Rust Compiler Error for callbacks

crashing_code.rs

extern crate libc;
extern crate native;

use libc::{c_short, c_int};

mod linux {
	use native::io::file::FileDesc;
	use libc::c_int;

	pub fn socketpair(domain: int, type_: int, protocol: int) -> Result<(FileDesc, FileDesc), int> {
		unsafe {
			let sv: [c_int, ..2] = [0, 0];
			let res = internal::socketpair(domain as c_int, type_ as c_int, protocol as c_int, sv.as_ptr());

			if res == 0 {
				assert!(sv[0] >= 0);
				assert!(sv[1] >= 0);

				let SOCK_CLOEXEC = 02000000;
				let close_on_exec = (type_ & SOCK_CLOEXEC) > 0;

				let left = FileDesc::new(sv[0], close_on_exec);
				let right = FileDesc::new(sv[1], close_on_exec);
				let pair = (left, right);

				return Ok(pair)
			} else {
				return Err(res as int)
			}
		}
	}

	mod internal {
		use native::io::file::fd_t;
		use libc::c_int;
		extern {
			pub fn socketpair(domain: c_int, type_: c_int, protocol: c_int, sv: *const fd_t) -> c_int;
		}
	}
}


mod libevent {
	use native::io::file::{FileDesc, fd_t};
	use libc::{c_short, c_int};
	use std::ptr::null;

	pub struct Base {
		ptr: *const c_int,
	}

	impl Base {
		pub fn new() -> Base {
			unsafe {
				let ptr = event_init();

				assert!(!ptr.is_null());
				return Base {
					ptr: ptr,
				}
			}
		}

		pub fn dispatch(&self) -> int {
			unsafe {
				return event_base_dispatch(self.ptr) as int
			}
		}

		extern "C"
		fn c_watch_fd_callback(ev:*const c_int, type_:c_short, cb: watch_fd_callback_t) {
			cb(ev, type_)
		}

		pub fn watch_fd(&self, fd: FileDesc, cb: watch_fd_callback_t) {
			unsafe {
				let EV_READ:c_short = 0x02;
				let ev = event_new(self.ptr, fd.fd(), EV_READ, Base::c_watch_fd_callback, cb);
				assert!(!ev.is_null());

				let res = event_add(ev, null());
				assert!(res == 0);
			}
		}
	}

	impl Drop for Base {
		fn drop(&mut self) {
			unsafe {
				event_base_free(self.ptr)
			}
		}
	}

	type watch_fd_callback_t = fn(*const c_int, c_short);
	type c_watch_fd_callback_t = extern fn(*const c_int, c_short, watch_fd_callback_t);	

	#[link(name="event")]
	extern {
		fn event_init() -> *const c_int;
		fn event_base_dispatch(ptr: *const c_int) -> c_int;
		fn event_base_loop(ptr: *const c_int, flags: c_int) -> c_int;
		fn event_base_free(ptr: *const c_int);

		fn event_new(base: *const c_int, fd: fd_t, events: c_short, cb: c_watch_fd_callback_t, args: watch_fd_callback_t) -> *const c_int;
		fn event_add(ev: *const c_int, timeout: *const c_int) -> c_int;
	}
}

fn printme(ev: *const c_int, flags: i16) {
	println!("hello");
}

fn main() {
	use linux::socketpair;
	use libc::consts::os::bsd44::{AF_UNIX, SOCK_DGRAM};

	let AF_UNSPEC = 0 as int;
	let domain = AF_UNIX as int;
	let type_ = SOCK_DGRAM as int;
	let protocol = AF_UNSPEC as int;

	let (mut fd1, fd2) = socketpair(domain, type_, protocol).ok().expect("socketpair failed!");
	println!("{}, {}",  fd1.fd(), fd2.fd());

	spawn(proc() {
		let ev = libevent::Base::new();
		ev.watch_fd(fd2, printme);
		println!("waiting...");
		ev.dispatch();
		println!("waiting done");
	});

	let buf:[u8, ..1] = [0];
	match fd1.inner_write(buf) {
		Err(x) => { println!("write() err: {}", x.detail.expect("Unknown error")) },
		_ => {},
	}

