Rework port for the ssh forwarding.

Till now, user has to provide port number (by commandline or through
config file), otherwise 2222 will be set. That's unfortunate in case you
need to have multiple machines and forgot about setting the correct
port. In this patch random port will be used if no port is provided.

box.py

@@ -3,6 +3,7 @@
 import argparse
 import collections.abc
 import os
+import random
 import shutil
 import string
 import subprocess
@@ -42,7 +43,6 @@ boxpy_data:
   disk_size: 10240
   key: ~/.ssh/id_rsa
   memory: 2048
-  port: 2222
 '''
 COMPLETIONS = {'bash': '''\
 _boxpy() {
@@ -494,7 +494,7 @@ class VBoxManage:
                             '--delete']) != 0:
             raise BoxVBoxFailure(f'Removing VM {self.name_or_uuid} failed')
 
-    def create(self, cpus, memory, port):
+    def create(self, cpus, memory, port=None):
         self.uuid = None
         memory = convert_to_mega(memory)
 
@@ -513,6 +513,9 @@ class VBoxManage:
         if not self.uuid:
             raise BoxVBoxFailure(f'Cannot create VM "{self.name_or_uuid}".')
 
+        if not port:
+            port = self._find_unused_port()
+
         if subprocess.call(['vboxmanage', 'modifyvm', self.name_or_uuid,
                             '--memory', str(memory),
                             '--cpus', str(cpus),
@@ -575,6 +578,48 @@ class VBoxManage:
                             f'--{nic}', kind]) != 0:
             raise BoxVBoxFailure(f'Cannot modify VM "{self.name_or_uuid}".')
 
+    def _find_unused_port(self):
+        self.get_vm_info()
+        try:
+            out = subprocess.check_output(['vboxmanage', 'list', 'vms'],
+                                          encoding=sys.getdefaultencoding(),
+                                          stderr=subprocess.DEVNULL)
+        except subprocess.CalledProcessError:
+            return 0
+
+        used_ports = []
+        for line in out.split('\n'):
+            if not line:
+                continue
+            vm_uuid = line.split('{')[1][:-1]
+            if self.vm_info['uuid'] == vm_uuid:
+                continue
+
+            try:
+                info = (subprocess
+                        .check_output(['vboxmanage', 'showvminfo', vm_uuid],
+                                      encoding=sys.getdefaultencoding(),
+                                      stderr=subprocess.DEVNULL))
+            except subprocess.CalledProcessError:
+                continue
+
+            for line in info.split('\n'):
+                if line.startswith('Config file:'):
+                    config = line.split('Config ' 'file:')[1].strip()
+
+            dom = xml.dom.minidom.parse(config)
+            gebtn = dom.getElementsByTagName
+
+            if len(gebtn('Forwarding')):
+                used_ports.append(gebtn('Forwarding')[0]
+                                  .getAttribute('hostport'))
+
+        while True:
+            port = random.randint(2000, 2999)
+            if port not in used_ports:
+                self.vm_info['port'] = port
+                return port
+
     def _get_vm_config(self):
         if self.vm_info.get('config_file'):
             return self.vm_info['config_file']
@@ -858,6 +903,9 @@ def vmcreate(args, conf=None):
     # dettach ISO image
     _cleanup(vbox, iso, image, path_to_iso)
     vbox.poweron()
+
+    # reread config to update fields
+    conf = Config(args, vbox)
     print('You can access your VM by issuing:')
     print(f'ssh -p {conf.port} -i {conf.ssh_key_path[:-4]} '
           f'{DISTROS[conf.distro]["username"]}@localhost')
@@ -937,7 +985,7 @@ def main():
     create.add_argument('-n', '--hostname',
                         help="VM hostname. Default same as vm name")
     create.add_argument('-p', '--port', help="set ssh port for VM, default "
-                        "2222")
+                        "random port from range 2000-2999")
     create.add_argument('-s', '--disk-size', help="disk size to be expanded "
                         "to. By default to 10GB")
     create.add_argument('-u', '--cpus', type=int, help="amount of CPUs to be "