std: Funnel read_to_end through to one location

This pushes the implementation detail of proxying `read_to_end` through to
`read_to_end_uninitialized` all the way down to the `FileDesc` and `Handle`
implementations on Unix/Windows. This way intermediate layers will also be able
to take advantage of this optimized implementation.

This commit also adds the optimized implementation for `ChildStdout` and
`ChildStderr`.

src/libstd/sys/unix/fd.rs

@@ -8,12 +8,15 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use io;
+use prelude::v1::*;
+
+use io::{self, Read};
 use libc::{self, c_int, size_t, c_void};
 use mem;
+use sync::atomic::{AtomicBool, Ordering};
 use sys::cvt;
 use sys_common::AsInner;
-use sync::atomic::{AtomicBool, Ordering};
+use sys_common::io::read_to_end_uninitialized;
 
 pub struct FileDesc {
     fd: c_int,
@@ -42,6 +45,11 @@ impl FileDesc {
         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)
+    }
+
     pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
         let ret = try!(cvt(unsafe {
             libc::write(self.fd,
@@ -118,6 +126,17 @@ impl FileDesc {
     }
 }
 
+#[unstable(reason = "not public", issue = "0", feature = "fd_read")]
+impl<'a> Read for &'a FileDesc {
+    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+        (**self).read(buf)
+    }
+
+    fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize> {
+        unsafe { read_to_end_uninitialized(self, buf) }
+    }
+}
+
 impl AsInner<c_int> for FileDesc {
     fn as_inner(&self) -> &c_int { &self.fd }
 }

src/libstd/sys/unix/fs.rs

@@ -486,6 +486,10 @@ impl File {
         self.0.read(buf)
     }
 
+    pub fn read_to_end(&self, buf: &mut Vec<u8>) -> io::Result<usize> {
+        self.0.read_to_end(buf)
+    }
+
     pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
         self.0.write(buf)
     }

src/libstd/sys/unix/net.rs

@@ -116,6 +116,10 @@ impl Socket {
         self.0.read(buf)
     }
 
+    pub fn read_to_end(&self, buf: &mut Vec<u8>) -> io::Result<usize> {
+        self.0.read_to_end(buf)
+    }
+
     pub fn set_timeout(&self, dur: Option<Duration>, kind: libc::c_int) -> io::Result<()> {
         let timeout = match dur {
             Some(dur) => {

src/libstd/sys/unix/pipe.rs

@@ -57,6 +57,10 @@ impl AnonPipe {
         self.0.read(buf)
     }
 
+    pub fn read_to_end(&self, buf: &mut Vec<u8>) -> io::Result<usize> {
+        self.0.read_to_end(buf)
+    }
+
     pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
         self.0.write(buf)
     }

src/libstd/sys/unix/stdio.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use prelude::v1::*;
+
 use io;
 use libc;
 use sys::fd::FileDesc;
@@ -25,6 +27,13 @@ impl Stdin {
         fd.into_raw();
         ret
     }
+
+    pub fn read_to_end(&self, buf: &mut Vec<u8>) -> io::Result<usize> {
+        let fd = FileDesc::new(libc::STDIN_FILENO);
+        let ret = fd.read_to_end(buf);
+        fd.into_raw();
+        ret
+    }
 }
 
 impl Stdout {