Can't get a secondary handle to a TcpStream

[CenTdemeern1]

Using TcpStream::try_clone() always nets Err(Os { code: 22, kind: InvalidInput, message: "Invalid argument" }). Am I doing something wrong, or is this a bug?

[ian-h-chamberlain]

Hmm, this might be a limitation of libctru... From what I can gather, try_clone() ultimately calls into this code to clone the file descriptor of the underlying socket: https://github.com/rust-lang/rust/blob/f33a8c6426074b7ce8d08740e9805fdca96ee150/library/std/src/os/fd/owned.rs#L101-L118

However, the fcntl implementation doesn't seem to support F_DUPFD (or similar) as a command:
https://github.com/devkitPro/libctru/blob/30dc65121dc37ad5faf33ca842fd8d63f425f04f/libctru/source/services/soc/soc_fcntl.c#L48-L51

Without upstream support, we'd probably be better off changing Rust std to return UNSUPPORTED_PLATFORM here, or possibly changing the implementation to use one of the dup functions, which I believe is supported by libctru? Either that, or upstreaming proper F_DUPFD support to libctru.

In the meantime, as a workaround, you can try using the dup calls yourself, I'm guessing it'd look something like this:

let fd = stream.as_raw_fd();
let new_stream = unsafe {
	let new_fd = libc::dup(fd);
	if new_fd < 0 {
		// handle error
	}
	TcpStream::from_raw_fd(new_fd)
};