How can I read from a specific raw file descriptor in Rust?
I think right now your best bet is probably using the libc crate for working with raw file descriptors.
The movement of FileDesc
to private scope was fallout from the runtime removal a few months back. See this RFC for some more context. std::os::unix
currently has the type Fd
, and I believe the long term idea is to expose more of the platform-specific functionality in that module.
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:
- How do I write to a specific raw file descriptor from Rust?