PTY output hangs when trying to read command output in terminal emulator

Question

I'm working on creating a terminal emulator in Rust, and I'm currently experimenting with pseudo-terminals (PTY) and trying to capture the output of shell commands executed within the PTY. However, I'm encountering an issue where the program hangs when trying to read the output from the PTY, and no output is printed to the terminal.

Here's the relevant part of my code:

use portable_pty::{CommandBuilder, PtySize, native_pty_system};
use std::io::Write;
use std::process::Command;
use anyhow::Result;
use anyhow::Error;

pub fn pyt() -> Result<(), Error> {

    // Use the native pty implementation for the system
    let pty_system = native_pty_system();
    
    // Create a new pty
    let mut pair = pty_system.openpty(PtySize {
        rows: 24,
        cols: 80,
        // Not all systems support pixel_width, pixel_height,
        // but it is good practice to set it to something
        // that matches the size of the selected font.  That
        // is more complex than can be shown here in this
        // brief example though!
        pixel_width: 0,
        pixel_height: 0,
    })?;
    
    // Spawn a shell into the pty
    let cmd = CommandBuilder::new("bash");
    let child = pair.slave.spawn_command(cmd)?;
    
    // Read and parse output from the pty with reader
    let mut reader = pair.master.try_clone_reader()?;
    
    // Send data to the pty by writing to the master
    writeln!(pair.master.take_writer()?, "dir\r\n")?;

    //output from the pty
    let mut output = String::new();
    reader.read_to_string(&mut output)?;
    println!("output: {}", output);

    Ok(())
}

I'm using the portable_pty crate to handle the PTY interactions. The code is supposed to:

1. Create a new PTY.
2. Spawn a bash shell into the PTY.
3. Write the command dir to the PTY.
4. Read and print the output from the PTY.

However, when I run this function, it hangs at the point of reading the output (reader.read_to_string(&mut output)), and nothing gets printed to the console. I'm not sure why it's not capturing the output from the dir command or why it hangs.

What I've tried

• Ensuring that the dir command is correctly written to the PTY.
• Verifying that the bash shell is spawning correctly within the PTY.

My question

How can I correctly read the output from the PTY without causing the program to hang? Is there a specific technique or method in Rust for handling PTY output asynchronously or non-blocking?