Auto merge of #31858 - alexcrichton:fix-networking-cast, r=brson

Similar to #31825 where the read/write limits were capped for files, this
implements similar limits when reading/writing networking types. On Unix this
shouldn't affect anything because the write size is already a `usize`, but on
Windows this will cap the read/write amounts to `i32::max_value`.

cc #31841

src/libstd/sys/common/net.rs

@@ -10,6 +10,7 @@
 
 use prelude::v1::*;
 
+use cmp;
 use ffi::{CStr, CString};
 use fmt;
 use io::{self, Error, ErrorKind};
@@ -198,10 +199,11 @@ impl TcpStream {
     }
 
     pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
+        let len = cmp::min(buf.len(), <wrlen_t>::max_value() as usize) as wrlen_t;
         let ret = try!(cvt(unsafe {
             c::send(*self.inner.as_inner(),
                     buf.as_ptr() as *const c_void,
-                    buf.len() as wrlen_t,
+                    len,
                     0)
         }));
         Ok(ret as usize)
@@ -358,21 +360,23 @@ impl UdpSocket {
     pub fn recv_from(&self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
         let mut storage: c::sockaddr_storage = unsafe { mem::zeroed() };
         let mut addrlen = mem::size_of_val(&storage) as c::socklen_t;
+        let len = cmp::min(buf.len(), <wrlen_t>::max_value() as usize) as wrlen_t;
 
         let n = try!(cvt(unsafe {
             c::recvfrom(*self.inner.as_inner(),
                         buf.as_mut_ptr() as *mut c_void,
-                        buf.len() as wrlen_t, 0,
+                        len, 0,
                         &mut storage as *mut _ as *mut _, &mut addrlen)
         }));
         Ok((n as usize, try!(sockaddr_to_addr(&storage, addrlen as usize))))
     }
 
     pub fn send_to(&self, buf: &[u8], dst: &SocketAddr) -> io::Result<usize> {
+        let len = cmp::min(buf.len(), <wrlen_t>::max_value() as usize) as wrlen_t;
         let (dstp, dstlen) = dst.into_inner();
         let ret = try!(cvt(unsafe {
             c::sendto(*self.inner.as_inner(),
-                      buf.as_ptr() as *const c_void, buf.len() as wrlen_t,
+                      buf.as_ptr() as *const c_void, len,
                       0, dstp, dstlen)
         }));
         Ok(ret as usize)

src/libstd/sys/windows/net.rs

@@ -8,6 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use cmp;
 use io;
 use libc::{c_int, c_void};
 use mem;
@@ -131,9 +132,9 @@ impl Socket {
     pub fn read(&self, buf: &mut [u8]) -> io::Result<usize> {
         // On unix when a socket is shut down all further reads return 0, so we
         // do the same on windows to map a shut down socket to returning EOF.
+        let len = cmp::min(buf.len(), i32::max_value() as usize) as i32;
         unsafe {
-            match c::recv(self.0, buf.as_mut_ptr() as *mut c_void,
-                             buf.len() as i32, 0) {
+            match c::recv(self.0, buf.as_mut_ptr() as *mut c_void, len, 0) {
                 -1 if c::WSAGetLastError() == c::WSAESHUTDOWN => Ok(0),
                 -1 => Err(last_error()),
                 n => Ok(n as usize)