3 files changed, 69 insertions, 37 deletions
diff --git a/src/encoding/json/encode.go b/src/encoding/json/encode.go
index 9c043593ce..578d551102 100644
--- a/src/encoding/json/encode.go
+++ b/src/encoding/json/encode.go
@@ -635,11 +635,12 @@ func stringEncoder(e *encodeState, v reflect.Value, opts encOpts) {
 		return
 	}
 	if opts.quoted {
-		b := make([]byte, 0, v.Len()+2)
-		b = append(b, '"')
-		b = append(b, []byte(v.String())...)
-		b = append(b, '"')
-		e.stringBytes(b, opts.escapeHTML)
+		e2 := newEncodeState()
+		// Since we encode the string twice, we only need to escape HTML
+		// the first time.
+		e2.string(v.String(), opts.escapeHTML)
+		e.stringBytes(e2.Bytes(), false)
+		encodeStatePool.Put(e2)
 	} else {
 		e.string(v.String(), opts.escapeHTML)
 	}
diff --git a/src/encoding/json/encode_test.go b/src/encoding/json/encode_test.go
index 5110c7de9b..7290eca06f 100644
--- a/src/encoding/json/encode_test.go
+++ b/src/encoding/json/encode_test.go
@@ -79,37 +79,66 @@ type StringTag struct {
 	NumberStr  Number  `json:",string"`
 }
 
-var stringTagExpected = `{
- "BoolStr": "true",
- "IntStr": "42",
- "UintptrStr": "44",
- "StrStr": "\"xzbit\"",
- "NumberStr": "46"
-}`
-
-func TestStringTag(t *testing.T) {
-	var s StringTag
-	s.BoolStr = true
-	s.IntStr = 42
-	s.UintptrStr = 44
-	s.StrStr = "xzbit"
-	s.NumberStr = "46"
-	got, err := MarshalIndent(&s, "", " ")
-	if err != nil {
-		t.Fatal(err)
-	}
-	if got := string(got); got != stringTagExpected {
-		t.Fatalf(" got: %s\nwant: %s\n", got, stringTagExpected)
+func TestRoundtripStringTag(t *testing.T) {
+	tests := []struct {
+		name string
+		in   StringTag
+		want string // empty to just test that we roundtrip
+	}{
+		{
+			name: "AllTypes",
+			in: StringTag{
+				BoolStr:    true,
+				IntStr:     42,
+				UintptrStr: 44,
+				StrStr:     "xzbit",
+				NumberStr:  "46",
+			},
+			want: `{
+				"BoolStr": "true",
+				"IntStr": "42",
+				"UintptrStr": "44",
+				"StrStr": "\"xzbit\"",
+				"NumberStr": "46"
+			}`,
+		},
+		{
+			// See golang.org/issues/38173.
+			name: "StringDoubleEscapes",
+			in: StringTag{
+				StrStr:    "\b\f\n\r\t\"\\",
+				NumberStr: "0", // just to satisfy the roundtrip
+			},
+			want: `{
+				"BoolStr": "false",
+				"IntStr": "0",
+				"UintptrStr": "0",
+				"StrStr": "\"\\u0008\\u000c\\n\\r\\t\\\"\\\\\"",
+				"NumberStr": "0"
+			}`,
+		},
 	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			// Indent with a tab prefix to make the multi-line string
+			// literals in the table nicer to read.
+			got, err := MarshalIndent(&test.in, "\t\t\t", "\t")
+			if err != nil {
+				t.Fatal(err)
+			}
+			if got := string(got); got != test.want {
+				t.Fatalf(" got: %s\nwant: %s\n", got, test.want)
+			}
 
-	// Verify that it round-trips.
-	var s2 StringTag
-	err = NewDecoder(bytes.NewReader(got)).Decode(&s2)
-	if err != nil {
-		t.Fatalf("Decode: %v", err)
-	}
-	if !reflect.DeepEqual(s, s2) {
-		t.Fatalf("decode didn't match.\nsource: %#v\nEncoded as:\n%s\ndecode: %#v", s, string(got), s2)
+			// Verify that it round-trips.
+			var s2 StringTag
+			if err := Unmarshal(got, &s2); err != nil {
+				t.Fatalf("Decode: %v", err)
+			}
+			if !reflect.DeepEqual(test.in, s2) {
+				t.Fatalf("decode didn't match.\nsource: %#v\nEncoded as:\n%s\ndecode: %#v", test.in, string(got), s2)
+			}
+		})
 	}
 }
 
diff --git a/src/encoding/json/stream_test.go b/src/encoding/json/stream_test.go
index ebb4f231d1..c9e5334337 100644
--- a/src/encoding/json/stream_test.go
+++ b/src/encoding/json/stream_test.go
@@ -144,14 +144,15 @@ func TestEncoderSetEscapeHTML(t *testing.T) {
 		},
 		{
 			"stringOption", stringOption,
-			`{"bar":"\"\u003chtml\u003efoobar\u003c/html\u003e\""}`,
+			`{"bar":"\"\\u003chtml\\u003efoobar\\u003c/html\\u003e\""}`,
 			`{"bar":"\"<html>foobar</html>\""}`,
 		},
 	} {
 		var buf bytes.Buffer
 		enc := NewEncoder(&buf)
 		if err := enc.Encode(tt.v); err != nil {
-			t.Fatalf("Encode(%s): %s", tt.name, err)
+			t.Errorf("Encode(%s): %s", tt.name, err)
+			continue
 		}
 		if got := strings.TrimSpace(buf.String()); got != tt.wantEscape {
 			t.Errorf("Encode(%s) = %#q, want %#q", tt.name, got, tt.wantEscape)
@@ -159,7 +160,8 @@ func TestEncoderSetEscapeHTML(t *testing.T) {
 		buf.Reset()
 		enc.SetEscapeHTML(false)
 		if err := enc.Encode(tt.v); err != nil {
-			t.Fatalf("SetEscapeHTML(false) Encode(%s): %s", tt.name, err)
+			t.Errorf("SetEscapeHTML(false) Encode(%s): %s", tt.name, err)
+			continue
 		}
 		if got := strings.TrimSpace(buf.String()); got != tt.want {
 			t.Errorf("SetEscapeHTML(false) Encode(%s) = %#q, want %#q",