Auto merge of #25078 - nham:std_net_impl_debug, r=alexcrichton

I'm uncertain whether the 3 implementations in `net2` should unwrap the socket address values. Without unwrapping it looks like this:

```
UdpSocket { addr: Ok(V4(127.0.0.1:34354)), inner: 3 }
TcpListener { addr: Ok(V4(127.0.0.1:9123)), inner: 4 }
TcpStream { addr: Ok(V4(127.0.0.1:9123)), peer: Ok(V4(127.0.0.1:58360)), inner: 5 }
```

One issue is that you can create, e.g. `UdpSocket`s with bad addresses, which means you can't just unwrap in the implementation:

```
#![feature(from_raw_os)]
use std::net::UdpSocket;
use std::os::unix::io::FromRawFd;

let sock: UdpSocket = unsafe { FromRawFd::from_raw_fd(-1) };
println!("{:?}", sock); // prints "UdpSocket { addr: Err(Error { repr: Os(9) }), inner: -1 }"

```

Fixes #23134.

1 files changed, 47 insertions, 0 deletions

diff --git a/src/libstd/sys/common/net2.rs b/src/libstd/sys/common/net2.rs
index 2b2c31d92ed..7da7071670a 100644
--- a/src/libstd/sys/common/net2.rs
+++ b/src/libstd/sys/common/net2.rs
@@ -11,6 +11,7 @@
 use prelude::v1::*;
 
 use ffi::{CStr, CString};
+use fmt;
 use io::{self, Error, ErrorKind};
 use libc::{self, c_int, c_char, c_void, socklen_t};
 use mem;
@@ -268,6 +269,24 @@ impl FromInner<Socket> for TcpStream {
     }
 }
 
+impl fmt::Debug for TcpStream {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let mut res = f.debug_struct("TcpStream");
+
+        if let Ok(addr) = self.socket_addr() {
+            res = res.field("addr", &addr);
+        }
+
+        if let Ok(peer) = self.peer_addr() {
+            res = res.field("peer", &peer);
+        }
+
+        let name = if cfg!(windows) {"socket"} else {"fd"};
+        res = res.field(name, &self.inner.as_inner());
+        res.finish()
+    }
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // TCP listeners
 ////////////////////////////////////////////////////////////////////////////////
@@ -327,6 +346,20 @@ impl FromInner<Socket> for TcpListener {
     }
 }
 
+impl fmt::Debug for TcpListener {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let mut res = f.debug_struct("TcpListener");
+
+        if let Ok(addr) = self.socket_addr() {
+            res = res.field("addr", &addr);
+        }
+
+        let name = if cfg!(windows) {"socket"} else {"fd"};
+        res = res.field(name, &self.inner.as_inner());
+        res.finish()
+    }
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // UDP
 ////////////////////////////////////////////////////////////////////////////////
@@ -445,3 +478,17 @@ impl FromInner<Socket> for UdpSocket {
         UdpSocket { inner: socket }
     }
 }
+
+impl fmt::Debug for UdpSocket {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let mut res = f.debug_struct("UdpSocket");
+
+        if let Ok(addr) = self.socket_addr() {
+            res = res.field("addr", &addr);
+        }
+
+        let name = if cfg!(windows) {"socket"} else {"fd"};
+        res = res.field(name, &self.inner.as_inner());
+        res.finish()
+    }
+}