Auto merge of #58357 - sfackler:vectored-io, r=alexcrichton

Add vectored read and write support

This functionality has lived for a while in the tokio ecosystem, where
it can improve performance by minimizing copies.

r? @alexcrichton

22 files changed, 525 insertions, 81 deletions

diff --git a/src/libstd/sys/cloudabi/io.rs b/src/libstd/sys/cloudabi/io.rs
new file mode 100644
index 00000000000..8b02d3fd19d
--- /dev/null
+++ b/src/libstd/sys/cloudabi/io.rs
@@ -0,0 +1,32 @@
+pub struct IoVec<'a>(&'a [u8]);
+
+impl<'a> IoVec<'a> {
+    #[inline]
+    pub fn new(buf: &'a [u8]) -> IoVec<'a> {
+        IoVec(buf)
+    }
+
+    #[inline]
+    pub fn as_slice(&self) -> &[u8] {
+        self.0
+    }
+}
+
+pub struct IoVecMut<'a>(&'a mut [u8]);
+
+impl<'a> IoVecMut<'a> {
+    #[inline]
+    pub fn new(buf: &'a mut [u8]) -> IoVecMut<'a> {
+        IoVecMut(buf)
+    }
+
+    #[inline]
+    pub fn as_slice(&self) -> &[u8] {
+        self.0
+    }
+
+    #[inline]
+    pub fn as_mut_slice(&mut self) -> &mut [u8] {
+        self.0
+    }
+}
diff --git a/src/libstd/sys/cloudabi/mod.rs b/src/libstd/sys/cloudabi/mod.rs
index cd621b76945..d9bc21861c9 100644
--- a/src/libstd/sys/cloudabi/mod.rs
+++ b/src/libstd/sys/cloudabi/mod.rs
@@ -1,4 +1,3 @@
-use io;
 use libc;
 use mem;
 
@@ -10,6 +9,7 @@ pub mod backtrace;
 #[path = "../unix/cmath.rs"]
 pub mod cmath;
 pub mod condvar;
+pub mod io;
 #[path = "../unix/memchr.rs"]
 pub mod memchr;
 pub mod mutex;
@@ -32,24 +32,24 @@ pub use self::shims::*;
 #[allow(dead_code)]
 pub fn init() {}
 
-pub fn decode_error_kind(errno: i32) -> io::ErrorKind {
+pub fn decode_error_kind(errno: i32) -> ::io::ErrorKind {
     match errno {
-        x if x == abi::errno::ACCES as i32 => io::ErrorKind::PermissionDenied,
-        x if x == abi::errno::ADDRINUSE as i32 => io::ErrorKind::AddrInUse,
-        x if x == abi::errno::ADDRNOTAVAIL as i32 => io::ErrorKind::AddrNotAvailable,
-        x if x == abi::errno::AGAIN as i32 => io::ErrorKind::WouldBlock,
-        x if x == abi::errno::CONNABORTED as i32 => io::ErrorKind::ConnectionAborted,
-        x if x == abi::errno::CONNREFUSED as i32 => io::ErrorKind::ConnectionRefused,
-        x if x == abi::errno::CONNRESET as i32 => io::ErrorKind::ConnectionReset,
-        x if x == abi::errno::EXIST as i32 => io::ErrorKind::AlreadyExists,
-        x if x == abi::errno::INTR as i32 => io::ErrorKind::Interrupted,
-        x if x == abi::errno::INVAL as i32 => io::ErrorKind::InvalidInput,
-        x if x == abi::errno::NOENT as i32 => io::ErrorKind::NotFound,
-        x if x == abi::errno::NOTCONN as i32 => io::ErrorKind::NotConnected,
-        x if x == abi::errno::PERM as i32 => io::ErrorKind::PermissionDenied,
-        x if x == abi::errno::PIPE as i32 => io::ErrorKind::BrokenPipe,
-        x if x == abi::errno::TIMEDOUT as i32 => io::ErrorKind::TimedOut,
-        _ => io::ErrorKind::Other,
+        x if x == abi::errno::ACCES as i32 => ::io::ErrorKind::PermissionDenied,
+        x if x == abi::errno::ADDRINUSE as i32 => ::io::ErrorKind::AddrInUse,
+        x if x == abi::errno::ADDRNOTAVAIL as i32 => ::io::ErrorKind::AddrNotAvailable,
+        x if x == abi::errno::AGAIN as i32 => ::io::ErrorKind::WouldBlock,
+        x if x == abi::errno::CONNABORTED as i32 => ::io::ErrorKind::ConnectionAborted,
+        x if x == abi::errno::CONNREFUSED as i32 => ::io::ErrorKind::ConnectionRefused,
+        x if x == abi::errno::CONNRESET as i32 => ::io::ErrorKind::ConnectionReset,
+        x if x == abi::errno::EXIST as i32 => ::io::ErrorKind::AlreadyExists,
+        x if x == abi::errno::INTR as i32 => ::io::ErrorKind::Interrupted,
+        x if x == abi::errno::INVAL as i32 => ::io::ErrorKind::InvalidInput,
+        x if x == abi::errno::NOENT as i32 => ::io::ErrorKind::NotFound,
+        x if x == abi::errno::NOTCONN as i32 => ::io::ErrorKind::NotConnected,
+        x if x == abi::errno::PERM as i32 => ::io::ErrorKind::PermissionDenied,
+        x if x == abi::errno::PIPE as i32 => ::io::ErrorKind::BrokenPipe,
+        x if x == abi::errno::TIMEDOUT as i32 => ::io::ErrorKind::TimedOut,
+        _ => ::io::ErrorKind::Other,
     }
 }
 
diff --git a/src/libstd/sys/cloudabi/shims/net.rs b/src/libstd/sys/cloudabi/shims/net.rs
index b4caa899a75..869a0ef87a7 100644
--- a/src/libstd/sys/cloudabi/shims/net.rs
+++ b/src/libstd/sys/cloudabi/shims/net.rs
@@ -1,5 +1,5 @@
 use fmt;
-use io;
+use io::{self, IoVec, IoVecMut};
 use net::{Ipv4Addr, Ipv6Addr, Shutdown, SocketAddr};
 use time::Duration;
 use sys::{unsupported, Void};
@@ -42,10 +42,18 @@ impl TcpStream {
         match self.0 {}
     }
 
