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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 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 {
        use path::{Path, PathBuf};
        use env;
        use rand::{self, Rng};
        use fs;

        pub struct TempDir(PathBuf);

        impl TempDir {
            pub fn join(&self, path: &str) -> PathBuf {
                let TempDir(ref p) = *self;
                p.join(path)
            }

            pub fn path<'a>(&'a self) -> &'a Path {
                let TempDir(ref p) = *self;
                p
            }
        }

        impl Drop for TempDir {
            fn drop(&mut self) {
                // Gee, seeing how we're testing the fs module I sure hope that we
                // at least implement this correctly!
                let TempDir(ref p) = *self;
                fs::remove_dir_all(p).unwrap();
            }
        }

        pub fn tmpdir() -> TempDir {
            let p = env::temp_dir();
            let mut r = rand::thread_rng();
            let ret = p.join(&format!("rust-{}", r.next_u32()));
            fs::create_dir(&ret).unwrap();
            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) }
            });
        }
    }

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