1 files changed, 131 insertions, 0 deletions
diff --git a/misc.go b/misc.go
new file mode 100644
index 0000000..132b177
--- /dev/null
+++ b/misc.go
@@ -0,0 +1,131 @@
+// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+package lowmemjson
+
+import (
+	"encoding/json"
+	"io"
+	"reflect"
+	"unicode/utf8"
+)
+
+const Tab = "\t"
+
+const hex = "0123456789abcdef"
+
+var (
+	numberType    = reflect.TypeOf(json.Number(""))
+	byteType      = reflect.TypeOf(byte(0))
+	byteSliceType = reflect.TypeOf(([]byte)(nil))
+)
+
+// generic I/O /////////////////////////////////////////////////////////////////
+
+func decodeRune[T interface{ []byte | string }](s T) (r rune, size int) {
+	iface := any(s)
+	if str, ok := iface.(string); ok {
+		return utf8.DecodeRuneInString(str)
+	} else {
+		return utf8.DecodeRune(iface.([]byte))
+	}
+}
+
+func writeByte(w io.Writer, c byte) error {
+	if br, ok := w.(interface{ WriteByte(byte) error }); ok {
+		return br.WriteByte(c)
+	}
+	var buf [1]byte
+	buf[0] = c
+	if _, err := w.Write(buf[:]); err != nil {
+		return err
+	}
+	return nil
+}
+
+func writeRune(w io.Writer, c rune) (int, error) {
+	if rw, ok := w.(interface{ WriteRune(rune) (int, error) }); ok {
+		return rw.WriteRune(c)
+	}
+	var buf [utf8.UTFMax]byte
+	n := utf8.EncodeRune(buf[:], c)
+	return w.Write(buf[:n])
+}
+
+// JSON string encoding ////////////////////////////////////////////////////////
+
+func UnicodeEscapeJSSafe(c rune, _ bool) bool {
+	// JSON is notionally a JS subset, but that's not actually
+	// true.
+	//
+	// http://timelessrepo.com/json-isnt-a-javascript-subset
+	switch c {
+	case '\u2028', '\u2029':
+		return true
+	default:
+		return false
+	}
+}
+
+func UnicodeEscapeHTMLSafe(c rune, wasEscaped bool) bool {
+	switch c {
+	case '&', '<', '>':
+		return true
+	default:
+		return UnicodeEscapeJSSafe(c, wasEscaped)
+	}
+}
+
+func UnicodeEscapeDefault(c rune, wasEscaped bool) bool {
+	switch c {
+	case '\b', '\f', utf8.RuneError:
+		return true
+	default:
+		return UnicodeEscapeHTMLSafe(c, wasEscaped)
+	}
+}
+
+func writeStringUnicodeEscape(w io.Writer, c rune) (int, error) {
+	buf := [6]byte{
+		'\\',
+		'u',
+		hex[(c>>12)&0xf],
+		hex[(c>>8)&0xf],
+		hex[(c>>4)&0xf],
+		hex[(c>>0)&0xf],
+	}
+	return w.Write(buf[:])
+}
+func writeStringShortEscape(w io.Writer, c byte) (int, error) {
+	buf := [2]byte{'\\', c}
+	return w.Write(buf[:])
+}
+func writeStringChar(w io.Writer, c rune, wasEscaped bool, escaper func(rune, bool) bool) (int, error) {
+	if escaper == nil {
+		escaper = UnicodeEscapeDefault
+	}
+	switch {
+	case c <= 0xFFFF && escaper(c, wasEscaped):
+		return writeStringUnicodeEscape(w, c)
+	case c == '"' || c == '\\':
+		return writeStringShortEscape(w, byte(c))
+	case c < 0x0020:
+		switch c {
+		case '\b':
+			return writeStringShortEscape(w, 'b')
+		case '\f':
+			return writeStringShortEscape(w, 'f')
+		case '\n':
+			return writeStringShortEscape(w, 'n')
+		case '\r':
+			return writeStringShortEscape(w, 'r')
+		case '\t':
+			return writeStringShortEscape(w, 't')
+		default:
+			return writeStringUnicodeEscape(w, c)
+		}
+	default:
+		return writeRune(w, c)
+	}
+}