Add vm modification function

Adds a function to modify an existing VM object's configuration,
either directly in-editor, or by replacing with a new XML config.
In replacement mode, there is no confirmation or diff, the new
configuration is simply written and reboot triggered if specified.
In editor mode, the users local EDITOR (or `vi`) is started with
a copy of the existing config. Upon writing and exiting, the
operator is presented with a diff of the changes and is asked to
confirm before writing them to Zookeeper.

Closes #13

pvc.py

@@ -25,6 +25,10 @@ import socket
 import time
 import uuid
 import re
+import tempfile
+import subprocess
+import difflib
+import colorama
 import click
 import lxml.objectify
 import configparser
@@ -819,6 +823,115 @@ def define_vm(config, target_hypervisor, selector):
     stopZKConnection(zk_conn)
 
 
+###############################################################################
+# pvc vm modify
+###############################################################################
+@click.command(name='modify', short_help='Modify an existing VM configuration.')
+@click.option(
+    '-e', '--editor', 'editor', is_flag=True,
+    help='Use local editor to modify existing config.'
+)
+@click.option(
+    '-r', '--restart', 'restart', is_flag=True,
+    help='Immediately restart VM to apply new config.'
+)
+@click.argument(
+    'domain'
+)
+@click.argument(
+    'config', type=click.File(), default=None, required=False
+)
+def modify_vm(domain, config, editor, restart):
+    """
+    Modify existing virtual machine DOMAIN, either in-editor or with replacement CONFIG. DOMAIN may be a UUID or name.
+    """
+
+    if editor == False and config == None:
+        click.echo('Either an XML config file or the "--editor" option must be specified.')
+        exit(1)
+
+    # Open a Zookeeper connection
+    zk_conn = startZKConnection(zk_host)
+
+    # Validate and obtain alternate passed value
+    if validateUUID(domain):
+        dom_name = searchClusterByUUID(zk_conn, domain)
+        dom_uuid = searchClusterByName(zk_conn, dom_name)
+    else:
+        dom_uuid = searchClusterByName(zk_conn, domain)
+        dom_name = searchClusterByUUID(zk_conn, dom_uuid)
+
+    if dom_uuid == None:
+        click.echo('ERROR: Could not find VM "{}" in the cluster!'.format(domain))
+        stopZKConnection(zk_conn)
+        exit(1)
+
+    # We're operating in edit-in-place mode
+    if editor == True:
+        # Grab the current config
+        current_vm_config = zk_conn.get('/domains/{}/xml'.format(dom_uuid))[0].decode('ascii')
+
+        # Write it to a tempfile
+        fd, path = tempfile.mkstemp()
+        fw = os.fdopen(fd, 'w')
+        fw.write(current_vm_config)
+        fw.close()
+
+        # Edit it
+        editor = os.getenv('EDITOR', 'vi')
+        subprocess.call('%s %s' % (editor, path), shell=True)
+
+        # Open the tempfile to read
+        with open(path, 'r') as fr:
+            new_vm_config = fr.read()
+            fr.close()
+
+        # Delete the tempfile
+        os.unlink(path)
+
+        # Show a diff and confirm
+        diff = list(difflib.unified_diff(current_vm_config.split('\n'), new_vm_config.split('\n'), fromfile='current', tofile='modified', fromfiledate='', tofiledate='', n=3, lineterm=''))
+        if len(diff) < 1:
+            click.echo('Aborting with no modifications.')
+            exit(0)
+
+        click.echo('Pending modifications:')
+        click.echo('')
+        for line in diff:
+            if re.match('^\+', line) != None:
+                click.echo(colorama.Fore.GREEN + line + colorama.Fore.RESET)
+            elif re.match('^\-', line) != None:
+                click.echo(colorama.Fore.RED + line + colorama.Fore.RESET)
+            elif re.match('^\^', line) != None:
+                click.echo(colorama.Fore.BLUE + line + colorama.Fore.RESET)
+            else:
+                click.echo(line)
+        click.echo('')
+
+        click.confirm('Write modifications to Zookeeper?', abort=True)
+
+        click.echo('Writing modified config of VM "{}".'.format(dom_name))
+
+    # We're operating in replace mode
+    else:
+        # Open the XML file
+        new_vm_config = config.read()
+        config.close()
+
+        click.echo('Replacing config of VM "{}".'.format(dom_name, config))
+
+    # Add the modified config to Zookeeper
+    transaction = zk_conn.transaction()
+    transaction.set_data('/domains/{}'.format(dom_uuid), dom_name.encode('ascii'))
+    transaction.set_data('/domains/{}/xml'.format(dom_uuid), new_vm_config.encode('ascii'))
+    if restart == True:
+        transaction.set_data('/domains/{}/state'.format(dom_uuid), 'restart'.encode('ascii'))
+    results = transaction.commit()
+
+    # Close the Zookeeper connection
+    stopZKConnection(zk_conn)
+
+
 ###############################################################################
 # pvc vm undefine
 ###############################################################################
@@ -1520,6 +1633,7 @@ node.add_command(node_info)
 node.add_command(node_list)
 
 vm.add_command(define_vm)
+vm.add_command(modify_vm)
 vm.add_command(undefine_vm)
 vm.add_command(start_vm)
 vm.add_command(restart_vm)