As of Rust 1.1, you can use FromRawFd
to create a File
from a specific file descriptor, but only on UNIX-like operating systems:
use std::{
fs::File,
io::{self, Read},
os::unix::io::FromRawFd,
};
fn main() -> io::Result<()> {
let mut f = unsafe { File::from_raw_fd(3) };
let mut input = String::new();
f.read_to_string(&mut input)?;
println!("I read: {}", input);
Ok(())
}
$ cat /tmp/output
Hello, world!
$ target/debug/example 3< /tmp/output
I read: Hello, world!
from_raw_fd
is unsafe:
This function is also unsafe as the primitives currently returned have the contract that they are the sole owner of the file descriptor they are wrapping. Usage of this function could accidentally allow violating this contract which can cause memory unsafety in code that relies on it being true.
The created File
will assume ownership of the file descriptor: when the File
goes out of scope, the file descriptor will be closed. You can avoid this by using either IntoRawFd
or mem::forget
.
See also: