swarm/src/connection: Test max_negotiating_inbound_streams (#2785)

Test that `HandlerWrapper` upholds the provided
`max_negotiating_inbound_streams` limit.

core/src/upgrade.rs

@@ -64,6 +64,7 @@ mod error;
 mod from_fn;
 mod map;
 mod optional;
+mod pending;
 mod select;
 mod transfer;
 
@@ -77,6 +78,7 @@ pub use self::{
     from_fn::{from_fn, FromFnUpgrade},
     map::{MapInboundUpgrade, MapInboundUpgradeErr, MapOutboundUpgrade, MapOutboundUpgradeErr},
     optional::OptionalUpgrade,
+    pending::PendingUpgrade,
     select::SelectUpgrade,
     transfer::{read_length_prefixed, read_varint, write_length_prefixed, write_varint},
 };

core/src/upgrade/pending.rs

@@ -0,0 +1,76 @@
+// Copyright 2022 Protocol Labs.
+// Copyright 2017-2018 Parity Technologies (UK) Ltd.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the "Software"),
+// to deal in the Software without restriction, including without limitation
+// the rights to use, copy, modify, merge, publish, distribute, sublicense,
+// and/or sell copies of the Software, and to permit persons to whom the
+// Software is furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+// DEALINGS IN THE SOFTWARE.
+
+use crate::upgrade::{InboundUpgrade, OutboundUpgrade, ProtocolName, UpgradeInfo};
+use futures::future;
+use std::iter;
+use void::Void;
+
+/// Implementation of [`UpgradeInfo`], [`InboundUpgrade`] and [`OutboundUpgrade`] that always
+/// returns a pending upgrade.
+#[derive(Debug, Copy, Clone)]
+pub struct PendingUpgrade<P> {
+    protocol_name: P,
+}
+
+impl<P> PendingUpgrade<P> {
+    pub fn new(protocol_name: P) -> Self {
+        Self { protocol_name }
+    }
+}
+
+impl<P> UpgradeInfo for PendingUpgrade<P>
+where
+    P: ProtocolName + Clone,
+{
+    type Info = P;
+    type InfoIter = iter::Once<P>;
+
+    fn protocol_info(&self) -> Self::InfoIter {
+        iter::once(self.protocol_name.clone())
+    }
+}
+
+impl<C, P> InboundUpgrade<C> for PendingUpgrade<P>
+where
+    P: ProtocolName + Clone,
+{
+    type Output = Void;
+    type Error = Void;
+    type Future = future::Pending<Result<Self::Output, Self::Error>>;
+
+    fn upgrade_inbound(self, _: C, _: Self::Info) -> Self::Future {
+        future::pending()
+    }
+}
+
+impl<C, P> OutboundUpgrade<C> for PendingUpgrade<P>
+where
+    P: ProtocolName + Clone,
+{
+    type Output = Void;
+    type Error = Void;
+    type Future = future::Pending<Result<Self::Output, Self::Error>>;
+
+    fn upgrade_outbound(self, _: C, _: Self::Info) -> Self::Future {
+        future::pending()
+    }
+}