diff --git a/vendor/github.com/json-iterator/go/iter_str.go b/vendor/github.com/json-iterator/go/iter_str.go
new file mode 100644
index 0000000..adc487e
--- /dev/null
+++ b/vendor/github.com/json-iterator/go/iter_str.go
@@ -0,0 +1,215 @@
+package jsoniter
+
+import (
+	"fmt"
+	"unicode/utf16"
+)
+
+// ReadString read string from iterator
+func (iter *Iterator) ReadString() (ret string) {
+	c := iter.nextToken()
+	if c == '"' {
+		for i := iter.head; i < iter.tail; i++ {
+			c := iter.buf[i]
+			if c == '"' {
+				ret = string(iter.buf[iter.head:i])
+				iter.head = i + 1
+				return ret
+			} else if c == '\\' {
+				break
+			} else if c < ' ' {
+				iter.ReportError("ReadString",
+					fmt.Sprintf(`invalid control character found: %d`, c))
+				return
+			}
+		}
+		return iter.readStringSlowPath()
+	} else if c == 'n' {
+		iter.skipThreeBytes('u', 'l', 'l')
+		return ""
+	}
+	iter.ReportError("ReadString", `expects " or n, but found `+string([]byte{c}))
+	return
+}
+
+func (iter *Iterator) readStringSlowPath() (ret string) {
+	var str []byte
+	var c byte
+	for iter.Error == nil {
+		c = iter.readByte()
+		if c == '"' {
+			return string(str)
+		}
+		if c == '\\' {
+			c = iter.readByte()
+			str = iter.readEscapedChar(c, str)
+		} else {
+			str = append(str, c)
+		}
+	}
+	iter.ReportError("readStringSlowPath", "unexpected end of input")
+	return
+}
+
+func (iter *Iterator) readEscapedChar(c byte, str []byte) []byte {
+	switch c {
+	case 'u':
+		r := iter.readU4()
+		if utf16.IsSurrogate(r) {
+			c = iter.readByte()
+			if iter.Error != nil {
+				return nil
+			}
+			if c != '\\' {
+				iter.unreadByte()
+				str = appendRune(str, r)
+				return str
+			}
+			c = iter.readByte()
+			if iter.Error != nil {
+				return nil
+			}
+			if c != 'u' {
+				str = appendRune(str, r)
+				return iter.readEscapedChar(c, str)
+			}
+			r2 := iter.readU4()
+			if iter.Error != nil {
+				return nil
+			}
+			combined := utf16.DecodeRune(r, r2)
+			if combined == '\uFFFD' {
+				str = appendRune(str, r)
+				str = appendRune(str, r2)
+			} else {
+				str = appendRune(str, combined)
+			}
+		} else {
+			str = appendRune(str, r)
+		}
+	case '"':
+		str = append(str, '"')
+	case '\\':
+		str = append(str, '\\')
+	case '/':
+		str = append(str, '/')
+	case 'b':
+		str = append(str, '\b')
+	case 'f':
+		str = append(str, '\f')
+	case 'n':
+		str = append(str, '\n')
+	case 'r':
+		str = append(str, '\r')
+	case 't':
+		str = append(str, '\t')
+	default:
+		iter.ReportError("readEscapedChar",
+			`invalid escape char after \`)
+		return nil
+	}
+	return str
+}
+
+// ReadStringAsSlice read string from iterator without copying into string form.
+// The []byte can not be kept, as it will change after next iterator call.
+func (iter *Iterator) ReadStringAsSlice() (ret []byte) {
+	c := iter.nextToken()
+	if c == '"' {
+		for i := iter.head; i < iter.tail; i++ {
+			// require ascii string and no escape
+			// for: field name, base64, number
+			if iter.buf[i] == '"' {
+				// fast path: reuse the underlying buffer
+				ret = iter.buf[iter.head:i]
+				iter.head = i + 1
+				return ret
+			}
+		}
+		readLen := iter.tail - iter.head
+		copied := make([]byte, readLen, readLen*2)
+		copy(copied, iter.buf[iter.head:iter.tail])
+		iter.head = iter.tail
+		for iter.Error == nil {
+			c := iter.readByte()
+			if c == '"' {
+				return copied
+			}
+			copied = append(copied, c)
+		}
+		return copied
+	}
+	iter.ReportError("ReadStringAsSlice", `expects " or n, but found `+string([]byte{c}))
+	return
+}
+
+func (iter *Iterator) readU4() (ret rune) {
+	for i := 0; i < 4; i++ {
+		c := iter.readByte()
+		if iter.Error != nil {
+			return
+		}
+		if c >= '0' && c <= '9' {
+			ret = ret*16 + rune(c-'0')
+		} else if c >= 'a' && c <= 'f' {
+			ret = ret*16 + rune(c-'a'+10)
+		} else if c >= 'A' && c <= 'F' {
+			ret = ret*16 + rune(c-'A'+10)
+		} else {
+			iter.ReportError("readU4", "expects 0~9 or a~f, but found "+string([]byte{c}))
+			return
+		}
+	}
+	return ret
+}
+
+const (
+	t1 = 0x00 // 0000 0000
+	tx = 0x80 // 1000 0000
+	t2 = 0xC0 // 1100 0000
+	t3 = 0xE0 // 1110 0000
+	t4 = 0xF0 // 1111 0000
+	t5 = 0xF8 // 1111 1000
+
+	maskx = 0x3F // 0011 1111
+	mask2 = 0x1F // 0001 1111
+	mask3 = 0x0F // 0000 1111
+	mask4 = 0x07 // 0000 0111
+
+	rune1Max = 1<<7 - 1
+	rune2Max = 1<<11 - 1
+	rune3Max = 1<<16 - 1
+
+	surrogateMin = 0xD800
+	surrogateMax = 0xDFFF
+
+	maxRune   = '\U0010FFFF' // Maximum valid Unicode code point.
+	runeError = '\uFFFD'     // the "error" Rune or "Unicode replacement character"
+)
+
+func appendRune(p []byte, r rune) []byte {
+	// Negative values are erroneous. Making it unsigned addresses the problem.
+	switch i := uint32(r); {
+	case i <= rune1Max:
+		p = append(p, byte(r))
+		return p
+	case i <= rune2Max:
+		p = append(p, t2|byte(r>>6))
+		p = append(p, tx|byte(r)&maskx)
+		return p
+	case i > maxRune, surrogateMin <= i && i <= surrogateMax:
+		r = runeError
+		fallthrough
+	case i <= rune3Max:
+		p = append(p, t3|byte(r>>12))
+		p = append(p, tx|byte(r>>6)&maskx)
+		p = append(p, tx|byte(r)&maskx)
+		return p
+	default:
+		p = append(p, t4|byte(r>>18))
+		p = append(p, tx|byte(r>>12)&maskx)
+		p = append(p, tx|byte(r>>6)&maskx)
+		p = append(p, tx|byte(r)&maskx)
+		return p
+	}
+}