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166 lines
3.0 KiB
166 lines
3.0 KiB
package quotedprintable
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import "io"
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const lineMaxLen = 76
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// A Writer is a quoted-printable writer that implements io.WriteCloser.
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type Writer struct {
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// Binary mode treats the writer's input as pure binary and processes end of
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// line bytes as binary data.
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Binary bool
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w io.Writer
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i int
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line [78]byte
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cr bool
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}
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// NewWriter returns a new Writer that writes to w.
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func NewWriter(w io.Writer) *Writer {
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return &Writer{w: w}
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}
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// Write encodes p using quoted-printable encoding and writes it to the
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// underlying io.Writer. It limits line length to 76 characters. The encoded
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// bytes are not necessarily flushed until the Writer is closed.
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func (w *Writer) Write(p []byte) (n int, err error) {
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for i, b := range p {
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switch {
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// Simple writes are done in batch.
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case b >= '!' && b <= '~' && b != '=':
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continue
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case isWhitespace(b) || !w.Binary && (b == '\n' || b == '\r'):
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continue
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}
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if i > n {
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if err := w.write(p[n:i]); err != nil {
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return n, err
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}
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n = i
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}
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if err := w.encode(b); err != nil {
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return n, err
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}
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n++
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}
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if n == len(p) {
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return n, nil
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}
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if err := w.write(p[n:]); err != nil {
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return n, err
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}
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return len(p), nil
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}
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// Close closes the Writer, flushing any unwritten data to the underlying
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// io.Writer, but does not close the underlying io.Writer.
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func (w *Writer) Close() error {
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if err := w.checkLastByte(); err != nil {
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return err
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}
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return w.flush()
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}
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// write limits text encoded in quoted-printable to 76 characters per line.
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func (w *Writer) write(p []byte) error {
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for _, b := range p {
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if b == '\n' || b == '\r' {
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// If the previous byte was \r, the CRLF has already been inserted.
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if w.cr && b == '\n' {
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w.cr = false
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continue
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}
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if b == '\r' {
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w.cr = true
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}
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if err := w.checkLastByte(); err != nil {
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return err
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}
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if err := w.insertCRLF(); err != nil {
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return err
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}
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continue
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}
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if w.i == lineMaxLen-1 {
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if err := w.insertSoftLineBreak(); err != nil {
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return err
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}
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}
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w.line[w.i] = b
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w.i++
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w.cr = false
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}
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return nil
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}
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func (w *Writer) encode(b byte) error {
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if lineMaxLen-1-w.i < 3 {
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if err := w.insertSoftLineBreak(); err != nil {
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return err
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}
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}
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w.line[w.i] = '='
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w.line[w.i+1] = upperhex[b>>4]
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w.line[w.i+2] = upperhex[b&0x0f]
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w.i += 3
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return nil
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}
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// checkLastByte encodes the last buffered byte if it is a space or a tab.
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func (w *Writer) checkLastByte() error {
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if w.i == 0 {
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return nil
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}
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b := w.line[w.i-1]
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if isWhitespace(b) {
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w.i--
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if err := w.encode(b); err != nil {
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return err
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}
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}
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return nil
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}
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func (w *Writer) insertSoftLineBreak() error {
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w.line[w.i] = '='
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w.i++
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return w.insertCRLF()
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}
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func (w *Writer) insertCRLF() error {
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w.line[w.i] = '\r'
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w.line[w.i+1] = '\n'
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w.i += 2
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return w.flush()
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}
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func (w *Writer) flush() error {
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if _, err := w.w.Write(w.line[:w.i]); err != nil {
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return err
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}
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w.i = 0
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return nil
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}
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func isWhitespace(b byte) bool {
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return b == ' ' || b == '\t'
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}
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