auto merge of #13814 : alexcrichton/rust/read-timeout, r=brson

This PR is an implementation of `set_timeout`, `set_read_timeout`, and `set_write_timeout` for TCP, UDP, and Unix streams (named pipes on windows).

The implementation was much more difficult than I imagined it was going to be throughout the 9 categories ({tcp, udp, unix} x {windows, unix, green}). The major snag is that libuv doesn't support canceling writes, so I chose to word the `set_write_timeout` documentation in such a way that it accomadates the behavior seen when running around with libgreen.

The first commit is from #13751, and I just included it to pre-emptively avoid rebase conflicts. The following commits are relevant to this PR. The tests aren't quite passing on windows just yet, but I should have those working by tomorrow once my VM is back up and running. For now, I wanted to see what others' thoughts were on this strategy.

Author: bors

src/libnative/io/c_unix.rs

@@ -27,6 +27,13 @@ pub static FIOCLEX: libc::c_ulong = 0x20006601;
 #[cfg(target_os = "android")]
 pub static FIOCLEX: libc::c_ulong = 0x5451;
 
+#[cfg(target_os = "macos")]
+#[cfg(target_os = "freebsd")]
+pub static MSG_DONTWAIT: libc::c_int = 0x80;
+#[cfg(target_os = "linux")]
+#[cfg(target_os = "android")]
+pub static MSG_DONTWAIT: libc::c_int = 0x40;
+
 extern {
     pub fn gettimeofday(timeval: *mut libc::timeval,
                         tzp: *libc::c_void) -> libc::c_int;

src/libnative/io/c_win32.rs

@@ -18,6 +18,7 @@ pub static WSADESCRIPTION_LEN: uint = 256;
 pub static WSASYS_STATUS_LEN: uint = 128;
 pub static FIONBIO: libc::c_long = 0x8004667e;
 static FD_SETSIZE: uint = 64;
+pub static MSG_DONTWAIT: libc::c_int = 0;
 
 pub struct WSADATA {
     pub wVersion: libc::WORD,

src/libnative/io/file_unix.rs

@@ -189,6 +189,9 @@ impl rtio::RtioPipe for FileDesc {
     fn close_write(&mut self) -> Result<(), IoError> {
         Err(io::standard_error(io::InvalidInput))
     }
+    fn set_timeout(&mut self, _t: Option<u64>) {}
+    fn set_read_timeout(&mut self, _t: Option<u64>) {}
+    fn set_write_timeout(&mut self, _t: Option<u64>) {}
 }
 
 impl rtio::RtioTTY for FileDesc {

src/libnative/io/file_win32.rs

@@ -221,6 +221,9 @@ impl rtio::RtioPipe for FileDesc {
     fn close_write(&mut self) -> IoResult<()> {
         Err(io::standard_error(io::InvalidInput))
     }
+    fn set_timeout(&mut self, _t: Option<u64>) {}
+    fn set_read_timeout(&mut self, _t: Option<u64>) {}
+    fn set_write_timeout(&mut self, _t: Option<u64>) {}
 }
 
 impl rtio::RtioTTY for FileDesc {