feat(http1): Add support for sending HTTP/1.1 Chunked Trailer Fields (#3375)

Closes #2719

Author: hjr3

src/proto/h1/conn.rs

@@ -8,7 +8,7 @@ use std::time::Duration;
 
 use crate::rt::{Read, Write};
 use bytes::{Buf, Bytes};
-use http::header::{HeaderValue, CONNECTION};
+use http::header::{HeaderValue, CONNECTION, TE};
 use http::{HeaderMap, Method, Version};
 use httparse::ParserConfig;
 
@@ -75,6 +75,7 @@ where
                 // We assume a modern world where the remote speaks HTTP/1.1.
                 // If they tell us otherwise, we'll downgrade in `read_head`.
                 version: Version::HTTP_11,
+                allow_trailer_fields: false,
             },
             _marker: PhantomData,
         }
@@ -264,6 +265,13 @@ where
             self.state.reading = Reading::Body(Decoder::new(msg.decode));
         }
 
+        self.state.allow_trailer_fields = msg
+            .head
+            .headers
+            .get(TE)
+            .map(|te_header| te_header == "trailers")
+            .unwrap_or(false);
+
         Poll::Ready(Some(Ok((msg.head, msg.decode, wants))))
     }
 
@@ -640,6 +648,31 @@ where
         self.state.writing = state;
     }
 
+    pub(crate) fn write_trailers(&mut self, trailers: HeaderMap) {
+        if T::is_server() && self.state.allow_trailer_fields == false {
+            debug!("trailers not allowed to be sent");
+            return;
+        }
+        debug_assert!(self.can_write_body() && self.can_buffer_body());
+
+        match self.state.writing {
+            Writing::Body(ref encoder) => {
+                if let Some(enc_buf) =
+                    encoder.encode_trailers(trailers, self.state.title_case_headers)
+                {
+                    self.io.buffer(enc_buf);
+
+                    self.state.writing = if encoder.is_last() || encoder.is_close_delimited() {
+                        Writing::Closed
+                    } else {
+                        Writing::KeepAlive
+                    };
+                }
+            }
+            _ => unreachable!("write_trailers invalid state: {:?}", self.state.writing),
+        }
+    }
+
     pub(crate) fn write_body_and_end(&mut self, chunk: B) {
         debug_assert!(self.can_write_body() && self.can_buffer_body());
         // empty chunks should be discarded at Dispatcher level
@@ -842,6 +875,8 @@ struct State {
     upgrade: Option<crate::upgrade::Pending>,
     /// Either HTTP/1.0 or 1.1 connection
     version: Version,
+    /// Flag to track if trailer fields are allowed to be sent
+    allow_trailer_fields: bool,
 }
 
 #[derive(Debug)]

src/proto/h1/dispatch.rs

@@ -351,27 +351,33 @@ where
                             *clear_body = true;
                             crate::Error::new_user_body(e)
                         })?;
-                        let chunk = if let Ok(data) = frame.into_data() {
-                            data
-                        } else {
-                            trace!("discarding non-data frame");
-                            continue;
-                        };
-                        let eos = body.is_end_stream();
-                        if eos {
-                            *clear_body = true;
-                            if chunk.remaining() == 0 {
-                                trace!("discarding empty chunk");
-                                self.conn.end_body()?;
+
+                        if frame.is_data() {
+                            let chunk = frame.into_data().unwrap_or_else(|_| unreachable!());
+                            let eos = body.is_end_stream();
+                            if eos {
+                                *clear_body = true;
+                                if chunk.remaining() == 0 {
+                                    trace!("discarding empty chunk");
+                                    self.conn.end_body()?;
+                                } else {
+                                    self.conn.write_body_and_end(chunk);
+                                }
                             } else {
-                                self.conn.write_body_and_end(chunk);
+                                if chunk.remaining() == 0 {
+                                    trace!("discarding empty chunk");
+                                    continue;
+                                }
+                                self.conn.write_body(chunk);
                             }
+                        } else if frame.is_trailers() {
+                            *clear_body = true;
+                            self.conn.write_trailers(
+                                frame.into_trailers().unwrap_or_else(|_| unreachable!()),
+                            );
                         } else {
-                            if chunk.remaining() == 0 {
-                                trace!("discarding empty chunk");
-                                continue;
-                            }
-                            self.conn.write_body(chunk);
+                            trace!("discarding unknown frame");
+                            continue;
                         }
                     } else {
                         *clear_body = true;

