Auto merge of #99 - jrmuizel:remove-retry, r=pcwalton

Remove mach_msg retry loop.

The idiomatic solution to dealing with the trailer bytes
is to just add the maximum trailer size to msg size returned by the
kernel.

Author: bors-servo

src/platform/macos/mod.rs

@@ -573,33 +573,29 @@ fn select(port: mach_port_t, blocking_mode: BlockingMode)
                                  timeout,
                                  MACH_PORT_NULL) {
             MACH_RCV_TOO_LARGE => {
-                // Do a loop. There's no way I know of to figure out precisely in advance how big
-                // the message actually is!
-                let mut extra_size = 8;
-                loop {
-                    let actual_size = (*message).header.msgh_size + extra_size;
-                    allocated_buffer = Some(libc::malloc(actual_size as size_t));
-                    setup_receive_buffer(slice::from_raw_parts_mut(
-                                            allocated_buffer.unwrap() as *mut u8,
-                                            actual_size as usize),
-                                         port);
-                    message = allocated_buffer.unwrap() as *mut Message;
-                    match mach_sys::mach_msg(message as *mut _,
-                                             flags,
-                                             0,
-                                             actual_size,
-                                             port,
-                                             timeout,
-                                             MACH_PORT_NULL) {
-                        MACH_MSG_SUCCESS => break,
-                        MACH_RCV_TOO_LARGE => {
-                            libc::free(allocated_buffer.unwrap() as *mut _);
-                            extra_size *= 2;
-                        }
-                        os_result => {
-                            libc::free(allocated_buffer.unwrap() as *mut _);
-                            return Err(MachError(os_result))
-                        }
+                // the actual size gets written into msgh_size by the kernel
+                let max_trailer_size = mem::size_of::<mach_sys::mach_msg_max_trailer_t>() as mach_sys::mach_msg_size_t;
+                let actual_size = (*message).header.msgh_size + max_trailer_size;
+                allocated_buffer = Some(libc::malloc(actual_size as size_t));
+                setup_receive_buffer(slice::from_raw_parts_mut(
+                                        allocated_buffer.unwrap() as *mut u8,
+                                        actual_size as usize),
+                                     port);
+                message = allocated_buffer.unwrap() as *mut Message;
+                match mach_sys::mach_msg(message as *mut _,
+                                         flags,
+                                         0,
+                                         actual_size,
+                                         port,
+                                         timeout,
+                                         MACH_PORT_NULL) {
+                    MACH_MSG_SUCCESS => {},
+                    MACH_RCV_TOO_LARGE => {
+                        panic!("message was bigger than we were told");
+                    }
+                    os_result => {
+                        libc::free(allocated_buffer.unwrap() as *mut _);
+                        return Err(MachError(os_result))
                     }
                 }
             }