Node.js tcp connection - node.js

Question

How to send "End" message after resolving promise? Sometimes I can send 2 "end" messages out of 4, sometimes 3. Files from FTP are being downloaded and it's ok. The only thing that doesn't work is sending "end" message after downloading a file. Do you have any idea why this code doesn't work properly?
This code was updated:
const ftp = require("jsftp");
const fs = require("fs");
const net = require("net");
const mkdirp = require("mkdirp");
class ftpCredentials {
constructor(host) {
this.user = "xxx";
this.pass = "xxx";
this.host = host;
}
}
const downloadFromFTP = (credentials, file) => {
const client = new ftpCredentials(credentials.host);
const ftpClient = new ftp(client);
return new Promise((res, rej) => {
let buf = null;
ftpClient.get(file, (err, stream) => {
if (!err && typeof stream !== "undefined") {
// Events
stream.on("data", (data) => {
if (buf === null) buf = new Buffer(data);
else buf = Buffer.concat([buf, data]);
});
stream.on("close", (err) => {
if (err) rej("FILE_ERROR");
const actualPath = `${credentials.path}/${file}`;
fs.writeFile(actualPath, buf, "binary", (err) => {
if (err) rej(err);
ftpClient.raw("quit", (err, data) => {
if (err) rej(err)
res(file);
});
});
});
// Resume stream
stream.resume();
} else {
rej("STREAM_ERROR");
}
});
})
}
const handleSavingFile = (credentials, filesOnFTP) => {
mkdirp(credentials.path, () => {
fs.readdir(credentials.path, (err, fileNames) => {
if (err) return err;
const needToConnectToFTP = filesOnFTP.filter(name => fileNames.indexOf(name) !== -1).length === 0;
const socketForEndMsg = net.createConnection(18005, credentials.host, () => {
Promise.all(filesOnFTP.map((file) => {
return new Promise((resolve, reject) => {
// The problem is here:
const socketWrite = socketForEndMsg.write(`End|ftp://${credentials.host}/${file}`, "UTF16LE");
resolve(socketWrite);
// Events
socketForEndMsg.on("error", () => {
console.log("Problem with sending End message!");
reject();
});
});
})).then(() => {
socketForEndMsg.end();
}).catch((err) => {
console.log(err);
});
});
})
})
}
const getScheme = (credentials) => {
const socketForData = net.createConnection(18005, credentials.host, () => socketForData.write("Scheme", "UTF16LE"));
// Events
socketForData.on("close", () => console.log("TCP Connection closed"));
socketForData.on("error", err => console.log(err));
socketForData.on("data", (data) => {
socketForData.end();
const toUTF16Format = Buffer.from(data).toString("UTF16LE");
const arrayFromTCPMessage = toUTF16Format.split(/\||;/);
const filteredImages = arrayFromTCPMessage.filter(item => item.startsWith("scheme"))
const isOK = arrayFromTCPMessage[0] === "OK";
if (isOK) {
handleSavingFile(credentials, filteredImages);
}
})
}
module.exports = getScheme;
Error message: Error: This socket is closed
at Socket._writeGeneric (net.js:722:18)
at Socket._write (net.js:782:8)
at doWrite (_stream_writable.js:407:12)
at writeOrBuffer (_stream_writable.js:393:5)
at Socket.Writable.write (_stream_writable.js:290:11)
at Promise (xxx\getScheme.js:56:29)
at new Promise (<anonymous>)
at Promise.all.filesOnFTP.map (xxx\getScheme.js:54:18)
at Array.map (<anonymous>)
at Socket.net.createConnection (xxx\getScheme.js:52:32)

Answer 1

I see that, you like to listen to error event & that made you to use Promise to catch the error. But, the placement of the error event handler registration is wrong, as it is inside .map function call. So, error event will be registered number of times of filesOnFTP length.
I've moved that error handler to next line & using writable flag to see, if the socket is still writable before writing to it. I have also added few more event handlers, which will give you more information about the socket status(for debugging, you can remove them later).
const handleSavingFile = (credentials, filesOnFTP) => {
mkdirp(credentials.path, () => {
fs.readdir(credentials.path, (err, fileNames) => {
if (err) return err;
const needToConnectToFTP = filesOnFTP.filter(name => fileNames.indexOf(name) !== -1).length === 0;
const socketForEndMsg = net.createConnection(18005, credentials.host, () => {
for(let file of filesOnFTP) {
// Before write to socket, check if it is writable still!
if(socketForEndMsg.writable) {
socketForEndMsg.write(`End|ftp://${credentials.host}/${file}`, "UTF16LE");
}
else {
console.log('Socket is not writable! May be closed already?');
}
}
});
// This is the correct place for the error handler!
socketForEndMsg.on("error", (error) => {
console.log("Problem with sending End message!", error);
});
socketForEndMsg.on("close", () => {
console.log("Socket is fully closed!");
});
socketForEndMsg.on("end", () => {
console.log("The other end of the socket has sent FIN packet!");
});
});
});
}
Let me know if this works!
Thanks!

Answer 2

You can try to wait for connection event on socketForEndMsg and then start sending your data
const handleSavingFile = (credentials, filesOnFTP) => {
mkdirp(credentials.path, () => {
fs.readdir(credentials.path, (err, fileNames) => {
if (err) return err;
const needToConnectToFTP = filesOnFTP.filter(name => fileNames.indexOf(name) !== -1).length === 0;
const socketForEndMsg = net.createConnection(18005, credentials.host);
socketForEndMsg.on('connect', () => {
Promise.all(filesOnFTP.map((file) => {
return new Promise((resolve, reject) => {
// The problem is here:
const socketWrite = socketForEndMsg.write(`End|ftp://${credentials.host}/${file}`, "UTF16LE");
resolve(socketWrite);
// Events
socketForEndMsg.on("error", () => {
console.log("Problem with sending End message!");
reject();
});
});
})).then(() => {
socketForEndMsg.end();
}).catch((err) => {
console.log(err);
});
})
})
})
}