src/proto/h1/encode.rs

@@ -1,10 +1,19 @@
+use std::collections::HashMap;
 use std::fmt;
 use std::io::IoSlice;
 
 use bytes::buf::{Chain, Take};
-use bytes::Buf;
+use bytes::{Buf, Bytes};
+use http::{
+    header::{
+        AUTHORIZATION, CACHE_CONTROL, CONTENT_ENCODING, CONTENT_LENGTH, CONTENT_RANGE,
+        CONTENT_TYPE, HOST, MAX_FORWARDS, SET_COOKIE, TE, TRAILER, TRANSFER_ENCODING,
+    },
+    HeaderMap, HeaderName, HeaderValue,
+};
 
 use super::io::WriteBuf;
+use super::role::{write_headers, write_headers_title_case};
 
 type StaticBuf = &'static [u8];
 
@@ -26,7 +35,7 @@ pub(crate) struct NotEof(u64);
 #[derive(Debug, PartialEq, Clone)]
 enum Kind {
     /// An Encoder for when Transfer-Encoding includes `chunked`.
-    Chunked,
+    Chunked(Option<Vec<HeaderValue>>),
     /// An Encoder for when Content-Length is set.
     ///
     /// Enforces that the body is not longer than the Content-Length header.
@@ -45,6 +54,7 @@ enum BufKind<B> {
     Limited(Take<B>),
     Chunked(Chain<Chain<ChunkSize, B>, StaticBuf>),
     ChunkedEnd(StaticBuf),
+    Trailers(Chain<Chain<StaticBuf, Bytes>, StaticBuf>),
 }
 
 impl Encoder {
@@ -55,7 +65,7 @@ impl Encoder {
         }
     }
     pub(crate) fn chunked() -> Encoder {
-        Encoder::new(Kind::Chunked)
+        Encoder::new(Kind::Chunked(None))
     }
 
     pub(crate) fn length(len: u64) -> Encoder {
@@ -67,6 +77,16 @@ impl Encoder {
         Encoder::new(Kind::CloseDelimited)
     }
 
+    pub(crate) fn into_chunked_with_trailing_fields(self, trailers: Vec<HeaderValue>) -> Encoder {
+        match self.kind {
+            Kind::Chunked(_) => Encoder {
+                kind: Kind::Chunked(Some(trailers)),
+                is_last: self.is_last,
+            },
+            _ => self,
+        }
+    }
+
     pub(crate) fn is_eof(&self) -> bool {
         matches!(self.kind, Kind::Length(0))
     }
@@ -89,10 +109,17 @@ impl Encoder {
         }
     }
 
+    pub(crate) fn is_chunked(&self) -> bool {
+        match self.kind {
+            Kind::Chunked(_) => true,
+            _ => false,
+        }
+    }
+
     pub(crate) fn end<B>(&self) -> Result<Option<EncodedBuf<B>>, NotEof> {
         match self.kind {
             Kind::Length(0) => Ok(None),
-            Kind::Chunked => Ok(Some(EncodedBuf {
+            Kind::Chunked(_) => Ok(Some(EncodedBuf {
                 kind: BufKind::ChunkedEnd(b"0\r\n\r\n"),
             })),
             #[cfg(feature = "server")]
@@ -109,7 +136,7 @@ impl Encoder {
         debug_assert!(len > 0, "encode() called with empty buf");
 
         let kind = match self.kind {
-            Kind::Chunked => {
+            Kind::Chunked(_) => {
                 trace!("encoding chunked {}B", len);
                 let buf = ChunkSize::new(len)
                     .chain(msg)
@@ -136,6 +163,53 @@ impl Encoder {
         EncodedBuf { kind }
     }
 
