registry/storagedriver/storagedriver.go

package storagedriver

import (
	"fmt"
	"io"
	"strconv"
	"strings"
)

// Version is a string representing the storage driver version, of the form
// Major.Minor.
// The registry must accept storage drivers with equal major version and greater
// minor version, but may not be compatible with older storage driver versions.
type Version string

// Major returns the major (primary) component of a version.
func (version Version) Major() uint {
	majorPart := strings.Split(string(version), ".")[0]
	major, _ := strconv.ParseUint(majorPart, 10, 0)
	return uint(major)
}

// Minor returns the minor (secondary) component of a version.
func (version Version) Minor() uint {
	minorPart := strings.Split(string(version), ".")[1]
	minor, _ := strconv.ParseUint(minorPart, 10, 0)
	return uint(minor)
}

// CurrentVersion is the current storage driver Version.
const CurrentVersion Version = "0.1"

// StorageDriver defines methods that a Storage Driver must implement for a
// filesystem-like key/value object storage.
type StorageDriver interface {
	// GetContent retrieves the content stored at "path" as a []byte.
	// This should primarily be used for small objects.
	GetContent(path string) ([]byte, error)

	// PutContent stores the []byte content at a location designated by "path".
	// This should primarily be used for small objects.
	PutContent(path string, content []byte) error

	// ReadStream retrieves an io.ReadCloser for the content stored at "path"
	// with a given byte offset.
	// May be used to resume reading a stream by providing a nonzero offset.
	ReadStream(path string, offset uint64) (io.ReadCloser, error)

	// WriteStream stores the contents of the provided io.ReadCloser at a
	// location designated by the given path.
	// The driver will know it has received the full contents when it has read
	// "size" bytes.
	// May be used to resume writing a stream by providing a nonzero offset.
	// The offset must be no larger than the CurrentSize for this path.
	WriteStream(path string, offset, size uint64, readCloser io.ReadCloser) error

	// CurrentSize retrieves the curernt size in bytes of the object at the
	// given path.
	// It should be safe to read or write anywhere up to this point.
	CurrentSize(path string) (uint64, error)

	// List returns a list of the objects that are direct descendants of the
	//given path.
	List(path string) ([]string, error)

	// Move moves an object stored at sourcePath to destPath, removing the
	// original object.
	// Note: This may be no more efficient than a copy followed by a delete for
	// many implementations.
	Move(sourcePath string, destPath string) error

	// Delete recursively deletes all objects stored at "path" and its subpaths.
	Delete(path string) error
}

// PathNotFoundError is returned when operating on a nonexistent path.
type PathNotFoundError struct {
	Path string
}

func (err PathNotFoundError) Error() string {
	return fmt.Sprintf("Path not found: %s", err.Path)
}

// InvalidOffsetError is returned when attempting to read or write from an
// invalid offset.
type InvalidOffsetError struct {
	Path   string
	Offset uint64
}

func (err InvalidOffsetError) Error() string {
	return fmt.Sprintf("Invalid offset: %d for path: %s", err.Offset, err.Path)
}