Want way to get BorrowedFd<'static> for 0 1 2 #90809

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1. the8472 commented on Nov 11, 2021

   

   the8472

   on Nov 11, 2021

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   #![feature(io_safety)]
   use std::os::unix::io::AsFd;
   use std::os::unix::prelude::BorrowedFd;
   
   fn main() {
       let stdout = std::io::stdout();
       let foo: BorrowedFd<'static> = Box::leak(Box::new(stdout)).as_fd();
       dbg!(foo);
   }

   [src/main.rs:8] foo = BorrowedFd {
       fd: 1,
   }
   
2. ijackson commented on Nov 12, 2021

   

   ijackson

   on Nov 12, 2021

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   Wow. Thank you. That is inspired. But also a bit bonkers :-). I'm not sure this is the most ergonomic API for this operation...
3. ijackson commented on Nov 12, 2021

   

   ijackson

   on Nov 12, 2021

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   (Just looked at the definition of io::Stdout and it's not a ZST.)
4. sunfishcode commented on Feb 10, 2022

   

   sunfishcode

   on Feb 10, 2022

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   Could you say more about what the user of such a function would look like? In what situations does one, as a user of std, need a BorrowedFd<'static>?
5. ids1024 commented on Jul 8, 2022

   

   ids1024

   on Jul 8, 2022

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   Everyone in the program is entitled to assume they exist

   It looks like it isn't strictly guaranteed by POSIX that this will always be the case on program start?

   If file descriptor 0, 1, or 2 would otherwise be closed after a successful call to one of the exec family of functions, implementations may open an unspecified file for the file descriptor in the new process image. If a standard utility or a conforming application is executed with file descriptor 0 not open for reading or with file descriptor 1 or 2 not open for writing, the environment in which the utility or application is executed shall be deemed non-conforming, and consequently the utility or application might not behave as described in this standard.

   Linux seems to do this so file descriptors 0, 1, and 2 will exist after exec. But it's not technically guaranteed.
6. the8472 commented on Jul 8, 2022

   

   the8472

   on Jul 8, 2022

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   Std tries to ensure that standard file descriptors are open at startup. There are ways those assumptions may be violated, but they involve non-Rust code (in which case we just blame that), unsafe or libraries that ought to be unsafe.

   So the current stance is that the standard descriptors can be assumed to be open, anything else is a bug.

   👍React with 👍1Reacted by Ian Douglas Scott
7. sunfishcode commented on Jul 8, 2022

   

   sunfishcode

   on Jul 8, 2022

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   With Rust 1.61.0, std now provides 'static references:

   https://blog.rust-lang.org/2022/05/19/Rust-1.61.0.html#static-handles-for-locked-stdio

   When the io_safety feature is available, you can call as_fd() on these to obtain a BorrowedFd<'static> without any unsafe.

   @ijackson Does that meet your needs?
8. Dylan-DPC commented on Feb 17, 2023

   

   Dylan-DPC

   on Feb 17, 2023

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   Closing this to clean up the issue tracker. Since there are alternatives possible already as explained above
9. Dylan-DPC

   closed this as completedon Feb 17, 2023