When Streams are dropped, close Connection (#221) (#222)

When all Streams are dropped / finished, the Connection was held
open until the peer hangs up. Instead, the Connection should hang up
once it knows that nothing more will be sent.

To fix this, we notify the Connection when a stream is no longer
referenced. On the Connection poll(), we check that there are no
active, held, reset streams or any references to the Streams
and transition to sending a GOAWAY if that is case.

The specific behavior depends on if running as a client or server.

tests/client_request.rs

@@ -13,7 +13,7 @@ fn handshake() {
         .write(SETTINGS_ACK)
         .build();
 
-    let (_, h2) = client::handshake(mock).wait().unwrap();
+    let (_client, h2) = client::handshake(mock).wait().unwrap();
 
     trace!("hands have been shook");
 
@@ -129,7 +129,12 @@ fn request_stream_id_overflows() {
                 let err = client.send_request(request, true).unwrap_err();
                 assert_eq!(err.to_string(), "user error: stream ID overflowed");
 
-                h2.expect("h2")
+                h2.expect("h2").map(|ret| {
+                    // Hold on to the `client` handle to avoid sending a GO_AWAY
+                    // frame.
+                    drop(client);
+                    ret
+                })
             })
         });
 
@@ -338,7 +343,11 @@ fn http_2_request_without_scheme_or_authority() {
 
             // first request is allowed
             assert!(client.send_request(request, true).is_err());
-            h2.expect("h2")
+            h2.expect("h2").map(|ret| {
+                // Hold on to the `client` handle to avoid sending a GO_AWAY frame.
+                drop(client);
+                ret
+            })
         });
 
     h2.join(srv).wait().expect("wait");
@@ -614,6 +623,7 @@ fn recv_too_big_headers() {
 
             conn.drive(req1.join(req2))
                 .and_then(|(conn, _)| conn.expect("client"))
+                .map(|c| (c, client))
         });
 
     client.join(srv).wait().expect("wait");