Display JSON in indented, colored format in api output

pkg/cmd/api/api.go

@@ -6,11 +6,13 @@ import (
 	"io/ioutil"
 	"net/http"
 	"os"
+	"regexp"
 	"strconv"
 	"strings"
 
 	"github.com/cli/cli/pkg/cmdutil"
 	"github.com/cli/cli/pkg/iostreams"
+	"github.com/cli/cli/pkg/jsoncolor"
 	"github.com/spf13/cobra"
 )
 
@@ -109,9 +111,18 @@ func apiRun(opts *ApiOptions) error {
 	}
 	defer resp.Body.Close()
 
-	_, err = io.Copy(opts.IO.Out, resp.Body)
-	if err != nil {
-		return err
+	isJSON, _ := regexp.MatchString(`[/+]json(;|$)`, resp.Header.Get("Content-Type"))
+
+	if isJSON && opts.IO.ColorEnabled() {
+		err = jsoncolor.Write(opts.IO.Out, resp.Body, "  ")
+		if err != nil {
+			return err
+		}
+	} else {
+		_, err = io.Copy(opts.IO.Out, resp.Body)
+		if err != nil {
+			return err
+		}
 	}
 
 	// TODO: detect GraphQL errors

pkg/iostreams/iostreams.go

@@ -5,19 +5,36 @@ import (
 	"io"
 	"io/ioutil"
 	"os"
+
+	"github.com/mattn/go-colorable"
+	"github.com/mattn/go-isatty"
 )
 
 type IOStreams struct {
 	In     io.ReadCloser
 	Out    io.Writer
 	ErrOut io.Writer
+
+	colorEnabled bool
+}
+
+func (s *IOStreams) ColorEnabled() bool {
+	return s.colorEnabled
 }
 
 func System() *IOStreams {
+	var out io.Writer = os.Stdout
+	var colorEnabled bool
+	if os.Getenv("NO_COLOR") == "" && isTerminal(os.Stdout) {
+		out = colorable.NewColorable(os.Stdout)
+		colorEnabled = true
+	}
+
 	return &IOStreams{
-		In:     os.Stdin,
-		Out:    os.Stdout,
-		ErrOut: os.Stderr,
+		In:           os.Stdin,
+		Out:          out,
+		ErrOut:       os.Stderr,
+		colorEnabled: colorEnabled,
 	}
 }
 
@@ -31,3 +48,7 @@ func Test() (*IOStreams, *bytes.Buffer, *bytes.Buffer, *bytes.Buffer) {
 		ErrOut: errOut,
 	}, in, out, errOut
 }
+
+func isTerminal(f *os.File) bool {
+	return isatty.IsTerminal(f.Fd()) || isatty.IsCygwinTerminal(f.Fd())
+}

pkg/jsoncolor/jsoncolor.go

@@ -0,0 +1,95 @@
+package jsoncolor
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"strings"
+)
+
+const (
+	colorDelim  = "1;38" // bright white
+	colorKey    = "1;34" // bright blue
+	colorNull   = "1;30" // gray
+	colorString = "32"   // green
+	colorBool   = "33"   // yellow
+)
+
+func Write(w io.Writer, r io.Reader, indent string) error {
+	dec := json.NewDecoder(r)
+	dec.UseNumber()
+
+	var idx int
+	var stack []json.Delim
+
+	for {
+		t, err := dec.Token()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return err
+		}
+
+		switch tt := t.(type) {
+		case json.Delim:
+			switch tt {
+			case '{', '[':
+				stack = append(stack, tt)
+				idx = 0
+				fmt.Fprintf(w, "\x1b[%sm%s\x1b[m", colorDelim, tt)
+				if dec.More() {
+					fmt.Fprint(w, "\n", strings.Repeat(indent, len(stack)))
+				}
+				continue
+			case '}', ']':
+				stack = stack[:len(stack)-1]
+				idx = 0
+				fmt.Fprintf(w, "\x1b[%sm%s\x1b[m", colorDelim, tt)
+			}
+		default:
+			b, err := json.Marshal(tt)
+			if err != nil {
+				return err
+			}
+
+			isKey := len(stack) > 0 && stack[len(stack)-1] == '{' && idx%2 == 0
+			idx++
+
+			var color string
+			if isKey {
+				color = colorKey
+			} else if tt == nil {
+				color = colorNull
+			} else {
+				switch t.(type) {
+				case string:
+					color = colorString
+				case bool:
+					color = colorBool
+				}
+			}
+
+			if color == "" {
+				_, _ = w.Write(b)
+			} else {
+				fmt.Fprintf(w, "\x1b[%sm%s\x1b[m", color, b)
+			}
+
+			if isKey {
+				fmt.Fprintf(w, "\x1b[%sm:\x1b[m ", colorDelim)
+				continue
+			}
+		}
+
+		if dec.More() {
+			fmt.Fprintf(w, "\x1b[%sm,\x1b[m\n%s", colorDelim, strings.Repeat(indent, len(stack)))
+		} else if len(stack) > 0 {
+			fmt.Fprint(w, "\n", strings.Repeat(indent, len(stack)-1))
+		} else {
+			fmt.Fprint(w, "\n")
+		}
+	}
+
+	return nil
+}