Proxy: use `Conditional` inside TLS configuration watches. (#1187)

Simplify the code and make it easier to report finer-grained
reasoning about what part(s) of the TLS configuration are
missing.

This is based on Eliza's PR #1186.

Signed-off-by: Brian Smith <brian@briansmith.org>

proxy/src/bind.rs

@@ -63,6 +63,10 @@ where
     protocol: Protocol,
 }
 
+// `Bind` cannot use `ConditionalConnectionConfig` since it uses a
+// `tls::Identity` and a `tls::ClientConfig` obtained from different sources.
+pub type ConditionalTlsClientConfig = Conditional<tls::ClientConfig, tls::ReasonForNoTls>;
+
 /// A type of service binding.
 ///
 /// Some services, for various reasons, may not be able to be used to serve multiple
@@ -75,7 +79,7 @@ where
     B: tower_h2::Body + Send + 'static,
     <B::Data as ::bytes::IntoBuf>::Buf: Send,
 {
-    Bound(WatchService<Option<tls::ClientConfig>, RebindTls<B>>),
+    Bound(WatchService<ConditionalTlsClientConfig, RebindTls<B>>),
     BindsPerRequest {
         // When `poll_ready` is called, the _next_ service to be used may be bound
         // ahead-of-time. This stack is used only to serve the next request to this
@@ -132,7 +136,7 @@ pub struct RebindTls<B> {
 
 pub type Service<B> = BoundService<B>;
 
-pub type Stack<B> = WatchService<Option<tls::ClientConfig>, RebindTls<B>>;
+pub type Stack<B> = WatchService<ConditionalTlsClientConfig, RebindTls<B>>;
 
 type StackInner<B> = Reconnect<NormalizeUri<NewHttp<B>>>;
 
@@ -226,26 +230,24 @@ where
     ///
     /// When the TLS client configuration is invalidated, this function will
     /// be called again to bind a new stack.
-    fn bind_inner_stack(&self, ep: &Endpoint, protocol: &Protocol)-> StackInner<B> {
+    fn bind_inner_stack(
+        &self,
+        ep: &Endpoint,
+        protocol: &Protocol,
+        tls_client_config: &ConditionalTlsClientConfig,
+    )-> StackInner<B> {
         debug!("bind_inner_stack endpoint={:?}, protocol={:?}", ep, protocol);
         let addr = ep.address();
 
-        // Like `tls::current_connection_config()` with optional identity.
-        let tls = match ep.tls_identity() {
-            Conditional::Some(identity) => {
-                // TODO: the watch should be an explicit field of `Bind`, rather
-                // than passed in the context.
-                match *self.ctx.tls_client_config_watch().borrow() {
-                    Some(ref config) =>
-                        Conditional::Some(tls::ConnectionConfig {
+        // Like `tls::current_connection_config()`.
+        let tls = ep.tls_identity().and_then(|identity| {
+            tls_client_config.as_ref().map(|config| {
+                tls::ConnectionConfig {
                     identity: identity.clone(),
-                            config: config.clone()
-                        }),
-                    None => Conditional::None(tls::ReasonForNoTls::NoConfig),
+                    config: config.clone(),
                 }
-            },
-            Conditional::None(why_no_identity) => Conditional::None(why_no_identity.into()),
-        };
+            })
+        });
 
         let client_ctx = ctx::transport::Client::new(
             &self.ctx,
@@ -307,8 +309,8 @@ where
         };
         // TODO: the watch should be an explicit field of `Bind`, rather
         // than passed in the context.
-        let tls_client_cfg = self.ctx.tls_client_config_watch().clone();
-        WatchService::new(tls_client_cfg, rebind)
+        let tls_client_config = self.ctx.tls_client_config_watch().clone();
+        WatchService::new(tls_client_config, rebind)
     }
 
     pub fn bind_service(&self, ep: &Endpoint, protocol: &Protocol) -> BoundService<B> {
@@ -578,19 +580,17 @@ impl Protocol {
 
