Add graphql-ws feature for subprotcol selection

On 2020-09-14 a revised version of the [GraphQL over
WebSocket](https://the-guild.dev/blog/graphql-over-websockets) spec was
released as [graphql-ws](https://github.com/enisdenjo/graphql-ws), which
differs from the de facto standard implemented by
[subscriptions-transport-ws](https://github.com/apollographql/subscriptions-transport-ws).

This adds a new `cargo` (non-default) feature, `graphql_ws`, which when enabled utilizes the new protocol spec.

Original [subscriptions-transport-ws
protocol](https://github.com/apollographql/subscriptions-transport-ws/blob/master/PROTOCOL.md)
Revised [graphql-ws
protocol](https://github.com/enisdenjo/graphql-ws/blob/master/PROTOCOL.md)

Cargo.toml

@@ -34,6 +34,8 @@ unblock = ["blocking"]
 string_number = ["num-traits"]
 # Used for doc(cfg())
 nightly = []
+# To enable the use of [graphql-ws spec](https://github.com/enisdenjo/graphql-ws)
+graphql_ws = []
 
 [dependencies]
 async-graphql-derive = { path = "derive", version = "=2.1.4" }

integrations/warp/Cargo.toml

@@ -11,6 +11,10 @@ repository = "https://github.com/async-graphql/async-graphql"
 keywords = ["futures", "async", "graphql"]
 categories = ["network-programming", "asynchronous"]
 
+[features]
+# To enable the use of [graphql-ws spec](https://github.com/enisdenjo/graphql-ws)
+graphql_ws = []
+
 [dependencies]
 async-graphql = { path = "../..", version = "=2.1.4" }
 

integrations/warp/src/subscription.rs

@@ -86,6 +86,17 @@ where
                 .await;
             }
         });
-        warp::reply::with_header(reply, "Sec-WebSocket-Protocol", "graphql-ws")
+
+        #[cfg(not(feature = "graphql_ws"))]
+        {
+            // confusingly, the old subprotocol name for the susbscription-transport-ws spec was
+            // `graphql-ws`
+            warp::reply::with_header(reply, "Sec-WebSocket-Protocol", "graphql-ws")
+        }
+        #[cfg(feature = "graphql_ws")]
+        {
+            // ...and the new one `graphql-transport-ws`
+            warp::reply::with_header(reply, "Sec-WebSocket-Protocol", "graphql-transport-ws")
+        }
     })
 }

src/http/websocket.rs

@@ -169,7 +169,9 @@ where
 #[serde(tag = "type", rename_all = "snake_case")]
 enum ClientMessage<'a> {
     ConnectionInit { payload: Option<serde_json::Value> },
+    #[cfg_attr(feature = "graphql_ws", serde(rename = "subscribe"))]
     Start { id: String, payload: Request },
+    #[cfg_attr(feature = "graphql_ws", serde(rename = "complete"))]
     Stop { id: &'a str },
     ConnectionTerminate,
 }
@@ -179,6 +181,7 @@ enum ClientMessage<'a> {
 enum ServerMessage<'a> {
     ConnectionError { payload: Error },
     ConnectionAck,
+    #[cfg_attr(feature = "graphql_ws", serde(rename = "next"))]
     Data { id: &'a str, payload: Box<Response> },
     // Not used by this library, as it's not necessary to send
     // Error {