func preconditionChecks()

in internal/storage/fake/bucket.go [304:392]
70 lines of code
15 McCabe index (conditional complexity)

func preconditionChecks(b *bucket, req *gcs.CreateObjectRequest, contents []byte) (err error) {
	// Find any existing record for this name.
	existingIndex := b.objects.find(req.Name)

	var existingRecord *fakeObject
	if existingIndex < len(b.objects) {
		existingRecord = &b.objects[existingIndex]
	}

	// Check the provided checksum, if any.
	if req.CRC32C != nil {
		actual := crc32.Checksum(contents, crc32cTable)
		if actual != *req.CRC32C {
			err = fmt.Errorf(
				"CRC32C mismatch: got 0x%08x, expected 0x%08x",
				actual,
				*req.CRC32C)

			return
		}
	}

	// Check the provided hash, if any.
	if req.MD5 != nil {
		actual := md5.Sum(contents)
		if actual != *req.MD5 {
			err = fmt.Errorf(
				"MD5 mismatch: got %s, expected %s",
				hex.EncodeToString(actual[:]),
				hex.EncodeToString(req.MD5[:]))

			return
		}
	}

	// Check preconditions.
	if req.GenerationPrecondition != nil {
		if *req.GenerationPrecondition == 0 && existingRecord != nil {
			err = &gcs.PreconditionError{
				Err: errors.New("precondition failed: object exists"),
			}

			return
		}

		if *req.GenerationPrecondition > 0 {
			if existingRecord == nil {
				err = &gcs.PreconditionError{
					Err: errors.New("precondition failed: object doesn't exist"),
				}

				return
			}

			existingGen := existingRecord.metadata.Generation
			if existingGen != *req.GenerationPrecondition {
				err = &gcs.PreconditionError{
					Err: fmt.Errorf(
						"precondition failed: object has generation %v",
						existingGen),
				}

				return
			}
		}
	}

	if req.MetaGenerationPrecondition != nil {
		if existingRecord == nil {
			err = &gcs.PreconditionError{
				Err: errors.New("precondition failed: object doesn't exist"),
			}

			return
		}

		existingMetaGen := existingRecord.metadata.MetaGeneration
		if existingMetaGen != *req.MetaGenerationPrecondition {
			err = &gcs.PreconditionError{
				Err: fmt.Errorf(
					"precondition failed: object has meta-generation %v",
					existingMetaGen),
			}
			return
		}
	}

	return
}