Avoid enabling multiple rustls backends by accident

For this, we had to:

- Make the choice(s) of backend explicit in tokio-xmpp features
- Avoid picking a backend through transitive dependencies in xmpp
  (reqwest->hyper->rustls).

In addition, we choose the default rustls backend by default and adapt
the examples so that they can cope with either situation.

tokio-xmpp/examples/contact_addr.rs

@@ -2,7 +2,12 @@ use futures::stream::StreamExt;
 use std::env::args;
 use std::process::exit;
 use std::str::FromStr;
-use tokio_xmpp::{rustls, Client, IqRequest, IqResponse};
+#[cfg(all(
+    feature = "tls-rust",
+    any(feature = "tls-rust-aws_lc_rs", feature = "tls-rust-ring")
+))]
+use tokio_xmpp::rustls;
+use tokio_xmpp::{Client, IqRequest, IqResponse};
 use xmpp_parsers::{
     disco::{DiscoInfoQuery, DiscoInfoResult},
     jid::{BareJid, Jid},
@@ -14,11 +19,20 @@ use xmpp_parsers::{
 async fn main() {
     env_logger::init();
 
-    #[cfg(feature = "tls-rust")]
+    #[cfg(all(feature = "tls-rust", feature = "tls-rust-aws_lc_rs"))]
     rustls::crypto::aws_lc_rs::default_provider()
         .install_default()
         .expect("failed to install rustls crypto provider");
 
+    #[cfg(all(
+        feature = "tls-rust",
+        feature = "tls-rust-ring",
+        not(feature = "tls-rust-aws_lc_rs")
+    ))]
+    rustls::crypto::ring::default_provider()
+        .install_default()
+        .expect("failed to install rustls crypto provider");
+
     let args: Vec<String> = args().collect();
     if args.len() != 4 {
         println!("Usage: {} <jid> <password> <target>", args[0]);

tokio-xmpp/examples/download_avatars.rs

@@ -4,7 +4,12 @@ use std::fs::{create_dir_all, File};
 use std::io::{self, Write};
 use std::process::exit;
 use std::str::FromStr;
-use tokio_xmpp::{rustls, Client, Stanza};
+#[cfg(all(
+    feature = "tls-rust",
+    any(feature = "tls-rust-aws_lc_rs", feature = "tls-rust-ring")
+))]
+use tokio_xmpp::rustls;
+use tokio_xmpp::{Client, Stanza};
 use xmpp_parsers::{
     avatar::{Data as AvatarData, Metadata as AvatarMetadata},
     caps::{compute_disco, hash_caps, Caps},
@@ -26,11 +31,20 @@ use xmpp_parsers::{
 async fn main() {
     env_logger::init();
 
-    #[cfg(feature = "tls-rust")]
+    #[cfg(all(feature = "tls-rust", feature = "tls-rust-aws_lc_rs"))]
     rustls::crypto::aws_lc_rs::default_provider()
         .install_default()
         .expect("failed to install rustls crypto provider");
 
+    #[cfg(all(
+        feature = "tls-rust",
+        feature = "tls-rust-ring",
+        not(feature = "tls-rust-aws_lc_rs")
+    ))]
+    rustls::crypto::ring::default_provider()
+        .install_default()
+        .expect("failed to install rustls crypto provider");
+
     let args: Vec<String> = args().collect();
     if args.len() != 3 {
         println!("Usage: {} <jid> <password>", args[0]);

tokio-xmpp/examples/echo_bot.rs

@@ -2,7 +2,12 @@ use futures::stream::StreamExt;
 use std::env::args;
 use std::process::exit;
 use std::str::FromStr;
-use tokio_xmpp::{rustls, Client};
+#[cfg(all(
+    feature = "tls-rust",
+    any(feature = "tls-rust-aws_lc_rs", feature = "tls-rust-ring")
+))]
+use tokio_xmpp::rustls;
+use tokio_xmpp::Client;
 use xmpp_parsers::jid::{BareJid, Jid};
 use xmpp_parsers::message::{Lang, Message, MessageType};
 use xmpp_parsers::presence::{Presence, Show as PresenceShow, Type as PresenceType};
@@ -11,11 +16,20 @@ use xmpp_parsers::presence::{Presence, Show as PresenceShow, Type as PresenceTyp
 async fn main() {
     env_logger::init();
 
-    #[cfg(feature = "tls-rust")]
+    #[cfg(all(feature = "tls-rust", feature = "tls-rust-aws_lc_rs"))]
     rustls::crypto::aws_lc_rs::default_provider()
         .install_default()
         .expect("failed to install rustls crypto provider");
 