+    pub(crate) fn encode_trailers<B>(
+        &self,
+        trailers: HeaderMap,
+        title_case_headers: bool,
+    ) -> Option<EncodedBuf<B>> {
+        match &self.kind {
+            Kind::Chunked(Some(ref allowed_trailer_fields)) => {
+                let allowed_trailer_field_map = allowed_trailer_field_map(&allowed_trailer_fields);
+
+                let mut cur_name = None;
+                let mut allowed_trailers = HeaderMap::new();
+
+                for (opt_name, value) in trailers {
+                    if let Some(n) = opt_name {
+                        cur_name = Some(n);
+                    }
+                    let name = cur_name.as_ref().expect("current header name");
+
+                    if allowed_trailer_field_map.contains_key(name.as_str())
+                        && valid_trailer_field(name)
+                    {
+                        allowed_trailers.insert(name, value);
+                    }
+                }
+
+                let mut buf = Vec::new();
+                if title_case_headers {
+                    write_headers_title_case(&allowed_trailers, &mut buf);
+                } else {
+                    write_headers(&allowed_trailers, &mut buf);
+                }
+
+                if buf.is_empty() {
+                    return None;
+                }
+
+                Some(EncodedBuf {
+                    kind: BufKind::Trailers(b"0\r\n".chain(Bytes::from(buf)).chain(b"\r\n")),
+                })
+            }
+            _ => {
+                debug!("attempted to encode trailers for non-chunked response");
+                None
+            }
+        }
+    }
+
     pub(super) fn encode_and_end<B>(&self, msg: B, dst: &mut WriteBuf<EncodedBuf<B>>) -> bool
     where
         B: Buf,
@@ -144,7 +218,7 @@ impl Encoder {
         debug_assert!(len > 0, "encode() called with empty buf");
 
         match self.kind {
-            Kind::Chunked => {
+            Kind::Chunked(_) => {
                 trace!("encoding chunked {}B", len);
                 let buf = ChunkSize::new(len)
                     .chain(msg)
@@ -181,6 +255,40 @@ impl Encoder {
     }
 }
 
+fn valid_trailer_field(name: &HeaderName) -> bool {
+    match name {
+        &AUTHORIZATION => false,
+        &CACHE_CONTROL => false,
+        &CONTENT_ENCODING => false,
+        &CONTENT_LENGTH => false,
+        &CONTENT_RANGE => false,
+        &CONTENT_TYPE => false,
+        &HOST => false,
+        &MAX_FORWARDS => false,
+        &SET_COOKIE => false,
+        &TRAILER => false,
+        &TRANSFER_ENCODING => false,
+        &TE => false,
+        _ => true,
+    }
+}
+
+fn allowed_trailer_field_map(allowed_trailer_fields: &Vec<HeaderValue>) -> HashMap<String, ()> {
+    let mut trailer_map = HashMap::new();
+
+    for header_value in allowed_trailer_fields {
+        if let Ok(header_str) = header_value.to_str() {
+            let items: Vec<&str> = header_str.split(',').map(|item| item.trim()).collect();
+
+            for item in items {
+                trailer_map.entry(item.to_string()).or_insert(());
+            }
+        }
+    }
+
+    trailer_map
+}
+
 impl<B> Buf for EncodedBuf<B>
 where
     B: Buf,
@@ -192,6 +300,7 @@ where
             BufKind::Limited(ref b) => b.remaining(),
             BufKind::Chunked(ref b) => b.remaining(),
             BufKind::ChunkedEnd(ref b) => b.remaining(),
+            BufKind::Trailers(ref b) => b.remaining(),
         }
     }
 
@@ -202,6 +311,7 @@ where
             BufKind::Limited(ref b) => b.chunk(),
             BufKind::Chunked(ref b) => b.chunk(),
             BufKind::ChunkedEnd(ref b) => b.chunk(),
+            BufKind::Trailers(ref b) => b.chunk(),
         }
     }
 
@@ -212,6 +322,7 @@ where
             BufKind::Limited(ref mut b) => b.advance(cnt),
             BufKind::Chunked(ref mut b) => b.advance(cnt),
             BufKind::ChunkedEnd(ref mut b) => b.advance(cnt),
+            BufKind::Trailers(ref mut b) => b.advance(cnt),
         }
     }
 
