Bug: Control connection times out despite active data channel

[JeredArc]

Bug Description

The FTP server (ftp-srv v4.6.3) terminates the control connection after the idle timeout period even when there is an active data transfer in progress. This causes uploads to fail for big files / slow transfer rates.

My particular case

• (Running on Windows 11 Pro, node v22.14.0)
• I created FtpSrv with timeout: 600000 (10 minutes) in the options
• I use it as upload interface into a database, so I provide a custom fs object with a write function returning a writeStream where I can also log the receiving of chunks
• I set up ftp command logging (listen to connection.commandSocket.on('data', ...), intercept connection.commandSocket.write)
• I have a device uploading files larger than 600 KB at approx 1 KB/s, meaning it takes longer than 10 minutes
• Exactly after 10 minutes the connection is closed, while upload on the data channel would still be going

The log

2025-04-04T13:25:54.189Z New connection from 192.168.223.30
2025-04-04T13:25:54.191Z [192.168.223.30] Server: 220 Ready
2025-04-04T13:25:54.288Z [192.168.223.30] Client: user username
2025-04-04T13:25:54.289Z [192.168.223.30] Server: 331 Username okay, awaiting password
2025-04-04T13:25:55.287Z [192.168.223.30] Client: pass password
2025-04-04T13:25:55.289Z [192.168.223.30] Server: 230 User logged in, proceed
2025-04-04T13:25:56.287Z [192.168.223.30] Client: pasv
2025-04-04T13:25:56.290Z [192.168.223.30] Server: 227 PASV OK (192,168,223,10,195,80)
2025-04-04T13:25:57.308Z [192.168.223.30] Client: cwd /
2025-04-04T13:25:57.309Z [192.168.223.30] Server: 250 "/"
2025-04-04T13:25:58.498Z [192.168.223.30] Client: stor filename.xml
2025-04-04T13:25:58.563Z [192.168.223.30] writeStream pipe event triggered for filename.xml
2025-04-04T13:25:58.563Z [192.168.223.30] Server: 150 File status okay; about to open data connection
2025-04-04T13:25:59.509Z [192.168.223.30] writeStream data chunk received for filename.xml (100 bytes)
2025-04-04T13:25:59.509Z [192.168.223.30] writeStream data chunk received for filename.xml: 100 bytes (total: 100 bytes)
2025-04-04T13:25:59.712Z [192.168.223.30] writeStream data chunk received for filename.xml: 200 bytes (total: 300 bytes)
2025-04-04T13:25:59.919Z [192.168.223.30] writeStream data chunk received for filename.xml: 200 bytes (total: 500 bytes)
2025-04-04T13:26:00.126Z [192.168.223.30] writeStream data chunk received for filename.xml: 200 bytes (total: 700 bytes)
2025-04-04T13:26:00.334Z [192.168.223.30] writeStream data chunk received for filename.xml: 273 bytes (total: 973 bytes)
2025-04-04T13:26:00.542Z [192.168.223.30] writeStream data chunk received for filename.xml: 264 bytes (total: 1237 bytes)
2025-04-04T13:26:00.750Z [192.168.223.30] writeStream data chunk received for filename.xml: 264 bytes (total: 1501 bytes)
...
2025-04-04T13:35:57.803Z [192.168.223.30] writeStream data chunk received for filename.xml: 172 bytes (total: 629729 bytes)
2025-04-04T13:35:58.010Z [192.168.223.30] writeStream data chunk received for filename.xml: 200 bytes (total: 629929 bytes)
2025-04-04T13:35:58.217Z [192.168.223.30] writeStream data chunk received for filename.xml: 172 bytes (total: 630101 bytes)
2025-04-04T13:35:58.424Z [192.168.223.30] writeStream data chunk received for filename.xml: 200 bytes (total: 630301 bytes)
2025-04-04T13:35:58.551Z [192.168.223.30] Server: 421 Closing connection
2025-04-04T13:35:58.553Z [192.168.223.30] Client disconnected

The connection is closed (421 Closing connection) exactly 10 minutes after the last control command (150 File status okay). The upload obviously fails.

A quick workaround (which I’ll probably use for now) is to send NOOP commands while data is received, but this should be handled by the server automatically.