(fix): prefer IPv4 DNS on Android

transport/src/client.rs

@@ -7,6 +7,27 @@ use wtransport::{ClientConfig as WTransportClientConfig, Endpoint};
 
 use crate::{ConnectionHandle, Policy, Receiver, Sender};
 
+#[cfg(target_os = "android")]
+#[derive(Debug)]
+struct AndroidDnsResolver;
+
+#[cfg(target_os = "android")]
+impl wtransport::config::DnsResolver for AndroidDnsResolver {
+    fn resolve(&self, host: &str) -> std::pin::Pin<Box<dyn wtransport::config::DnsLookupFuture>> {
+        let host = host.to_string();
+        Box::pin(async move {
+            let mut fallback = None;
+            for address in tokio::net::lookup_host(host).await? {
+                if address.is_ipv4() {
+                    return Ok(Some(address));
+                }
+                fallback.get_or_insert(address);
+            }
+            Ok(fallback)
+        })
+    }
+}
+
 #[cfg(feature = "insecure-tls")]
 mod noop_verifier {
     use rustls::{
@@ -268,11 +289,13 @@ fn client_config_from_roots(
         transport_config
     };
 
-    Ok(WTransportClientConfig::builder()
+    let config = WTransportClientConfig::builder()
         .with_bind_default()
         .with_custom_tls_and_transport(tls_config, transport_config)
         .keep_alive_interval(policy.keep_alive_interval)
         .max_idle_timeout(policy.max_idle_timeout)
-        .map_err(|e| CommunicationError::Other(e.to_string()))?
+        .map_err(|e| CommunicationError::Other(e.to_string()))?;
-        .build())
+    #[cfg(target_os = "android")]
+    let config = config.dns_resolver(AndroidDnsResolver);
+    Ok(config.build())
 }