@@ -222,6 +333,7 @@ where
             BufKind::Limited(ref b) => b.chunks_vectored(dst),
             BufKind::Chunked(ref b) => b.chunks_vectored(dst),
             BufKind::ChunkedEnd(ref b) => b.chunks_vectored(dst),
+            BufKind::Trailers(ref b) => b.chunks_vectored(dst),
         }
     }
 }
@@ -327,7 +439,16 @@ impl std::error::Error for NotEof {}
 
 #[cfg(test)]
 mod tests {
+    use std::iter::FromIterator;
+
     use bytes::BufMut;
+    use http::{
+        header::{
+            AUTHORIZATION, CACHE_CONTROL, CONTENT_ENCODING, CONTENT_LENGTH, CONTENT_RANGE,
+            CONTENT_TYPE, HOST, MAX_FORWARDS, SET_COOKIE, TE, TRAILER, TRANSFER_ENCODING,
+        },
+        HeaderMap, HeaderName, HeaderValue,
+    };
 
     use super::super::io::Cursor;
     use super::Encoder;
@@ -402,4 +523,145 @@ mod tests {
         assert!(!encoder.is_eof());
         encoder.end::<()>().unwrap();
     }
+
+    #[test]
+    fn chunked_with_valid_trailers() {
+        let encoder = Encoder::chunked();
+        let trailers = vec![HeaderValue::from_static("chunky-trailer")];
+        let encoder = encoder.into_chunked_with_trailing_fields(trailers);
+
+        let headers = HeaderMap::from_iter(
+            vec![
+                (
+                    HeaderName::from_static("chunky-trailer"),
+                    HeaderValue::from_static("header data"),
+                ),
+                (
+                    HeaderName::from_static("should-not-be-included"),
+                    HeaderValue::from_static("oops"),
+                ),
+            ]
+            .into_iter(),
+        );
+
+        let buf1 = encoder.encode_trailers::<&[u8]>(headers, false).unwrap();
+
+        let mut dst = Vec::new();
+        dst.put(buf1);
+        assert_eq!(dst, b"0\r\nchunky-trailer: header data\r\n\r\n");
+    }
+
+    #[test]
+    fn chunked_with_multiple_trailer_headers() {
+        let encoder = Encoder::chunked();
+        let trailers = vec![
+            HeaderValue::from_static("chunky-trailer"),
+            HeaderValue::from_static("chunky-trailer-2"),
+        ];
+        let encoder = encoder.into_chunked_with_trailing_fields(trailers);
+
+        let headers = HeaderMap::from_iter(
+            vec![
+                (
+                    HeaderName::from_static("chunky-trailer"),
+                    HeaderValue::from_static("header data"),
+                ),
+                (
+                    HeaderName::from_static("chunky-trailer-2"),
+                    HeaderValue::from_static("more header data"),
+                ),
+            ]
+            .into_iter(),
+        );
+
+        let buf1 = encoder.encode_trailers::<&[u8]>(headers, false).unwrap();
+
+        let mut dst = Vec::new();
+        dst.put(buf1);
+        assert_eq!(
+            dst,
+            b"0\r\nchunky-trailer: header data\r\nchunky-trailer-2: more header data\r\n\r\n"
+        );
+    }
+
+    #[test]
+    fn chunked_with_no_trailer_header() {
+        let encoder = Encoder::chunked();
+
+        let headers = HeaderMap::from_iter(
+            vec![(
+                HeaderName::from_static("chunky-trailer"),
+                HeaderValue::from_static("header data"),
+            )]
+            .into_iter(),
+        );
+
+        assert!(encoder
+            .encode_trailers::<&[u8]>(headers.clone(), false)
+            .is_none());
+
+        let trailers = vec![];
+        let encoder = encoder.into_chunked_with_trailing_fields(trailers);
+
+        assert!(encoder.encode_trailers::<&[u8]>(headers, false).is_none());
+    }
+
+    #[test]
+    fn chunked_with_invalid_trailers() {
+        let encoder = Encoder::chunked();
+
+        let trailers = format!(
+            "{},{},{},{},{},{},{},{},{},{},{},{}",
+            AUTHORIZATION,
+            CACHE_CONTROL,
+            CONTENT_ENCODING,
+            CONTENT_LENGTH,
+            CONTENT_RANGE,
+            CONTENT_TYPE,
+            HOST,
+            MAX_FORWARDS,
+            SET_COOKIE,
+            TRAILER,
+            TRANSFER_ENCODING,
+            TE,
+        );
+        let trailers = vec![HeaderValue::from_str(&trailers).unwrap()];
+        let encoder = encoder.into_chunked_with_trailing_fields(trailers);
+
+        let mut headers = HeaderMap::new();
+        headers.insert(AUTHORIZATION, HeaderValue::from_static("header data"));
+        headers.insert(CACHE_CONTROL, HeaderValue::from_static("header data"));
+        headers.insert(CONTENT_ENCODING, HeaderValue::from_static("header data"));
+        headers.insert(CONTENT_LENGTH, HeaderValue::from_static("header data"));
+        headers.insert(CONTENT_RANGE, HeaderValue::from_static("header data"));
+        headers.insert(CONTENT_TYPE, HeaderValue::from_static("header data"));
+        headers.insert(HOST, HeaderValue::from_static("header data"));
+        headers.insert(MAX_FORWARDS, HeaderValue::from_static("header data"));
+        headers.insert(SET_COOKIE, HeaderValue::from_static("header data"));
+        headers.insert(TRAILER, HeaderValue::from_static("header data"));
+        headers.insert(TRANSFER_ENCODING, HeaderValue::from_static("header data"));
+        headers.insert(TE, HeaderValue::from_static("header data"));
+
+        assert!(encoder.encode_trailers::<&[u8]>(headers, true).is_none());
+    }
+
+    #[test]
+    fn chunked_with_title_case_headers() {
+        let encoder = Encoder::chunked();
+        let trailers = vec![HeaderValue::from_static("chunky-trailer")];
+        let encoder = encoder.into_chunked_with_trailing_fields(trailers);
+
+        let headers = HeaderMap::from_iter(
+            vec![(
+                HeaderName::from_static("chunky-trailer"),
+                HeaderValue::from_static("header data"),
+            )]
+            .into_iter(),
+        );
+        let buf1 = encoder.encode_trailers::<&[u8]>(headers, true).unwrap();
+
+        let mut dst = Vec::new();
+        dst.put(buf1);
+        assert_eq!(dst, b"0\r\nChunky-Trailer: header data\r\n\r\n");
+    }
 }

