native: Implement timeouts for unix networking

This commit has an implementation of the previous commit's timeout interface for
I/O objects on unix platforms. For implementation details, see the large comment
at the end of libnative/io/net.rs which talks about the general strategy taken.

Thankfully, all of these implementations can share code because they're
performing all the same operations.

This commit does not implement timeouts for named pipes on windows, only tcp/udp
objects on windows (which are quite similar to their unix equivalents).

Author: alexcrichton

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 {