+    pub fn read_vectored(&self, _: &mut [IoVecMut<'_>]) -> io::Result<usize> {
+        match self.0 {}
+    }
+
     pub fn write(&self, _: &[u8]) -> io::Result<usize> {
         match self.0 {}
     }
 
+    pub fn write_vectored(&self, _: &[IoVec<'_>]) -> io::Result<usize> {
+        match self.0 {}
+    }
+
     pub fn peer_addr(&self) -> io::Result<SocketAddr> {
         match self.0 {}
     }
diff --git a/src/libstd/sys/redox/io.rs b/src/libstd/sys/redox/io.rs
new file mode 100644
index 00000000000..8b02d3fd19d
--- /dev/null
+++ b/src/libstd/sys/redox/io.rs
@@ -0,0 +1,32 @@
+pub struct IoVec<'a>(&'a [u8]);
+
+impl<'a> IoVec<'a> {
+    #[inline]
+    pub fn new(buf: &'a [u8]) -> IoVec<'a> {
+        IoVec(buf)
+    }
+
+    #[inline]
+    pub fn as_slice(&self) -> &[u8] {
+        self.0
+    }
+}
+
+pub struct IoVecMut<'a>(&'a mut [u8]);
+
+impl<'a> IoVecMut<'a> {
+    #[inline]
+    pub fn new(buf: &'a mut [u8]) -> IoVecMut<'a> {
+        IoVecMut(buf)
+    }
+
+    #[inline]
+    pub fn as_slice(&self) -> &[u8] {
+        self.0
+    }
+
+    #[inline]
+    pub fn as_mut_slice(&mut self) -> &mut [u8] {
+        self.0
+    }
+}
diff --git a/src/libstd/sys/redox/mod.rs b/src/libstd/sys/redox/mod.rs
index c106db8ddfa..c3878349bb3 100644
--- a/src/libstd/sys/redox/mod.rs
+++ b/src/libstd/sys/redox/mod.rs
@@ -1,6 +1,6 @@
 #![allow(dead_code, missing_docs, nonstandard_style)]
 
-use io::{self, ErrorKind};
+use ::io::{ErrorKind};
 
 pub use libc::strlen;
 pub use self::rand::hashmap_random_keys;
@@ -17,6 +17,7 @@ pub mod ext;
 pub mod fast_thread_local;
 pub mod fd;
 pub mod fs;
+pub mod io;
 pub mod memchr;
 pub mod mutex;
 pub mod net;
@@ -63,8 +64,8 @@ pub fn decode_error_kind(errno: i32) -> ErrorKind {
     }
 }
 
-pub fn cvt(result: Result<usize, syscall::Error>) -> io::Result<usize> {
-    result.map_err(|err| io::Error::from_raw_os_error(err.errno))
+pub fn cvt(result: Result<usize, syscall::Error>) -> ::io::Result<usize> {
+    result.map_err(|err| ::io::Error::from_raw_os_error(err.errno))
 }
 
 #[doc(hidden)]
@@ -82,9 +83,9 @@ macro_rules! impl_is_minus_one {
 
 impl_is_minus_one! { i8 i16 i32 i64 isize }
 
-pub fn cvt_libc<T: IsMinusOne>(t: T) -> io::Result<T> {
+pub fn cvt_libc<T: IsMinusOne>(t: T) -> ::io::Result<T> {
     if t.is_minus_one() {
-        Err(io::Error::last_os_error())
+        Err(::io::Error::last_os_error())
     } else {
         Ok(t)
     }
diff --git a/src/libstd/sys/redox/net/tcp.rs b/src/libstd/sys/redox/net/tcp.rs
index e0353b130bb..abb9f72c324 100644
--- a/src/libstd/sys/redox/net/tcp.rs
+++ b/src/libstd/sys/redox/net/tcp.rs
@@ -1,5 +1,5 @@
 use cmp;
-use io::{self, Error, ErrorKind, Result};
+use io::{self, Error, ErrorKind, Result, IoVec, IoVecMut};
 use mem;
 use net::{SocketAddr, Shutdown};
 use path::Path;
@@ -34,10 +34,24 @@ impl TcpStream {
         self.0.read(buf)
     }
 
+    pub fn read_vectored(&self, bufs: &mut [IoVecMut<'_>]) -> io::Result<usize> {
+        match bufs.iter_mut().find(|b| !b.is_empty()) {
+            Some(buf) => self.read(buf),
+            None => Ok(0),
+        }
+    }
+
     pub fn write(&self, buf: &[u8]) -> Result<usize> {
         self.0.write(buf)
     }
 
+    pub fn write_vectored(&self, bufs: &[IoVec<'_>]) -> io::Result<usize> {
+        match bufs.iter().find(|b| !b.is_empty()) {
+            Some(buf) => self.write(buf),
+            None => Ok(0),
+        }
+    }
+
     pub fn take_error(&self) -> Result<Option<Error>> {
         Ok(None)
     }
diff --git a/src/libstd/sys/sgx/io.rs b/src/libstd/sys/sgx/io.rs
new file mode 100644
index 00000000000..8b02d3fd19d
--- /dev/null
+++ b/src/libstd/sys/sgx/io.rs
@@ -0,0 +1,32 @@
+pub struct IoVec<'a>(&'a [u8]);
+
+impl<'a> IoVec<'a> {
+    #[inline]
+    pub fn new(buf: &'a [u8]) -> IoVec<'a> {
+        IoVec(buf)
+    }
+
+    #[inline]
+    pub fn as_slice(&self) -> &[u8] {
+        self.0
+    }
+}
+
+pub struct IoVecMut<'a>(&'a mut [u8]);
+
+impl<'a> IoVecMut<'a> {
+    #[inline]
+    pub fn new(buf: &'a mut [u8]) -> IoVecMut<'a> {
+        IoVecMut(buf)
+    }
+
+    #[inline]
+    pub fn as_slice(&self) -> &[u8] {
+        self.0
+    }
+
+    #[inline]
+    pub fn as_mut_slice(&mut self) -> &mut [u8] {
+        self.0
+    }
+}
diff --git a/src/libstd/sys/sgx/mod.rs b/src/libstd/sys/sgx/mod.rs
index 4225ecbb206..403dd61187f 100644
--- a/src/libstd/sys/sgx/mod.rs
+++ b/src/libstd/sys/sgx/mod.rs
@@ -3,7 +3,6 @@
 //! This module contains the facade (aka platform-specific) implementations of
 //! OS level functionality for Fortanix SGX.
 
