func CombineUnwrappedShares()

in client/shares/shares.go [180:214]

• 25 lines of code
• 7 McCabe index (conditional complexity)

func CombineUnwrappedShares(keyCfg *configpb.KeyConfig, unwrappedShares []UnwrappedShare) ([]byte, error) {
	// Reconstitute DEK.
	var combinedShares []byte

	switch keyCfg.KeySplittingAlgorithm.(type) {
	// DEK wasn't split, so combined shares is just the sole share.
	case *configpb.KeyConfig_NoSplit:
		if len(unwrappedShares) != 1 {
			return nil, fmt.Errorf("number of unwrapped shares is %v but expected 1 for 'no split' option", len(unwrappedShares))
		}

		combinedShares = unwrappedShares[0].Share

	// Reverse Shamir's Secret Sharing to reconstitute the whole DEK.
	case *configpb.KeyConfig_Shamir:
		if len(unwrappedShares) < int(keyCfg.GetShamir().GetThreshold()) {
			return nil, fmt.Errorf("only successfully unwrapped %v shares, which is fewer than threshold of %v", len(unwrappedShares), keyCfg.GetShamir().GetThreshold())
		}
		var err error
		combinedShares, err = CombineShares(unwrappedShares, int(keyCfg.GetShamir().GetShares()), int(keyCfg.GetShamir().GetThreshold()))
		if err != nil {
			return nil, fmt.Errorf("Error combining DEK shares: %v", err)
		}

	default:
		return nil, fmt.Errorf("Unknown key splitting algorithm")

	}

	if len(combinedShares) != int(DEKBytes) {
		return nil, fmt.Errorf("Reconstituted DEK has the wrong length")
	}

	return combinedShares, nil
}