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diff --git a/src/system/io/error.rs b/src/system/io/error.rs
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+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+
+use std::error;
+use std::fmt;
+use std::result;
+
+/// A specialized [`Result`](../result/enum.Result.html) type for I/O
+/// operations.
+///
+/// This type is broadly used across `std::io` for any operation which may
+/// produce an error.
+///
+/// This typedef is generally used to avoid writing out `io::Error` directly and
+/// is otherwise a direct mapping to `Result`.
+///
+/// While usual Rust style is to import types directly, aliases of `Result`
+/// often are not, to make it easier to distinguish between them. `Result` is
+/// generally assumed to be `std::result::Result`, and so users of this alias
+/// will generally use `io::Result` instead of shadowing the prelude's import
+/// of `std::result::Result`.
+///
+/// # Examples
+///
+/// A convenience function that bubbles an `io::Result` to its caller:
+///
+/// ```
+/// use std::io;
+///
+/// fn get_string() -> io::Result<String> {
+///     let mut buffer = String::new();
+///
+///     try!(io::stdin().read_line(&mut buffer));
+///
+///     Ok(buffer)
+/// }
+/// ```
+pub type Result<T> = result::Result<T, Error>;
+
+/// The error type for I/O operations of the `Read`, `Write`, `Seek`, and
+/// associated traits.
+///
+/// Errors mostly originate from the underlying OS, but custom instances of
+/// `Error` can be created with crafted error messages and a particular value of
+/// `ErrorKind`.
+#[derive(Debug)]
+pub struct Error {
+    repr: Repr,
+}
+
+enum Repr {
+    Os(i32),
+    Custom(Box<Custom>),
+}
+
+#[derive(Debug)]
+struct Custom {
+    kind: ErrorKind,
+    error: Box<error::Error+Send+Sync>,
+}
+
+/// A list specifying general categories of I/O error.
+///
+/// This list is intended to grow over time and it is not recommended to
+/// exhaustively match against it.
+#[derive(Copy, PartialEq, Eq, Clone, Debug)]
+#[allow(deprecated)]
+pub enum ErrorKind {
+    /// An entity was not found, often a file.
+    NotFound,
+    /// The operation lacked the necessary privileges to complete.
+    PermissionDenied,
+    /// The connection was refused by the remote server.
+    ConnectionRefused,
+    /// The connection was reset by the remote server.
+    ConnectionReset,
+    /// The connection was aborted (terminated) by the remote server.
+    ConnectionAborted,
+    /// The network operation failed because it was not connected yet.
+    NotConnected,
+    /// A socket address could not be bound because the address is already in
+    /// use elsewhere.
+    AddrInUse,
+    /// A nonexistent interface was requested or the requested address was not
+    /// local.
+    AddrNotAvailable,
+    /// The operation failed because a pipe was closed.
+    BrokenPipe,
+    /// An entity already exists, often a file.
+    AlreadyExists,
+    /// The operation needs to block to complete, but the blocking operation was
+    /// requested to not occur.
+    WouldBlock,
+    /// A parameter was incorrect.
+    InvalidInput,
+    /// Data not valid for the operation were encountered.
+    ///
+    /// Unlike `InvalidInput`, this typically means that the operation
+    /// parameters were valid, however the error was caused by malformed
+    /// input data.
+    ///
+    /// For example, a function that reads a file into a string will error with
+    /// `InvalidData` if the file's contents are not valid UTF-8.
+    InvalidData,
+    /// The I/O operation's timeout expired, causing it to be canceled.
+    TimedOut,
+    /// An error returned when an operation could not be completed because a
+    /// call to `write` returned `Ok(0)`.
+    ///
+    /// This typically means that an operation could only succeed if it wrote a
+    /// particular number of bytes but only a smaller number of bytes could be
+    /// written.
+    WriteZero,
+    /// This operation was interrupted.
+    ///
+    /// Interrupted operations can typically be retried.
+    Interrupted,
+    /// Any I/O error not part of this list.
+    Other,
+
+    /// An error returned when an operation could not be completed because an
+    /// "end of file" was reached prematurely.
+    ///
+    /// This typically means that an operation could only succeed if it read a
+    /// particular number of bytes but only a smaller number of bytes could be
+    /// read.
+    UnexpectedEof,
+
+    /// Any I/O error not part of this list.
+    #[doc(hidden)]
+    __Nonexhaustive,
+}
+
+impl Error {
+    /// Creates a new I/O error from a known kind of error as well as an
+    /// arbitrary error payload.
+    ///
+    /// This function is used to generically create I/O errors which do not
+    /// originate from the OS itself. The `error` argument is an arbitrary
+    /// payload which will be contained in this `Error`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::io::{Error, ErrorKind};
+    ///
+    /// // errors can be created from strings
+    /// let custom_error = Error::new(ErrorKind::Other, "oh no!");
+    ///
+    /// // errors can also be created from other errors
+    /// let custom_error2 = Error::new(ErrorKind::Interrupted, custom_error);
+    /// ```
+    pub fn new<E>(kind: ErrorKind, error: E) -> Error
+        where E: Into<Box<error::Error+Send+Sync>>
+    {
+        Self::_new(kind, error.into())
+    }
+
+    fn _new(kind: ErrorKind, error: Box<error::Error+Send+Sync>) -> Error {
+        Error {
+            repr: Repr::Custom(Box::new(Custom {
+                kind: kind,
+                error: error,
+            }))
+        }
+    }
+
+    /// Creates a new instance of an `Error` from a particular OS error code.
+    pub fn from_raw_os_error(code: i32) -> Error {
+        Error { repr: Repr::Os(code) }
+    }
+
+    /// Returns the OS error that this error represents (if any).
