I try to execute long processes sequentially with node.js (docker exec commands).
I do:
const childProcess = require('child_process');
const execWithPromise = async command => {
return new Promise(async resolve => {
const process = childProcess.exec(command);
process.on('exit', err => resolve(err));
process.on('close', err => resolve(err));
});
};
const run = async () => {
await execWithPromise('/usr/local/bin/docker exec -i -t cucumber node long-running-script.js');
await execWithPromise('/usr/local/bin/docker exec -i -t cucumber node long-running-script.js');
};
run();
But the promise is resolved immediately with a result of 1. In both cases. The command runs on the commandline just fine.
Why is it returning immediately?
child_process.exec
expects a callback as the second or third argument. It doesn't return a promise. You have a few choices depending on your use case and version of node. The following work with node 16.x
Use a callback and return the resolve.
const execWithPromise = command =>
new Promise((resolve, reject) => {
childProcess.exec(command, (err, stout, sterr) => {
if(err) {
reject(sterr)
} else {
resolve(stout)
}
})
})
Use spawn instead (keeping most of your code)
const execWithPromise = command =>
new Promise((resolve, reject) => {
const process = childProcess.spawn(command);
let data = '';
let error = '';
process.stdout.on('data', stdout => {
data += stdout.toString();
});
process.stderr.on('data', stderr => {
error += stderr.toString();
});
process.on('error', err => {
reject(err);
})
process.on('close', code => {
if (code !== 0) {
reject(error)
} else {
resolve(data)
}
process.stdin.end();
});
});
Use execSync
const execWithPromise = command => childProcess.execSync(command).toString();