Enforce monotonic stream IDs for push promises (#275)

Previously, monotonic stream IDs (spec 5.1.1) for push promises were not
enforced. This was due to push promises going through an entirely
separate code path than normally initiated streams.

This patch unifies the code path for initializing streams via both
HEADERS and PUSH_PROMISE. This is done by first calling `recv.open` in
both cases.

Closes #272

tests/h2-tests/tests/push_promise.rs

@@ -199,3 +199,109 @@ fn recv_push_promise_with_unsafe_method_is_stream_error() {
 fn recv_push_promise_with_wrong_authority_is_stream_error() {
     // if server is foo.com, :authority = bar.com is stream error
 }
+
+#[test]
+fn recv_push_promise_skipped_stream_id() {
+    // tests that by default, received push promises work
+    // TODO: once API exists, read the pushed response
+    let _ = ::env_logger::try_init();
+
+    let (io, srv) = mock::new();
+    let mock = srv.assert_client_handshake()
+        .unwrap()
+        .recv_settings()
+        .recv_frame(
+            frames::headers(1)
+                .request("GET", "https://http2.akamai.com/")
+                .eos(),
+        )
+        .send_frame(frames::push_promise(1, 4).request("GET", "https://http2.akamai.com/style.css"))
+        .send_frame(frames::push_promise(1, 2).request("GET", "https://http2.akamai.com/style.css"))
+        .recv_frame(frames::go_away(0).protocol_error())
+        .close()
+        ;
+
+    let h2 = client::handshake(io).unwrap().and_then(|(mut client, h2)| {
+        let request = Request::builder()
+            .method(Method::GET)
+            .uri("https://http2.akamai.com/")
+            .body(())
+            .unwrap();
+
+        let req = client
+            .send_request(request, true)
+            .unwrap()
+            .0
+            .then(|res| {
+                assert!(res.is_err());
+                Ok::<_, ()>(())
+            });
+
+            // client should see a protocol error
+            let conn = h2.then(|res| {
+                let err = res.unwrap_err();
+                assert_eq!(
+                    err.to_string(),
+                    "protocol error: unspecific protocol error detected"
+                );
+                Ok::<(), ()>(())
+            });
+
+            conn.unwrap().join(req)
+    });
+
+    h2.join(mock).wait().unwrap();
+}
+
+#[test]
+fn recv_push_promise_dup_stream_id() {
+    // tests that by default, received push promises work
+    // TODO: once API exists, read the pushed response
+    let _ = ::env_logger::try_init();
+
+    let (io, srv) = mock::new();
+    let mock = srv.assert_client_handshake()
+        .unwrap()
+        .recv_settings()
+        .recv_frame(
+            frames::headers(1)
+                .request("GET", "https://http2.akamai.com/")
+                .eos(),
+        )
+        .send_frame(frames::push_promise(1, 2).request("GET", "https://http2.akamai.com/style.css"))
+        .send_frame(frames::push_promise(1, 2).request("GET", "https://http2.akamai.com/style.css"))
+        .recv_frame(frames::go_away(0).protocol_error())
+        .close()
+        ;
+
+    let h2 = client::handshake(io).unwrap().and_then(|(mut client, h2)| {
+        let request = Request::builder()
+            .method(Method::GET)
+            .uri("https://http2.akamai.com/")
+            .body(())
+            .unwrap();
+
+        let req = client
+            .send_request(request, true)
+            .unwrap()
+            .0
+            .then(|res| {
+                assert!(res.is_err());
+                Ok::<_, ()>(())
+            });
+
+            // client should see a protocol error
+            let conn = h2.then(|res| {
+                let err = res.unwrap_err();
+                assert_eq!(
+                    err.to_string(),
+                    "protocol error: unspecific protocol error detected"
+                );
+                Ok::<(), ()>(())
+            });
+
+            conn.unwrap().join(req)
+    });
+
+    h2.join(mock).wait().unwrap();
+}