 // ===== impl RebindTls =====
 
-impl<B> Rebind<Option<tls::ClientConfig>> for RebindTls<B>
+impl<B> Rebind<ConditionalTlsClientConfig> for RebindTls<B>
 where
     B: tower_h2::Body + Send + 'static,
     <B::Data as ::bytes::IntoBuf>::Buf: Send,
 {
     type Service = StackInner<B>;
-    fn rebind(&mut self, _cfg: &Option<tls::ClientConfig>) -> Self::Service {
+    fn rebind(&mut self, tls: &ConditionalTlsClientConfig) -> Self::Service {
         debug!(
             "rebinding endpoint stack for {:?}:{:?} on TLS config change",
             self.endpoint, self.protocol,
         );
-        // We don't actually pass in the config, as `self.bind` also already
-        // owns a config watch of its own.
-        self.bind.bind_inner_stack(&self.endpoint, &self.protocol)
+        self.bind.bind_inner_stack(&self.endpoint, &self.protocol, tls)
     }
 }

proxy/src/conditional.rs

@@ -22,7 +22,7 @@ where
 impl<C, R> std::fmt::Debug for Conditional<C, R>
 where
     C: Clone + std::fmt::Debug,
-    R: Clone + std::fmt::Debug
+    R: Clone + std::fmt::Debug,
 {
     fn fmt(&self, f: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
         match self {
@@ -72,10 +72,33 @@ where
     C: Clone,
     R: Copy + Clone,
 {
+    pub fn and_then<CR, RR, F>(self, f: F) -> Conditional<CR, RR>
+    where
+        CR: Clone,
+        R: Into<RR>,
+        RR: Clone,
+        F: FnOnce(C) -> Conditional<CR, RR>,
+    {
+        match self {
+            Conditional::Some(c) => f(c),
+            Conditional::None(r) => Conditional::None(r.into()),
+        }
+    }
+
     pub fn as_ref<'a>(&'a self) -> Conditional<&'a C, R> {
         match self {
             Conditional::Some(c) => Conditional::Some(&c),
             Conditional::None(r) => Conditional::None(*r),
         }
     }
+
+    pub fn map<CR, RR, F>(self, f: F) -> Conditional<CR, RR>
+    where
+        CR: Clone,
+        R: Into<RR>,
+        RR: Clone,
+        F: FnOnce(C) -> CR,
+    {
+        self.and_then(|c| Conditional::Some(f(c)))
+    }
 }

proxy/src/ctx/transport.rs

@@ -42,10 +42,7 @@ impl TlsStatus {
     pub fn from<C>(c: &Conditional<C, tls::ReasonForNoTls>) -> Self
     where C: Clone + std::fmt::Debug
     {
-        match c {
-            Conditional::Some(_) => Conditional::Some(()),
-            Conditional::None(r) => Conditional::None(*r),
-        }
+        c.as_ref().map(|_| ())
     }
 }
 

proxy/src/lib.rs

@@ -264,13 +264,12 @@ where
                 config.inbound_router_capacity,
                 config.inbound_router_max_idle_age,
             );
-            let tls_settings = match &config.tls_settings {
-                Conditional::Some(settings) => Conditional::Some(tls::ConnectionConfig {
+            let tls_settings = config.tls_settings.as_ref().map(|settings| {
+                tls::ConnectionConfig {
                     identity: settings.service_identity.clone(),
                     config: tls_server_config
-                }),
-                Conditional::None(r) => Conditional::None(*r),
-            };
+                }
+            });
             serve(
                 inbound_listener,
                 tls_settings,

proxy/src/transport/tls/config.rs

@@ -72,8 +72,8 @@ impl std::fmt::Debug for ClientConfig {
 #[derive(Clone)]
 pub struct ServerConfig(pub(super) Arc<rustls::ServerConfig>);
 
