Allow overriding the DNS resolver for the blocking client. (#2260)

src/blocking/client.rs

@@ -16,6 +16,7 @@ use tokio::sync::{mpsc, oneshot};
 use super::request::{Request, RequestBuilder};
 use super::response::Response;
 use super::wait;
+use crate::dns::Resolve;
 #[cfg(feature = "__tls")]
 use crate::tls;
 #[cfg(feature = "__tls")]
@@ -920,6 +921,15 @@ impl ClientBuilder {
         self.with_inner(|inner| inner.resolve_to_addrs(domain, addrs))
     }
 
+    /// Override the DNS resolver implementation.
+    ///
+    /// Pass an `Arc` wrapping a trait object implementing `Resolve`.
+    /// Overrides for specific names passed to `resolve` and `resolve_to_addrs` will
+    /// still be applied on top of this resolver.
+    pub fn dns_resolver<R: Resolve + 'static>(self, resolver: Arc<R>) -> ClientBuilder {
+        self.with_inner(|inner| inner.dns_resolver(resolver))
+    }
+
     // private
 
     fn with_inner<F>(mut self, func: F) -> ClientBuilder