Method newDecrypter

backend/crypt/cipher.go:793–818

newDecrypter creates a new file handle decrypting on the fly

(rc io.ReadCloser)

// newDecrypter creates a new file handle decrypting on the fly
func (c *Cipher) newDecrypter(rc io.ReadCloser) (*decrypter, error) {
	fh := &decrypter{
		rc:      rc,
		c:       c,
		buf:     c.getBlock(),
		readBuf: c.getBlock(),
		limit:   -1,
	}
	// Read file header (magic + nonce)
	readBuf := (*fh.readBuf)[:fileHeaderSize]
	n, err := readers.ReadFill(fh.rc, readBuf)
	if n < fileHeaderSize && err == io.EOF {
		// This read from 0..fileHeaderSize-1 bytes
		return nil, fh.finishAndClose(ErrorEncryptedFileTooShort)
	} else if err != io.EOF && err != nil {
		return nil, fh.finishAndClose(err)
	}
	// check the magic
	if !bytes.Equal(readBuf[:fileMagicSize], fileMagicBytes) {
		return nil, fh.finishAndClose(ErrorEncryptedBadMagic)
	}
	// retrieve the nonce
	fh.nonce.fromBuf(readBuf[fileMagicSize:])
	fh.initialNonce = fh.nonce
	return fh, nil
}

// newDecrypterSeek creates a new file handle decrypting on the fly
func (c *Cipher) newDecrypterSeek(ctx context.Context, open OpenRangeSeek, offset, limit int64) (fh *decrypter, err error) {