205 lines
6.3 KiB
Rust
205 lines
6.3 KiB
Rust
//! Builder types to compose layers and services
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use tower_layer::{Identity, Layer, Stack};
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use std::fmt;
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/// Declaratively construct Service values.
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///
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/// `ServiceBuilder` provides a [builder-like interface][builder] for composing
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/// layers to be applied to a `Service`.
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///
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/// # Service
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///
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/// A [`Service`](tower_service::Service) is a trait representing an
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/// asynchronous function of a request to a response. It is similar to `async
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/// fn(Request) -> Result<Response, Error>`.
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///
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/// A `Service` is typically bound to a single transport, such as a TCP
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/// connection. It defines how _all_ inbound or outbound requests are handled
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/// by that connection.
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///
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///
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/// [builder]: https://doc.rust-lang.org/1.0.0/style/ownership/builders.html
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///
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/// # Order
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///
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/// The order in which layers are added impacts how requests are handled. Layers
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/// that are added first will be called with the request first. The argument to
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/// `service` will be last to see the request.
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///
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/// ```
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/// # use tower::Service;
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/// # use tower::builder::ServiceBuilder;
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/// # async fn wrap<S>(svc: S) where S: Service<(), Error = &'static str> + 'static + Send, S::Future: Send {
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/// ServiceBuilder::new()
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/// .buffer(100)
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/// .concurrency_limit(10)
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/// .service(svc)
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/// # ;
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/// # }
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/// ```
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///
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/// In the above example, the buffer layer receives the request first followed
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/// by `concurrency_limit`. `buffer` enables up to 100 request to be in-flight
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/// **on top of** the requests that have already been forwarded to the next
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/// layer. Combined with `concurrency_limit`, this allows up to 110 requests to be
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/// in-flight.
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///
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/// ```
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/// # use tower::Service;
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/// # use tower::builder::ServiceBuilder;
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/// # async fn wrap<S>(svc: S) where S: Service<(), Error = &'static str> + 'static + Send, S::Future: Send {
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/// ServiceBuilder::new()
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/// .concurrency_limit(10)
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/// .buffer(100)
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/// .service(svc)
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/// # ;
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/// # }
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/// ```
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///
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/// The above example is similar, but the order of layers is reversed. Now,
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/// `concurrency_limit` applies first and only allows 10 requests to be in-flight
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/// total.
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///
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/// # Examples
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///
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/// A `Service` stack with a single layer:
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///
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/// ```
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/// # use tower::Service;
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/// # use tower::builder::ServiceBuilder;
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/// # use tower_limit::concurrency::ConcurrencyLimitLayer;
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/// # async fn wrap<S>(svc: S) where S: Service<(), Error = &'static str> + 'static + Send, S::Future: Send {
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/// ServiceBuilder::new()
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/// .concurrency_limit(5)
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/// .service(svc);
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/// # ;
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/// # }
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/// ```
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///
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/// A `Service` stack with _multiple_ layers that contain rate limiting,
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/// in-flight request limits, and a channel-backed, clonable `Service`:
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///
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/// ```
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/// # use tower::Service;
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/// # use tower::builder::ServiceBuilder;
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/// # use std::time::Duration;
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/// # async fn wrap<S>(svc: S) where S: Service<(), Error = &'static str> + 'static + Send, S::Future: Send {
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/// ServiceBuilder::new()
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/// .buffer(5)
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/// .concurrency_limit(5)
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/// .rate_limit(5, Duration::from_secs(1))
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/// .service(svc);
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/// # ;
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/// # }
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/// ```
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#[derive(Clone)]
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pub struct ServiceBuilder<L> {
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layer: L,
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}
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impl ServiceBuilder<Identity> {
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/// Create a new `ServiceBuilder`.
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pub fn new() -> Self {
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ServiceBuilder {
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layer: Identity::new(),
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}
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}
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}
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impl<L> ServiceBuilder<L> {
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/// Add a new layer `T` into the `ServiceBuilder`.
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pub fn layer<T>(self, layer: T) -> ServiceBuilder<Stack<T, L>> {
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ServiceBuilder {
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layer: Stack::new(layer, self.layer),
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}
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}
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/// Buffer requests when when the next layer is out of capacity.
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#[cfg(feature = "buffer")]
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pub fn buffer<Request>(
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self,
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bound: usize,
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) -> ServiceBuilder<Stack<crate::buffer::BufferLayer<Request>, L>> {
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self.layer(crate::buffer::BufferLayer::new(bound))
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}
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/// Limit the max number of in-flight requests.
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///
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/// A request is in-flight from the time the request is received until the
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/// response future completes. This includes the time spent in the next
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/// layers.
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#[cfg(feature = "limit")]
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pub fn concurrency_limit(
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self,
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max: usize,
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) -> ServiceBuilder<Stack<crate::limit::ConcurrencyLimitLayer, L>> {
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self.layer(crate::limit::ConcurrencyLimitLayer::new(max))
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}
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/// Drop requests when the next layer is unable to respond to requests.
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///
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/// Usually, when a layer or service does not have capacity to process a
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/// request (i.e., `poll_ready` returns `NotReady`), the caller waits until
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/// capacity becomes available.
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///
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/// `load_shed` immediately responds with an error when the next layer is
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/// out of capacity.
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#[cfg(feature = "load-shed")]
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pub fn load_shed(self) -> ServiceBuilder<Stack<crate::load_shed::LoadShedLayer, L>> {
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self.layer(crate::load_shed::LoadShedLayer::new())
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}
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/// Limit requests to at most `num` per the given duration
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#[cfg(feature = "limit")]
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pub fn rate_limit(
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self,
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num: u64,
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per: std::time::Duration,
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) -> ServiceBuilder<Stack<crate::limit::RateLimitLayer, L>> {
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self.layer(crate::limit::RateLimitLayer::new(num, per))
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}
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/// Retry failed requests.
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///
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/// `policy` must implement [`Policy`].
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///
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/// [`Policy`]: ../retry/trait.Policy.html
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#[cfg(feature = "retry")]
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pub fn retry<P>(self, policy: P) -> ServiceBuilder<Stack<crate::retry::RetryLayer<P>, L>> {
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self.layer(crate::retry::RetryLayer::new(policy))
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}
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/// Fail requests that take longer than `timeout`.
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///
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/// If the next layer takes more than `timeout` to respond to a request,
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/// processing is terminated and an error is returned.
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#[cfg(feature = "timeout")]
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pub fn timeout(
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self,
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timeout: std::time::Duration,
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) -> ServiceBuilder<Stack<crate::timeout::TimeoutLayer, L>> {
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self.layer(crate::timeout::TimeoutLayer::new(timeout))
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}
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/// Obtains the underlying `Layer` implementation.
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pub fn into_inner(self) -> L {
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self.layer
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}
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/// Wrap the service `S` with the layers.
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pub fn service<S>(self, service: S) -> L::Service
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where
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L: Layer<S>,
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{
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self.layer.layer(service)
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}
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}
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impl<L: fmt::Debug> fmt::Debug for ServiceBuilder<L> {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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f.debug_tuple("ServiceBuilder").field(&self.layer).finish()
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}
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}
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