+    ///
+    /// If this `Error` was constructed via `last_os_error` or
+    /// `from_raw_os_error`, then this function will return `Some`, otherwise
+    /// it will return `None`.
+    pub fn raw_os_error(&self) -> Option<i32> {
+        match self.repr {
+            Repr::Os(i) => Some(i),
+            Repr::Custom(..) => None,
+        }
+    }
+
+    /// Returns a reference to the inner error wrapped by this error (if any).
+    ///
+    /// If this `Error` was constructed via `new` then this function will
+    /// return `Some`, otherwise it will return `None`.
+    pub fn get_ref(&self) -> Option<&(error::Error+Send+Sync+'static)> {
+        match self.repr {
+            Repr::Os(..) => None,
+            Repr::Custom(ref c) => Some(&*c.error),
+        }
+    }
+
+    /// Returns a mutable reference to the inner error wrapped by this error
+    /// (if any).
+    ///
+    /// If this `Error` was constructed via `new` then this function will
+    /// return `Some`, otherwise it will return `None`.
+    pub fn get_mut(&mut self) -> Option<&mut (error::Error+Send+Sync+'static)> {
+        match self.repr {
+            Repr::Os(..) => None,
+            Repr::Custom(ref mut c) => Some(&mut *c.error),
+        }
+    }
+
+    /// Consumes the `Error`, returning its inner error (if any).
+    ///
+    /// If this `Error` was constructed via `new` then this function will
+    /// return `Some`, otherwise it will return `None`.
+    pub fn into_inner(self) -> Option<Box<error::Error+Send+Sync>> {
+        match self.repr {
+            Repr::Os(..) => None,
+            Repr::Custom(c) => Some(c.error)
+        }
+    }
+
+    /// Returns the corresponding `ErrorKind` for this error.
+    pub fn kind(&self) -> ErrorKind {
+        match self.repr {
+            Repr::Os(_code) => ErrorKind::Other,
+            Repr::Custom(ref c) => c.kind,
+        }
+    }
+}
+
+impl fmt::Debug for Repr {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        match *self {
+            Repr::Os(ref code) =>
+                fmt.debug_struct("Os").field("code", code).finish(),
+            Repr::Custom(ref c) => fmt.debug_tuple("Custom").field(c).finish(),
+        }
+    }
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        match self.repr {
+            Repr::Os(code) => {
+                write!(fmt, "os error {}", code)
+            }
+            Repr::Custom(ref c) => c.error.fmt(fmt),
+        }
+    }
+}
+
+impl error::Error for Error {
+    fn description(&self) -> &str {
+        match self.repr {
+            Repr::Os(..) => match self.kind() {
+                ErrorKind::NotFound => "entity not found",
+                ErrorKind::PermissionDenied => "permission denied",
+                ErrorKind::ConnectionRefused => "connection refused",
+                ErrorKind::ConnectionReset => "connection reset",
+                ErrorKind::ConnectionAborted => "connection aborted",
+                ErrorKind::NotConnected => "not connected",
+                ErrorKind::AddrInUse => "address in use",
+                ErrorKind::AddrNotAvailable => "address not available",
+                ErrorKind::BrokenPipe => "broken pipe",
+                ErrorKind::AlreadyExists => "entity already exists",
+                ErrorKind::WouldBlock => "operation would block",
+                ErrorKind::InvalidInput => "invalid input parameter",
+                ErrorKind::InvalidData => "invalid data",
+                ErrorKind::TimedOut => "timed out",
+                ErrorKind::WriteZero => "write zero",
+                ErrorKind::Interrupted => "operation interrupted",
+                ErrorKind::Other => "other os error",
+                ErrorKind::UnexpectedEof => "unexpected end of file",
+                ErrorKind::__Nonexhaustive => unreachable!()
+            },
+            Repr::Custom(ref c) => c.error.description(),
+        }
+    }
+
+    fn cause(&self) -> Option<&error::Error> {
+        match self.repr {
+            Repr::Os(..) => None,
+            Repr::Custom(ref c) => c.error.cause(),
+        }
+    }
+}
+
+fn _assert_error_is_sync_send() {
+    fn _is_sync_send<T: Sync+Send>() {}
+    _is_sync_send::<Error>();
+}
+
+#[cfg(test)]
+mod test {
+    use prelude::v1::*;
+    use super::{Error, ErrorKind};
+    use error;
+    use fmt;
+    use sys::os::error_string;
+
+    #[test]
+    fn test_debug_error() {
+        let code = 6;
+        let msg = error_string(code);
+        let err = Error { repr: super::Repr::Os(code) };
+        let expected = format!("Error {{ repr: Os {{ code: {:?}, message: {:?} }} }}", code, msg);
+        assert_eq!(format!("{:?}", err), expected);
+    }
+
+    #[test]
+    fn test_downcasting() {
+        #[derive(Debug)]
+        struct TestError;
+
+        impl fmt::Display for TestError {
+            fn fmt(&self, _: &mut fmt::Formatter) -> fmt::Result {
+                Ok(())
+            }
+        }
+
+        impl error::Error for TestError {
+            fn description(&self) -> &str {
+                "asdf"
+            }
+        }
+
+        // we have to call all of these UFCS style right now since method
+        // resolution won't implicitly drop the Send+Sync bounds
+        let mut err = Error::new(ErrorKind::Other, TestError);
+        assert!(err.get_ref().unwrap().is::<TestError>());
+        assert_eq!("asdf", err.get_ref().unwrap().description());
+        assert!(err.get_mut().unwrap().is::<TestError>());
+        let extracted = err.into_inner().unwrap();
+        extracted.downcast::<TestError>().unwrap();
+    }
+}