src/proto/h1/role.rs

@@ -625,6 +625,7 @@ impl Server {
         };
 
         let mut encoder = Encoder::length(0);
+        let mut allowed_trailer_fields: Option<Vec<HeaderValue>> = None;
         let mut wrote_date = false;
         let mut cur_name = None;
         let mut is_name_written = false;
@@ -811,6 +812,38 @@ impl Server {
                 header::DATE => {
                     wrote_date = true;
                 }
+                header::TRAILER => {
+                    // check that we actually can send a chunked body...
+                    if msg.head.version == Version::HTTP_10
+                        || !Server::can_chunked(msg.req_method, msg.head.subject)
+                    {
+                        continue;
+                    }
+
+                    if !is_name_written {
+                        is_name_written = true;
+                        header_name_writer.write_header_name_with_colon(
+                            dst,
+                            "trailer: ",
+                            header::TRAILER,
+                        );
+                        extend(dst, value.as_bytes());
+                    } else {
+                        extend(dst, b", ");
+                        extend(dst, value.as_bytes());
+                    }
+
+                    match allowed_trailer_fields {
+                        Some(ref mut allowed_trailer_fields) => {
+                            allowed_trailer_fields.push(value);
+                        }
+                        None => {
+                            allowed_trailer_fields = Some(vec![value]);
+                        }
+                    }
+
+                    continue 'headers;
+                }
                 _ => (),
             }
             //TODO: this should perhaps instead combine them into
@@ -895,6 +928,12 @@ impl Server {
             extend(dst, b"\r\n");
         }
 