-use io;
 use os::raw::c_char;
 use sync::atomic::{AtomicBool, Ordering};
 
@@ -20,6 +19,7 @@ pub mod env;
 pub mod ext;
 pub mod fd;
 pub mod fs;
+pub mod io;
 pub mod memchr;
 pub mod mutex;
 pub mod net;
@@ -41,12 +41,12 @@ pub fn init() {
 
 /// This function is used to implement functionality that simply doesn't exist.
 /// Programs relying on this functionality will need to deal with the error.
-pub fn unsupported<T>() -> io::Result<T> {
+pub fn unsupported<T>() -> ::io::Result<T> {
     Err(unsupported_err())
 }
 
-pub fn unsupported_err() -> io::Error {
-    io::Error::new(io::ErrorKind::Other,
+pub fn unsupported_err() -> ::io::Error {
+    ::io::Error::new(::io::ErrorKind::Other,
                    "operation not supported on SGX yet")
 }
 
@@ -55,58 +55,58 @@ pub fn unsupported_err() -> io::Error {
 /// returned, the program might very well be able to function normally. This is
 /// what happens when `SGX_INEFFECTIVE_ERROR` is set to `true`. If it is
 /// `false`, the behavior is the same as `unsupported`.
-pub fn sgx_ineffective<T>(v: T) -> io::Result<T> {
+pub fn sgx_ineffective<T>(v: T) -> ::io::Result<T> {
     static SGX_INEFFECTIVE_ERROR: AtomicBool = AtomicBool::new(false);
     if SGX_INEFFECTIVE_ERROR.load(Ordering::Relaxed) {
-        Err(io::Error::new(io::ErrorKind::Other,
+        Err(::io::Error::new(::io::ErrorKind::Other,
                        "operation can't be trusted to have any effect on SGX"))
     } else {
         Ok(v)
     }
 }
 
-pub fn decode_error_kind(code: i32) -> io::ErrorKind {
+pub fn decode_error_kind(code: i32) -> ::io::ErrorKind {
     use fortanix_sgx_abi::Error;
 
     // FIXME: not sure how to make sure all variants of Error are covered
     if code == Error::NotFound as _ {
-        io::ErrorKind::NotFound
+        ::io::ErrorKind::NotFound
     } else if code == Error::PermissionDenied as _ {
-        io::ErrorKind::PermissionDenied
+        ::io::ErrorKind::PermissionDenied
     } else if code == Error::ConnectionRefused as _ {
-        io::ErrorKind::ConnectionRefused
+        ::io::ErrorKind::ConnectionRefused
     } else if code == Error::ConnectionReset as _ {
-        io::ErrorKind::ConnectionReset
+        ::io::ErrorKind::ConnectionReset
     } else if code == Error::ConnectionAborted as _ {
-        io::ErrorKind::ConnectionAborted
+        ::io::ErrorKind::ConnectionAborted
     } else if code == Error::NotConnected as _ {
-        io::ErrorKind::NotConnected
+        ::io::ErrorKind::NotConnected
     } else if code == Error::AddrInUse as _ {
-        io::ErrorKind::AddrInUse
+        ::io::ErrorKind::AddrInUse
     } else if code == Error::AddrNotAvailable as _ {
-        io::ErrorKind::AddrNotAvailable
+        ::io::ErrorKind::AddrNotAvailable
     } else if code == Error::BrokenPipe as _ {
-        io::ErrorKind::BrokenPipe
+        ::io::ErrorKind::BrokenPipe
     } else if code == Error::AlreadyExists as _ {
-        io::ErrorKind::AlreadyExists
+        ::io::ErrorKind::AlreadyExists
     } else if code == Error::WouldBlock as _ {
-        io::ErrorKind::WouldBlock
+        ::io::ErrorKind::WouldBlock
     } else if code == Error::InvalidInput as _ {
-        io::ErrorKind::InvalidInput
+        ::io::ErrorKind::InvalidInput
     } else if code == Error::InvalidData as _ {
-        io::ErrorKind::InvalidData
+        ::io::ErrorKind::InvalidData
     } else if code == Error::TimedOut as _ {
-        io::ErrorKind::TimedOut
+        ::io::ErrorKind::TimedOut
     } else if code == Error::WriteZero as _ {
-        io::ErrorKind::WriteZero
+        ::io::ErrorKind::WriteZero
     } else if code == Error::Interrupted as _ {
-        io::ErrorKind::Interrupted
+        ::io::ErrorKind::Interrupted
     } else if code == Error::Other as _ {
-        io::ErrorKind::Other
+        ::io::ErrorKind::Other
     } else if code == Error::UnexpectedEof as _ {
-        io::ErrorKind::UnexpectedEof
+        ::io::ErrorKind::UnexpectedEof
     } else {
-        io::ErrorKind::Other
+        ::io::ErrorKind::Other
     }
 }
 
diff --git a/src/libstd/sys/sgx/net.rs b/src/libstd/sys/sgx/net.rs
index 6e86b06b286..c4c2de43ff7 100644
--- a/src/libstd/sys/sgx/net.rs
+++ b/src/libstd/sys/sgx/net.rs
@@ -1,5 +1,5 @@
 use fmt;
-use io;
+use io::{self, IoVec, IoVecMut};
 use net::{SocketAddr, Shutdown, Ipv4Addr, Ipv6Addr, ToSocketAddrs};
 use time::Duration;
 use sys::{unsupported, Void, sgx_ineffective, AsInner, FromInner, IntoInner, TryIntoInner};
@@ -103,10 +103,26 @@ impl TcpStream {
         self.inner.inner.read(buf)
     }
 
+    pub fn read_vectored(&self, buf: &mut [IoVecMut<'_>]) -> io::Result<usize> {
+        let buf = match buf.get_mut(0) {
+            Some(buf) => buf,
+            None => return Ok(0),
+        };
+        self.read(buf)
+    }
+
     pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
         self.inner.inner.write(buf)
     }
 
+    pub fn write_vectored(&self, buf: &[IoVec<'_>]) -> io::Result<usize> {
+        let buf = match buf.get(0) {
+            Some(buf) => buf,
+            None => return Ok(0),
+        };
+        self.write(buf)
+    }
+
     pub fn peer_addr(&self) -> io::Result<SocketAddr> {
         addr_to_sockaddr(&self.peer_addr)
     }
diff --git a/src/libstd/sys/unix/ext/net.rs b/src/libstd/sys/unix/ext/net.rs
index acc064acfcd..4b60ea654c1 100644
--- a/src/libstd/sys/unix/ext/net.rs
+++ b/src/libstd/sys/unix/ext/net.rs
@@ -18,7 +18,7 @@ mod libc {
 use ascii;
 use ffi::OsStr;
 use fmt;
-use io::{self, Initializer};
+use io::{self, Initializer, IoVec, IoVecMut};
 use mem;
 use net::{self, Shutdown};
 use os::unix::ffi::OsStrExt;
@@ -551,6 +551,10 @@ impl io::Read for UnixStream {
         io::Read::read(&mut &*self, buf)
     }
 
+    fn read_vectored(&mut self, bufs: &mut [IoVecMut<'_>]) -> io::Result<usize> {
+        io::Read::read_vectored(&mut &*self, bufs)
+    }
+
     #[inline]
     unsafe fn initializer(&self) -> Initializer {
         Initializer::nop()
@@ -563,6 +567,10 @@ impl<'a> io::Read for &'a UnixStream {
         self.0.read(buf)
     }
 
+    fn read_vectored(&mut self, bufs: &mut [IoVecMut<'_>]) -> io::Result<usize> {
+        self.0.read_vectored(bufs)
+    }
+
     #[inline]
     unsafe fn initializer(&self) -> Initializer {
         Initializer::nop()
@@ -575,6 +583,10 @@ impl io::Write for UnixStream {
         io::Write::write(&mut &*self, buf)
     }
 
+    fn write_vectored(&mut self, bufs: &[IoVec<'_>]) -> io::Result<usize> {
+        io::Write::write_vectored(&mut &*self, bufs)
+    }
+
     fn flush(&mut self) -> io::Result<()> {
         io::Write::flush(&mut &*self)
     }
@@ -586,6 +598,10 @@ impl<'a> io::Write for &'a UnixStream {
         self.0.write(buf)
     }
 
+    fn write_vectored(&mut self, bufs: &[IoVec<'_>]) -> io::Result<usize> {
+        self.0.write_vectored(bufs)
+    }
+
     fn flush(&mut self) -> io::Result<()> {
         Ok(())
     }
@@ -1511,6 +1527,25 @@ mod test {
     }
 
     #[test]
+    fn vectored() {
+        let (mut s1, mut s2) = or_panic!(UnixStream::pair());
+
+        let len = or_panic!(s1.write_vectored(
+            &[IoVec::new(b"hello"), IoVec::new(b" "), IoVec::new(b"world!")],
+        ));
+        assert_eq!(len, 12);
+
+        let mut buf1 = [0; 6];
+        let mut buf2 = [0; 7];
+        let len = or_panic!(s2.read_vectored(
+            &mut [IoVecMut::new(&mut buf1), IoVecMut::new(&mut buf2)],
+        ));
+        assert_eq!(len, 12);
+        assert_eq!(&buf1, b"hello ");
+        assert_eq!(&buf2, b"world!\0");
+    }
+
+    #[test]
     fn pair() {
         let msg1 = b"hello";
         let msg2 = b"world!";
diff --git a/src/libstd/sys/unix/fd.rs b/src/libstd/sys/unix/fd.rs
index 2cbd9536f4d..6946b7b5dfa 100644
--- a/src/libstd/sys/unix/fd.rs
+++ b/src/libstd/sys/unix/fd.rs
@@ -1,7 +1,7 @@
 #![unstable(reason = "not public", issue = "0", feature = "fd")]
 
 use cmp;
-use io::{self, Read, Initializer};
+use io::{self, Read, Initializer, IoVec, IoVecMut};
 use libc::{self, c_int, c_void, ssize_t};
 use mem;
 use sync::atomic::{AtomicBool, Ordering};
@@ -52,6 +52,15 @@ impl FileDesc {
         Ok(ret as usize)
     }
 
+    pub fn read_vectored(&self, bufs: &mut [IoVecMut<'_>]) -> io::Result<usize> {
+        let ret = cvt(unsafe {
+            libc::readv(self.fd,
+                        bufs.as_ptr() as *const libc::iovec,
+                        cmp::min(bufs.len(), c_int::max_value() as usize) as c_int)
+        })?;
+        Ok(ret as usize)
+    }
+
     pub fn read_to_end(&self, buf: &mut Vec<u8>) -> io::Result<usize> {
         let mut me = self;
         (&mut me).read_to_end(buf)
@@ -105,6 +114,15 @@ impl FileDesc {
         Ok(ret as usize)
     }
 
+    pub fn write_vectored(&self, bufs: &[IoVec<'_>]) -> io::Result<usize> {
+        let ret = cvt(unsafe {
+            libc::writev(self.fd,
+                         bufs.as_ptr() as *const libc::iovec,
+                         cmp::min(bufs.len(), c_int::max_value() as usize) as c_int)
+        })?;
+        Ok(ret as usize)
+    }
+
     pub fn write_at(&self, buf: &[u8], offset: u64) -> io::Result<usize> {
         #[cfg(target_os = "android")]
         use super::android::cvt_pwrite64;
diff --git a/src/libstd/sys/unix/io.rs b/src/libstd/sys/unix/io.rs
new file mode 100644
index 00000000000..65e4c6e0577
--- /dev/null
+++ b/src/libstd/sys/unix/io.rs
@@ -0,0 +1,61 @@
+use marker::PhantomData;
+use libc::{iovec, c_void};
+use slice;
+
+#[repr(transparent)]
+pub struct IoVec<'a> {
+    vec: iovec,
+    _p: PhantomData<&'a [u8]>,
+}
+
+impl<'a> IoVec<'a> {
+    #[inline]
+    pub fn new(buf: &'a [u8]) -> IoVec<'a> {
+        IoVec {
+            vec: iovec {
+                iov_base: buf.as_ptr() as *mut u8 as *mut c_void,
+                iov_len: buf.len()
+            },
+            _p: PhantomData,
+        }
+    }
+
+    #[inline]
+    pub fn as_slice(&self) -> &[u8] {
+        unsafe {
+            slice::from_raw_parts(self.vec.iov_base as *mut u8, self.vec.iov_len)
+        }
+    }
+}
+
+pub struct IoVecMut<'a> {
+    vec: iovec,
+    _p: PhantomData<&'a mut [u8]>,
+}
+
+impl<'a> IoVecMut<'a> {
+    #[inline]
+    pub fn new(buf: &'a mut [u8]) -> IoVecMut<'a> {
+        IoVecMut {
+            vec: iovec {
+                iov_base: buf.as_mut_ptr() as *mut c_void,
+                iov_len: buf.len()
+            },
+            _p: PhantomData,
+        }
+    }
+
+    #[inline]
+    pub fn as_slice(&self) -> &[u8] {
+        unsafe {
+            slice::from_raw_parts(self.vec.iov_base as *mut u8, self.vec.iov_len)
+        }
+    }
+
+    #[inline]
+    pub fn as_mut_slice(&mut self) -> &mut [u8] {
+        unsafe {
+            slice::from_raw_parts_mut(self.vec.iov_base as *mut u8, self.vec.iov_len)
+        }
+    }
+}
diff --git a/src/libstd/sys/unix/l4re.rs b/src/libstd/sys/unix/l4re.rs
index 48037310c8d..4775e29fb57 100644
--- a/src/libstd/sys/unix/l4re.rs
+++ b/src/libstd/sys/unix/l4re.rs
@@ -5,7 +5,7 @@ macro_rules! unimpl {
 pub mod net {
     #![allow(warnings)]
     use fmt;
-    use io;
+    use io::{self, IoVec, IoVecMut};
     use libc;
     use net::{SocketAddr, Shutdown, Ipv4Addr, Ipv6Addr};
     use sys_common::{AsInner, FromInner, IntoInner};
@@ -46,6 +46,10 @@ pub mod net {
             unimpl!();
         }
 
+        pub fn read_vectored(&self, _: &mut [IoVecMut<'_>]) -> io::Result<usize> {
+            unimpl!();
+        }
+
         pub fn peek(&self, _: &mut [u8]) -> io::Result<usize> {
             unimpl!();
         }
@@ -62,6 +66,10 @@ pub mod net {
             unimpl!();
         }
 
+        pub fn write_vectored(&self, _: &[IoVec<'_>]) -> io::Result<usize> {
+            unimpl!();
+        }
+
         pub fn set_timeout(&self, _: Option<Duration>, _: libc::c_int) -> io::Result<()> {
             unimpl!();
         }
@@ -144,10 +152,18 @@ pub mod net {
             unimpl!();
         }
 
+        pub fn read_vectored(&self, _: &mut [IoVecMut<'_>]) -> io::Result<usize> {
+            unimpl!();
+        }
+
         pub fn write(&self, _: &[u8]) -> io::Result<usize> {
             unimpl!();
         }
 
+        pub fn write_vectored(&self, _: &[IoVec<'_>]) -> io::Result<usize> {
+            unimpl!();
+        }
+
         pub fn peer_addr(&self) -> io::Result<SocketAddr> {
             unimpl!();
         }
diff --git a/src/libstd/sys/unix/mod.rs b/src/libstd/sys/unix/mod.rs
index b36c117fd09..0de1a223fbd 100644
--- a/src/libstd/sys/unix/mod.rs
+++ b/src/libstd/sys/unix/mod.rs
@@ -1,6 +1,6 @@
 #![allow(missing_docs, nonstandard_style)]
 
-use io::{self, ErrorKind};
+use io::ErrorKind;
 use libc;
 
 #[cfg(any(rustdoc, target_os = "linux"))] pub use os::linux as platform;
@@ -39,6 +39,7 @@ pub mod fast_thread_local;
 pub mod fd;
 pub mod fs;
 pub mod memchr;
+pub mod io;
 pub mod mutex;
 #[cfg(not(target_os = "l4re"))]
 pub mod net;
@@ -126,15 +127,15 @@ macro_rules! impl_is_minus_one {
 
 impl_is_minus_one! { i8 i16 i32 i64 isize }
 
-pub fn cvt<T: IsMinusOne>(t: T) -> io::Result<T> {
+pub fn cvt<T: IsMinusOne>(t: T) -> ::io::Result<T> {
     if t.is_minus_one() {
-        Err(io::Error::last_os_error())
+        Err(::io::Error::last_os_error())
     } else {
         Ok(t)
     }
 }
 
