Add a validation-specific Ansible output callback

The validations have a few specifics in how they're used and what
information is important. So this formats the validation output in a way
that should highlight the failures themselves and make it more obvious
what went wrong and what to do when a validation fails.

Change-Id: I9730f2dd04868c5de46ae90bd545865d17aec530
Closes-Bug: #1625526

ansible.cfg

@@ -0,0 +1,4 @@
+[defaults]
+retry_files_enabled = False
+host_key_checking=False
+stdout_callback = validation_output

validations/callback_plugins/validation_output.py

@@ -0,0 +1,152 @@
+#!/usr/bin/env python
+
+# -*- coding: utf-8 -*-
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+# implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from __future__ import print_function
+
+import pprint
+
+from ansible.plugins.callback import CallbackBase
+
+
+FAILURE_TEMPLATE = """\
+Task '{}' failed:
+Host: {}
+Message: {}
+"""
+
+
+WARNING_TEMPLATE = """\
+Task '{}' succeded, but had some warnings:
+Host: {}
+Warnings:
+"""
+
+
+def indent(text):
+    '''Indent the given text by four spaces.'''
+    return ''.join('    {}\n'.format(line) for line in text.splitlines())
+
+
+def print_failure_message(host_name, task_name, results):
+    '''Print a human-readable error info from Ansible result dictionary.'''
+    def is_script(results):
+        return ('rc' in results and
+                'invocation' in results and
+                results['invocation'].get('module_name') == 'script' and
+                '_raw_params' in results['invocation'].get('module_args', {}))
+
+    display_full_results = False
+    if 'rc' in results and 'cmd' in results:
+        command = results['cmd']
+        # The command can be either a list or a string. Concat if it's a list:
+        if type(command) == list:
+            command = " ".join(results['cmd'])
+        message = "Command `{}` exited with code: {}".format(
+            command, results['rc'])
+        # There may be an optional message attached to the command. Display it:
+        if 'msg' in results:
+            message = message + ": " + results['msg']
+    elif is_script(results):
+        script_name = results['invocation']['module_args']['_raw_params']
+        message = "Script `{}` exited with code: {}".format(
+            script_name, results['rc'])
+    elif 'msg' in results:
+        message = results['msg']
+    else:
+        message = "Unknown error"
+        display_full_results = True
+    print(FAILURE_TEMPLATE.format(task_name, host_name, message))
+    stdout = results.get('module_stdout', results.get('stdout', ''))
+    if stdout:
+        print('stdout:')
+        print(indent(stdout))
+    stderr = results.get('module_stderr', results.get('stderr', ''))
+    if stderr:
+        print('stderr:')
+        print(indent(stderr))
+    if display_full_results:
+        print("Could not get an error message. Here is the Ansible output:")
+        pprint.pprint(results, indent=4)
+    warnings = results.get('warnings', [])
+    if warnings:
+        print("Warnings:")
+        for warning in warnings:
+            print("*", warning)
+        print("")
+
+
+# TODO(shadower): test with async settings
+class CallbackModule(CallbackBase):
+    CALLBACK_VERSION = 2.0
+    CALLBACK_TYPE = 'stdout'
+    CALLBACK_NAME = 'validation_output'
+
+    def __init__(self, display=None):
+        super(CallbackModule, self).__init__(display)
+
+    def v2_playbook_on_play_start(self, play):
+        pass  # No need to notify that a play started
+
+    def v2_playbook_on_task_start(self, task, is_conditional):
+        pass  # No need to notify that a task started
+
+    def v2_runner_on_ok(self, result, **kwargs):
+        host_name = result._host
+        task_name = result._task.get_name()
+        results = result._result  # A dict of the module name etc.
+        warnings = results.get('warnings', [])
+        # Print only tasks that produced some warnings:
+        if warnings:
+            print(WARNING_TEMPLATE.format(task_name, host_name))
+            for warning in warnings:
+                print("*", warning)
+
+    def v2_runner_on_failed(self, result, **kwargs):
+        host_name = result._host
+        task_name = result._task.get_name()
+
+        result_dict = result._result  # A dict of the module name etc.
+        if 'results' in result_dict:
+            # The task is a list of items under `results`
+            for item in result_dict['results']:
+                if item.get('failed', False):
+                    print_failure_message(host_name, task_name, item)
+        else:
+            # The task is a "normal" module invocation
+            print_failure_message(host_name, task_name, result_dict)
+
+    def v2_runner_on_skipped(self, result, **kwargs):
+        pass  # No need to print skipped tasks
+
+    def v2_runner_on_unreachable(self, result, **kwargs):
+        host_name = result._host
+        task_name = result._task.get_name()
+        results = {'msg': 'The host is unreachable.'}
+        print_failure_message(host_name, task_name, results)
+
+    def v2_playbook_on_stats(self, stats):
+        def failed(host):
+            return (stats.summarize(host).get('failures', 0) > 0 or
+                    stats.summarize(host).get('unreachable', 0) > 0)
+
+        hosts = sorted(stats.processed.keys())
+        failed_hosts = [host for host in hosts if failed(host)]
+        if failed_hosts:
+            print("Failure! The validation failed for the following hosts:")
+            for host in hosts:
+                print("*", host)
+        else:
+            print("Success! The validation passed for all hosts.")