Unescape characters in inspect JSON format output

This patch changes the way the inspect command output is displayed
on the screen when the format is set to JSON.

Note: if the output is redirected to a file the output is *not*
escaped.

For example, before this commit if you run:
$ sudo podman inspect --format "json" daveimg
[
   {
   ...
      "Author": "Dave \u003cdave@corp.io\u003e",
   }
   ...
]

with this patch the output will be:
[
   {
   ...
      "Author": "Dave <dave@corp.io>",
   }
   ...
]

Signed-off-by: Boaz Shuster <ripcurld.github@gmail.com>

Closes: #602
Approved by: mheon

cmd/podman/formats/formats.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"encoding/json"
 	"fmt"
+	"io"
 	"os"
 	"strings"
 	"text/tabwriter"
@@ -55,12 +56,23 @@ type YAMLStruct struct {
 	Output interface{}
 }
 
+func setJSONFormatEncoder(isTerminal bool, w io.Writer) *json.Encoder {
+	enc := json.NewEncoder(w)
+	enc.SetIndent("", "    ")
+	if isTerminal {
+		enc.SetEscapeHTML(false)
+	}
+	return enc
+}
+
 // Out method for JSON Arrays
 func (j JSONStructArray) Out() error {
-	data, err := json.MarshalIndent(j.Output, "", "    ")
-	if err != nil {
+	buf := bytes.NewBuffer(nil)
+	enc := setJSONFormatEncoder(terminal.IsTerminal(int(os.Stdout.Fd())), buf)
+	if err := enc.Encode(j.Output); err != nil {
 		return err
 	}
+	data := buf.Bytes()
 
 	// JSON returns a byte array with a literal null [110 117 108 108] in it
 	// if it is passed empty data.  We used bytes.Compare to see if that is

cmd/podman/formats/formats_test.go

@@ -0,0 +1,42 @@
+package formats
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+
+	"github.com/projectatomic/libpod/pkg/inspect"
+)
+
+func TestSetJSONFormatEncoder(t *testing.T) {
+	tt := []struct {
+		name       string
+		imageData  *inspect.ImageData
+		expected   string
+		isTerminal bool
+	}{
+		{
+			name:       "HTML tags are not escaped",
+			imageData:  &inspect.ImageData{Author: "dave <dave@corp.io>"},
+			expected:   `"Author": "dave <dave@corp.io>"`,
+			isTerminal: true,
+		},
+		{
+			name:       "HTML tags are escaped",
+			imageData:  &inspect.ImageData{Author: "dave <dave@corp.io>"},
+			expected:   `"Author": "dave \u003cdave@corp.io\u003e"`,
+			isTerminal: false,
+		},
+	}
+
+	for _, tc := range tt {
+		buf := bytes.NewBuffer(nil)
+		enc := setJSONFormatEncoder(tc.isTerminal, buf)
+		if err := enc.Encode(tc.imageData); err != nil {
+			t.Errorf("test %#v failed encoding: %s", tc.name, err)
+		}
+		if !strings.Contains(buf.String(), tc.expected) {
+			t.Errorf("test %#v expected output to contain %#v. Output:\n%v\n", tc.name, tc.expected, buf.String())
+		}
+	}
+}