only send trailer fields if TE: trailers request header is present

src/proto/h1/conn.rs

@@ -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,
         }
@@ -266,8 +267,12 @@ where
 
         if let Some(Ok(te_value)) = msg.head.headers.get("te").map(|v| v.to_str()) {
             if te_value.eq_ignore_ascii_case("trailers") {
-                wants = wants.add(Wants::TRAILERS);
+                self.state.allow_trailer_fields = true;
+            } else {
+                self.state.allow_trailer_fields = false;
             }
+        } else {
+            self.state.allow_trailer_fields = false;
         }
 
         Poll::Ready(Some(Ok((msg.head, msg.decode, wants))))
@@ -647,6 +652,11 @@ where
     }
 
     pub(crate) fn write_trailers(&mut self, trailers: HeaderMap) {
+        if 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 {
@@ -869,6 +879,8 @@ 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/mod.rs

@@ -112,7 +112,6 @@ impl Wants {
     const EMPTY: Wants = Wants(0b00);
     const EXPECT: Wants = Wants(0b01);
     const UPGRADE: Wants = Wants(0b10);
-    const TRAILERS: Wants = Wants(0b100);
 
     #[must_use]
     fn add(self, other: Wants) -> Wants {

tests/server.rs

@@ -2640,6 +2640,49 @@ fn http1_trailer_fields() {
     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
 // -------------------------------------------------