-pub type ClientConfigWatch = Watch<Option<ClientConfig>>;
-pub type ServerConfigWatch = Watch<Option<ServerConfig>>;
+pub type ClientConfigWatch = Watch<Conditional<ClientConfig, ReasonForNoTls>>;
+pub type ServerConfigWatch = Watch<Conditional<ServerConfig, ReasonForNoTls>>;
 
 /// The configuration in effect for a client (`ClientConfig`) or server
 /// (`ServerConfig`) TLS connection.
@@ -267,15 +267,15 @@ pub fn watch_for_config_changes(settings: Conditional<&CommonSettings, ReasonFor
     let settings = if let Conditional::Some(settings) = settings {
         settings.clone()
     } else {
-        let (client_watch, _) = Watch::new(None);
-        let (server_watch, _) = Watch::new(None);
+        let (client_watch, _) = Watch::new(Conditional::None(ReasonForNoTls::NoConfig));
+        let (server_watch, _) = Watch::new(Conditional::None(ReasonForNoTls::NoConfig));
         let no_future = future::empty();
         return (client_watch, server_watch, Box::new(no_future));
     };
 
     let changes = settings.stream_changes(Duration::from_secs(1));
-    let (client_watch, client_store) = Watch::new(None);
-    let (server_watch, server_store) = Watch::new(None);
+    let (client_watch, client_store) = Watch::new(Conditional::None(ReasonForNoTls::NoConfig));
+    let (server_watch, server_store) = Watch::new(Conditional::None(ReasonForNoTls::NoConfig));
 
     // `Store::store` will return an error iff all watchers have been dropped,
     // so we'll use `fold` to cancel the forwarding future. Eventually, we can
@@ -286,10 +286,10 @@ pub fn watch_for_config_changes(settings: Conditional<&CommonSettings, ReasonFor
             (client_store, server_store),
             |(mut client_store, mut server_store), ref config| {
                 client_store
-                    .store(Some(ClientConfig::from(config)))
+                    .store(Conditional::Some(ClientConfig::from(config)))
                     .map_err(|_| trace!("all client config watchers dropped"))?;
                 server_store
-                    .store(Some(ServerConfig::from(config)))
+                    .store(Conditional::Some(ServerConfig::from(config)))
                     .map_err(|_| trace!("all server config watchers dropped"))?;
                 Ok((client_store, server_store))
             })
@@ -332,7 +332,7 @@ impl ClientConfig {
     /// `ClientConfigWatch`. We can't use `#[cfg(test)]` here because the
     /// benchmarks use this.
     pub fn no_tls() -> ClientConfigWatch {
-        let (watch, _) = Watch::new(None);
+        let (watch, _) = Watch::new(Conditional::None(ReasonForNoTls::NoConfig));
         watch
     }
 }
@@ -362,22 +362,18 @@ impl ServerConfig {
     }
 }
 
-pub fn current_connection_config<C>(watch: &ConditionalConnectionConfig<Watch<Option<C>>>)
+pub fn current_connection_config<C>(
+    watch: &ConditionalConnectionConfig<Watch<Conditional<C, ReasonForNoTls>>>)
     -> ConditionalConnectionConfig<C> where C: Clone
 {
-    match watch {
-        Conditional::Some(c) => {
-            match *c.config.borrow() {
-                Some(ref config) =>
-                    Conditional::Some(ConnectionConfig {
+    watch.as_ref().and_then(|c| {
+        c.config.borrow().as_ref().map(|config| {
+            ConnectionConfig {
                 identity: c.identity.clone(),
                 config: config.clone()
-                    }),
-                None => Conditional::None(ReasonForNoTls::NoConfig),
-            }
-        },
-        Conditional::None(r) => Conditional::None(*r),
             }
+        })
+    })
 }
 
 fn load_file_contents(path: &PathBuf) -> Result<Vec<u8>, Error> {