Add basic interceptor support

tonic-interop/Cargo.toml

@@ -22,6 +22,7 @@ http = "0.1"
 futures-core-preview = "=0.3.0-alpha.18"
 futures-util-preview = "=0.3.0-alpha.18"
 async-stream = "0.1.1"
+tower = "0.3.0-alpha.1a"
 
 console = "0.7"
 structopt = "0.2"

tonic-interop/src/bin/server.rs

@@ -1,6 +1,9 @@
 use structopt::StructOpt;
 use tonic::Server;
 use tonic_interop::server;
+// TODO: move GrpcService out of client since it can be used for the
+// server too.
+use tonic::client::GrpcService;
 
 #[derive(StructOpt)]
 struct Opts {
@@ -26,6 +29,16 @@ async fn main() -> std::result::Result<(), Box<dyn std::error::Error>> {
         builder.tls(ca, key);
     }
 
+    builder.interceptor_fn(|svc, req| {
+        println!("INBOUND REQUEST={:?}", req);
+        let call = svc.call(req);
+        async move {
+            let res = call.await?;
+            println!("OUTBOUND RESPONSE={:?}", res);
+            Ok(res)
+        }
+    });
+
     builder.serve(addr, test_service).await?;
 
     Ok(())