implement BodyReader for easy consumption of Body

I need `serde_json::from_reader(req.body_mut().reader())`.

src/http.rs

@@ -1,9 +1,9 @@
 use crate::executor;
 
 use core::fmt;
-use std::io;
 use std::pin::Pin;
 use std::task::{Context, Poll};
+use std::{cmp, debug_assert, io};
 
 use futures_core::Stream;
 use hyper::body::HttpBody;
@@ -109,6 +109,14 @@ impl Body {
  {
  Body(hyper::Body::wrap_stream(ReaderStream::new(reader)))
  }
+
+ /// Create a [`BodyReader`] that implements [`std::io::Read`].
+ pub fn reader(&mut self) -> BodyReader<'_> {
+ BodyReader {
+ body: self,
+ prev_bytes: Bytes::new(),
+ }
+ }
 }
 
 impl<T> From<T> for Body
@@ -134,6 +142,48 @@ impl Iterator for Body {
  }
 }
 
+/// Wraps [`Body`] and implements [`std::io::Read`]
+pub struct BodyReader<'b> {
+ body: &'b mut Body,
+ prev_bytes: Bytes,
+}
+
+impl<'b> std::io::Read for BodyReader<'b> {
+ fn read(&mut self, mut buf: &mut [u8]) -> io::Result<usize> {
+ let mut written = 0;
+ loop {
+ if buf.is_empty() {
+ return Ok(written);
+ }
+
+ if !self.prev_bytes.is_empty() {
+ let chunk_size = cmp::min(buf.len(), self.prev_bytes.len());
+ let prev_bytes_rest = self.prev_bytes.split_to(chunk_size);
+ buf[..chunk_size].copy_from_slice(&self.prev_bytes[..chunk_size]);
+ self.prev_bytes = prev_bytes_rest;
+ buf = &mut buf[chunk_size..];
+ written += chunk_size;
+ continue;
+ }
+
+ if written != 0 {
+ // pulling from an interator can block, and we have something to return
+ // already, so return it
+ return Ok(written);
+ }
+
+ debug_assert!(self.prev_bytes.is_empty());
+ debug_assert!(written == 0);
+
+ self.prev_bytes = if let Some(next) = self.body.next() {
+ next?
+ } else {
+ return Ok(written);
+ }
+ }
+ }
+}
+
 impl fmt::Debug for Body {
  fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  self.0.fmt(f)