datastore

type DS interface {

	// Kind returns string representation of datastore kind (i.e. "Memory")
	Kind() string

	// Address returns string representing datastore address
	Address() string

	// Open returns a read stream for given blob name or an error. In case blob
	// is not found in datastore, returned error must be of ErrNotFound type.
	//
	// The blob may be detected to be invalid (not passing the validation),
	// in that case, either the Open call or the Read method from the returned
	// reader will return ErrInvalidData error.
	//
	// If a non-nil error is returned, the writer will be nil. Otherwise it
	// is necessary to call the `Close` on the returned reader once done
	// with the reader.
	Open(ctx context.Context, name *common.BlobName) (io.ReadCloser, error)

	// Update retrieves an update for given blob. The data is read from given
	// reader until it returns either EOF, ending successful save, or any other
	// error which will cancel the save - in such case this error will be
	// returned from this function. If the data does not pass validation,
	// ErrInvalidData will be returned.
	Update(ctx context.Context, name *common.BlobName, r io.Reader) error

	// Exists does check whether blob of given name exists in the datastore.
	// Partially written blobs are equal to non-existing ones. Boolean value
	// returned indicates whether the blob exists or not, non-nil error indicates
	// that there was an error while trying to check blob's existence.
	Exists(ctx context.Context, name *common.BlobName) (bool, error)

	// Delete tries to remove blob with given name from the datastore.
	// If blob does not exist (which includes partially written blobs)
	// ErrNotFound will be returned. If blob is being opened at the moment
	// of removal, all opened references to the blob must still be able to
	// read the blob data. After the `Delete` call succeeds, trying to read
	// the blob with the `Open` should end up with an ErrNotFound error
	// until the blob is updated again with a successful `Update` call.
	Delete(ctx context.Context, name *common.BlobName) error
}

type WriteCloseCanceller interface {
	io.WriteCloser
	Cancel()
}