Make TCP connect handle EINTR correctly

According to the POSIX standard, if connect() is interrupted by a
signal that is caught while blocked waiting to establish a connection,
connect() shall fail and set errno to EINTR, but the connection
request shall not be aborted, and the connection shall be established
asynchronously. When the connection has been established asynchronously,
select() and poll() shall indicate that the file descriptor for the
socket is ready for writing.

When we try to call connect() again, the connection can already
be istablished asynchronously and we get EISCONN error. In this
case we should not return error (as we previously did).

library/std/src/sys/unix/mod.rs

@@ -323,10 +323,18 @@ where
     F: FnMut() -> T,
 {
     loop {
-        match cvt(f()) {
-            Err(ref e) if e.is_interrupted() => {}
-            other => return other,
+        let t = f();
+        if t.is_minus_one() {
+            let e = crate::io::Error::last_os_error();
+            if e.is_interrupted() {
+                continue;
+            }
+            if e.raw_os_error() == Some(libc::EISCONN) {
+                return Ok(t);
+            }
+            return Err(e);
         }
+        return Ok(t);
     }
 }
 

library/std/src/sys_common/net.rs

@@ -229,6 +229,7 @@ impl TcpStream {
 
         let (addr, len) = addr.into_inner();
         cvt_r(|| unsafe { c::connect(sock.as_raw(), addr.as_ptr(), len) })?;
+        sock.take_error()?;
         Ok(TcpStream { inner: sock })
     }