[SOLVED] Using Deno to interact through SSH hangs on p.output()

Issue

I'm looking to create an SSH sub-process and then interact with the server. I'm hung up on a basic step which is to simply wait until the SSH process has connected. I know that this ssh command connects fine because when I run it with inherit instead of piped, the ssh shell shows up as expected.

If I understand correctly, p.output() listens for stdout until it reaches EOF. I'm assuming that when SSH has connected, it streams the stdout, but does not EOF, and so p.output() never gets called.

const encoder = new TextEncoder();
const decoder = new TextDecoder();

const p=Deno.run({
     cmd: ["ssh", "root@mywebsite"],
     stdout: "piped",
     stderr: "piped",
     stdin: "piped"
});

const command = (cmd : string) => p.stdin.write(encoder.encode(cmd))
const getOutput = async () => decoder.decode(await p.output())

await p.output() // <----- Hangs here
await command("cd /home/dev/www")
await command("ls -la")
console.log(await getOutput())

await p.status()
console.log("done")

Solution

It hangs because .output will resolve once the entire process output has been read, meaning that until ssh command has finished, it will not resolve.

Also have in mind that you need to add \n at the end of each command, otherwise it'll never be triggered.

await command("cd /home\n");
await command("ls -la\n");
// if you don't finish the ssh session, .output will never resolve
await command("exit\n");
// now it will work correctly
console.log(await getOutput());

In any case if you don't want to close the session to read the output of a given command, what you need to do is use p.stdout.readable or p.stdout.read(buf) instead.

for await const(const chunk of p.stdout.readable) {
   // parse chunk and do something
}

Answered By - Marcos Casagrande

Answer Checked By - Mary Flores (WPSolving Volunteer)