moby/graph/service.go

package graph

import (
	"fmt"
	"github.com/dotcloud/docker/engine"
	"github.com/dotcloud/docker/image"
	"github.com/dotcloud/docker/utils"
)

func (s *TagStore) Install(eng *engine.Engine) error {
	eng.Register("image_set", s.CmdSet)
	eng.Register("image_tag", s.CmdTag)
	eng.Register("image_get", s.CmdGet)
	return nil
}

// CmdSet stores a new image in the graph.
// Images are stored in the graph using 4 elements:
//	- A user-defined ID
//	- A collection of metadata describing the image
//	- A directory tree stored as a tar archive (also called the "layer")
//	- A reference to a "parent" ID on top of which the layer should be applied
//
// NOTE: even though the parent ID is only useful in relation to the layer and how
// to apply it (ie you could represent the full directory tree as 'parent_layer + layer',
// it is treated as a top-level property of the image. This is an artifact of early
// design and should probably be cleaned up in the future to simplify the design.
//
// Syntax: image_set ID
// Input:
//	- Layer content must be streamed in tar format on stdin. An empty input is
//	valid and represents a nil layer.
//
//	- Image metadata must be passed in the command environment.
//		'json': a json-encoded object with all image metadata.
//			It will be stored as-is, without any encoding/decoding artifacts.
//			That is a requirement of the current registry client implementation,
//			because a re-encoded json might invalidate the image checksum at
//			the next upload, even with functionaly identical content.
func (s *TagStore) CmdSet(job *engine.Job) engine.Status {
	if len(job.Args) != 1 {
		return job.Errorf("usage: %s NAME", job.Name)
	}
	var (
		imgJSON = []byte(job.Getenv("json"))
		layer   = job.Stdin
	)
	if len(imgJSON) == 0 {
		return job.Errorf("mandatory key 'json' is not set")
	}
	// We have to pass an *image.Image object, even though it will be completely
	// ignored in favor of the redundant json data.
	// FIXME: the current prototype of Graph.Register is stupid and redundant.
	img, err := image.NewImgJSON(imgJSON)
	if err != nil {
		return job.Error(err)
	}
	if err := s.graph.Register(imgJSON, layer, img); err != nil {
		return job.Error(err)
	}
	return engine.StatusOK
}

// CmdTag assigns a new name and tag to an existing image. If the tag already exists,
// it is changed and the image previously referenced by the tag loses that reference.
// This may cause the old image to be garbage-collected if its reference count reaches zero.
//
// Syntax: image_tag NEWNAME OLDNAME
// Example: image_tag shykes/myapp:latest shykes/myapp:1.42.0
func (s *TagStore) CmdTag(job *engine.Job) engine.Status {
	if len(job.Args) != 2 {
		return job.Errorf("usage: %s NEWNAME OLDNAME", job.Name)
	}
	var (
		newName = job.Args[0]
		oldName = job.Args[1]
	)
	newRepo, newTag := utils.ParseRepositoryTag(newName)
	// FIXME: Set should either parse both old and new name, or neither.
	// 	the current prototype is inconsistent.
	if err := s.Set(newRepo, newTag, oldName, true); err != nil {
		return job.Error(err)
	}
	return engine.StatusOK
}

// CmdGet returns information about an image.
// If the image doesn't exist, an empty object is returned, to allow
// checking for an image's existence.
func (s *TagStore) CmdGet(job *engine.Job) engine.Status {
	if len(job.Args) != 1 {
		return job.Errorf("usage: %s NAME", job.Name)
	}
	name := job.Args[0]
	res := &engine.Env{}
	img, err := s.LookupImage(name)
	// Note: if the image doesn't exist, LookupImage returns
	// nil, nil.
	if err != nil {
		return job.Error(err)
	}
	if img != nil {
		// We don't directly expose all fields of the Image objects,
		// to maintain a clean public API which we can maintain over
		// time even if the underlying structure changes.
		// We should have done this with the Image object to begin with...
		// but we didn't, so now we're doing it here.
		//
		// Fields that we're probably better off not including:
		//	- ID (the caller already knows it, and we stay more flexible on
		//		naming down the road)
		//	- Parent. That field is really an implementation detail of
		//		layer storage ("layer is a diff against this other layer).
		//		It doesn't belong at the same level as author/description/etc.
		//	- Config/ContainerConfig. Those structs have the same sprawl problem,
		//		so we shouldn't include them wholesale either.
		//	- Comment: initially created to fulfill the "every image is a git commit"
		//		metaphor, in practice people either ignore it or use it as a
		//		generic description field which it isn't. On deprecation shortlist.
		res.Set("created", fmt.Sprintf("%v", img.Created))
		res.Set("author", img.Author)
		res.Set("os", img.OS)
		res.Set("architecture", img.Architecture)
		res.Set("docker_version", img.DockerVersion)
	}
	res.WriteTo(job.Stdout)
	return engine.StatusOK
}