I'm looking for a way to mimick a terminal for some automated testing: i.e. start a process and then interact with it via sending data to stdin and reading from stdout. E.g. sending some lines of input to stdin including ctrl-c
and ctrl-\
which should result in sending signals to the process.
Using std::process::Commannd
I'm able to send input to e.g. cat
and I'm also seeing its output on stdout, but sending ctrl-c
(as I understand that is 3
) does not cause SIGINT
sent to the shell. E.g. this program should terminate:
use std::process::{Command, Stdio};
use std::io::Write;
fn main() {
let mut child = Command::new("sh")
.arg("-c").arg("-i").arg("cat")
.stdin(Stdio::piped())
.spawn().unwrap();
let mut stdin = child.stdin.take().unwrap();
stdin.write(&[3]).expect("cannot send ctrl-c");
child.wait();
}
I suspect the issue is that sending ctrl-c
needs the some tty and via sh -i
it's only in "interactive mode".
Do I need to go full fledged and use e.g. termion
or ncurses
?
Update: I confused shell and terminal in the original question. I cleared this up now. Also I mentioned ssh
which should have been sh
.
The simplest way is to directly send the SIGINT signal to the child process. This can be done easily using nix
's signal::kill
function:
// add `nix = "0.15.0"` to your Cargo.toml
use std::process::{Command, Stdio};
use std::io::Write;
fn main() {
// spawn child process
let mut child = Command::new("cat")
.stdin(Stdio::piped())
.spawn().unwrap();
// send "echo\n" to child's stdin
let mut stdin = child.stdin.take().unwrap();
writeln!(stdin, "echo");
// sleep a bit so that child can process the input
std::thread::sleep(std::time::Duration::from_millis(500));
// send SIGINT to the child
nix::sys::signal::kill(
nix::unistd::Pid::from_raw(child.id() as i32),
nix::sys::signal::Signal::SIGINT
).expect("cannot send ctrl-c");
// wait for child to terminate
child.wait().unwrap();
}
You should be able to send all kinds of signals using this method. For more advanced "interactivity" (e.g. child programs like vi
that query terminal size) you'd need to create a pseudoterminal like @hansaplast did in his solution.
After a lot of research I figured out it's not too much work to do the pty fork myself. There's pty-rs, but it has bugs and seems unmaintained.
The following code needs pty
module of nix
which is not yet on crates.io, so Cargo.toml
needs this for now:
[dependencies]
nix = {git = "https://github.com/nix-rust/nix.git"}
The following code runs cat in a tty and then writes/reads from it and sends Ctrl-C (3
):
extern crate nix;
use std::path::Path;
use nix::pty::{posix_openpt, grantpt, unlockpt, ptsname};
use nix::fcntl::{O_RDWR, open};
use nix::sys::stat;
use nix::unistd::{fork, ForkResult, setsid, dup2};
use nix::libc::{STDIN_FILENO, STDOUT_FILENO, STDERR_FILENO};
use std::os::unix::io::{AsRawFd, FromRawFd};
use std::io::prelude::*;
use std::io::{BufReader, LineWriter};
fn run() -> std::io::Result<()> {
// Open a new PTY master
let master_fd = posix_openpt(O_RDWR)?;
// Allow a slave to be generated for it
grantpt(&master_fd)?;
unlockpt(&master_fd)?;
// Get the name of the slave
let slave_name = ptsname(&master_fd)?;
match fork() {
Ok(ForkResult::Child) => {
setsid()?; // create new session with child as session leader
let slave_fd = open(Path::new(&slave_name), O_RDWR, stat::Mode::empty())?;
// assign stdin, stdout, stderr to the tty, just like a terminal does
dup2(slave_fd, STDIN_FILENO)?;
dup2(slave_fd, STDOUT_FILENO)?;
dup2(slave_fd, STDERR_FILENO)?;
std::process::Command::new("cat").status()?;
}
Ok(ForkResult::Parent { child: _ }) => {
let f = unsafe { std::fs::File::from_raw_fd(master_fd.as_raw_fd()) };
let mut reader = BufReader::new(&f);
let mut writer = LineWriter::new(&f);
writer.write_all(b"hello world\n")?;
let mut s = String::new();
reader.read_line(&mut s)?; // what we just wrote in
reader.read_line(&mut s)?; // what cat wrote out
writer.write(&[3])?; // send ^C
writer.flush()?;
let mut buf = [0; 2]; // needs bytewise read as ^C has no newline
reader.read(&mut buf)?;
s += &String::from_utf8_lossy(&buf).to_string();
println!("{}", s);
println!("cat exit code: {:?}", wait::wait()?); // make sure cat really exited
}
Err(_) => println!("error"),
}
Ok(())
}
fn main() {
run().expect("could not execute command");
}
Output:
hello world
hello world
^C
cat exit code: Signaled(2906, SIGINT, false)
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