Tracking Issue for `CStr::from_bytes_until_nul` #95027

ericseppanen · 2022-03-16T22:37:56Z

Feature gate: #![feature(cstr_from_bytes_until_nul)]

This is a tracking issue for adding member fn to CStr that convert from a byte slice, without the caller needing to know where the nul byte is located within the slice.

This is intended for use in FFI calls, where a foreign function wrote a string into a Rust-allocated buffer. The existing member fns fall short in this case:

CStr::from_ptr is unsafe and may read past the end of the buffer if no nul byte is found.
CStr::from_bytes_with_nul only works if there is exactly one nul byte at the end of the slice.

The proposed new member fn (tentatively named from_bytes_until_nul) is easier and can be used safely on any byte slice.

Public API

// std::ffi:

pub struct FromBytesUntilNulError(...);

impl CStr {
    pub fn from_bytes_until_nul(bytes: &[u8]) -> Result<&CStr, FromBytesUntilNulError>;
}

Steps / History

CStr Implementation: add CStr method that accepts any slice containing a nul-terminated string #94984
Final comment period (FCP): Stabilize feature cstr_from_bytes_until_nul #107429 (comment)
Stabilization PR: Stabilize feature cstr_from_bytes_until_nul #107429

Unresolved Questions

CString API needs to be designed.
With CStr eventually revised to just be a pointer, rather than (ptr, len) pair, then this becomes a little less good. See add CStr method that accepts any slice containing a nul-terminated string #94984 (comment) for details.

The text was updated successfully, but these errors were encountered:

Stargateur · 2022-08-01T13:50:14Z

CStr::from_bytes_with_nul only works if there is exactly one nul byte at the end of the slice.

That a better doc that real doc

ensuring that the byte slice is nul-terminated and does not contain any interior nul bytes.

for exemple, [97, 98, 99, 100, 0, 0, 0, 0] could be interpreted as no interior nul bytes unlike the example b"he\0llo\0".

jimblandy · 2022-10-06T18:24:42Z

We could have avoided the unsafe block that led to gfx-rs/wgpu#3076 by using this function. I hope it gets stabilized.

tgross35 · 2023-01-18T21:52:39Z

Would it be possible to separately feature gate cstring_from_bytes_until_nul, instead of both CStr and CString being under cstr_from_bytes_until_nul? I ask because this CStr version is straightforward, has been around for almost a year, is very useful for FFI, and is already mentioned in the forums quite often - imho, probably ready for FCP.

However, the CString version hasn't even merged yet. I just don't think it's worth delaying the CStr stabilization for another year or so while waiting on CString::from_vec_until_nul to get merged & mature a while.

tgross35 · 2023-01-28T22:44:45Z

Hey @ericseppanen I hope you don't mind, but I've opened stabilization PR #107429 without any CString implementation. If you have any concerns just let me know and I can close / adjust it as needed

ericseppanen · 2023-01-29T18:35:37Z

I'm not sure which issue to comment on, but I'm happy with whatever others want to do. I was never sure why the CString bit (#96186) stalled, but it's at least partially my own fault as I was too shy to beg for more reviews.

I'll try to find time to rebase that commit and poke the reviewers again.

tgross35 · 2023-01-29T22:12:04Z

Okiedoke, as long as you don't have any qualms about the cstr part going stable. Sorry to leapfrog you and start the stabilization, but I wasn't sure if you were still active on github.

Yeah, things have a tendency to stall a bit when they're close to the merge phase and there isn't really any open debate or strong need to drive discussion. Not your fault!

m-ou-se · 2023-01-30T13:54:57Z

Would it be possible to separately feature gate cstring_from_bytes_until_nul, instead of both CStr and CString being under cstr_from_bytes_until_nul?

Good idea. I've edited this tracking issue so it only covers CStr::from_bytes_until_nul.

…bilization, r=dtolnay Stabilize feature `cstr_from_bytes_until_nul` This PR seeks to stabilize `cstr_from_bytes_until_nul`. Partially addresses rust-lang#95027 This function has only been on nightly for about 10 months, but I think it is simple enough that there isn't harm discussing stabilization. It has also had at least a handful of mentions on both the user forum and the discord, so it seems like it's already in use or at least known. This needs FCP still. Comment on potential discussion points: - eventual conversion of `CStr` to be a single thin pointer: this function will still be useful to provide a safe way to create a `CStr` after this change. - should this return a length too, to address concerns about the `CStr` change? I don't see it as being particularly useful, and it seems less ergonomic (i.e. returning `Result<(&CStr, usize), FromBytesUntilNulError>`). I think users that also need this length without the additional `strlen` call are likely better off using a combination of other methods, but this is up for discussion - `CString::from_vec_until_nul`: this is also useful, but it doesn't even have a nightly implementation merged yet. I propose feature gating that separately, as opposed to blocking this `CStr` implementation on that Possible alternatives: A user can use `from_bytes_with_nul` on a slice up to `my_slice[..my_slice.iter().find(|c| c == 0).unwrap()]`. However; that is significantly less ergonomic, and is a bit more work for the compiler to optimize compared the direct `memchr` call that this wraps. ## New stable API ```rs // both in core::ffi pub struct FromBytesUntilNulError(()); impl CStr { pub const fn from_bytes_until_nul( bytes: &[u8] ) -> Result<&CStr, FromBytesUntilNulError> } ``` cc `@ericseppanen` original author, `@Mark-Simulacrum` original reviewer, `@m-ou-se` brought up some issues on the thin pointer CStr `@rustbot` modify labels: +T-libs-api +needs-fcp

