Make HTTP/2 optional via 'http2' feature.

Closes #2030.

core/http/Cargo.toml

@@ -18,6 +18,7 @@ edition = "2018"
 default = []
 tls = ["rustls", "tokio-rustls", "rustls-pemfile"]
 mtls = ["tls", "x509-parser"]
+http2 = ["hyper/http2"]
 private-cookies = ["cookie/private", "cookie/key-expansion"]
 serde = ["uncased/with-serde-alloc", "serde_"]
 uuid = ["uuid_"]
@@ -50,7 +51,7 @@ optional = true
 [dependencies.hyper]
 version = "0.14.9"
 default-features = false
-features = ["http1", "http2", "runtime", "server", "stream"]
+features = ["http1", "runtime", "server", "stream"]
 
 [dependencies.serde_]
 package = "serde"

core/http/src/tls/listener.rs

@@ -64,7 +64,12 @@ impl TlsListener {
             .map_err(|e| io::Error::new(io::ErrorKind::Other, format!("bad TLS config: {}", e)))?;
 
         tls_config.ignore_client_order = c.prefer_server_order;
-        tls_config.alpn_protocols = vec![b"h2".to_vec(), b"http/1.1".to_vec()];
+
+        tls_config.alpn_protocols = vec![b"http/1.1".to_vec()];
+        if cfg!(feature = "http2") {
+            tls_config.alpn_protocols.insert(0, b"h2".to_vec());
+        }
+
         tls_config.session_storage = ServerSessionMemoryCache::new(1024);
         tls_config.ticketer = rustls::Ticketer::new()
             .map_err(|e| io::Error::new(io::ErrorKind::Other, format!("bad TLS ticketer: {}", e)))?;

core/lib/Cargo.toml

@@ -19,9 +19,10 @@ edition = "2018"
 all-features = true
 
 [features]
-default = []
+default = ["http2"]
 tls = ["rocket_http/tls"]
 mtls = ["rocket_http/mtls", "tls"]
+http2 = ["rocket_http/http2"]
 secrets = ["rocket_http/private-cookies"]
 json = ["serde_json", "tokio/io-util"]
 msgpack = ["rmp-serde", "tokio/io-util"]

core/lib/src/lib.rs

@@ -56,25 +56,33 @@
 //!
 //! ## Features
 //!
-//! To avoid compiling unused dependencies, Rocket gates certain features, all
-//! of which are disabled by default:
+//! To avoid compiling unused dependencies, Rocket gates certain features. With
+//! the exception of `http2`, all are disabled by default:
 //!
 //! | Feature   | Description                                             |
 //! |-----------|---------------------------------------------------------|
 //! | `secrets` | Support for authenticated, encrypted [private cookies]. |
 //! | `tls`     | Support for [TLS] encrypted connections.                |
 //! | `mtls`    | Support for verified clients via [mutual TLS].          |
+//! | `http2`   | Support for HTTP/2 (enabled by default).                |
 //! | `json`    | Support for [JSON (de)serialization].                   |
 //! | `msgpack` | Support for [MessagePack (de)serialization].            |
 //! | `uuid`    | Support for [UUID value parsing and (de)serialization]. |
 //!
-//! Features can be selectively enabled in `Cargo.toml`:
+//! Disabled features can be selectively enabled in `Cargo.toml`:
 //!
 //! ```toml
 //! [dependencies]
 //! rocket = { version = "0.5.0-rc.1", features = ["secrets", "tls", "json"] }
 //! ```
 //!
+//! Conversely, HTTP/2 can be disabled:
+//!
+//! ```toml
+//! [dependencies]
+//! rocket = { version = "0.5.0-rc.1", default-features = false }
+//! ```
+//!
 //! [JSON (de)serialization]: crate::serde::json
 //! [MessagePack (de)serialization]: crate::serde::msgpack
 //! [UUID value parsing and (de)serialization]: crate::serde::uuid

core/lib/src/server.rs

@@ -405,13 +405,6 @@ impl Rocket<Orbit> {
             });
         }
 
-        // Determine keep-alives.
-        let http1_keepalive = self.config.keep_alive != 0;
-        let http2_keep_alive = match self.config.keep_alive {
-            0 => None,
-            n => Some(Duration::from_secs(n as u64))
-        };
-
         // Set up cancellable I/O from the given listener. Shutdown occurs when
         // `Shutdown` (`TripWire`) resolves. This can occur directly through a
         // notification or indirectly through an external signal which, when
@@ -438,6 +431,9 @@ impl Rocket<Orbit> {
             });
         }
 
+        // Save the keep-alive value for later use; we're about to move `self`.
+        let keep_alive = self.config.keep_alive;
+
         // Create the Hyper `Service`.
         let rocket = Arc::new(self);
         let service_fn = move |conn: &CancellableIo<_, L::Connection>| {
@@ -456,10 +452,17 @@ impl Rocket<Orbit> {
 
         // NOTE: `hyper` uses `tokio::spawn()` as the default executor.
         let listener = CancellableListener::new(shutdown.clone(), listener, grace, mercy);
-        let server = hyper::Server::builder(Incoming::new(listener))
-            .http1_keepalive(http1_keepalive)
+        let builder = hyper::Server::builder(Incoming::new(listener));
+
+        #[cfg(feature = "http2")]
+        let builder = builder.http2_keep_alive_interval(match keep_alive {
+            0 => None,
+            n => Some(Duration::from_secs(n as u64))
+        });
+
+        let server = builder
+            .http1_keepalive(keep_alive != 0)
             .http1_preserve_header_case(true)
-            .http2_keep_alive_interval(http2_keep_alive)
             .serve(hyper::service::make_service_fn(service_fn))
             .with_graceful_shutdown(shutdown.clone())
             .map_err(|e| Error::new(ErrorKind::Runtime(Box::new(e))));

scripts/test.sh

@@ -118,6 +118,7 @@ function test_core() {
     secrets
     tls
     mtls
+    http2
     json
     msgpack
     uuid