Add encoding/json from standard library

internal/3rdparty/json/fold.go

@@ -0,0 +1,48 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package json
+
+import (
+	"unicode"
+	"unicode/utf8"
+)
+
+// foldName returns a folded string such that foldName(x) == foldName(y)
+// is identical to bytes.EqualFold(x, y).
+func foldName(in []byte) []byte {
+	// This is inlinable to take advantage of "function outlining".
+	var arr [32]byte // large enough for most JSON names
+	return appendFoldedName(arr[:0], in)
+}
+
+func appendFoldedName(out, in []byte) []byte {
+	for i := 0; i < len(in); {
+		// Handle single-byte ASCII.
+		if c := in[i]; c < utf8.RuneSelf {
+			if 'a' <= c && c <= 'z' {
+				c -= 'a' - 'A'
+			}
+			out = append(out, c)
+			i++
+			continue
+		}
+		// Handle multi-byte Unicode.
+		r, n := utf8.DecodeRune(in[i:])
+		out = utf8.AppendRune(out, foldRune(r))
+		i += n
+	}
+	return out
+}
+
+// foldRune is returns the smallest rune for all runes in the same fold set.
+func foldRune(r rune) rune {
+	for {
+		r2 := unicode.SimpleFold(r)
+		if r2 <= r {
+			return r2
+		}
+		r = r2
+	}
+}