-pub fn cvt_r<T, F>(mut f: F) -> io::Result<T>
+pub fn cvt_r<T, F>(mut f: F) -> ::io::Result<T>
     where T: IsMinusOne,
           F: FnMut() -> T
 {
diff --git a/src/libstd/sys/unix/net.rs b/src/libstd/sys/unix/net.rs
index d780d71c376..521d9b42517 100644
--- a/src/libstd/sys/unix/net.rs
+++ b/src/libstd/sys/unix/net.rs
@@ -1,5 +1,5 @@
 use ffi::CStr;
-use io;
+use io::{self, IoVec, IoVecMut};
 use libc::{self, c_int, c_void, size_t, sockaddr, socklen_t, EAI_SYSTEM, MSG_PEEK};
 use mem;
 use net::{SocketAddr, Shutdown};
@@ -241,6 +241,10 @@ impl Socket {
         self.recv_with_flags(buf, MSG_PEEK)
     }
 
+    pub fn read_vectored(&self, bufs: &mut [IoVecMut<'_>]) -> io::Result<usize> {
+        self.0.read_vectored(bufs)
+    }
+
     fn recv_from_with_flags(&self, buf: &mut [u8], flags: c_int)
                             -> io::Result<(usize, SocketAddr)> {
         let mut storage: libc::sockaddr_storage = unsafe { mem::zeroed() };
@@ -269,6 +273,10 @@ impl Socket {
         self.0.write(buf)
     }
 
+    pub fn write_vectored(&self, bufs: &[IoVec<'_>]) -> io::Result<usize> {
+        self.0.write_vectored(bufs)
+    }
+
     pub fn set_timeout(&self, dur: Option<Duration>, kind: libc::c_int) -> io::Result<()> {
         let timeout = match dur {
             Some(dur) => {
diff --git a/src/libstd/sys/wasm/io.rs b/src/libstd/sys/wasm/io.rs
new file mode 100644
index 00000000000..8b02d3fd19d
--- /dev/null
+++ b/src/libstd/sys/wasm/io.rs
@@ -0,0 +1,32 @@
+pub struct IoVec<'a>(&'a [u8]);
+
+impl<'a> IoVec<'a> {
+    #[inline]
+    pub fn new(buf: &'a [u8]) -> IoVec<'a> {
+        IoVec(buf)
+    }
+
+    #[inline]
+    pub fn as_slice(&self) -> &[u8] {
+        self.0
+    }
+}
+
+pub struct IoVecMut<'a>(&'a mut [u8]);
+
+impl<'a> IoVecMut<'a> {
+    #[inline]
+    pub fn new(buf: &'a mut [u8]) -> IoVecMut<'a> {
+        IoVecMut(buf)
+    }
+
+    #[inline]
+    pub fn as_slice(&self) -> &[u8] {
+        self.0
+    }
+
+    #[inline]
+    pub fn as_mut_slice(&mut self) -> &mut [u8] {
+        self.0
+    }
+}
diff --git a/src/libstd/sys/wasm/mod.rs b/src/libstd/sys/wasm/mod.rs
index e21455ec6da..e71c6bcd7fe 100644
--- a/src/libstd/sys/wasm/mod.rs
+++ b/src/libstd/sys/wasm/mod.rs
@@ -14,7 +14,6 @@
 //! compiling for wasm. That way it's a compile time error for something that's
 //! guaranteed to be a runtime error!
 
-use io;
 use os::raw::c_char;
 use ptr;
 use sys::os_str::Buf;
@@ -29,6 +28,7 @@ pub mod backtrace;
 pub mod cmath;
 pub mod env;
 pub mod fs;
+pub mod io;
 pub mod memchr;
 pub mod net;
 pub mod os;
@@ -63,17 +63,17 @@ cfg_if! {
 pub fn init() {
 }
 
-pub fn unsupported<T>() -> io::Result<T> {
+pub fn unsupported<T>() -> ::io::Result<T> {
     Err(unsupported_err())
 }
 
-pub fn unsupported_err() -> io::Error {
-    io::Error::new(io::ErrorKind::Other,
+pub fn unsupported_err() -> ::io::Error {
+    ::io::Error::new(::io::ErrorKind::Other,
                    "operation not supported on wasm yet")
 }
 
-pub fn decode_error_kind(_code: i32) -> io::ErrorKind {
-    io::ErrorKind::Other
+pub fn decode_error_kind(_code: i32) -> ::io::ErrorKind {
+    ::io::ErrorKind::Other
 }
 
 // This enum is used as the storage for a bunch of types which can't actually
diff --git a/src/libstd/sys/wasm/net.rs b/src/libstd/sys/wasm/net.rs
index 81e4e8255bf..d9f5d538432 100644
--- a/src/libstd/sys/wasm/net.rs
+++ b/src/libstd/sys/wasm/net.rs
@@ -1,5 +1,5 @@
 use fmt;
-use io;
+use io::{self, IoVec, IoVecMut};
 use net::{SocketAddr, Shutdown, Ipv4Addr, Ipv6Addr};
 use time::Duration;
 use sys::{unsupported, Void};
@@ -40,10 +40,18 @@ impl TcpStream {
         match self.0 {}
     }
 
+    pub fn read_vectored(&self, _: &mut [IoVecMut<'_>]) -> io::Result<usize> {
+        match self.0 {}
+    }
+
     pub fn write(&self, _: &[u8]) -> io::Result<usize> {
         match self.0 {}
     }
 
+    pub fn write_vectored(&self, _: &[IoVec<'_>]) -> io::Result<usize> {
+        match self.0 {}
+    }
+
     pub fn peer_addr(&self) -> io::Result<SocketAddr> {
         match self.0 {}
     }
diff --git a/src/libstd/sys/windows/c.rs b/src/libstd/sys/windows/c.rs
index 28fd4df386e..a78b599204b 100644
--- a/src/libstd/sys/windows/c.rs
+++ b/src/libstd/sys/windows/c.rs
@@ -57,6 +57,9 @@ pub type LPWSAPROTOCOL_INFO = *mut WSAPROTOCOL_INFO;
 pub type LPSTR = *mut CHAR;
 pub type LPWSTR = *mut WCHAR;
 pub type LPFILETIME = *mut FILETIME;
+pub type LPWSABUF = *mut WSABUF;
+pub type LPWSAOVERLAPPED = *mut c_void;
+pub type LPWSAOVERLAPPED_COMPLETION_ROUTINE = *mut c_void;
 
 pub type PCONDITION_VARIABLE = *mut CONDITION_VARIABLE;
 pub type PLARGE_INTEGER = *mut c_longlong;
@@ -325,6 +328,12 @@ pub struct WSADATA {
 }
 
