Implement a json formatter in cliff

This change replaces the cliff-tablib json formatter with an internal
replacement. It differs from the tablib formatter in the following ways:
- by default outputs with an indent of 2 spaces. The --noindent formatting
  argument outputs with no indentation, to save space or to pipe to tools
  which can't handle multi-line input.
- emit_one serialises a simple dict where the column name is the key
and the data item is the value (rather than a list of dicts with
'Field' and 'Value' keys)

The cliff release which contains this change will need a corresponding
cliff-tablib release which removes the json formatter from its setup.py
entry_points.

Change-Id: I7f9b1f339d96ead347a0c9d95ec7004a78d8c9d5
Related-Bug: #1308744

cliff/formatters/json_format.py

@@ -0,0 +1,30 @@
+"""Output formatters for JSON.
+"""
+
+import json
+
+from .base import ListFormatter, SingleFormatter
+
+
+class JSONFormatter(ListFormatter, SingleFormatter):
+
+    def add_argument_group(self, parser):
+        group = parser.add_argument_group(title='json formatter')
+        group.add_argument(
+            '--noindent',
+            action='store_true',
+            dest='noindent',
+            help='whether to disable indenting the JSON'
+        )
+
+    def emit_list(self, column_names, data, stdout, parsed_args):
+        items = []
+        for item in data:
+            items.append(dict(zip(column_names, item)))
+        indent = None if parsed_args.noindent else 2
+        json.dump(items, stdout, indent=indent)
+
+    def emit_one(self, column_names, data, stdout, parsed_args):
+        one = dict(zip(column_names, data))
+        indent = None if parsed_args.noindent else 2
+        json.dump(one, stdout, indent=indent)

cliff/tests/test_formatters_json.py

@@ -0,0 +1,71 @@
+#!/usr/bin/env python
+from six import StringIO
+import json
+
+from cliff.formatters import json_format
+
+import mock
+
+
+def test_json_format_one():
+    sf = json_format.JSONFormatter()
+    c = ('a', 'b', 'c', 'd')
+    d = ('A', 'B', 'C', '"escape me"')
+    expected = {
+        'a': 'A',
+        'b': 'B',
+        'c': 'C',
+        'd': '"escape me"'
+    }
+    args = mock.Mock()
+    sf.add_argument_group(args)
+
+    args.noindent = True
+    output = StringIO()
+    sf.emit_one(c, d, output, args)
+    value = output.getvalue()
+    print(len(value.splitlines()))
+    assert 1 == len(value.splitlines())
+    actual = json.loads(value)
+    assert expected == actual
+
+    args.noindent = False
+    output = StringIO()
+    sf.emit_one(c, d, output, args)
+    value = output.getvalue()
+    assert 6 == len(value.splitlines())
+    actual = json.loads(value)
+    assert expected == actual
+
+
+def test_json_format_list():
+    sf = json_format.JSONFormatter()
+    c = ('a', 'b', 'c')
+    d = (
+        ('A1', 'B1', 'C1'),
+        ('A2', 'B2', 'C2'),
+        ('A3', 'B3', 'C3')
+    )
+    expected = [
+        {'a': 'A1', 'b': 'B1', 'c': 'C1'},
+        {'a': 'A2', 'b': 'B2', 'c': 'C2'},
+        {'a': 'A3', 'b': 'B3', 'c': 'C3'}
+    ]
+    args = mock.Mock()
+    sf.add_argument_group(args)
+
+    args.noindent = True
+    output = StringIO()
+    sf.emit_list(c, d, output, args)
+    value = output.getvalue()
+    assert 1 == len(value.splitlines())
+    actual = json.loads(value)
+    assert expected == actual
+
+    args.noindent = False
+    output = StringIO()
+    sf.emit_list(c, d, output, args)
+    value = output.getvalue()
+    assert 17 == len(value.splitlines())
+    actual = json.loads(value)
+    assert expected == actual

doc/source/list_commands.rst

@@ -114,11 +114,35 @@ mappings.
     - Name: cliffdemo
       Size: 4096
 
+json
+----
+
+The ``json`` formatter produces an array of objects in indented JSON
+format.
+
+::
+
+    (.venv)$ cliffdemo files -f json
+    [
+      {
+        "Name": "source", 
+        "Size": 4096
+      }, 
+      {
+        "Name": "Makefile", 
+        "Size": 5569
+      }, 
+      {
+        "Name": "build", 
+        "Size": 4096
+      }
+    ]
+
 Other Formatters
 ----------------
 
-Formatters using tablib_ to produce JSON and HTML are available
-as part of `cliff-tablib`_.
+A formatter using tablib_ to produce HTML is available as part of
+`cliff-tablib`_.
 
 .. _cliff-tablib: https://github.com/dreamhost/cliff-tablib
 

doc/source/show_commands.rst

@@ -100,11 +100,28 @@ the field name is the key.
     GID: 1000
     Modified Time: 1393531476.9587486
 
+json
+----
+
+The ``json`` formatter produces a JSON object where the field name
+is the key.
+
+::
+
+    (.venv)$ cliffdemo file -f json setup.py
+    {
+      "Modified Time": 1438726433.8055942, 
+      "GID": 1000, 
+      "UID": 1000, 
+      "Name": "setup.py", 
+      "Size": 1028
+    }
+
 Other Formatters
 ----------------
 
-Formatters using tablib_ to produce JSON and HTML are available
-as part of `cliff-tablib`_.
+A formatter using tablib_ to produce HTML is available as part of
+`cliff-tablib`_.
 
 .. _cliff-tablib: https://github.com/dreamhost/cliff-tablib
 

setup.cfg

@@ -31,12 +31,14 @@ cliff.formatter.list =
     csv = cliff.formatters.commaseparated:CSVLister
     value = cliff.formatters.value:ValueFormatter
     yaml = cliff.formatters.yaml_format:YAMLFormatter
+    json = cliff.formatters.json_format:JSONFormatter
 
 cliff.formatter.show =
     table = cliff.formatters.table:TableFormatter
     shell = cliff.formatters.shell:ShellFormatter
     value = cliff.formatters.value:ValueFormatter
     yaml = cliff.formatters.yaml_format:YAMLFormatter
+    json = cliff.formatters.json_format:JSONFormatter
 
 cliff.formatter.completion =
     bash = cliff.complete:CompleteBash