test: Test filtermail-transport

Adds filtermail-transport tests and
a test setup for recording SMTP transactions.

Signed-off-by: Jagoda Ślązak <jslazak@jslazak.com>

filtermail/src/tcp.rs

@@ -0,0 +1,59 @@
+//! TCP related code.
+
+use async_trait::async_trait;
+use tokio::io::{AsyncRead, AsyncWrite};
+use tokio::net::{TcpStream, ToSocketAddrs};
+
+#[cfg(test)]
+pub mod rec_stream;
+
+/// Abstraction over [`TcpStream`] allowing e.g. mocking it.
+pub trait TcpStreamTrait: AsyncRead + AsyncWrite + Unpin + Send + Sync + Sized + 'static {
+    /// Returns the remote address that this stream is connected to.
+    fn peer_addr(&self) -> std::io::Result<std::net::SocketAddr>;
+
+    /// Sets the value of the `TCP_NODELAY` option on this socket.
+    fn set_nodelay(&self, nodelay: bool) -> std::io::Result<()>;
+}
+
+/// Trait adding a `connect` method similar to [`TcpStream::connect`],
+/// that allows passing additional context when creating the stream.
+#[async_trait]
+pub trait TcpConnect: TcpStreamTrait {
+    /// Type of additional context passed to [`TcpConnect::connect`].
+    type ConnectionContext: Send + Sync + Clone + 'static;
+
+    /// Opens a TCP connection to a remote host.
+    async fn connect<A: ToSocketAddrs + Send>(
+        addr: A,
+        context: Self::ConnectionContext,
+    ) -> std::io::Result<Self>;
+}
+
+impl TcpStreamTrait for TcpStream {
+    /// Returns the remote address that this stream is connected to.
+    ///
+    /// Delegates to [`TcpStream::peer_addr`].
+    fn peer_addr(&self) -> std::io::Result<std::net::SocketAddr> {
+        TcpStream::peer_addr(self)
+    }
+
+    /// Sets the value of the `TCP_NODELAY` option on this socket.
+    ///
+    /// Delegates to [`TcpStream::set_nodelay`].
+    fn set_nodelay(&self, nodelay: bool) -> std::io::Result<()> {
+        TcpStream::set_nodelay(self, nodelay)
+    }
+}
+
+#[async_trait]
+impl TcpConnect for TcpStream {
+    type ConnectionContext = ();
+
+    /// Opens a TCP connection to a remote host.
+    ///
+    /// Delegates to [`TcpStream::connect`].
+    async fn connect<A: ToSocketAddrs + Send>(addr: A, _: ()) -> std::io::Result<Self> {
+        TcpStream::connect(addr).await
+    }
+}