Deno.run hangs when a child process returns more than 8200 characters and the stdout == piped.

[CarlosOnline]

Deno.run hangs when a child process returns more than 8200 characters and the stdout == piped.

Repro source code is in repository: https://github.com/CarlosOnline/deno-bugs.git

Repro:

• git clone https://github.com/CarlosOnline/deno-bugs.git
• cd deno-bugs
• deno.exe run -A repro-run-hang.ts

Deno will hang between 8100 and 8200 characters.

Test code:

"a".repeat(parseInt(Deno.args[0]))

Repro code:

/**
 * Execute Deno.run with file that generates specified length of characters.
 * @param length Length of output to generate.
 */
async function Run(length: number) {
  console.log(`Running with length ${length}`);

  const p = Deno.run({
    cmd: [
      "deno",
      "run",
      "--allow-read",
      ".\\write-output.ts",
      length.toString(),
    ],
    stdout: "piped",
    stderr: "piped",
  });

  const { code } = await p.status();
  const rawOutput = await p.output();
  console.log(`Exit code: ${code} length: ${rawOutput.length}`);
}

/**
 * Loop through different lengths until hangs or succeeds.
 */
for (let idx = 100; idx < 10000; idx += 100) {
  await Run(idx);
}

console.log("Success");

[piscisaureus]

You have to read from stdout to avoid this.
Your program is waiting for the child process to exit first (await p.status).

[CarlosOnline]

I don't understand, the Deno example shows to wait for the status.
Plus the code works for output less than 8200 characters long.

https://deno.land/manual@v1.12.2/examples/subprocess

Should I skip const { code } = await p.status(); the line instead?

const { code } = await p.status();

// Reading the outputs closes their pipes
const rawOutput = await p.output();
const rawError = await p.stderrOutput();