Rfcs: RFC: std::string::String could provide options about UTF BOM

[hanyuwei70]

std::string::String should :

• correctly accept byte stream with or without UTF BOM,
• when converts to &str or [u8], should be with or without UTF BOM by caller.

p.s. I am not native English speaker, so may what I describe may differ from my original meaning.

[Centril]

Hey there. Thank you for your interest in designing Rust!

I think you can find more interest in the issue if you post it over at: https://internals.rust-lang.org/ :)

[H2CO3]

String and &str are explicitly designed to store and refer to UTF-8 data, so parsing/storing/emitting a BOM doesn't quite make sense. Its use in UTF-8 text is even explicitly discouraged by the Unicode standard itself, as it's essentially useless and it also breaks ASCII-compatibility.

[SimonSapin]

Copy of my comment on https://github.com/rust-lang/rust/issues/50386#issuecomment-386035566, which was about "stripping" the BOM.

It’s not clear what is being proposed. Which APIs exactly should strip?

And more importantly, why? I tend to think of these standard library API as low-level primitives, and feel that BOM removal would tend to belong more in a higher library that might for example also support multiple encodings and detect the presence of a BOM to help pick one. And even then, maybe not always. https://docs.rs/encoding_rs/0.7.2/encoding_rs/struct.Decoder.html#impl has different methods for different use cases, only some of them remove a BOM.

[hanyuwei70]

@H2CO3 @SimonSapin
UTF8 with BOM should be accepted. What I want is just to let BOM go, not disturbing other components.
And it's rather difficult to determine BOM for it does not show up in println!.

[joshtriplett]

String shouldn't have magic treatment for any characters. It makes sense for encoding/decoding methods to have options for handling the BOM, such as those @SimonSapin mentioned, but none of that should happen internally to String.

[WiSaGaN]

We may consider adding a method like

pub fn from_utf8_with_bom(vec: Vec<u8>) -> Result<String, FromUtf8Error>

or even

pub fn from_utf8_with_optional_bom(vec: Vec<u8>) -> Result<String, FromUtf8Error>

But like comments below, this shouldn't affect String internal. And this may also just live in an external crate rather than std.