	println!("wrote!");
}

gistfile1.txt

70c70,75
< 		pub fn watch_fd(&self, fd: FileDesc, cb: extern fn(*const c_int, c_short, *const c_int)) {
---
> 		extern "C"
> 		fn c_watch_fd_callback(ev:*const c_int, type_:c_short, cb: watch_fd_callback_t) {
> 			cb(ev, type_)
> 		}
> 
> 		pub fn watch_fd(&self, fd: FileDesc, cb: watch_fd_callback_t) {
73c78
< 				let ev = event_new(self.ptr, fd.fd(), EV_READ, cb, null());
---
> 				let ev = event_new(self.ptr, fd.fd(), EV_READ, Base::c_watch_fd_callback, cb);
89a95,97
> 	type watch_fd_callback_t = fn(*const c_int, c_short);
> 	type c_watch_fd_callback_t = extern fn(*const c_int, c_short, watch_fd_callback_t);	
> 
97c105
< 		fn event_new(base: *const c_int, fd: fd_t, events: c_short, cb: extern fn(*const c_int, c_short, *const c_int), args: *const c_int) -> *const c_int;
---
> 		fn event_new(base: *const c_int, fd: fd_t, events: c_short, cb: c_watch_fd_callback_t, args: watch_fd_callback_t) -> *const c_int;
102,103c110
< extern "C"
< fn printme(ev: *const c_int, flags: c_short, args: *const c_int) {
---
> fn printme(ev: *const c_int, flags: i16) {

working_code.rs

extern crate libc;
extern crate native;

use libc::{c_short, c_int};

mod linux {
	use native::io::file::FileDesc;
	use libc::c_int;

	pub fn socketpair(domain: int, type_: int, protocol: int) -> Result<(FileDesc, FileDesc), int> {
		unsafe {
			let sv: [c_int, ..2] = [0, 0];
			let res = internal::socketpair(domain as c_int, type_ as c_int, protocol as c_int, sv.as_ptr());

			if res == 0 {
				assert!(sv[0] >= 0);
				assert!(sv[1] >= 0);

				let SOCK_CLOEXEC = 02000000;
				let close_on_exec = (type_ & SOCK_CLOEXEC) > 0;

				let left = FileDesc::new(sv[0], close_on_exec);
				let right = FileDesc::new(sv[1], close_on_exec);
				let pair = (left, right);

				return Ok(pair)
			} else {
				return Err(res as int)
			}
		}
	}

	mod internal {
		use native::io::file::fd_t;
		use libc::c_int;
		extern {
			pub fn socketpair(domain: c_int, type_: c_int, protocol: c_int, sv: *const fd_t) -> c_int;
		}
	}
}


mod libevent {
	use native::io::file::{FileDesc, fd_t};
	use libc::{c_short, c_int};
	use std::ptr::null;

	pub struct Base {
		ptr: *const c_int,
	}

	impl Base {
		pub fn new() -> Base {
			unsafe {
				let ptr = event_init();

				assert!(!ptr.is_null());
				return Base {
					ptr: ptr,
				}
			}
		}

		pub fn dispatch(&self) -> int {
			unsafe {
				return event_base_dispatch(self.ptr) as int
			}
		}

		pub fn watch_fd(&self, fd: FileDesc, cb: extern fn(*const c_int, c_short, *const c_int)) {
			unsafe {
				let EV_READ:c_short = 0x02;
				let ev = event_new(self.ptr, fd.fd(), EV_READ, cb, null());
				assert!(!ev.is_null());

				let res = event_add(ev, null());
				assert!(res == 0);
			}
		}
	}

	impl Drop for Base {
		fn drop(&mut self) {
			unsafe {
				event_base_free(self.ptr)
			}
		}
	}

	#[link(name="event")]
	extern {
		fn event_init() -> *const c_int;
		fn event_base_dispatch(ptr: *const c_int) -> c_int;
		fn event_base_loop(ptr: *const c_int, flags: c_int) -> c_int;
		fn event_base_free(ptr: *const c_int);

		fn event_new(base: *const c_int, fd: fd_t, events: c_short, cb: extern fn(*const c_int, c_short, *const c_int), args: *const c_int) -> *const c_int;
		fn event_add(ev: *const c_int, timeout: *const c_int) -> c_int;
	}
}

extern "C"
fn printme(ev: *const c_int, flags: c_short, args: *const c_int) {
	println!("hello");
}

fn main() {
	use linux::socketpair;
	use libc::consts::os::bsd44::{AF_UNIX, SOCK_DGRAM};

	let AF_UNSPEC = 0 as int;
	let domain = AF_UNIX as int;
	let type_ = SOCK_DGRAM as int;
	let protocol = AF_UNSPEC as int;

	let (mut fd1, fd2) = socketpair(domain, type_, protocol).ok().expect("socketpair failed!");
	println!("{}, {}",  fd1.fd(), fd2.fd());

	spawn(proc() {
		let ev = libevent::Base::new();
		ev.watch_fd(fd2, printme);
		println!("waiting...");
		ev.dispatch();
		println!("waiting done");
	});

	let buf:[u8, ..1] = [0];
	match fd1.inner_write(buf) {
		Err(x) => { println!("write() err: {}", x.detail.expect("Unknown error")) },
		_ => {},
	}

	println!("wrote!");
}