`std::io::Read` provides byte-order reading trait (original) (raw)

Proposal

Problem statement

The std::io::Read implementation is far too rudimentary and a real pain to work with. I haven't even found any decent third-party libraries. Take the byteorder library as an example, its code and implementation leave much to be desired.

use std::io::Cursor; use byteorder::{BigEndian, ReadBytesExt};

let mut rdr = Cursor::new(vec![2, 5, 3, 0]); // Note that we use type parameters to indicate which kind of byte order // we want! assert_eq!(517, rdr.read_u16::().unwrap()); assert_eq!(768, rdr.read_u16::().unwrap());

It's too long and troublesome to write.
Internal implementation may involve copying.

Motivating examples or use cases

Add two traits: ReadLeOrder and ReadBeOrder
The ReadLeOrder Trait is use in the context, so the byte order for reading has already been specified.

use std::io::{ Read, byte_order::ReadLeOrder };

fn test(reader: &mut Read) { let x1 = reader.read_u8()?; let x2 = reader.read_u32()?; let x3: u64 = reader.read_as()?; // Generic Support let arr: [u16; 200] = reader.read_as()?; // Generic Support }

Solution sketch

Add two traits: ReadLeOrder and ReadBeOrder
They should reside in a different module from std::io::Read, assuming it is std::io::byte_order
Specialize impl <T: std::io::Read> ReadXxOrder for T
Or only provide the generic function read_as; functions like read_u32 are unnecessary
Support for arrays and external types can utilize read_as, which may require adding the relevant trait
Minimize unnecessary copy operations

Alternatives

At a minimum, provide number byte-order reads for the standard library.
Other trait extensions are not provided.

byteorder

What happens now?

This issue contains an API change proposal (or ACP) and is part of the libs-api team feature lifecycle. Once this issue is filed, the libs-api team will review open proposals as capability becomes available. Current response times do not have a clear estimate, but may be up to several months.

Possible responses

The libs team may respond in various different ways. First, the team will consider the problem (this doesn't require any concrete solution or alternatives to have been proposed):

We think this problem seems worth solving, and the standard library might be the right place to solve it.
We think that this probably doesn't belong in the standard library.

Second, if there's a concrete solution:

We think this specific solution looks roughly right, approved, you or someone else should implement this. (Further review will still happen on the subsequent implementation PR.)
We're not sure this is the right solution, and the alternatives or other materials don't give us enough information to be sure about that. Here are some questions we have that aren't answered, or rough ideas about alternatives we'd want to see discussed.

std::io::Read provides byte-order reading trait (original) (raw)