Add go-charset and chardet to vendor

vendor/github.com/paulrosania/go-charset/charset/codepage.go

@@ -0,0 +1,133 @@
+package charset
+
+import (
+	"fmt"
+	"unicode/utf8"
+)
+
+func init() {
+	registerClass("cp", fromCodePage, toCodePage)
+}
+
+type translateFromCodePage struct {
+	byte2rune *[256]rune
+	scratch   []byte
+}
+
+type cpKeyFrom string
+type cpKeyTo string
+
+func (p *translateFromCodePage) Translate(data []byte, eof bool) (int, []byte, error) {
+	p.scratch = ensureCap(p.scratch, len(data)*utf8.UTFMax)[:0]
+	buf := p.scratch
+	for _, x := range data {
+		r := p.byte2rune[x]
+		if r < utf8.RuneSelf {
+			buf = append(buf, byte(r))
+			continue
+		}
+		size := utf8.EncodeRune(buf[len(buf):cap(buf)], r)
+		buf = buf[0 : len(buf)+size]
+	}
+	return len(data), buf, nil
+}
+
+type toCodePageInfo struct {
+	rune2byte map[rune]byte
+	// same gives the number of runes at start of code page that map exactly to
+	// unicode.
+	same rune
+}
+
+type translateToCodePage struct {
+	toCodePageInfo
+	scratch []byte
+}
+
+func (p *translateToCodePage) Translate(data []byte, eof bool) (int, []byte, error) {
+	p.scratch = ensureCap(p.scratch, len(data))
+	buf := p.scratch[:0]
+
+	for i := 0; i < len(data); {
+		r := rune(data[i])
+		size := 1
+		if r >= utf8.RuneSelf {
+			r, size = utf8.DecodeRune(data[i:])
+			if size == 1 && !eof && !utf8.FullRune(data[i:]) {
+				return i, buf, nil
+			}
+		}
+
+		var b byte
+		if r < p.same {
+			b = byte(r)
+		} else {
+			var ok bool
+			b, ok = p.rune2byte[r]
+			if !ok {
+				b = '?'
+			}
+		}
+		buf = append(buf, b)
+		i += size
+	}
+	return len(data), buf, nil
+}
+
+func fromCodePage(arg string) (Translator, error) {
+	runes, err := cache(cpKeyFrom(arg), func() (interface{}, error) {
+		data, err := readFile(arg)
+		if err != nil {
+			return nil, err
+		}
+		runes := []rune(string(data))
+		if len(runes) != 256 {
+			return nil, fmt.Errorf("charset: %q has wrong rune count (%d)", arg, len(runes))
+		}
+		r := new([256]rune)
+		copy(r[:], runes)
+		return r, nil
+	})
+	if err != nil {
+		return nil, err
+	}
+	return &translateFromCodePage{byte2rune: runes.(*[256]rune)}, nil
+}
+
+func toCodePage(arg string) (Translator, error) {
+	m, err := cache(cpKeyTo(arg), func() (interface{}, error) {
+		data, err := readFile(arg)
+		if err != nil {
+			return nil, err
+		}
+
+		info := toCodePageInfo{
+			rune2byte: make(map[rune]byte),
+			same:      256,
+		}
+		atStart := true
+		i := rune(0)
+		for _, r := range string(data) {
+			if atStart {
+				if r == i {
+					i++
+					continue
+				}
+				info.same = i
+				atStart = false
+			}
+			info.rune2byte[r] = byte(i)
+			i++
+		}
+		// TODO fix tables
+		// fmt.Printf("%s, same = %d\n", arg, info.same)
+		if i != 256 {
+			return nil, fmt.Errorf("charset: %q has wrong rune count (%d)", arg, i)
+		}
+		return info, nil
+	})
+	if err != nil {
+		return nil, err
+	}
+	return &translateToCodePage{toCodePageInfo: m.(toCodePageInfo)}, nil
+}