fix(transport): Propagate errors in tls_config instead of unwrap/panic (#385)

* Propagate errors in tls_config instead of unwrap

Ran into `tls_connector` failing and causing our app to panic and shutdown as it seems there wasn't any way to avoid panicking in `tls_config`.

So after talking to @LucioFranco briefly `tls_config` now returns a `Result` instead and propagates errors to the caller, where they can be handled.

* Fix compile warning when tls feature is disabled

examples/src/gcp/client.rs

@@ -32,7 +32,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
         .domain_name("pubsub.googleapis.com");
 
     let channel = Channel::from_static(ENDPOINT)
-        .tls_config(tls_config)
+        .tls_config(tls_config)?
         .connect()
         .await?;
 

examples/src/tls/client.rs

@@ -15,7 +15,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
         .domain_name("example.com");
 
     let channel = Channel::from_static("http://[::1]:50051")
-        .tls_config(tls)
+        .tls_config(tls)?
         .connect()
         .await?;
 

examples/src/tls/server.rs

@@ -60,7 +60,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
     let server = EchoServer::default();
 
     Server::builder()
-        .tls_config(ServerTlsConfig::new().identity(identity))
+        .tls_config(ServerTlsConfig::new().identity(identity))?
         .add_service(pb::echo_server::EchoServer::new(server))
         .serve(addr)
         .await?;

examples/src/tls_client_auth/client.rs

@@ -19,7 +19,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
         .identity(client_identity);
 
     let channel = Channel::from_static("http://[::1]:50051")
-        .tls_config(tls)
+        .tls_config(tls)?
         .connect()
         .await?;
 

examples/src/tls_client_auth/server.rs

@@ -68,7 +68,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
         .client_ca_root(client_ca_cert);
 
     Server::builder()
-        .tls_config(tls)
+        .tls_config(tls)?
         .add_service(pb::echo_server::EchoServer::new(server))
         .serve(addr)
         .await?;