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.

3 files changed, 47 insertions, 7 deletions

diff --git a/src/libstd/sys/wasm/io.rs b/src/libstd/sys/wasm/io.rs
new file mode 100644
index 00000000000..9ee5788c580
--- /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) -> &'a [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) -> &'a [u8] {
+        self.0
+    }
+
+    #[inline]
+    pub fn as_mut_slice(&mut self) -> &'a 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 {}
     }