func nextImageUploadReq()

in nmxact/xact/image.go [160:219]
41 lines of code
10 McCabe index (conditional complexity)

func nextImageUploadReq(s sesn.Sesn, upgrade bool, data []byte, off int, imageNum int) (
	*nmp.ImageUploadReq, error) {
	var hash []byte = nil

	// Ensure we produce consistent requests while we calculate the chunk
	// length.
	txFilter, _ := s.Filters()
	if txFilter != nil {
		txFilter.Freeze()
		defer txFilter.Unfreeze()
	}

	// For 1st chunk we'll need valid data hash
	if off == 0 {
		sha := sha256.Sum256(data)
		hash = sha[:]
	}

	seq := nmxutil.NextNmpSeq()

	// Find chunk length
	chunklen, err := findChunkLen(s, hash, upgrade, data, off, imageNum, seq)
	if err != nil {
		return nil, err
	}

	// For 1st chunk we need to send at least full header so if it does not
	// fit we'll recalculate without hash
	if off == 0 && chunklen < IMAGE_UPLOAD_MIN_1ST_CHUNK {
		hash = nil
		chunklen, err = findChunkLen(s, hash, upgrade, data, off, imageNum, seq)
		if err != nil {
			return nil, err
		}
	}

	// If calculated chunk length is not enough to send at least single byte
	// we can't do much more...
	if chunklen <= 0 {
		return nil, fmt.Errorf("Cannot create image upload request; "+
			"MTU too low to fit any image data; max-payload-size=%d chunklen %d",
			s.MtuOut(), chunklen)
	}

	r := buildImageUploadReq(len(data), hash, upgrade,
		data[off:off+chunklen], off, imageNum, seq)

	// Request above should encode just fine since we calculate proper chunk
	// length but (at least for now) let's double check it
	enc, err := mgmt.EncodeMgmt(s, r.Msg())
	if err != nil {
		return nil, err
	}
	if len(enc) > s.MtuOut() {
		return nil, fmt.Errorf("Invalid chunk length; payload-size=%d "+
			"max-payload-size=%d", len(enc), s.MtuOut())
	}

	return r, nil
}