Add Read::initializer.

This is an API that allows types to indicate that they can be passed
buffers of uninitialized memory which can improve performance.

src/libstd/sys_common/io.rs

@@ -7,51 +7,8 @@
 // <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 io;
-use io::ErrorKind;
-use io::Read;
-use slice::from_raw_parts_mut;
-
 pub const DEFAULT_BUF_SIZE: usize = 8 * 1024;
 
-// Provides read_to_end functionality over an uninitialized buffer.
-// This function is unsafe because it calls the underlying
-// read function with a slice into uninitialized memory. The default
-// implementation of read_to_end for readers will zero out new memory in
-// the buf before passing it to read, but avoiding this zero can often
-// lead to a fairly significant performance win.
-//
-// Implementations using this method have to adhere to two guarantees:
-//  *  The implementation of read never reads the buffer provided.
-//  *  The implementation of read correctly reports how many bytes were written.
-pub unsafe fn read_to_end_uninitialized(r: &mut Read, buf: &mut Vec<u8>) -> io::Result<usize> {
-
-    let start_len = buf.len();
-    buf.reserve(16);
-
-    // Always try to read into the empty space of the vector (from the length to the capacity).
-    // If the vector ever fills up then we reserve an extra byte which should trigger the normal
-    // reallocation routines for the vector, which will likely double the size.
-    //
-    // This function is similar to the read_to_end function in std::io, but the logic about
-    // reservations and slicing is different enough that this is duplicated here.
-    loop {
-        if buf.len() == buf.capacity() {
-            buf.reserve(1);
-        }
-
-        let buf_slice = from_raw_parts_mut(buf.as_mut_ptr().offset(buf.len() as isize),
-                                           buf.capacity() - buf.len());
-
-        match r.read(buf_slice) {
-            Ok(0) => { return Ok(buf.len() - start_len); }
-            Ok(n) => { let len = buf.len() + n; buf.set_len(len); },
-            Err(ref e) if e.kind() == ErrorKind::Interrupted => { }
-            Err(e) => { return Err(e); }
-        }
-    }
-}
-
 #[cfg(test)]
 #[allow(dead_code)] // not used on emscripten
 pub mod test {
@@ -91,89 +48,3 @@ pub mod test {
         TempDir(ret)
     }
 }
-
-#[cfg(test)]
-mod tests {
-    use io::prelude::*;
-    use super::*;
-    use io;
-    use io::{ErrorKind, Take, Repeat, repeat};
-    use slice::from_raw_parts;
-
-    struct ErrorRepeat {
-        lr: Take<Repeat>
-    }
-
-    fn error_repeat(byte: u8, limit: u64) -> ErrorRepeat {
-        ErrorRepeat { lr: repeat(byte).take(limit) }
-    }
-
-    impl Read for ErrorRepeat {
-        fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
-            let ret = self.lr.read(buf);
-            if let Ok(0) = ret {
-                return Err(io::Error::new(ErrorKind::Other, ""))
-            }
-            ret
-        }
-    }
-
-    fn init_vec_data() -> Vec<u8> {
-        let mut vec = vec![10u8; 200];
-        unsafe { vec.set_len(0); }
-        vec
-    }
-
-    fn assert_all_eq(buf: &[u8], value: u8) {
-        for n in buf {
-            assert_eq!(*n, value);
-        }
-    }
-
-    fn validate(buf: &Vec<u8>, good_read_len: usize) {
-        assert_all_eq(buf, 1u8);
-        let cap = buf.capacity();
-        let end_slice = unsafe { from_raw_parts(buf.as_ptr().offset(good_read_len as isize),
-                                                    cap - good_read_len) };
-        assert_all_eq(end_slice, 10u8);
-    }
-
-    #[test]
-    fn read_to_end_uninit_error() {
-        let mut er = error_repeat(1,100);
-        let mut vec = init_vec_data();
-        if let Err(_) = unsafe { read_to_end_uninitialized(&mut er, &mut vec) } {
-            validate(&vec, 100);
-        } else {
-            assert!(false);
-        }
-    }
-
-    #[test]
-    fn read_to_end_uninit_zero_len_vec() {
-        let mut er = repeat(1).take(100);
-        let mut vec = Vec::new();
-        let n = unsafe{ read_to_end_uninitialized(&mut er, &mut vec).unwrap() };
-        assert_all_eq(&vec, 1u8);
-        assert_eq!(vec.len(), n);
-    }
-
-    #[test]
-    fn read_to_end_uninit_good() {
-        let mut er = repeat(1).take(100);
-        let mut vec = init_vec_data();
-        let n = unsafe{ read_to_end_uninitialized(&mut er, &mut vec).unwrap() };
-        validate(&vec, 100);
-        assert_eq!(vec.len(), n);
-    }
-
-    #[bench]
-    #[cfg_attr(target_os = "emscripten", ignore)]
-    fn bench_uninitialized(b: &mut ::test::Bencher) {
-        b.iter(|| {
-            let mut lr = repeat(1).take(10000000);
-            let mut vec = Vec::with_capacity(1024);
-            unsafe { read_to_end_uninitialized(&mut lr, &mut vec) }
-        });
-    }
-}

src/libstd/sys_common/net.rs

@@ -243,10 +243,6 @@ impl TcpStream {
         self.inner.read(buf)
     }
 
-    pub fn read_to_end(&self, buf: &mut Vec<u8>) -> io::Result<usize> {
-        self.inner.read_to_end(buf)
-    }
-
     pub fn write(&self, buf: &[u8]) -> io::Result<usize> {
         let len = cmp::min(buf.len(), <wrlen_t>::max_value() as usize) as wrlen_t;
         let ret = cvt(unsafe {