add Client config to disable server push

- Adds `Client::builder().enable_push(false)` to disable push
- Client sends a GO_AWAY if receiving a push when it's disabled

tests/push_promise.rs

@@ -0,0 +1,109 @@
+extern crate h2_test_support;
+use h2_test_support::prelude::*;
+
+#[test]
+fn recv_push_works() {
+    // tests that by default, received push promises work
+    // TODO: once API exists, read the pushed response
+    let _ = ::env_logger::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::headers(1).response(200).eos())
+        .send_frame(frames::headers(2).response(200).eos());
+
+    let h2 = Client::handshake(io).unwrap().and_then(|mut h2| {
+        let request = Request::builder()
+            .method(Method::GET)
+            .uri("https://http2.akamai.com/")
+            .body(())
+            .unwrap();
+        let req = h2.request(request, true)
+            .unwrap()
+            .unwrap()
+            .and_then(|resp| {
+                assert_eq!(resp.status(), StatusCode::OK);
+                Ok(())
+            });
+
+        h2.drive(req)
+    });
+
+    h2.join(mock).wait().unwrap();
+}
+
+#[test]
+fn recv_push_when_push_disabled_is_conn_error() {
+    let _ = ::env_logger::init();
+
+    let (io, srv) = mock::new();
+    let mock = srv.assert_client_handshake()
+        .unwrap()
+        .ignore_settings()
+        .recv_frame(
+            frames::headers(1)
+                .request("GET", "https://http2.akamai.com/")
+                .eos(),
+        )
+        .send_frame(
+            frames::push_promise(1, 3).request("GET", "https://http2.akamai.com/style.css"),
+        )
+        .send_frame(frames::headers(1).response(200).eos())
+        .recv_frame(frames::go_away(0).protocol_error());
+
+    let h2 = Client::builder()
+        .enable_push(false)
+        .handshake::<_, Bytes>(io)
+        .unwrap()
+        .and_then(|mut h2| {
+            let request = Request::builder()
+                .method(Method::GET)
+                .uri("https://http2.akamai.com/")
+                .body(())
+                .unwrap();
+            let req = h2.request(request, true).unwrap().then(|res| {
+                let err = res.unwrap_err();
+                assert_eq!(
+                    err.to_string(),
+                    "protocol error: unspecific protocol error detected"
+                );
+                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]
+#[ignore]
+fn recv_push_promise_with_unsafe_method_is_stream_error() {
+    // for instance, when :method = POST
+}
+
+#[test]
+#[ignore]
+fn recv_push_promise_with_wrong_authority_is_stream_error() {
+    // if server is foo.com, :authority = bar.com is stream error
+}