Allow installing as a service on macOS via brew

[marcleblanc2]

Hello! I have Mac Minis running as network management hosts on my customers' networks, and would like to install iperf3 as a service on these, so I can test network performance from different points in their networks.

Considering iperf3 is already in Homebrew, I believe this can be achieved by adding a service block to the formula file; example from colima here.

I'm not sure how the formula files are maintained, so I thought I'd pitch it here and ask for direction, if there's anything I can do to help make this happen.

The alternative is writing a plist file, and figuring out how to use launchctl to register it as a service, which doesn't scale as well.

[marcleblanc2]

Finally got a first success running iperf3 as a service, for anyone else who stumbles upon this. Save the below code in a file com.user.iperf3.plist, and run the commands in the comment as needed. Having this managed by brew would be much easier :)

<!--
# Runs iperf3 as a system service, and starts at boot

# Update the service after making a change to the plist file
sudo launchctl bootout system/com.user.iperf3 ; \
sudo cp com.user.iperf3.plist /Library/LaunchDaemons/ && \
sudo launchctl bootstrap system /Library/LaunchDaemons/com.user.iperf3.plist

# Copy the plist file
sudo cp com.user.iperf3.plist /Library/LaunchDaemons/

# Register the service
sudo launchctl bootstrap system /Library/LaunchDaemons/com.user.iperf3.plist

# Enable the service
sudo launchctl enable system/com.user.iperf3

# Start the service, print the PID
sudo launchctl kickstart -p system/com.user.iperf3

# Check registered services
sudo launchctl list | grep -v com.apple

# Show service information
sudo launchctl print system/com.user.iperf3

# List listening ports to check if it's running
netstat -anvp tcp | awk 'NR<3 || /LISTEN/'

# List running processes to check if it's running
ps -ef | grep iperf

# Unregister the service
sudo launchctl bootout system/com.user.iperf3

# RTFM
man launchctl
# https://ss64.com/mac/launchctl.html

# TODO: This runs in a privileged context, need to find a way to create a service user and run in their context
sudo launchctl bootout user/502/com.user.iperf3 ; \
sudo cp com.user.iperf3.plist /Library/LaunchAgents/ && \
sudo launchctl bootstrap user/502 /Library/LaunchAgents/com.user.iperf3.plist
# Bootstrap failed: 5: Input/output error

-->

<?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>com.user.iperf3</string>
        <key>ProgramArguments</key>
        <array>
            <string>/bin/sh</string>
            <string>-c</string>
            <string>/opt/homebrew/bin/iperf3 --server --verbose</string>
        </array>
        <key>StandardOutPath</key>
        <string>/var/log/iperf3.log</string>
        <key>StandardErrorPath</key>
        <string>/var/log/iperf3.log</string>
        <key>RunAtLoad</key>
        <true />
        <key>KeepAlive</key>
        <true />
    </dict>
</plist>