user if the user wishes to use the fragment directly,
/// without the support of [`Pipeline`][pipeline::Pipeline].
fn create(&self, name: &'static str) -> Result<Self::Resource, AnyError> {
trace!("End to end creation of {}", name);
let mut seed = self.make_seed(name)?;
self.make_resource(&mut seed, name)
}
/// An initialization routine.
///
/// This will be called once by a [`Pipeline`][pipeline::Pipeline] before the first use of the
/// fragment. This allows the fragment to configure the [`Builder`][crate::Builder] or
/// [`Spirit`][crate::Spirit] the pipeline will be used in.
///
/// The implementation may leave it at the default (empty) implementation in case no special
/// setup is needed.
fn init<B: Extensible<Ok = B>>(builder: B, _: &'static str) -> Result<B, AnyError>
where
B::Config: DeserializeOwned + Send + Sync + 'static,
B::Opts: StructOpt + Send + Sync + 'static,
{
Ok(builder)
}
}
impl<'a, F> Fragment for &'a F
where
F: Fragment,
{
type Driver = RefDriver<F::Driver>;
type Installer = F::Installer;
type Seed = F::Seed;
type Resource = F::Resource;
const RUN_BEFORE_CONFIG: bool = F::RUN_BEFORE_CONFIG;
fn make_seed(&self, name: &'static str) -> Result<Self::Seed, AnyError> {
F::make_seed(*self, name)
}
fn make_resource(
&self,
seed: &mut Self::Seed,
name: &'static str,
) -> Result<Self::Resource, AnyError> {
F::make_resource(*self, seed, name)
}
fn init<B: Extensible<Ok = B>>(builder: B, name: &'static str) -> Result<B, AnyError>
where
B::Config: DeserializeOwned + Send + Sync + 'static,
B::Opts: StructOpt + Send + Sync + 'static,
{
F::init(builder, name)
}
}
// TODO: Export the macro for other containers?
// TODO: The where-* should be where-?
macro_rules! fragment_for_seq {
($cond: ident => $container: ident<$base: ident $(, $extra: ident)*> $(where $($bounds: tt)+)?) => {
impl<$base: Fragment + $cond + 'static $(, $extra)*> Fragment
for $container<$base $(, $extra)*>
$(
where
$($bounds)+
)*
{
type Driver = SeqDriver<$base, $base::Driver>;
type Installer = SeqInstaller<$base::Installer>;
type Seed = Vec<$base::Seed>;
type Resource = Vec<$base::Resource>;
const RUN_BEFORE_CONFIG: bool = $base::RUN_BEFORE_CONFIG;
fn make_seed(&self, name: &'static str) -> Result<Self::Seed, AnyError> {
self.iter().map(|i| i.make_seed(name)).collect()
}
fn make_resource(&self, seed: &mut Self::Seed, name: &'static str)
-> Result<Self::Resource, AnyError>
{
self.iter()
.zip(seed)
.map(|(i, s)| i.make_resource(s, name))
.collect()
}
fn init<B: Extensible<Ok = B>>(builder: B, name: &'static str) -> Result<B, AnyError>
where
B::Config: DeserializeOwned + Send + Sync + 'static,
B::Opts: StructOpt + Send + Sync + 'static,
{
$base::init(builder, name)
}
}
}
}
fragment_for_seq!(Stackable => Vec<T>);
fragment_for_seq!(Stackable => BTreeSet<T>);
fragment_for_seq!(Stackable => LinkedList<T>);
fragment_for_seq!(Stackable => BinaryHeap<T> where T: Ord);
fragment_for_seq!(Stackable => HashSet<T, S> where T: Eq + Hash, S: BuildHasher);
fragment_for_seq!(Optional => Option<T>);
/// A helper macro to implement a simple [`Fragment`].
///
/// The full implementation of a [`Fragment`] requires a lot of work that is not usually needed.
///
/// In case the [`Fragment`] should not implement the two-stage creation, this can be used to cut
/// down on the boilerplate a bit.
///
/// # Examples
///
/// ```rust
/// use spirit::AnyError;
/// use spirit::simple_fragment;
/// use spirit::fragment::Installer;
///
/// // The message as a resource
/// struct Message(String);
///
/// // An installer of a resource
/// #[derive(Default)]
/// struct MessageInstaller;
///
/// impl<O, C> Installer<Message, O, C> for MessageInstaller {
/// type UninstallHandle = ();
/// fn install(&mut self, message: Message, _name: &str) {
/// println!("{}", message.0);
/// }
/// }
///
/// // Configuration of a message from the config file
/// # #[allow(dead_code)] // Allow not using this structure.
/// struct MessageCfg {
/// msg: String,
/// }
///
/// simple_fragment! {
/// impl Fragment for MessageCfg {
/// type Resource = Message;
/// type Installer = MessageInstaller;
/// fn create(&self, _name: &'static str) -> Result<Message, AnyError> {
/// Ok(Message(self.msg.clone()))
/// }
/// }
/// }
/// # fn main() {}
/// ```
///
/// If the [`Driver`] is not provided (as in the above example), the [trivial
/// driver][crate::fragment::driver::Trivial] is going to be used.
