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//! Apply a transformation to the response body.
//!
//! # Example
//!
//! ```
//! use bytes::Bytes;
//! use http::{Request, Response};
//! use hyper::Body;
//! use std::convert::Infallible;
//! use std::{pin::Pin, task::{Context, Poll}};
//! use tower::{ServiceBuilder, service_fn, ServiceExt, Service};
//! use tower_http::map_response_body::MapResponseBodyLayer;
//! use futures::ready;
//!
//! // A wrapper for a `hyper::Body` that prints the size of data chunks
//! struct PrintChunkSizesBody {
//! inner: Body,
//! }
//!
//! impl PrintChunkSizesBody {
//! fn new(inner: Body) -> Self {
//! Self { inner }
//! }
//! }
//!
//! impl http_body::Body for PrintChunkSizesBody {
//! type Data = Bytes;
//! type Error = hyper::Error;
//!
//! fn poll_data(
//! mut self: Pin<&mut Self>,
//! cx: &mut Context<'_>,
//! ) -> Poll<Option<Result<Self::Data, Self::Error>>> {
//! if let Some(chunk) = ready!(Pin::new(&mut self.inner).poll_data(cx)?) {
//! println!("chunk size = {}", chunk.len());
//! Poll::Ready(Some(Ok(chunk)))
//! } else {
//! Poll::Ready(None)
//! }
//! }
//!
//! fn poll_trailers(
//! mut self: Pin<&mut Self>,
//! cx: &mut Context<'_>,
//! ) -> Poll<Result<Option<hyper::HeaderMap>, Self::Error>> {
//! Pin::new(&mut self.inner).poll_trailers(cx)
//! }
//!
//! fn is_end_stream(&self) -> bool {
//! self.inner.is_end_stream()
//! }
//!
//! fn size_hint(&self) -> http_body::SizeHint {
//! self.inner.size_hint()
//! }
//! }
//!
//! async fn handle<B>(_: Request<B>) -> Result<Response<Body>, Infallible> {
//! // ...
//! # Ok(Response::new(Body::empty()))
//! }
//!
//! # #[tokio::main]
//! # async fn main() -> Result<(), Box<dyn std::error::Error>> {
//! let mut svc = ServiceBuilder::new()
//! // Wrap response bodies in `PrintChunkSizesBody`
//! .layer(MapResponseBodyLayer::new(PrintChunkSizesBody::new))
//! .service_fn(handle);
//!
//! // Call the service
//! let request = Request::new(Body::from("foobar"));
//!
//! svc.ready().await?.call(request).await?;
//! # Ok(())
//! # }
//! ```
use futures_core::ready;
use http::{Request, Response};
use pin_project_lite::pin_project;
use std::future::Future;
use std::{
fmt,
pin::Pin,
task::{Context, Poll},
};
use tower_layer::Layer;
use tower_service::Service;
/// Apply a transformation to the response body.
///
/// See the [module docs](crate::map_response_body) for an example.
#[derive(Clone)]
pub struct MapResponseBodyLayer<F> {
f: F,
}
impl<F> MapResponseBodyLayer<F> {
/// Create a new [`MapResponseBodyLayer`].
///
/// `F` is expected to be a function that takes a body and returns another body.
pub fn new(f: F) -> Self {
Self { f }
}
}
impl<S, F> Layer<S> for MapResponseBodyLayer<F>
where
F: Clone,
{
type Service = MapResponseBody<S, F>;
fn layer(&self, inner: S) -> Self::Service {
MapResponseBody::new(inner, self.f.clone())
}
}
impl<F> fmt::Debug for MapResponseBodyLayer<F> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("MapResponseBodyLayer")
.field("f", &std::any::type_name::<F>())
.finish()
}
}
/// Apply a transformation to the response body.
///
/// See the [module docs](crate::map_response_body) for an example.
#[derive(Clone)]
pub struct MapResponseBody<S, F> {
inner: S,
f: F,
}
impl<S, F> MapResponseBody<S, F> {
/// Create a new [`MapResponseBody`].
///
/// `F` is expected to be a function that takes a body and returns another body.
pub fn new(service: S, f: F) -> Self {
Self { inner: service, f }
}
/// Returns a new [`Layer`] that wraps services with a `MapResponseBodyLayer` middleware.
///
/// [`Layer`]: tower_layer::Layer
pub fn layer(f: F) -> MapResponseBodyLayer<F> {
MapResponseBodyLayer::new(f)
}
define_inner_service_accessors!();
}
impl<F, S, ReqBody, ResBody, NewResBody> Service<Request<ReqBody>> for MapResponseBody<S, F>
where
S: Service<Request<ReqBody>, Response = Response<ResBody>>,
F: FnMut(ResBody) -> NewResBody + Clone,
{
type Response = Response<NewResBody>;
type Error = S::Error;
type Future = ResponseFuture<S::Future, F>;
fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
self.inner.poll_ready(cx)
}
fn call(&mut self, req: Request<ReqBody>) -> Self::Future {
ResponseFuture {
inner: self.inner.call(req),
f: self.f.clone(),
}
}
}
impl<S, F> fmt::Debug for MapResponseBody<S, F>
where
S: fmt::Debug,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("MapResponseBody")
.field("inner", &self.inner)
.field("f", &std::any::type_name::<F>())
.finish()
}
}
pin_project! {
/// Response future for [`MapResponseBody`].
pub struct ResponseFuture<Fut, F> {
#[pin]
inner: Fut,
f: F,
}
}
impl<Fut, F, ResBody, E, NewResBody> Future for ResponseFuture<Fut, F>
where
Fut: Future<Output = Result<Response<ResBody>, E>>,
F: FnMut(ResBody) -> NewResBody,
{
type Output = Result<Response<NewResBody>, E>;
fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
let this = self.project();
let res = ready!(this.inner.poll(cx)?);
Poll::Ready(Ok(res.map(this.f)))
}
}