…bilization, r=dtolnay Stabilize feature `cstr_from_bytes_until_nul` This PR seeks to stabilize `cstr_from_bytes_until_nul`. Partially addresses rust-lang#95027 This function has only been on nightly for about 10 months, but I think it is simple enough that there isn't harm discussing stabilization. It has also had at least a handful of mentions on both the user forum and the discord, so it seems like it's already in use or at least known. This needs FCP still. Comment on potential discussion points: - eventual conversion of `CStr` to be a single thin pointer: this function will still be useful to provide a safe way to create a `CStr` after this change. - should this return a length too, to address concerns about the `CStr` change? I don't see it as being particularly useful, and it seems less ergonomic (i.e. returning `Result<(&CStr, usize), FromBytesUntilNulError>`). I think users that also need this length without the additional `strlen` call are likely better off using a combination of other methods, but this is up for discussion - `CString::from_vec_until_nul`: this is also useful, but it doesn't even have a nightly implementation merged yet. I propose feature gating that separately, as opposed to blocking this `CStr` implementation on that Possible alternatives: A user can use `from_bytes_with_nul` on a slice up to `my_slice[..my_slice.iter().find(|c| c == 0).unwrap()]`. However; that is significantly less ergonomic, and is a bit more work for the compiler to optimize compared the direct `memchr` call that this wraps. ## New stable API ```rs // both in core::ffi pub struct FromBytesUntilNulError(()); impl CStr { pub const fn from_bytes_until_nul( bytes: &[u8] ) -> Result<&CStr, FromBytesUntilNulError> } ``` cc ``@ericseppanen`` original author, ``@Mark-Simulacrum`` original reviewer, ``@m-ou-se`` brought up some issues on the thin pointer CStr ``@rustbot`` modify labels: +T-libs-api +needs-fcp

…bilization, r=dtolnay Stabilize feature `cstr_from_bytes_until_nul` This PR seeks to stabilize `cstr_from_bytes_until_nul`. Partially addresses rust-lang#95027 This function has only been on nightly for about 10 months, but I think it is simple enough that there isn't harm discussing stabilization. It has also had at least a handful of mentions on both the user forum and the discord, so it seems like it's already in use or at least known. This needs FCP still. Comment on potential discussion points: - eventual conversion of `CStr` to be a single thin pointer: this function will still be useful to provide a safe way to create a `CStr` after this change. - should this return a length too, to address concerns about the `CStr` change? I don't see it as being particularly useful, and it seems less ergonomic (i.e. returning `Result<(&CStr, usize), FromBytesUntilNulError>`). I think users that also need this length without the additional `strlen` call are likely better off using a combination of other methods, but this is up for discussion - `CString::from_vec_until_nul`: this is also useful, but it doesn't even have a nightly implementation merged yet. I propose feature gating that separately, as opposed to blocking this `CStr` implementation on that Possible alternatives: A user can use `from_bytes_with_nul` on a slice up to `my_slice[..my_slice.iter().find(|c| c == 0).unwrap()]`. However; that is significantly less ergonomic, and is a bit more work for the compiler to optimize compared the direct `memchr` call that this wraps. ## New stable API ```rs // both in core::ffi pub struct FromBytesUntilNulError(()); impl CStr { pub const fn from_bytes_until_nul( bytes: &[u8] ) -> Result<&CStr, FromBytesUntilNulError> } ``` cc ```@ericseppanen``` original author, ```@Mark-Simulacrum``` original reviewer, ```@m-ou-se``` brought up some issues on the thin pointer CStr ```@rustbot``` modify labels: +T-libs-api +needs-fcp

tgross35 · 2023-07-01T00:23:07Z

Since cstr_from_bytes_until_nul has been stabilized (#107429 1.69), I think this issue could be closed. @ericseppanen do you perhaps want to start a new tracking issue for cstring_from_bytes_until_nul?

ericseppanen · 2023-07-01T06:01:01Z

Sure, we can close this. I'm not sure if a new tracking issue is needed, since the CString::from_vec_until_nul PR (#96186) is not making progress. If someone wants to bring it back to life, feel free to persuade the reviewers.

tgross35 · 2023-07-01T08:10:24Z

Fwiw that PR is labeled waiting on author, you can comment @rustbot ready to change it to waiting on review

aswild · 2023-07-13T21:07:25Z

Hi @ericseppanen,
Was it intentional to add FromBytesUntilNulError only in core::ffi and not re-export it in std::ffi?

