Implement SubscriptionClient for HttpClient (#563)

Closes https://github.com/paritytech/jsonrpsee/issues/448

This PR adds an implementation for `SubscriptionClient` to the `HttpClient` struct, which makes it possible for http clients to use macro-generated RPC servers. If an http client tries to set up a subscription it will fail with a `HttpNotImplemented` error.

http-client/src/client.rs

@@ -26,9 +26,9 @@
 
 use crate::transport::HttpTransportClient;
 use crate::types::{
-	traits::Client,
+	traits::{Client, SubscriptionClient},
 	v2::{Id, NotificationSer, ParamsSer, RequestSer, Response, RpcError},
-	CertificateStore, Error, RequestIdManager, TEN_MB_SIZE_BYTES,
+	CertificateStore, Error, RequestIdManager, Subscription, TEN_MB_SIZE_BYTES,
 };
 use async_trait::async_trait;
 use fnv::FnvHashMap;
@@ -194,3 +194,27 @@ impl Client for HttpClient {
 		Ok(responses)
 	}
 }
+
+#[async_trait]
+impl SubscriptionClient for HttpClient {
+	/// Send a subscription request to the server. Not implemented for HTTP; will always return [`Error::HttpNotImplemented`].
+	async fn subscribe<'a, N>(
+		&self,
+		_subscribe_method: &'a str,
+		_params: Option<ParamsSer<'a>>,
+		_unsubscribe_method: &'a str,
+	) -> Result<Subscription<N>, Error>
+	where
+		N: DeserializeOwned,
+	{
+		Err(Error::HttpNotImplemented)
+	}
+
+	/// Subscribe to a specific method. Not implemented for HTTP; will always return [`Error::HttpNotImplemented`].
+	async fn subscribe_to_method<'a, N>(&self, _method: &'a str) -> Result<Subscription<N>, Error>
+	where
+		N: DeserializeOwned,
+	{
+		Err(Error::HttpNotImplemented)
+	}
+}

tests/tests/proc_macros.rs

@@ -28,7 +28,11 @@
 
 use std::net::SocketAddr;
 
-use jsonrpsee::{ws_client::*, ws_server::WsServerBuilder};
+use jsonrpsee::{
+	http_client::HttpClientBuilder, http_server::HttpServerBuilder, types::Error, ws_client::*,
+	ws_server::WsServerBuilder,
+};
+
 use serde_json::value::RawValue;
 
 mod rpc_impl {
@@ -305,3 +309,18 @@ async fn multiple_blocking_calls_overlap() {
 	// Each request takes 50ms, added 10ms margin for scheduling
 	assert!(elapsed < Duration::from_millis(60), "Expected less than 60ms, got {:?}", elapsed);
 }
+
+#[tokio::test]
+async fn subscriptions_do_not_work_for_http_servers() {
+	let htserver = HttpServerBuilder::default().build("127.0.0.1:0".parse().unwrap()).unwrap();
+	let addr = htserver.local_addr().unwrap();
+	let htserver_url = format!("http://{}", addr);
+	let _handle = htserver.start(RpcServerImpl.into_rpc()).unwrap();
+
+	let htclient = HttpClientBuilder::default().build(&htserver_url).unwrap();
+
+	assert_eq!(htclient.sync_method().await.unwrap(), 10);
+	assert!(htclient.sub().await.is_err());
+	assert!(matches!(htclient.sub().await, Err(Error::HttpNotImplemented)));
+	assert_eq!(htclient.sync_method().await.unwrap(), 10);
+}

types/src/error.rs

@@ -160,6 +160,9 @@ pub enum Error {
 	/// Custom error.
 	#[error("Custom error: {0}")]
 	Custom(String),
+	/// Not implemented for HTTP clients.
+	#[error("Not implemented")]
+	HttpNotImplemented,
 }
 
 impl Error {