+        if encoder.is_chunked() {
+            if let Some(allowed_trailer_fields) = allowed_trailer_fields {
+                encoder = encoder.into_chunked_with_trailing_fields(allowed_trailer_fields);
+            }
+        }
+
         Ok(encoder.set_last(is_last))
     }
 }
@@ -1302,6 +1341,19 @@ impl Client {
             }
         };
 
+        let encoder = encoder.map(|enc| {
+            if enc.is_chunked() {
+                let allowed_trailer_fields: Vec<HeaderValue> =
+                    headers.get_all(header::TRAILER).iter().cloned().collect();
+
+                if !allowed_trailer_fields.is_empty() {
+                    return enc.into_chunked_with_trailing_fields(allowed_trailer_fields);
+                }
+            }
+
+            enc
+        });
+
         // This is because we need a second mutable borrow to remove
         // content-length header.
         if let Some(encoder) = encoder {
@@ -1464,8 +1516,7 @@ fn title_case(dst: &mut Vec<u8>, name: &[u8]) {
     }
 }
 
-#[cfg(feature = "client")]
-fn write_headers_title_case(headers: &HeaderMap, dst: &mut Vec<u8>) {
+pub(crate) fn write_headers_title_case(headers: &HeaderMap, dst: &mut Vec<u8>) {
     for (name, value) in headers {
         title_case(dst, name.as_str().as_bytes());
         extend(dst, b": ");
@@ -1474,8 +1525,7 @@ fn write_headers_title_case(headers: &HeaderMap, dst: &mut Vec<u8>) {
     }
 }
 
-#[cfg(feature = "client")]
-fn write_headers(headers: &HeaderMap, dst: &mut Vec<u8>) {
+pub(crate) fn write_headers(headers: &HeaderMap, dst: &mut Vec<u8>) {
     for (name, value) in headers {
         extend(dst, name.as_str().as_bytes());
         extend(dst, b": ");

tests/client.rs

@@ -5,6 +5,7 @@ use std::convert::Infallible;
 use std::fmt;
 use std::future::Future;
 use std::io::{Read, Write};
+use std::iter::FromIterator;
 use std::net::{SocketAddr, TcpListener};
 use std::pin::Pin;
 use std::thread;
@@ -13,7 +14,7 @@ use std::time::Duration;
 use http::uri::PathAndQuery;
 use http_body_util::{BodyExt, StreamBody};
 use hyper::body::Frame;
-use hyper::header::HeaderValue;
+use hyper::header::{HeaderMap, HeaderName, HeaderValue};
 use hyper::{Method, Request, StatusCode, Uri, Version};
 
 use bytes::Bytes;
@@ -409,6 +410,15 @@ macro_rules! __client_req_prop {
             Frame::data,
         )));
     }};
+
+    ($req_builder:ident, $body:ident, $addr:ident, body_stream_with_trailers: $body_e:expr) => {{
+        use support::trailers::StreamBodyWithTrailers;
+        let (body, trailers) = $body_e;
+        $body = BodyExt::boxed(StreamBodyWithTrailers::with_trailers(
+            futures_util::TryStreamExt::map_ok(body, Frame::data),
+            trailers,
+        ));
+    }};
 }
 
 macro_rules! __client_req_header {
@@ -632,6 +642,44 @@ test! {
             body: &b"hello"[..],
 }
 
+test! {
+    name: client_post_req_body_chunked_with_trailer,
+
+    server:
+        expected: "\
+            POST / HTTP/1.1\r\n\
+            trailer: chunky-trailer\r\n\
+            host: {addr}\r\n\
+            transfer-encoding: chunked\r\n\
+            \r\n\
+            5\r\n\
+            hello\r\n\
+            0\r\n\
+            chunky-trailer: header data\r\n\
+            \r\n\
+            ",
+        reply: REPLY_OK,
+
+    client:
+        request: {
+            method: POST,
+            url: "http://{addr}/",
+            headers: {
+                "trailer" => "chunky-trailer",
+            },
+            body_stream_with_trailers: (
+                (futures_util::stream::once(async { Ok::<_, Infallible>(Bytes::from("hello"))})),
+                HeaderMap::from_iter(vec![(
+                    HeaderName::from_static("chunky-trailer"),
+                    HeaderValue::from_static("header data")
+                )].into_iter())),
+        },
+        response:
+            status: OK,
+            headers: {},
+            body: None,
+}
+
 test! {
     name: client_get_req_body_sized,
 

