Feat: Add a feature flag to ignore connection headers

According to the RFC, when encountering connection headers, H2 should
treat them as protocol errors. However, in reality there are servers
just setting these headers but only for informational purpose.

This feature allow the receiving end to just ignore these headers
without bailing the entire stream.

Cargo.toml

@@ -24,6 +24,7 @@ rust-version = "1.56"
 [features]
 # Enables `futures::Stream` implementations for various types.
 stream = []
+ignore_connection_header = []
 
 # Enables **unstable** APIs. Any API exposed by this feature has no backwards
 # compatibility guarantees. In other words, you should not use this feature for

src/frame/headers.rs

@@ -871,16 +871,25 @@ impl HeaderBlock {
             match header {
                 Field { name, value } => {
                     // Connection level header fields are not supported and must
-                    // result in a protocol error.
+                    // result in a protocol error. However in reality there are
+                    // servers setting these headers. Some of these headers are
+                    // purely informational and can be simply ignored without
+                    // affecting the integrity of the stream.
 
-                    if name == header::CONNECTION
-                        || name == header::TRANSFER_ENCODING
+                    if name == header::TRANSFER_ENCODING {
+                        tracing::trace!("load_hpack; connection level header");
+                        malformed = true;
+                    } else if name == header::CONNECTION
                         || name == header::UPGRADE
                         || name == "keep-alive"
                         || name == "proxy-connection"
                     {
-                        tracing::trace!("load_hpack; connection level header");
-                        malformed = true;
+                        if cfg!(feature = "ignore_connection_header") {
+                            tracing::trace!("load_hpack; connection level header ignored");
+                        } else {
+                            tracing::trace!("load_hpack; connection level header");
+                            malformed = true;
+                        }
                     } else if name == header::TE && value != "trailers" {
                         tracing::trace!(
                             "load_hpack; TE header not set to trailers; val={:?}",

tests/h2-support/Cargo.toml

@@ -4,6 +4,9 @@ version = "0.1.0"
 authors = ["Carl Lerche <[email protected]>"]
 edition = "2018"
 
+[features]
+ignore_connection_header = ["h2/ignore_connection_header"]
+
 [dependencies]
 h2 = { path = "../..", features = ["stream", "unstable"] }
 

tests/h2-tests/Cargo.toml

@@ -5,6 +5,9 @@ authors = ["Carl Lerche <[email protected]>"]
 publish = false
 edition = "2018"
 
+[features]
+ignore_connection_header = ["h2-support/ignore_connection_header"]
+
 [dependencies]
 
 [dev-dependencies]

tests/h2-tests/tests/server.rs

@@ -528,25 +528,84 @@ async fn recv_connection_header() {
     };
 
     let client = async move {
-        let settings = client.assert_server_handshake().await;
-        assert_default_settings!(settings);
-        client.send_frame(req(1, "connection", "foo")).await;
-        client.send_frame(req(3, "keep-alive", "5")).await;
-        client.send_frame(req(5, "proxy-connection", "bar")).await;
-        client
-            .send_frame(req(7, "transfer-encoding", "chunked"))
-            .await;
-        client.send_frame(req(9, "upgrade", "HTTP/2")).await;
-        client.recv_frame(frames::reset(1).protocol_error()).await;
-        client.recv_frame(frames::reset(3).protocol_error()).await;
-        client.recv_frame(frames::reset(5).protocol_error()).await;
-        client.recv_frame(frames::reset(7).protocol_error()).await;
-        client.recv_frame(frames::reset(9).protocol_error()).await;
+        if cfg!(feature = "ignore_connection_header") {
+            let settings = client.assert_server_handshake().await;
+            assert_default_settings!(settings);
+            client
+                .send_frame(
+                    frames::headers(1)
+                        .request("GET", "https://example.com/")
+                        .field("connection", "foo")
+                        .eos(),
+                )
+                .await;
+            client
+                .send_frame(
+                    frames::headers(3)
+                        .request("GET", "https://example.com/")
+                        .field("keep-alive", "5")
+                        .eos(),
+                )
+                .await;
+            client
+                .send_frame(
+                    frames::headers(5)
+                        .request("GET", "https://example.com/")
+                        .field("proxy-connection", "bar")
+                        .eos(),
+                )
+                .await;
+            client
+                .send_frame(
+                    frames::headers(7)
+                        .request("GET", "https://example.com/")
+                        .field("upgrade", "HTTP/2")
+                        .eos(),
+                )
+                .await;
+            client
+                .recv_frame(frames::headers(1).response(200).eos())
+                .await;
+            client
+                .recv_frame(frames::headers(3).response(200).eos())
+                .await;
+            client
+                .recv_frame(frames::headers(5).response(200).eos())
+                .await;
+            client
+                .recv_frame(frames::headers(7).response(200).eos())
+                .await;
+        } else {
+            let settings = client.assert_server_handshake().await;
+            assert_default_settings!(settings);
+            client.send_frame(req(1, "connection", "foo")).await;
+            client.send_frame(req(3, "keep-alive", "5")).await;
+            client.send_frame(req(5, "proxy-connection", "bar")).await;
+            client
+                .send_frame(req(7, "transfer-encoding", "chunked"))
+                .await;
+            client.send_frame(req(9, "upgrade", "HTTP/2")).await;
+            client.recv_frame(frames::reset(1).protocol_error()).await;
+            client.recv_frame(frames::reset(3).protocol_error()).await;
+            client.recv_frame(frames::reset(5).protocol_error()).await;
+            client.recv_frame(frames::reset(7).protocol_error()).await;
+            client.recv_frame(frames::reset(9).protocol_error()).await;
+        }
     };
 
     let srv = async move {
         let mut srv = server::handshake(io).await.expect("handshake");
-        assert!(srv.next().await.is_none());
+        if cfg!(feature = "ignore_connection_header") {
+            while let Some(stream) = srv.next().await {
+                let (req, mut stream) = stream.unwrap();
+                // the headers are ignored
+                assert_eq!(req.headers().len(), 0);
+                let rsp = http::Response::builder().status(200).body(()).unwrap();
+                stream.send_response(rsp, true).unwrap();
+            }
+        } else {
+            assert!(srv.next().await.is_none());
+        }
     };
 
     join(client, srv).await;