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