tests/server.rs

@@ -19,7 +19,7 @@ use futures_channel::oneshot;
 use futures_util::future::{self, Either, FutureExt};
 use h2::client::SendRequest;
 use h2::{RecvStream, SendStream};
-use http::header::{HeaderName, HeaderValue};
+use http::header::{HeaderMap, HeaderName, HeaderValue};
 use http_body_util::{combinators::BoxBody, BodyExt, Empty, Full, StreamBody};
 use hyper::rt::Timer;
 use hyper::rt::{Read as AsyncRead, Write as AsyncWrite};
@@ -2595,6 +2595,94 @@ async fn http2_keep_alive_count_server_pings() {
         .expect("timed out waiting for pings");
 }
 
+#[test]
+fn http1_trailer_fields() {
+    let body = futures_util::stream::once(async move { Ok("hello".into()) });
+    let mut headers = HeaderMap::new();
+    headers.insert("chunky-trailer", "header data".parse().unwrap());
+    // Invalid trailer field that should not be sent
+    headers.insert("Host", "www.example.com".parse().unwrap());
+    // Not specified in Trailer header, so should not be sent
+    headers.insert("foo", "bar".parse().unwrap());
+
+    let server = serve();
+    server
+        .reply()
+        .header("transfer-encoding", "chunked")
+        .header("trailer", "chunky-trailer")
+        .body_stream_with_trailers(body, headers);
+    let mut req = connect(server.addr());
+    req.write_all(
+        b"\
+        GET / HTTP/1.1\r\n\
+        Host: example.domain\r\n\
+        Connection: keep-alive\r\n\
+        TE: trailers\r\n\
+        \r\n\
+    ",
+    )
+    .expect("writing");
+
+    let chunky_trailer_chunk = b"\r\nchunky-trailer: header data\r\n\r\n";
+    let res = read_until(&mut req, |buf| buf.ends_with(chunky_trailer_chunk)).expect("reading");
+    let sres = s(&res);
+
+    let expected_head =
+        "HTTP/1.1 200 OK\r\ntransfer-encoding: chunked\r\ntrailer: chunky-trailer\r\n";
+    assert_eq!(&sres[..expected_head.len()], expected_head);
+
+    // skip the date header
+    let date_fragment = "GMT\r\n\r\n";
+    let pos = sres.find(date_fragment).expect("find GMT");
+    let body = &sres[pos + date_fragment.len()..];
+
+    let expected_body = "5\r\nhello\r\n0\r\nchunky-trailer: header data\r\n\r\n";
+    assert_eq!(body, expected_body);
+}
+
+#[test]
+fn http1_trailer_fields_not_allowed() {
+    let body = futures_util::stream::once(async move { Ok("hello".into()) });
+    let mut headers = HeaderMap::new();
+    headers.insert("chunky-trailer", "header data".parse().unwrap());
+
+    let server = serve();
+    server
+        .reply()
+        .header("transfer-encoding", "chunked")
+        .header("trailer", "chunky-trailer")
+        .body_stream_with_trailers(body, headers);
+    let mut req = connect(server.addr());
+
+    // TE: trailers is not specified in request headers
+    req.write_all(
+        b"\
+        GET / HTTP/1.1\r\n\
+        Host: example.domain\r\n\
+        Connection: keep-alive\r\n\
+        \r\n\
+    ",
+    )
+    .expect("writing");
+
+    let last_chunk = b"\r\n0\r\n\r\n";
+    let res = read_until(&mut req, |buf| buf.ends_with(last_chunk)).expect("reading");
+    let sres = s(&res);
+
+    let expected_head =
+        "HTTP/1.1 200 OK\r\ntransfer-encoding: chunked\r\ntrailer: chunky-trailer\r\n";
+    assert_eq!(&sres[..expected_head.len()], expected_head);
+
+    // skip the date header
+    let date_fragment = "GMT\r\n\r\n";
+    let pos = sres.find(date_fragment).expect("find GMT");
+    let body = &sres[pos + date_fragment.len()..];
+
+    // no trailer fields should be sent because TE: trailers was not in request headers
+    let expected_body = "5\r\nhello\r\n0\r\n\r\n";
+    assert_eq!(body, expected_body);
+}
+
 // -------------------------------------------------
 // the Server that is used to run all the tests with
 // -------------------------------------------------
@@ -2700,6 +2788,19 @@ impl<'a> ReplyBuilder<'a> {
         self.tx.lock().unwrap().send(Reply::Body(body)).unwrap();
     }
 
