core::io cleanup

[catamorphism]

Address FIXMEs in core::io:

• Unbuffered operations?
• Make seekable orthogonal
• In reader::read_chars(), handle the case where eof occurs in the middle of a Unicode char
• In reader::read_char(), make sure it's valid to return -1
• In reader::read_le_uint, deal with EOF
• Improve forwarding implementation of reader
• Restructure top-level stdin() and file_reader()
• fileflags in buffered_file_writer()
• Make stdin, stdout, stderr consts
• Figure out why stdin() is different from stdout() and stderr()
• Optimize mem_buffer::write()
• Implement read_whole_file() in a low-level way
• Improve fsync::FILE_res_sync()

[Dretch]

In addition, io::WriterUtil has these methods but there are no corresponding read methods on io::ReaderUtil:

fn write_be_u64(n: u64);
fn write_be_u32(n: u32);
fn write_be_u16(n: u16);
fn write_be_i64(n: i64);
fn write_be_i32(n: i32);
fn write_be_i16(n: i16);
fn write_le_u64(n: u64);
fn write_le_u32(n: u32);
fn write_le_u16(n: u16);
fn write_le_i64(n: i64);
fn write_le_i32(n: i32);
fn write_le_i16(n: i16);
fn write_u8(n: u8);

[acertain]

Unbuffered operations please!

[catamorphism]

Nominating for milestone 2 (backwards-compatible).

[kud1ing]

The proposed changes look similar to what Go offers:

• http://golang.org/pkg/io/
  • Closer is the interface that wraps the basic Close method.
  • Seeker is the interface that wraps the basic Seek method.
• http://golang.org/pkg/bufio/ for buffered I/O
• http://golang.org/pkg/io/ioutil/
  • ReadAll reads from r until an error or EOF and returns the data it read.

[kud1ing]

See also https://github.com/mozilla/rust/wiki/Lib-io#3-research-of-libraries-from-other-languages

[graydon]

closing as WONTFIX due to #4248 and specifically #6169