dotcloud/docker

package portallocator

import (
    "bytes"
    "fmt"
    "os/exec"
)

func getDynamicPortRange() (start int, end int, err error) {
    portRangeKernelSysctl := []string{"net.inet.ip.portrange.hifirst", "net.ip.portrange.hilast"}
    portRangeLowCmd := exec.Command("/sbin/sysctl", portRangeKernelSysctl[0])
    var portRangeLowOut bytes.Buffer
    portRangeLowCmd.Stdout = &portRangeLowOut
    cmdErr := portRangeLowCmd.Run()
    if cmdErr != nil {
        return 0, 0, fmt.Errorf("port allocator - sysctl net.inet.ip.portrange.hifirst failed: %v", err)
    }
    n, err := fmt.Sscanf(portRangeLowOut.String(), "%d", &start)
    if n != 1 || err != nil {
        if err == nil {
            err = fmt.Errorf("unexpected count of parsed numbers (%d)", n)
        }
        return 0, 0, fmt.Errorf("port allocator - failed to parse system ephemeral port range start from %s: %v", portRangeLowOut.String(), err)
    }

    portRangeHighCmd := exec.Command("/sbin/sysctl", portRangeKernelSysctl[1])
    var portRangeHighOut bytes.Buffer
    portRangeHighCmd.Stdout = &portRangeHighOut
    cmdErr = portRangeHighCmd.Run()
    if cmdErr != nil {
        return 0, 0, fmt.Errorf("port allocator - sysctl net.inet.ip.portrange.hilast failed: %v", err)
    }
    n, err = fmt.Sscanf(portRangeHighOut.String(), "%d", &end)
    if n != 1 || err != nil {
        if err == nil {
            err = fmt.Errorf("unexpected count of parsed numbers (%d)", n)
        }
        return 0, 0, fmt.Errorf("port allocator - failed to parse system ephemeral port range end from %s: %v", portRangeHighOut.String(), err)
    }
    return start, end, nil
}