+    fn body_stream_with_trailers<S>(self, stream: S, trailers: HeaderMap)
+    where
+        S: futures_util::Stream<Item = Result<Bytes, BoxError>> + Send + Sync + 'static,
+    {
+        use futures_util::TryStreamExt;
+        use hyper::body::Frame;
+        use support::trailers::StreamBodyWithTrailers;
+        let mut stream_body = StreamBodyWithTrailers::new(stream.map_ok(Frame::data));
+        stream_body.set_trailers(trailers);
+        let body = BodyExt::boxed(stream_body);
+        self.tx.lock().unwrap().send(Reply::Body(body)).unwrap();
+    }
+
     #[allow(dead_code)]
     fn error<E: Into<BoxError>>(self, err: E) {
         self.tx

tests/support/mod.rs

@@ -24,6 +24,8 @@ mod tokiort;
 #[allow(unused)]
 pub use tokiort::{TokioExecutor, TokioIo, TokioTimer};
 
+pub mod trailers;
+
 #[allow(unused_macros)]
 macro_rules! t {
     (

tests/support/trailers.rs

@@ -0,0 +1,76 @@
+use bytes::Buf;
+use futures_util::stream::Stream;
+use http::header::HeaderMap;
+use http_body::{Body, Frame};
+use pin_project_lite::pin_project;
+use std::{
+    pin::Pin,
+    task::{Context, Poll},
+};
+
+pin_project! {
+    /// A body created from a [`Stream`].
+    #[derive(Clone, Debug)]
+    pub struct StreamBodyWithTrailers<S> {
+        #[pin]
+        stream: S,
+        trailers: Option<HeaderMap>,
+    }
+}
+
+impl<S> StreamBodyWithTrailers<S> {
+    /// Create a new `StreamBodyWithTrailers`.
+    pub fn new(stream: S) -> Self {
+        Self {
+            stream,
+            trailers: None,
+        }
+    }
+
+    pub fn with_trailers(stream: S, trailers: HeaderMap) -> Self {
+        Self {
+            stream,
+            trailers: Some(trailers),
+        }
+    }
+
+    pub fn set_trailers(&mut self, trailers: HeaderMap) {
+        self.trailers = Some(trailers);
+    }
+}
+
+impl<S, D, E> Body for StreamBodyWithTrailers<S>
+where
+    S: Stream<Item = Result<Frame<D>, E>>,
+    D: Buf,
+{
+    type Data = D;
+    type Error = E;
+
+    fn poll_frame(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<Result<Frame<Self::Data>, Self::Error>>> {
+        let project = self.project();
+        match project.stream.poll_next(cx) {
+            Poll::Ready(Some(result)) => Poll::Ready(Some(result)),
+            Poll::Ready(None) => match project.trailers.take() {
+                Some(trailers) => Poll::Ready(Some(Ok(Frame::trailers(trailers)))),
+                None => Poll::Ready(None),
+            },
+            Poll::Pending => Poll::Pending,
+        }
+    }
+}
+
+impl<S: Stream> Stream for StreamBodyWithTrailers<S> {
+    type Item = S::Item;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        self.project().stream.poll_next(cx)
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.stream.size_hint()
+    }
+}