Add utility function to convert body into bytes (#2373)

Co-authored-by: David Pedersen <david.pdrsn@gmail.com>

axum/CHANGELOG.md

@@ -7,7 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 # Unreleased
 
-- None.
+- **added:** Add `axum::body::to_bytes` ([#2373])
+
+[#2373]: https://github.com/tokio-rs/axum/pull/2373
 
 # 0.7.1 (27. November, 2023)
 

axum/src/body/mod.rs

@@ -8,3 +8,47 @@ pub use bytes::Bytes;
 
 #[doc(inline)]
 pub use axum_core::body::Body;
+
+use http_body_util::{BodyExt, Limited};
+
+/// Converts [`Body`] into [`Bytes`] and limits the maximum size of the body.
+///
+/// # Example
+///
+/// ```rust
+/// use axum::body::{to_bytes, Body};
+///
+/// # async fn foo() -> Result<(), axum_core::Error> {
+/// let body = Body::from(vec![1, 2, 3]);
+/// // Use `usize::MAX` if you don't care about the maximum size.
+/// let bytes = to_bytes(body, usize::MAX).await?;
+/// assert_eq!(&bytes[..], &[1, 2, 3]);
+/// # Ok(())
+/// # }
+/// ```
+///
+/// You can detect if the limit was hit by checking the source of the error:
+///
+/// ```rust
+/// use axum::body::{to_bytes, Body};
+/// use http_body_util::LengthLimitError;
+///
+/// # #[tokio::main]
+/// # async fn main() {
+/// let body = Body::from(vec![1, 2, 3]);
+/// match to_bytes(body, 1).await {
+///     Ok(_bytes) => panic!("should have hit the limit"),
+///     Err(err) => {
+///         let source = std::error::Error::source(&err).unwrap();
+///         assert!(source.is::<LengthLimitError>());
+///     }
+/// }
+/// # }
+/// ```
+pub async fn to_bytes(body: Body, limit: usize) -> Result<Bytes, axum_core::Error> {
+    Limited::new(body, limit)
+        .collect()
+        .await
+        .map(|col| col.to_bytes())
+        .map_err(axum_core::Error::new)
+}