 #[repr(C)]
+pub struct WSABUF {
+    pub len: ULONG,
+    pub buf: *mut CHAR,
+}
+
+#[repr(C)]
 pub struct WSAPROTOCOL_INFO {
     pub dwServiceFlags1: DWORD,
     pub dwServiceFlags2: DWORD,
@@ -988,6 +997,22 @@ extern "system" {
                                dwProcessId: DWORD,
                                lpProtocolInfo: LPWSAPROTOCOL_INFO)
                                -> c_int;
+    pub fn WSASend(s: SOCKET,
+                   lpBuffers: LPWSABUF,
+                   dwBufferCount: DWORD,
+                   lpNumberOfBytesSent: LPDWORD,
+                   dwFlags: DWORD,
+                   lpOverlapped: LPWSAOVERLAPPED,
+                   lpCompletionRoutine: LPWSAOVERLAPPED_COMPLETION_ROUTINE)
+                   -> c_int;
+    pub fn WSARecv(s: SOCKET,
+                   lpBuffers: LPWSABUF,
+                   dwBufferCount: DWORD,
+                   lpNumberOfBytesRecvd: LPDWORD,
+                   lpFlags: LPDWORD,
+                   lpOverlapped: LPWSAOVERLAPPED,
+                   lpCompletionRoutine: LPWSAOVERLAPPED_COMPLETION_ROUTINE)
+                   -> c_int;
     pub fn GetCurrentProcessId() -> DWORD;
     pub fn WSASocketW(af: c_int,
                       kind: c_int,
diff --git a/src/libstd/sys/windows/io.rs b/src/libstd/sys/windows/io.rs
new file mode 100644
index 00000000000..662e3047923
--- /dev/null
+++ b/src/libstd/sys/windows/io.rs
@@ -0,0 +1,63 @@
+use marker::PhantomData;
+use slice;
+use sys::c;
+
+#[repr(transparent)]
+pub struct IoVec<'a> {
+    vec: c::WSABUF,
+    _p: PhantomData<&'a [u8]>,
+}
+
+impl<'a> IoVec<'a> {
+    #[inline]
+    pub fn new(buf: &'a [u8]) -> IoVec<'a> {
+        assert!(buf.len() <= c::ULONG::max_value() as usize);
+        IoVec {
+            vec: c::WSABUF {
+                len: buf.len() as c::ULONG,
+                buf: buf.as_ptr() as *mut u8 as *mut c::CHAR,
+            },
+            _p: PhantomData,
+        }
+    }
+
+    #[inline]
+    pub fn as_slice(&self) -> &[u8] {
+        unsafe {
+            slice::from_raw_parts(self.vec.buf as *mut u8, self.vec.len as usize)
+        }
+    }
+}
+
+pub struct IoVecMut<'a> {
+    vec: c::WSABUF,
+    _p: PhantomData<&'a mut [u8]>,
+}
+
+impl<'a> IoVecMut<'a> {
+    #[inline]
+    pub fn new(buf: &'a mut [u8]) -> IoVecMut<'a> {
+        assert!(buf.len() <= c::ULONG::max_value() as usize);
+        IoVecMut {
+            vec: c::WSABUF {
+                len: buf.len() as c::ULONG,
+                buf: buf.as_mut_ptr() as *mut c::CHAR,
+            },
+            _p: PhantomData,
+        }
+    }
+
+    #[inline]
+    pub fn as_slice(&self) -> &[u8] {
+        unsafe {
+            slice::from_raw_parts(self.vec.buf as *mut u8, self.vec.len as usize)
+        }
+    }
+
+    #[inline]
+    pub fn as_mut_slice(&mut self) -> &mut [u8] {
+        unsafe {
+            slice::from_raw_parts_mut(self.vec.buf as *mut u8, self.vec.len as usize)
+        }
+    }
+}
diff --git a/src/libstd/sys/windows/mod.rs b/src/libstd/sys/windows/mod.rs
index e97e436efbf..56c76a169fe 100644
--- a/src/libstd/sys/windows/mod.rs
+++ b/src/libstd/sys/windows/mod.rs
@@ -2,7 +2,7 @@
 
 use ptr;
 use ffi::{OsStr, OsString};
-use io::{self, ErrorKind};
+use io::ErrorKind;
 use os::windows::ffi::{OsStrExt, OsStringExt};
 use path::PathBuf;
 use time::Duration;
@@ -26,6 +26,7 @@ pub mod ext;
 pub mod fast_thread_local;
 pub mod fs;
 pub mod handle;
+pub mod io;
 pub mod memchr;
 pub mod mutex;
 pub mod net;
@@ -75,12 +76,12 @@ pub fn decode_error_kind(errno: i32) -> ErrorKind {
     }
 }
 