I'm used to everything from core (and alloc) to be re-exported under the same name in std, so it was a bit of a surprise to see an error message when trying to use std::ffi::{CStr, FromBytesUntilNulError}.

tgross35 · 2023-07-13T21:36:46Z

@aswild I don't think anybody would object to a reexport - are you interested in making a PR for that change?

It would need to go through FCP (as it changes public API) but I think it's small enough that that could happen on the PR.

ericseppanen · 2023-07-13T22:16:43Z

Hi @ericseppanen, Was it intentional to add FromBytesUntilNulError only in core::ffi and not re-export it in std::ffi?

Not intentional; probably just me not knowing I was supposed to do it.

aswild · 2023-07-14T14:30:29Z

Sure, I can give making a PR a try! I haven't contributed to the standard library before so I apologize in advance if I get the #[stable] attribute wrong at first.

Like the other CStr and CString error types, make a re-export for std::ffi::FromBytesUntilNulError. This seems to have slipped through the cracks in the cstr_from_bytes_until_nul implementation and core_c_str migration. Tracking Issue: rust-lang#95027

…r=dtolnay Re-export core::ffi::FromBytesUntilNulError in std::ffi Like the other CStr and CString error types, make a re-export for std::ffi::FromBytesUntilNulError. This seems to have slipped through the cracks in the cstr_from_bytes_until_nul implementation and core_c_str migration. Tracking Issue: rust-lang#95027

ericseppanen added C-tracking-issue Category: A tracking issue for an RFC or an unstable feature. T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. labels Mar 16, 2022

This was referenced Mar 16, 2022

add CStr method that accepts any slice containing a nul-terminated string #94984

Merged

add CString::from_vec_until_nul #95160

Closed

ericseppanen mentioned this issue Apr 18, 2022

add CString::from_vec_until_nul #96186

Closed

tgross35 mentioned this issue Jan 28, 2023

Stabilize feature cstr_from_bytes_until_nul #107429

Merged

m-ou-se changed the title ~~Tracking Issue for CString/CStr::from_bytes_until_nul~~ Tracking Issue for CStr::from_bytes_until_nul Jan 30, 2023

ericseppanen closed this as completed Jul 1, 2023

aswild mentioned this issue Jul 14, 2023

Re-export core::ffi::FromBytesUntilNulError in std::ffi #113701

Merged

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Tracking Issue for `CStr::from_bytes_until_nul` #95027

Tracking Issue for `CStr::from_bytes_until_nul` #95027

ericseppanen commented Mar 16, 2022 •

edited by m-ou-se

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Stargateur commented Aug 1, 2022 •

edited

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jimblandy commented Oct 6, 2022

tgross35 commented Jan 18, 2023

tgross35 commented Jan 28, 2023

ericseppanen commented Jan 29, 2023

tgross35 commented Jan 29, 2023

m-ou-se commented Jan 30, 2023

tgross35 commented Jul 1, 2023

ericseppanen commented Jul 1, 2023

tgross35 commented Jul 1, 2023

aswild commented Jul 13, 2023

tgross35 commented Jul 13, 2023 •

edited

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ericseppanen commented Jul 13, 2023

aswild commented Jul 14, 2023

Tracking Issue for CStr::from_bytes_until_nul #95027

Tracking Issue for CStr::from_bytes_until_nul #95027

Comments

ericseppanen commented Mar 16, 2022 • edited by m-ou-se Loading

Public API

Steps / History

Unresolved Questions

Stargateur commented Aug 1, 2022 • edited Loading

jimblandy commented Oct 6, 2022

tgross35 commented Jan 18, 2023

tgross35 commented Jan 28, 2023

ericseppanen commented Jan 29, 2023

tgross35 commented Jan 29, 2023

m-ou-se commented Jan 30, 2023

tgross35 commented Jul 1, 2023

ericseppanen commented Jul 1, 2023

tgross35 commented Jul 1, 2023

aswild commented Jul 13, 2023

tgross35 commented Jul 13, 2023 • edited Loading

ericseppanen commented Jul 13, 2023

aswild commented Jul 14, 2023

Tracking Issue for `CStr::from_bytes_until_nul` #95027

Tracking Issue for `CStr::from_bytes_until_nul` #95027

ericseppanen commented Mar 16, 2022 •

edited by m-ou-se

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Stargateur commented Aug 1, 2022 •

edited

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tgross35 commented Jul 13, 2023 •

edited

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