Allow building an upgrade from an async function (#1383)

* Allow building an upgrade from an async function

* Some styling

core/src/upgrade/from_fn.rs

@@ -0,0 +1,109 @@
+// Copyright 2020 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::{Endpoint, upgrade::{InboundUpgrade, OutboundUpgrade, ProtocolName, UpgradeInfo}};
+
+use futures::prelude::*;
+use std::iter;
+
+/// Initializes a new [`FromFnUpgrade`].
+///
+/// # Example
+///
+/// ```
+/// # use libp2p_core::transport::{Transport, MemoryTransport};
+/// # use libp2p_core::upgrade;
+/// # use std::io;
+/// let _transport = MemoryTransport::default()
+///     .and_then(move |out, cp| {
+///         upgrade::apply(out, upgrade::from_fn("/foo/1", move |mut sock, endpoint| async move {
+///             if endpoint.is_dialer() {
+///                 upgrade::write_one(&mut sock, "some handshake data").await?;
+///             } else {
+///                 let handshake_data = upgrade::read_one(&mut sock, 1024).await?;
+///                 if handshake_data != b"some handshake data" {
+///                     return Err(upgrade::ReadOneError::from(io::Error::from(io::ErrorKind::Other)));
+///                 }
+///             }
+///             Ok(sock)
+///         }), cp, upgrade::Version::V1)
+///     });
+/// ```
+///
+pub fn from_fn<P, F, C, Fut, Out, Err>(protocol_name: P, fun: F) -> FromFnUpgrade<P, F>
+where
+    // Note: these bounds are there in order to help the compiler infer types
+    P: ProtocolName + Clone,
+    F: FnOnce(C, Endpoint) -> Fut,
+    Fut: Future<Output = Result<Out, Err>>,
+{
+    FromFnUpgrade { protocol_name, fun }
+}
+
+/// Implements the `UpgradeInfo`, `InboundUpgrade` and `OutboundUpgrade` traits.
+///
+/// The upgrade consists in calling the function passed when creating this struct.
+#[derive(Debug, Clone)]
+pub struct FromFnUpgrade<P, F> {
+    protocol_name: P,
+    fun: F,
+}
+
+impl<P, F> UpgradeInfo for FromFnUpgrade<P, F>
+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, F, Fut, Err, Out> InboundUpgrade<C> for FromFnUpgrade<P, F>
+where
+    P: ProtocolName + Clone,
+    F: FnOnce(C, Endpoint) -> Fut,
+    Fut: Future<Output = Result<Out, Err>>,
+{
+    type Output = Out;
+    type Error = Err;
+    type Future = Fut;
+
+    fn upgrade_inbound(self, sock: C, _: Self::Info) -> Self::Future {
+        (self.fun)(sock, Endpoint::Listener)
+    }
+}
+
+impl<C, P, F, Fut, Err, Out> OutboundUpgrade<C> for FromFnUpgrade<P, F>
+where
+    P: ProtocolName + Clone,
+    F: FnOnce(C, Endpoint) -> Fut,
+    Fut: Future<Output = Result<Out, Err>>,
+{
+    type Output = Out;
+    type Error = Err;
+    type Future = Fut;
+
+    fn upgrade_outbound(self, sock: C, _: Self::Info) -> Self::Future {
+        (self.fun)(sock, Endpoint::Dialer)
+    }
+}

core/src/upgrade/mod.rs

@@ -61,6 +61,7 @@ mod apply;
 mod denied;
 mod either;
 mod error;
+mod from_fn;
 mod map;
 mod optional;
 mod select;
@@ -75,6 +76,7 @@ pub use self::{
     denied::DeniedUpgrade,
     either::EitherUpgrade,
     error::UpgradeError,
+    from_fn::{from_fn, FromFnUpgrade},
     map::{MapInboundUpgrade, MapOutboundUpgrade, MapInboundUpgradeErr, MapOutboundUpgradeErr},
     optional::OptionalUpgrade,
     select::SelectUpgrade,