test/parallel/test-child-process-double-pipe.js

// Copyright Joyent, Inc. and other Node contributors.
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'use strict';
const {
  isWindows,
  mustCall,
  mustCallAtLeast,
} = require('../common');
const assert = require('assert');
const os = require('os');
const spawn = require('child_process').spawn;
const debug = require('util').debuglog('test');

// We're trying to reproduce:
// $ echo "hello\nnode\nand\nworld" | grep o | sed s/o/a/

let grep, sed, echo;

if (isWindows) {
  grep = spawn('grep', ['--binary', 'o']);
  sed = spawn('sed', ['--binary', 's/o/O/']);
  echo = spawn('cmd.exe',
               ['/c', 'echo', 'hello&&', 'echo',
                'node&&', 'echo', 'and&&', 'echo', 'world']);
} else {
  grep = spawn('grep', ['o']);
  sed = spawn('sed', ['s/o/O/']);
  echo = spawn('echo', ['hello\nnode\nand\nworld\n']);
}

// If the spawn function leaks file descriptors to subprocesses, grep and sed
// hang.
// This happens when calling pipe(2) and then forgetting to set the
// FD_CLOEXEC flag on the resulting file descriptors.
//
// This test checks child processes exit, meaning they don't hang like
// explained above.


// pipe echo | grep
echo.stdout.on('data', mustCallAtLeast((data) => {
  debug(`grep stdin write ${data.length}`);
  if (!grep.stdin.write(data)) {
    echo.stdout.pause();
  }
}));

// TODO(@jasnell): This does not appear to ever be
// emitted. It's not clear if it is necessary.
grep.stdin.on('drain', (data) => {
  echo.stdout.resume();
});

// Propagate end from echo to grep
echo.stdout.on('end', mustCall((code) => {
  grep.stdin.end();
}));

echo.on('exit', mustCall(() => {
  debug('echo exit');
}));

grep.on('exit', mustCall(() => {
  debug('grep exit');
}));

sed.on('exit', mustCall(() => {
  debug('sed exit');
}));


// pipe grep | sed
grep.stdout.on('data', mustCallAtLeast((data) => {
  debug(`grep stdout ${data.length}`);
  if (!sed.stdin.write(data)) {
    grep.stdout.pause();
  }
}));

// TODO(@jasnell): This does not appear to ever be
// emitted. It's not clear if it is necessary.
sed.stdin.on('drain', (data) => {
  grep.stdout.resume();
});

// Propagate end from grep to sed
grep.stdout.on('end', mustCall((code) => {
  debug('grep stdout end');
  sed.stdin.end();
}));


let result = '';

// print sed's output
sed.stdout.on('data', mustCallAtLeast((data) => {
  result += data.toString('utf8', 0, data.length);
  debug(data);
}));

sed.stdout.on('end', mustCall((code) => {
  assert.strictEqual(result, `hellO${os.EOL}nOde${os.EOL}wOrld${os.EOL}`);
}));