Improve verbose errors for socket addresses

Moves the point of adding error context to the net::addr module so that
we have access to the raw address input and can include it in the error
message.

src/net/addr.rs

@@ -1,11 +1,12 @@
+use std::future::Future;
 use std::mem;
 use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
 use std::net::{SocketAddr, SocketAddrV4, SocketAddrV6};
 use std::pin::Pin;
-use std::future::Future;
 
 use crate::io;
 use crate::task::{spawn_blocking, Context, JoinHandle, Poll};
+use crate::utils::Context as ErrorContext;
 
 cfg_not_docs! {
     macro_rules! ret {
@@ -67,6 +68,18 @@ pub enum ToSocketAddrsFuture<I> {
     Done,
 }
 
+/// Wrap `std::io::Error` with additional message
+///
+/// Keeps the original error kind and stores the original I/O error as `source`.
+impl<T> ErrorContext for ToSocketAddrsFuture<T> {
+    fn context(self, message: impl Fn() -> String) -> Self {
+        match self {
+            ToSocketAddrsFuture::Ready(res) => ToSocketAddrsFuture::Ready(res.context(message)),
+            x => x,
+        }
+    }
+}
+
 impl<I: Iterator<Item = SocketAddr>> Future for ToSocketAddrsFuture<I> {
     type Output = io::Result<I>;
 
@@ -110,7 +123,9 @@ impl ToSocketAddrs for SocketAddrV4 {
         impl Future<Output = Self::Iter>,
         ToSocketAddrsFuture<Self::Iter>
     ) {
-        SocketAddr::V4(*self).to_socket_addrs()
+        SocketAddr::V4(*self)
+            .to_socket_addrs()
+            .context(|| format!("could not resolve address `{}`", self))
     }
 }
 
@@ -123,7 +138,9 @@ impl ToSocketAddrs for SocketAddrV6 {
         impl Future<Output = Self::Iter>,
         ToSocketAddrsFuture<Self::Iter>
     ) {
-        SocketAddr::V6(*self).to_socket_addrs()
+        SocketAddr::V6(*self)
+            .to_socket_addrs()
+            .context(|| format!("could not resolve address `{}`", self))
     }
 }
 
@@ -195,7 +212,9 @@ impl ToSocketAddrs for (&str, u16) {
 
         let host = host.to_string();
         let task = spawn_blocking(move || {
-            std::net::ToSocketAddrs::to_socket_addrs(&(host.as_str(), port))
+            let addr = (host.as_str(), port);
+            std::net::ToSocketAddrs::to_socket_addrs(&addr)
+                .context(|| format!("could not resolve address `{:?}`", addr))
         });
         ToSocketAddrsFuture::Resolving(task)
     }
@@ -215,7 +234,10 @@ impl ToSocketAddrs for str {
         }
 
         let addr = self.to_string();
-        let task = spawn_blocking(move || std::net::ToSocketAddrs::to_socket_addrs(addr.as_str()));
+        let task = spawn_blocking(move || {
+            std::net::ToSocketAddrs::to_socket_addrs(addr.as_str())
+                .context(|| format!("could not resolve address `{:?}`", addr))
+        });
         ToSocketAddrsFuture::Resolving(task)
     }
 }

src/net/tcp/listener.rs

@@ -8,7 +8,6 @@ use crate::net::driver::Watcher;
 use crate::net::{TcpStream, ToSocketAddrs};
 use crate::stream::Stream;
 use crate::task::{Context, Poll};
-use crate::utils::Context as _;
 
 /// A TCP socket server, listening for connections.
 ///
@@ -78,8 +77,7 @@ impl TcpListener {
         let mut last_err = None;
         let addrs = addrs
             .to_socket_addrs()
-            .await
-            .context(|| String::from("could not resolve addresses"))?;
+            .await?;
 
         for addr in addrs {
             match mio::net::TcpListener::bind(&addr) {

src/net/tcp/stream.rs

@@ -74,8 +74,7 @@ impl TcpStream {
         let mut last_err = None;
         let addrs = addrs
             .to_socket_addrs()
-            .await
-            .context(|| String::from("could not resolve addresses"))?;
+            .await?;
 
         for addr in addrs {
             let res = spawn_blocking(move || {

src/net/udp/mod.rs

@@ -71,8 +71,7 @@ impl UdpSocket {
         let mut last_err = None;
         let addrs = addrs
             .to_socket_addrs()
-            .await
-            .context(|| String::from("could not resolve addresses"))?;
+            .await?;
 
         for addr in addrs {
             match mio::net::UdpSocket::bind(&addr) {

tests/verbose_errors.rs

@@ -1,4 +1,4 @@
-use async_std::{fs, task};
+use async_std::{fs, io, net::ToSocketAddrs, task};
 
 #[test]
 fn open_file() {
@@ -14,3 +14,18 @@ fn open_file() {
         }
     })
 }
+
+#[test]
+fn resolve_address() {
+    task::block_on(async {
+        let non_existing_addr = "ashjudlkahasdasdsikdhajik.asdasdasdasdasdasd.fjuiklashdbflasas:80";
+        let res: Result<_, io::Error> = non_existing_addr.to_socket_addrs().await;
+        match res {
+            Ok(_) => panic!("Found address with random name: We live in a simulation"),
+            Err(e) => assert_eq!(
+                "could not resolve address `\"ashjudlkahasdasdsikdhajik.asdasdasdasdasdasd.fjuiklashdbflasas:80\"`",
+                &format!("{}", e)
+            ),
+        }
+    })
+}