-pub fn to_u16s<S: AsRef<OsStr>>(s: S) -> io::Result<Vec<u16>> {
-    fn inner(s: &OsStr) -> io::Result<Vec<u16>> {
+pub fn to_u16s<S: AsRef<OsStr>>(s: S) -> ::io::Result<Vec<u16>> {
+    fn inner(s: &OsStr) -> ::io::Result<Vec<u16>> {
         let mut maybe_result: Vec<u16> = s.encode_wide().collect();
         if maybe_result.iter().any(|&u| u == 0) {
-            return Err(io::Error::new(io::ErrorKind::InvalidInput,
-                                      "strings passed to WinAPI cannot contain NULs"));
+            return Err(::io::Error::new(::io::ErrorKind::InvalidInput,
+                                        "strings passed to WinAPI cannot contain NULs"));
         }
         maybe_result.push(0);
         Ok(maybe_result)
@@ -102,7 +103,7 @@ pub fn to_u16s<S: AsRef<OsStr>>(s: S) -> io::Result<Vec<u16>> {
 // Once the syscall has completed (errors bail out early) the second closure is
 // yielded the data which has been read from the syscall. The return value
 // from this closure is then the return value of the function.
-fn fill_utf16_buf<F1, F2, T>(mut f1: F1, f2: F2) -> io::Result<T>
+fn fill_utf16_buf<F1, F2, T>(mut f1: F1, f2: F2) -> ::io::Result<T>
     where F1: FnMut(*mut u16, c::DWORD) -> c::DWORD,
           F2: FnOnce(&[u16]) -> T
 {
@@ -134,7 +135,7 @@ fn fill_utf16_buf<F1, F2, T>(mut f1: F1, f2: F2) -> io::Result<T>
             c::SetLastError(0);
             let k = match f1(buf.as_mut_ptr(), n as c::DWORD) {
                 0 if c::GetLastError() == 0 => 0,
-                0 => return Err(io::Error::last_os_error()),
+                0 => return Err(::io::Error::last_os_error()),
                 n => n,
             } as usize;
             if k == n && c::GetLastError() == c::ERROR_INSUFFICIENT_BUFFER {
@@ -157,7 +158,7 @@ fn wide_char_to_multi_byte(code_page: u32,
                            flags: u32,
                            s: &[u16],
                            no_default_char: bool)
-                           -> io::Result<Vec<i8>> {
+                           -> ::io::Result<Vec<i8>> {
     unsafe {
         let mut size = c::WideCharToMultiByte(code_page,
                                               flags,
@@ -168,7 +169,7 @@ fn wide_char_to_multi_byte(code_page: u32,
                                               ptr::null(),
                                               ptr::null_mut());
         if size == 0 {
-            return Err(io::Error::last_os_error());
+            return Err(::io::Error::last_os_error());
         }
 
         let mut buf = Vec::with_capacity(size as usize);
@@ -185,10 +186,10 @@ fn wide_char_to_multi_byte(code_page: u32,
                                       if no_default_char { &mut used_default_char }
                                       else { ptr::null_mut() });
         if size == 0 {
-            return Err(io::Error::last_os_error());
+            return Err(::io::Error::last_os_error());
         }
         if no_default_char && used_default_char == c::TRUE {
-            return Err(io::Error::new(io::ErrorKind::InvalidData,
+            return Err(::io::Error::new(::io::ErrorKind::InvalidData,
                                       "string cannot be converted to requested code page"));
         }
 
@@ -220,9 +221,9 @@ macro_rules! impl_is_zero {
 
 impl_is_zero! { i8 i16 i32 i64 isize u8 u16 u32 u64 usize }
 
-pub fn cvt<I: IsZero>(i: I) -> io::Result<I> {
+pub fn cvt<I: IsZero>(i: I) -> ::io::Result<I> {
     if i.is_zero() {
-        Err(io::Error::last_os_error())
+        Err(::io::Error::last_os_error())
     } else {
         Ok(i)
     }
diff --git a/src/libstd/sys/windows/net.rs b/src/libstd/sys/windows/net.rs
index acda81dcde5..76be26a9d1a 100644
--- a/src/libstd/sys/windows/net.rs
+++ b/src/libstd/sys/windows/net.rs
@@ -1,7 +1,7 @@
 #![unstable(issue = "0", feature = "windows_net")]
 
 use cmp;
-use io::{self, Read};
+use io::{self, Read, IoVec, IoVecMut};
 use libc::{c_int, c_void, c_ulong, c_long};
 use mem;
 use net::{SocketAddr, Shutdown};
@@ -207,6 +207,30 @@ impl Socket {
         self.recv_with_flags(buf, 0)
     }
 
+    pub fn read_vectored(&self, bufs: &mut [IoVecMut<'_>]) -> io::Result<usize> {
+        // On unix when a socket is shut down all further reads return 0, so we
+        // do the same on windows to map a shut down socket to returning EOF.
+        let len = cmp::min(bufs.len(), c::DWORD::max_value() as usize) as c::DWORD;
+        let mut nread = 0;
+        let mut flags = 0;
+        unsafe {
+            let ret = c::WSARecv(
+                self.0,
+                bufs.as_mut_ptr() as *mut c::WSABUF,
+                len,
+                &mut nread,
+                &mut flags,
+                ptr::null_mut(),
+                ptr::null_mut(),
+            );
+            match ret {
+                0 => Ok(nread as usize),
+                _ if c::WSAGetLastError() == c::WSAESHUTDOWN => Ok(0),
+                _ => Err(last_error()),
+            }
+        }
+    }
+
     pub fn peek(&self, buf: &mut [u8]) -> io::Result<usize> {
         self.recv_with_flags(buf, c::MSG_PEEK)
     }
@@ -243,6 +267,23 @@ impl Socket {
         self.recv_from_with_flags(buf, c::MSG_PEEK)
     }
 
+    pub fn write_vectored(&self, bufs: &[IoVec<'_>]) -> io::Result<usize> {
+        let len = cmp::min(bufs.len(), c::DWORD::max_value() as usize) as c::DWORD;
+        let mut nwritten = 0;
+        unsafe {
+            cvt(c::WSASend(
+                self.0,
+                bufs.as_ptr() as *const c::WSABUF as *mut c::WSABUF,
+                len,
+                &mut nwritten,
+                0,
+                ptr::null_mut(),
+                ptr::null_mut(),
+            ))?;
+        }
+        Ok(nwritten as usize)
+    }
+
     pub fn set_timeout(&self, dur: Option<Duration>,
                        kind: c_int) -> io::Result<()> {
         let timeout = match dur {