fix: netcup and DuckDNS.

vendor/github.com/dimchansky/utfbom/utfbom.go

@@ -0,0 +1,174 @@
+// Package utfbom implements the detection of the BOM (Unicode Byte Order Mark) and removing as necessary.
+// It wraps an io.Reader object, creating another object (Reader) that also implements the io.Reader
+// interface but provides automatic BOM checking and removing as necessary.
+package utfbom
+
+import (
+	"errors"
+	"io"
+)
+
+// Encoding is type alias for detected UTF encoding.
+type Encoding int
+
+// Constants to identify detected UTF encodings.
+const (
+	// Unknown encoding, returned when no BOM was detected
+	Unknown Encoding = iota
+
+	// UTF8, BOM bytes: EF BB BF
+	UTF8
+
+	// UTF-16, big-endian, BOM bytes: FE FF
+	UTF16BigEndian
+
+	// UTF-16, little-endian, BOM bytes: FF FE
+	UTF16LittleEndian
+
+	// UTF-32, big-endian, BOM bytes: 00 00 FE FF
+	UTF32BigEndian
+
+	// UTF-32, little-endian, BOM bytes: FF FE 00 00
+	UTF32LittleEndian
+)
+
+const maxConsecutiveEmptyReads = 100
+
+// Skip creates Reader which automatically detects BOM (Unicode Byte Order Mark) and removes it as necessary.
+// It also returns the encoding detected by the BOM.
+// If the detected encoding is not needed, you can call the SkipOnly function.
+func Skip(rd io.Reader) (*Reader, Encoding) {
+	// Is it already a Reader?
+	b, ok := rd.(*Reader)
+	if ok {
+		return b, Unknown
+	}
+
+	enc, left, err := detectUtf(rd)
+	return &Reader{
+		rd:  rd,
+		buf: left,
+		err: err,
+	}, enc
+}
+
+// SkipOnly creates Reader which automatically detects BOM (Unicode Byte Order Mark) and removes it as necessary.
+func SkipOnly(rd io.Reader) *Reader {
+	r, _ := Skip(rd)
+	return r
+}
+
+// Reader implements automatic BOM (Unicode Byte Order Mark) checking and
+// removing as necessary for an io.Reader object.
+type Reader struct {
+	rd  io.Reader // reader provided by the client
+	buf []byte    // buffered data
+	err error     // last error
+}
+
+// Read is an implementation of io.Reader interface.
+// The bytes are taken from the underlying Reader, but it checks for BOMs, removing them as necessary.
+func (r *Reader) Read(p []byte) (n int, err error) {
+	if len(p) == 0 {
+		return 0, nil
+	}
+
+	if r.buf == nil {
+		if r.err != nil {
+			return 0, r.readErr()
+		}
+
+		return r.rd.Read(p)
+	}
+
+	// copy as much as we can
+	n = copy(p, r.buf)
+	r.buf = nilIfEmpty(r.buf[n:])
+	return n, nil
+}
+
+func (r *Reader) readErr() error {
+	err := r.err
+	r.err = nil
+	return err
+}
+
+var errNegativeRead = errors.New("utfbom: reader returned negative count from Read")
+
+func detectUtf(rd io.Reader) (enc Encoding, buf []byte, err error) {
+	buf, err = readBOM(rd)
+
+	if len(buf) >= 4 {
+		if isUTF32BigEndianBOM4(buf) {
+			return UTF32BigEndian, nilIfEmpty(buf[4:]), err
+		}
+		if isUTF32LittleEndianBOM4(buf) {
+			return UTF32LittleEndian, nilIfEmpty(buf[4:]), err
+		}
+	}
+
+	if len(buf) > 2 && isUTF8BOM3(buf) {
+		return UTF8, nilIfEmpty(buf[3:]), err
+	}
+
+	if (err != nil && err != io.EOF) || (len(buf) < 2) {
+		return Unknown, nilIfEmpty(buf), err
+	}
+
+	if isUTF16BigEndianBOM2(buf) {
+		return UTF16BigEndian, nilIfEmpty(buf[2:]), err
+	}
+	if isUTF16LittleEndianBOM2(buf) {
+		return UTF16LittleEndian, nilIfEmpty(buf[2:]), err
+	}
+
+	return Unknown, nilIfEmpty(buf), err
+}
+
+func readBOM(rd io.Reader) (buf []byte, err error) {
+	const maxBOMSize = 4
+	var bom [maxBOMSize]byte // used to read BOM
+
+	// read as many bytes as possible
+	for nEmpty, n := 0, 0; err == nil && len(buf) < maxBOMSize; buf = bom[:len(buf)+n] {
+		if n, err = rd.Read(bom[len(buf):]); n < 0 {
+			panic(errNegativeRead)
+		}
+		if n > 0 {
+			nEmpty = 0
+		} else {
+			nEmpty++
+			if nEmpty >= maxConsecutiveEmptyReads {
+				err = io.ErrNoProgress
+			}
+		}
+	}
+	return
+}
+
+func isUTF32BigEndianBOM4(buf []byte) bool {
+	return buf[0] == 0x00 && buf[1] == 0x00 && buf[2] == 0xFE && buf[3] == 0xFF
+}
+
+func isUTF32LittleEndianBOM4(buf []byte) bool {
+	return buf[0] == 0xFF && buf[1] == 0xFE && buf[2] == 0x00 && buf[3] == 0x00
+}
+
+func isUTF8BOM3(buf []byte) bool {
+	return buf[0] == 0xEF && buf[1] == 0xBB && buf[2] == 0xBF
+}
+
+func isUTF16BigEndianBOM2(buf []byte) bool {
+	return buf[0] == 0xFE && buf[1] == 0xFF
+}
+
+func isUTF16LittleEndianBOM2(buf []byte) bool {
+	return buf[0] == 0xFF && buf[1] == 0xFE
+}
+
+func nilIfEmpty(buf []byte) (res []byte) {
+	if len(buf) > 0 {
+		res = buf
+	}
+	return
+}