Catch the status of a child process as a stream error

Nobody has claimed this yet.

I am using `duplexify` to create a duplex stream out of a child process. This enables me to create complex pipelines, combining processes with other streams. So, I wrote a simple function that wraps `duplexify` and `child_process.spawn` as follows:

function run(program, args) {
const child = spawn(program, args, {
stdio: ["pipe", "pipe", "inherit"],
});
const stream = duplexify(child.stdin, child.stdout);
child.on("error", (err) => {
stream.destroy(err);
});
return stream;
}

Now I can use the stream returned by `run` with `stream.pipeline`. The only issue that I have with this solution is that I would like `run` to wait for the child processes' exit status, and if it is not zero, forward an error to the duplex stream. I tried to address this by adding a `final` method as follows:

function run(program, args) {
const child = spawn(program, args, {
stdio: ["pipe", "pipe", "inherit"],
});
const final = (stream, callback) => {
child.on("exit", (code, signal) => {
if (code !== 0)
callback(new Error("child process failed"));
else
callback();
});
};
const stream = duplexify(child.stdin, child.stdout, {final});
child.on("error", (err) => {
stream.destroy(err);
});
return stream;
}

but the `final` function never gets called by `duplexify`. Is there a way to solve this issue with `duplexify`?

Start by reading duplexify's finalization behavior and the Node.js child_process exit and error events used in the example. Determine how a nonzero child exit can be surfaced through the duplex stream, and verify that successful exits complete normally while failures reach stream.pipeline as errors.

Written by the indexing model from the issue text.