mukan-ignite/ignite/pkg/availableport/availableport.go

package availableport

import (
	"crypto/rand"
	"fmt"
	"math/big"
	"net"

	"git.cw.tr/mukan-network/mukan-ignite/ignite/pkg/errors"
	"git.cw.tr/mukan-network/mukan-ignite/ignite/pkg/safeconverter"
)

type availablePortOptions struct {
	minPort uint
	maxPort uint
}

type Options func(o *availablePortOptions)

func WithMaxPort(maxPort uint) Options {
	return func(o *availablePortOptions) {
		o.maxPort = maxPort
	}
}

func WithMinPort(minPort uint) Options {
	return func(o *availablePortOptions) {
		o.minPort = minPort
	}
}

// Find finds n number of unused ports.
// it is not guaranteed that these ports will not be allocated to
// another program in the time of calling Find().
func Find(n uint, options ...Options) (ports []uint, err error) {
	// Defining them before so we can set a value depending on the AvailablePortOptions
	opts := availablePortOptions{
		minPort: 44000,
		maxPort: 55000,
	}

	for _, apply := range options {
		apply(&opts)
	}
	// If the number of ports required is bigger than the range, this stops it
	if opts.maxPort < opts.minPort {
		return nil, errors.Errorf("invalid ports range: max < min (%d < %d)", opts.maxPort, opts.minPort)
	}

	// If the number of ports required is bigger than the range, this stops it
	if n > (opts.maxPort - opts.minPort) {
		return nil, errors.Errorf("invalid amount of ports requested: limit is %d", opts.maxPort-opts.minPort)
	}

	// Marker to point if a port is already added in the list
	registered := make(map[uint]bool)
	i := safeconverter.ToInt[uint](n)
	for len(registered) < i {
		// Greater or equal to min and lower than max
		totalPorts := opts.maxPort - opts.minPort + 1

		randomPort, _ := rand.Int(rand.Reader, big.NewInt(safeconverter.ToInt64[uint](totalPorts)))
		port := uint(randomPort.Uint64()) + opts.minPort

		conn, err := net.Dial("tcp", fmt.Sprintf(":%d", port))
		// if there is an error, this might mean that no one is listening from this port
		// which is what we need.
		if err == nil {
			conn.Close()
			continue
		}
		if conn != nil {
			defer conn.Close()
		}

		// if the port is already registered we skip it to the next one
		// otherwise it's added to the ports list and pointed in our map
		if registered[port] {
			continue
		}
		ports = append(ports, port)
		registered[port] = true
	}
	return ports, nil
}