Support tabs on MarshalIndent

config.go

@@ -14,6 +14,7 @@ import (
 // The API is created from Config by Froze.
 type Config struct {
 	IndentionStep                 int
+	IndentionChar                 byte
 	MarshalFloatWith6Digits       bool
 	EscapeHTML                    bool
 	SortMapKeys                   bool
@@ -47,26 +48,30 @@ type API interface {
 // ConfigDefault the default API
 var ConfigDefault = Config{
 	EscapeHTML: true,
+	IndentionChar: ' ',
 }.Froze()
 
 // ConfigCompatibleWithStandardLibrary tries to be 100% compatible with standard library behavior
 var ConfigCompatibleWithStandardLibrary = Config{
 	EscapeHTML:             true,
 	SortMapKeys:            true,
 	ValidateJsonRawMessage: true,
+	IndentionChar: ' ',
 }.Froze()
 
 // ConfigFastest marshals float with only 6 digits precision
 var ConfigFastest = Config{
 	EscapeHTML:                    false,
 	MarshalFloatWith6Digits:       true, // will lose precession
 	ObjectFieldMustBeSimpleString: true, // do not unescape object field
+	IndentionChar: ' ',
 }.Froze()
 
 type frozenConfig struct {
 	configBeforeFrozen            Config
 	sortMapKeys                   bool
 	indentionStep                 int
+	indentionChar                 byte
 	objectFieldMustBeSimpleString bool
 	onlyTaggedField               bool
 	disallowUnknownFields         bool
@@ -125,6 +130,7 @@ func (cfg Config) Froze() API {
 	api := &frozenConfig{
 		sortMapKeys:                   cfg.SortMapKeys,
 		indentionStep:                 cfg.IndentionStep,
+		indentionChar:                 cfg.IndentionChar,
 		objectFieldMustBeSimpleString: cfg.ObjectFieldMustBeSimpleString,
 		onlyTaggedField:               cfg.OnlyTaggedField,
 		disallowUnknownFields:         cfg.DisallowUnknownFields,
@@ -300,15 +306,26 @@ func (cfg *frozenConfig) Marshal(v interface{}) ([]byte, error) {
 }
 
 func (cfg *frozenConfig) MarshalIndent(v interface{}, prefix, indent string) ([]byte, error) {
+	var useTabs bool
 	if prefix != "" {
 		panic("prefix is not supported")
 	}
+	// some rudimentary error checking
+	newCfg := cfg.configBeforeFrozen
+	newCfg.IndentionChar = ' '
 	for _, r := range indent {
-		if r != ' ' {
-			panic("indent can only be space")
+		if r != ' ' && r != '\t' {
+			panic("indent can only be space or tabs")
+		}
+		if r == ' ' && useTabs {
+			panic("indent cannot be mixed space and tabs")
+		}
+		if r == '\t' {
+			useTabs = true
+			newCfg.IndentionChar = '\t'
 		}
 	}
-	newCfg := cfg.configBeforeFrozen
+
 	newCfg.IndentionStep = len(indent)
 	return newCfg.frozeWithCacheReuse().Marshal(v)
 }

config_test.go

@@ -0,0 +1,24 @@
+package jsoniter
+
+import (
+	"testing"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestFrozenConfig_MarshalIndentErrors(t *testing.T) {
+	var panicOccured interface{} = nil
+
+	defer func() {
+		panicOccured = recover()
+	}()
+	_, err := MarshalIndent(`{"foo":"bar"}`, "", "\n\n")
+
+	assert.NoError(t, err)
+	assert.NotNil(t, panicOccured, "MarshalIndent should panic due to invalid indent chars")
+
+	panicOccured = nil
+	_, err = MarshalIndent(`{"foo":"bar"}`, "", " \t ")
+	panicOccured = recover()
+	assert.NoError(t, err)
+	assert.NotNil(t, panicOccured, "MarshalIndent should panic due to mixed spaces and tabs")
+}

stream.go

@@ -206,6 +206,6 @@ func (stream *Stream) writeIndention(delta int) {
 	stream.writeByte('\n')
 	toWrite := stream.indention - delta
 	for i := 0; i < toWrite; i++ {
-		stream.buf = append(stream.buf, ' ')
+		stream.buf = append(stream.buf, stream.cfg.indentionChar)
 	}
 }

stream_test.go

@@ -31,11 +31,18 @@ func Test_writeBytes_should_grow_buffer(t *testing.T) {
 
 func Test_writeIndention_should_grow_buffer(t *testing.T) {
 	should := require.New(t)
-	stream := NewStream(Config{IndentionStep: 2}.Froze(), nil, 1)
+	stream := NewStream(Config{IndentionStep: 2, IndentionChar:' '}.Froze(), nil, 1)
 	stream.WriteVal([]int{1, 2, 3})
 	should.Equal("[\n  1,\n  2,\n  3\n]", string(stream.Buffer()))
 }
 
+func Test_writeIndention_with_tabs_should_grow_buffer(t *testing.T) {
+	should := require.New(t)
+	stream := NewStream(Config{IndentionStep: 2, IndentionChar: '\t'}.Froze(), nil, 1)
+	stream.WriteVal([]int{1, 2, 3})
+	should.Equal("[\n		1,\n		2,\n		3\n]", string(stream.Buffer()))
+}
+
 func Test_writeRaw_should_grow_buffer(t *testing.T) {
 	should := require.New(t)
 	stream := NewStream(ConfigDefault, nil, 1)