node: Add --field option (#922)

This lets the user add fields to be printed in the table and
allows printing arbitrary data that wasn't possible to show before,
except when using `--json`.

cli/dcoscli/data/help/node.txt

@@ -4,7 +4,7 @@ Description:
 Usage:
     dcos node --help
     dcos node --info
-    dcos node [--json]
+    dcos node [--json | --field=<field>...]
     dcos node --version
     dcos node diagnostics (--list | --status | --cancel) [--json]
     dcos node diagnostics create (<nodes>)...
@@ -52,6 +52,9 @@ Options:
         Show DC/OS component logs.
     --config-file=<path>
         Path to SSH configuration file.
+    --field=<field>
+        Name of extra field to include in the output of `dcos node`.
+        Can be repeated multiple times to add several fields.
     --filter=<filter>
         Filter logs by field and value. Filter must be a string separated by colon.
         For example: --filter _PID:0 --filter _UID:1.

cli/dcoscli/node/main.py

@@ -115,7 +115,7 @@ def _cmds():
 
         cmds.Command(
             hierarchy=['node'],
-            arg_keys=['--json'],
+            arg_keys=['--json', '--field'],
             function=_list)
     ]
 
@@ -458,12 +458,15 @@ def _info():
     return 0
 
 
-def _list(json_):
+def _list(json_, extra_field_names):
     """List DC/OS nodes
 
     :param json_: If true, output json.
         Otherwise, output a human readable table.
     :type json_: bool
+    :param extra_field_names: List of additional field names to include in
+        table output
+    :type extra_field_names: [str]
     :returns: process return code
     :rtype: int
     """
@@ -473,7 +476,16 @@ def _list(json_):
     if json_:
         emitter.publish(slaves)
     else:
-        table = tables.slave_table(slaves)
+        for extra_field_name in extra_field_names:
+            field_name = extra_field_name.split(':')[-1]
+            if len(slaves) > 0:
+                try:
+                    tables._dotted_itemgetter(field_name)(slaves[0])
+                except KeyError:
+                    emitter.publish(errors.DefaultError(
+                        'Field "%s" is invalid.' % field_name))
+                    return
+        table = tables.slave_table(slaves, extra_field_names)
         output = six.text_type(table)
         if output:
             emitter.publish(output)

cli/dcoscli/tables.py

@@ -1,5 +1,6 @@
 import copy
 import datetime
+import operator
 import posixpath
 
 import textwrap
@@ -839,11 +840,13 @@ def auth_provider_table(providers):
     return tb
 
 
-def slave_table(slaves):
+def slave_table(slaves, field_names=()):
     """Returns a PrettyTable representation of the provided DC/OS slaves
 
     :param slaves: slaves to render.  dicts from /mesos/state-summary
     :type slaves: [dict]
+    :param field_names: Extra fields to add to the table
+    :type slaves: [str]
     :rtype: PrettyTable
     """
 
@@ -853,10 +856,46 @@ def slave_table(slaves):
         ('ID', lambda s: s['id'])
     ])
 
-    tb = table(fields, slaves, sortby="HOSTNAME")
+    for field_name in field_names:
+        if field_name.upper() in fields:
+            continue
+        if ':' in field_name:
+            heading, field_name = field_name.split(':', 1)
+        else:
+            heading = field_name
+        fields[heading.upper()] = _dotted_itemgetter(field_name.lower())
+
+    sortby = list(fields.keys())[0]
+    tb = table(fields, slaves, sortby=sortby)
     return tb
 
 
+def _dotted_itemgetter(field_name):
+    """Returns a func that gets the value in a nested dict where the
+    `field_name` is a dotted path to the key.
+
+    Example:
+
+      >>> from dcoscli.tables import _dotted_itemgetter
+      >>> d1 = {'a': {'b': {'c': 21}}}
+      >>> d2 = {'a': {'b': {'c': 22}}}
+      >>> func = _dotted_itemgetter('a.b.c')
+      >>> func(d1)
+      21
+      >>> func(d2)
+      22
+
+    :param field_name: dotted path to key in nested dict
+    :type field_name: str
+    :rtype: callable
+    """
+
+    if '.' not in field_name:
+        return operator.itemgetter(field_name)
+    head, tail = field_name.split('.', 1)
+    return lambda d: _dotted_itemgetter(tail)(d[head])
+
+
 def _format_unix_timestamp(ts):
     """ Formats a unix timestamp in a `dcos task ls --long` format.
 
@@ -976,7 +1015,10 @@ def truncate_table(fields, objs, limits, **kwargs):
         :type function: function
         :rtype: PrettyTable
         """
-        result = str(function(obj))
+        try:
+            result = str(function(obj))
+        except KeyError:
+            result = 'N/A'
         if (limits is not None and limits.get(key) is not None):
             result = textwrap.\
                 shorten(result, width=limits.get(key), placeholder='...')

cli/tests/integrations/test_node.py

@@ -45,6 +45,17 @@ def test_node_table():
     assert len(stdout.decode('utf-8').split('\n')) > 2
 
 
+def test_node_table_field_option():
+    returncode, stdout, stderr = exec_command(
+        ['dcos', 'node', '--field=disk_used:used_resources.disk'])
+
+    assert returncode == 0
+    assert stderr == b''
+    lines = stdout.decode('utf-8').splitlines()
+    assert len(lines) > 2
+    assert lines[0].split() == ['HOSTNAME', 'IP', 'ID', 'DISK_USED']
+
+
 def test_node_log_empty():
     stderr = b"You must choose one of --leader or --mesos-id.\n"
     assert_command(['dcos', 'node', 'log'], returncode=1, stderr=stderr)