Surprising Node.js/bash interaction

testspawn.js

/*
 * testspawn.js: exercises surprising interaction between Node.js "spawn" and
 * bash.  To use this:
 *
 * (1) Create a file in the same directory called "foo.rc", with just one line:
 *
 *     echo "loaded foo.rc"
 *
 * (2) Run this program as:
 *
 *     $ node testspawn.js
 *
 * This program uses Node's child_process.spawn in a loop to invoke
 * "bash --rcfile foo.rc -c /bin/true" (that is, invoke "/bin/true").  The
 * surprising behavior is that sometimes you will see "loaded foo.rc", but
 * sometimes you won't.  The reason for this is complicated.
 *
 * In this case, bash determines whether to load the bashrc file based on
 * whether it believes its stdin refers to a network socket.  On systems with
 * getpeername(2), bash attempts to detect this by calling getpeername(2) on
 * stdin to see if it returns ENOTSOCK or EINVAL.  When Node's spawn is invoked
 * with default arguments, Node creates a pipe from the parent to the child
 * process's stdin, and that pipe is implemented with a Unix domain socket.
 * You'd therefore expect that bash would always load the bashrc file when
 * invoked this way from Node.  However, getpeername(2) returns EINVAL on
 * sockets that have been shutdown (see [1]).  (It's unclear if this means the
 * send- or receive-side has been shutdown, but based on the illumos kernel
 * implementation, this appears to mean that the *send* side has been shut
 * down.)  Whether this is the case appears to depend on when Node actually
 * shuts down its end of the socket, which appears to happen when we call end().
 *
 * The program below uses a random interval between 0 and "maxtime" milliseconds
 * between spawning the child and shutting down the socket.  On my system, this
 * results in seeing each behavior roughly 50% of the time.
 *
 * The implications of this can be quite significant: if you use Node.js to
 * invoke "bash", it can be invoked with a totally different environment (as
 * determined by your ~/.bashrc file) depending on the timing.
 *
 * [1] http://pubs.opengroup.org/onlinepubs/7908799/xns/getpeername.html
 */

var maxtime = 5;

function go()
{
        console.log('spawning');

        var child = mod_child.spawn('bash',
            [ '--rcfile', 'foo.rc', '-c', '/bin/true' ], {
                'env': {},
                'stdio': [ null, process.stdout, process.stderr ]
            });

        child.on('exit', go);

        setTimeout(function () {
                child.stdin.end();
        }, Math.round(Math.random() * maxtime));
}

go();