node-socket-activation is a socket activation library for Node.js.

Service management framework	OS	Supported?
launchd	macOS 10.9 or later	👍
systemd	Compatible Linux distro	👍

Using yarn:

yarn add socket-activation

Using npm:

npm install --save socket-activation

const net = require('net')

const sockets = require('socket-activation')

// There may be more than one fd, e.g. if you select the "IPv4v6"
// SockFamily which listens to both IPv4 and IPv6. Up to you to
// decide if you want to error out or setup multiple servers as
// follows.
for (const fd of sockets.collect('app')) {
  const server = net.createServer(conn => {
    conn.end('hello!\n')
  })

  server.on('error', err => {
    throw err
  })

  server.listen({ fd }, () => {
    const addr = server.address()
    console.log('Listening on', addr)
  })
}

See the examples directory for more examples incl. supporting both socket activation and direct execution.

Normally you'd put this in ~/Library/LaunchAgents.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
    <dict>
        <key>Label</key>
        <string>org.example.app</string>
        <key>ProgramArguments</key>
        <array>
            <string>/usr/local/bin/node</string>
            <string>ABSOLUTE_PATH_TO_YOUR_JS_FILE</string>
        </array>
        <key>Sockets</key>
        <dict>
            <key>app</key>
            <array>
                <dict>
                    <key>SockFamily</key>
                    <string>IPv4</string>
                    <key>SockServiceName</key>
                    <string>3000</string>
                </dict>
            </array>
        </dict>
        <key>StandardErrorPath</key>
        <string>/tmp/org.example.app.err</string>
        <key>StandardOutPath</key>
        <string>/tmp/org.example.app.out</string>
    </dict>
</plist>

There's no need to set RunAtLoad, launchd will start your app on the first request.

Enable and start listening by running:

launchctl load ~/Library/LaunchAgents/org.example.app.plist

Normally you'd put these in /etc/systemd/system.

[Unit]
RefuseManualStart=true

[Service]
Restart=always
ExecStart=/usr/local/bin/node ABSOLUTE_PATH_TO_YOUR_JS_FILE

[Socket]
ListenStream=127.0.0.1:3000
NoDelay=true
FileDescriptorName=app

[Install]
WantedBy=sockets.target

Enable and start listening by running:

systemctl enable app.socket
systemctl start app.socket

There's no need to enable the service, systemd will start it on the first request.

Returns the list of fds the system has managed for us. This operation consumes the list and can therefore only be performed once per launch. Subsequent calls with the same name throw an Error. It's your responsibility not to do that.

The name is case sensitive and must match the name of the socket. Under systemd, the setting is FileDescriptorName=. Under launchd, the <key>...</key> of the socket definition defines the name.

Note that the method returns an Array of fds. For example, there may be more than one fd if you select the "IPv4v6" SockFamily in launchd.plist which listens to both IPv4 and IPv6, or if several ListenStream are given in systemd.socket. Up to you to decide if you want to error out when given multiple fds or setup multiple listeners.

The API is the same for all supported service managers.

This method throws an Error if:

• The process was not launched by the service management framework (or with launchd, if there's no matching socket).
  • Error .code is 'ESRCH'
• There is no matching socket.
  • Error .code is 'ENOENT'
• The fd list has already been collected previously.
  • Error .code is 'EALREADY'
• An internal system error occurred.

See LICENSE.