+    #[cfg(all(
+        feature = "tls-rust",
+        feature = "tls-rust-ring",
+        not(feature = "tls-rust-aws_lc_rs")
+    ))]
+    rustls::crypto::ring::default_provider()
+        .install_default()
+        .expect("failed to install rustls crypto provider");
+
     let args: Vec<String> = args().collect();
     if args.len() != 3 {
         println!("Usage: {} <jid> <password>", args[0]);

tokio-xmpp/examples/echo_component.rs

@@ -6,17 +6,31 @@ use xmpp_parsers::jid::Jid;
 use xmpp_parsers::message::{Lang, Message, MessageType};
 use xmpp_parsers::presence::{Presence, Show as PresenceShow, Type as PresenceType};
 
-use tokio_xmpp::{connect::DnsConfig, rustls, Component};
+#[cfg(all(
+    feature = "tls-rust",
+    any(feature = "tls-rust-aws_lc_rs", feature = "tls-rust-ring")
+))]
+use tokio_xmpp::rustls;
+use tokio_xmpp::{connect::DnsConfig, Component};
 
 #[tokio::main]
 async fn main() {
     env_logger::init();
 
-    #[cfg(feature = "tls-rust")]
+    #[cfg(all(feature = "tls-rust", feature = "tls-rust-aws_lc_rs"))]
     rustls::crypto::aws_lc_rs::default_provider()
         .install_default()
         .expect("failed to install rustls crypto provider");
 
+    #[cfg(all(
+        feature = "tls-rust",
+        feature = "tls-rust-ring",
+        not(feature = "tls-rust-aws_lc_rs")
+    ))]
+    rustls::crypto::ring::default_provider()
+        .install_default()
+        .expect("failed to install rustls crypto provider");
+
     let args: Vec<String> = args().collect();
     if args.len() < 3 || args.len() > 4 {
         println!("Usage: {} <jid> <password> [server:port]", args[0]);

tokio-xmpp/examples/echo_server.rs

@@ -1,20 +1,33 @@
 use futures::{SinkExt, StreamExt};
 use tokio::{self, io, net::TcpSocket};
 
+#[cfg(all(
+    feature = "tls-rust",
+    any(feature = "tls-rust-aws_lc_rs", feature = "tls-rust-ring")
+))]
+use tokio_xmpp::rustls;
 use tokio_xmpp::{
     minidom::Element,
     parsers::stream_features::StreamFeatures,
-    rustls,
     xmlstream::{accept_stream, StreamHeader, Timeouts},
 };
 
 #[tokio::main]
 async fn main() -> Result<(), io::Error> {
-    #[cfg(feature = "tls-rust")]
+    #[cfg(all(feature = "tls-rust", feature = "tls-rust-aws_lc_rs"))]
     rustls::crypto::aws_lc_rs::default_provider()
         .install_default()
         .expect("failed to install rustls crypto provider");
 
+    #[cfg(all(
+        feature = "tls-rust",
+        feature = "tls-rust-ring",
+        not(feature = "tls-rust-aws_lc_rs")
+    ))]
+    rustls::crypto::ring::default_provider()
+        .install_default()
+        .expect("failed to install rustls crypto provider");
+
     // TCP socket
     let address = "127.0.0.1:5222".parse().unwrap();
     let socket = TcpSocket::new_v4()?;

tokio-xmpp/examples/keep_connection.rs

@@ -19,6 +19,11 @@ use rand::{thread_rng, Rng};
 
 use futures::StreamExt;
 
+#[cfg(all(
+    feature = "tls-rust",
+    any(feature = "tls-rust-aws_lc_rs", feature = "tls-rust-ring")
+))]
+use tokio_xmpp::rustls;
 use tokio_xmpp::{
     connect::{DnsConfig, StartTlsServerConnector},
     parsers::{
@@ -26,7 +31,6 @@ use tokio_xmpp::{
         jid::{BareJid, Jid},
         ping,
     },
-    rustls,
     stanzastream::StanzaStream,
     xmlstream::Timeouts,
 };
@@ -35,11 +39,20 @@ use tokio_xmpp::{
 async fn main() {
     env_logger::init();
 
-    #[cfg(feature = "tls-rust")]
+    #[cfg(all(feature = "tls-rust", feature = "tls-rust-aws_lc_rs"))]
     rustls::crypto::aws_lc_rs::default_provider()
         .install_default()
         .expect("failed to install rustls crypto provider");
 
+    #[cfg(all(
+        feature = "tls-rust",
+        feature = "tls-rust-ring",
+        not(feature = "tls-rust-aws_lc_rs")
+    ))]
+    rustls::crypto::ring::default_provider()
+        .install_default()
+        .expect("failed to install rustls crypto provider");
+
     let args: Vec<String> = args().collect();
     if args.len() != 3 {
         println!("Usage: {} <jid> <password>", args[0]);