///
/// [`Fragment`]: crate::fragment::Fragment
/// [`Driver`]: crate::fragment::driver::Driver
#[macro_export]
macro_rules! simple_fragment {
(impl Fragment for $ty: ty {
type Resource = $resource: ty;
type Installer = $installer: ty;
fn create(&$self: tt, $name: tt: &'static str) -> $result: ty $block: block
}) => {
$crate::simple_fragment! {
impl Fragment for $ty {
type Driver = $crate::fragment::driver::Trivial;
type Resource = $resource;
type Installer = $installer;
fn create(&$self, $name: &'static str) -> $result $block
}
}
};
(impl Fragment for $ty: ty {
type Driver = $driver: ty;
type Resource = $resource: ty;
type Installer = $installer: ty;
fn create(&$self: tt, $name: tt: &'static str) -> $result: ty $block: block
}) => {
impl $crate::fragment::Fragment for $ty {
type Driver = $driver;
type Resource = $resource;
type Installer = $installer;
type Seed = ();
fn make_seed(&self, _: &'static str) -> Result<(), AnyError> {
Ok(())
}
fn make_resource(&$self, _: &mut (), $name: &'static str) -> $result $block
}
}
}
// TODO: How do we stack maps, etc?
// TODO: Arcs, Rcs, Mutexes, refs, ...
/// A trait describing something that extracts a fragment from configuration and command line
/// options.
///
/// The extractor is used every time a [`Pipeline`] is triggered, to get the
/// fragment out.
///
/// Usually, an extractor is a closure, but something else can implement the trait too.
///
/// Users usually don't need to interact with this trait directly.
///
/// Note that the extractor is lifetime-parametric. Usually the real extractor implements the trait
/// for all lifetimes (and it is not useful otherwise). This allows returning references into the
/// configuration, the [`Pipeline`] is able to work with that (given new enough `rustc` ‒ there
/// were some bugs preventing it from working; if that's the case, you can clone and return owned
/// values).
///
/// [`Pipeline`]: pipeline::Pipeline
pub trait Extractor<'a, O, C> {
/// The fragment being extracted.
type Fragment: Fragment + 'a;
/// The actual call of the extractor.
///
/// The extractor is allowed to either reference into the configuration (or command line
/// options) or create something new out of it (including structures containing references
/// there).
///
/// It is not uncommon to combine information from both to form a fragment.
fn extract(&mut self, opts: &'a O, config: &'a C) -> Self::Fragment;
}
impl<'a, O: 'a, C: 'a, F, R> Extractor<'a, O, C> for F
where
F: FnMut(&'a O, &'a C) -> R,
R: Fragment + 'a,
{
type Fragment = R;
fn extract(&mut self, opts: &'a O, config: &'a C) -> R {
self(opts, config)
}
}
/// A transformation of resources.
///
/// A [`Pipeline`] can contain a transformation of the [`Resource`] produced by the [`Fragment`].
/// This trait describes a transformation.
///
/// Note that transformations in a pipeline are usually composed together.
///
/// The transformation is also allowed (and sometimes required) to either transform or replace the
/// [`Installer`] of the [`Pipeline`]. The old [`Installer`] might not be able to install the new
/// [`Resource`] (since the type can change during the transformation) or might not even exist.
///
/// A transformation can be quite arbitrary thing that simply takes the old resource and produces
/// something new. But more often that not, it is used to somehow make a „dead“ resource (eg. a
/// network socket) „alive“ (eg. wrap it into a future that is then installed) ‒ or, in other
/// words, to tie the resource to some functionality.
///
/// It is also possible to use a transformation to post-process and tweak the resource a bit (add
/// more loggers, change a bit of configuration of the resource, ...).
///
/// # Type parameters
///
/// * `InputResource` is the resource on the transformation input; this one will be changed every
/// time the transformation is called.
/// * `InputInstaller` is the original installer that was present in the pipeline before the
/// transformation got added. Note that not all installers at that point are able to install the
/// `InputResource`. But if it is able, it can be used to delegate from the
/// [`OutputInstaller`][Transformation::OutputInstaller] (or just use it vanilla).
/// * `SubFragment` is the fragments the [`Transformation`] will be used on. Each
/// [`Resource`][Fragment::Resource] is always accompanied by the [`Fragment`] it came from. Note
/// that this might be some sub-part of the original [`Fragment`], as the [`Driver`] is allowed
/// to cut it into smaller pieces.
///
/// [`Resource`]: Fragment::Resource
/// [`Pipeline`]: pipeline::Pipeline
pub trait Transformation<InputResource, InputInstaller, SubFragment> {
/// The type of resource after the transformation.
type OutputResource: 'static;
/// The type of installer after the transformation.
///
/// This can be something completely new, or something that somehow delegates or uses the
/// `InputResource`.
type OutputInstaller;
/// Creates the installer.
///
/// This is called by the pipeline exactly once, with the original installer, to produce the
/// transformed installer.
///
/// Note that some transformations are composed from multiple transformations and they are
/// *not* mandated to call this method. Nevertheless, it is violation of contract to call this
/// more than once.
fn installer(&mut self, installer: InputInstaller, name: &'static str)
-> Self::OutputInstaller;
/// Transforms one instance of the resource.
///
/// The `fragment` parameter was the fragment that was used to create the resource. Note that
/// there might have been some other transformations between the creation and *this*
/// transformation and therefore the resource produced by the `fragment` might be something
/// else than what is being put into the transformation.
///
/// Nevertheless, the transformation is allowed to look into the fragment ‒ for example to
/// examine additional configuration not used to directly create the resource, but maybe
/// configure the „alive“ part that this transformation adds.
fn transform(
&mut self,
resource: InputResource,
fragment: &SubFragment,
name: &'static str,
) -> Result<Self::OutputResource, AnyError>;
}