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graph.go
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graph.go
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package docker
import (
"fmt"
"io"
"io/ioutil"
"net/http"
"os"
"path"
"path/filepath"
"strings"
"time"
)
// A Graph is a store for versioned filesystem images and the relationship between them.
type Graph struct {
Root string
idIndex *TruncIndex
httpClient *http.Client
}
// NewGraph instantiates a new graph at the given root path in the filesystem.
// `root` will be created if it doesn't exist.
func NewGraph(root string) (*Graph, error) {
abspath, err := filepath.Abs(root)
if err != nil {
return nil, err
}
// Create the root directory if it doesn't exists
if err := os.Mkdir(root, 0700); err != nil && !os.IsExist(err) {
return nil, err
}
graph := &Graph{
Root: abspath,
idIndex: NewTruncIndex(),
}
if err := graph.restore(); err != nil {
return nil, err
}
return graph, nil
}
func (graph *Graph) restore() error {
dir, err := ioutil.ReadDir(graph.Root)
if err != nil {
return err
}
for _, v := range dir {
id := v.Name()
graph.idIndex.Add(id)
}
return nil
}
// FIXME: Implement error subclass instead of looking at the error text
// Note: This is the way golang implements os.IsNotExists on Plan9
func (graph *Graph) IsNotExist(err error) bool {
return err != nil && strings.Contains(err.Error(), "does not exist")
}
// Exists returns true if an image is registered at the given id.
// If the image doesn't exist or if an error is encountered, false is returned.
func (graph *Graph) Exists(id string) bool {
if _, err := graph.Get(id); err != nil {
return false
}
return true
}
// Get returns the image with the given id, or an error if the image doesn't exist.
func (graph *Graph) Get(name string) (*Image, error) {
id, err := graph.idIndex.Get(name)
if err != nil {
return nil, err
}
// FIXME: return nil when the image doesn't exist, instead of an error
img, err := LoadImage(graph.imageRoot(id))
if err != nil {
return nil, err
}
if img.Id != id {
return nil, fmt.Errorf("Image stored at '%s' has wrong id '%s'", id, img.Id)
}
img.graph = graph
return img, nil
}
// Create creates a new image and registers it in the graph.
func (graph *Graph) Create(layerData Archive, container *Container, comment, author string, config *Config) (*Image, error) {
img := &Image{
Id: GenerateId(),
Comment: comment,
Created: time.Now(),
DockerVersion: VERSION,
Author: author,
Config: config,
}
if container != nil {
img.Parent = container.Image
img.Container = container.Id
img.ContainerConfig = *container.Config
}
if err := graph.Register(layerData, img); err != nil {
return nil, err
}
img.Checksum()
return img, nil
}
// Register imports a pre-existing image into the graph.
// FIXME: pass img as first argument
func (graph *Graph) Register(layerData Archive, img *Image) error {
if err := ValidateId(img.Id); err != nil {
return err
}
// (This is a convenience to save time. Race conditions are taken care of by os.Rename)
if graph.Exists(img.Id) {
return fmt.Errorf("Image %s already exists", img.Id)
}
tmp, err := graph.Mktemp("")
defer os.RemoveAll(tmp)
if err != nil {
return fmt.Errorf("Mktemp failed: %s", err)
}
if err := StoreImage(img, layerData, tmp); err != nil {
return err
}
// Commit
if err := os.Rename(tmp, graph.imageRoot(img.Id)); err != nil {
return err
}
img.graph = graph
graph.idIndex.Add(img.Id)
return nil
}
// TempLayerArchive creates a temporary archive of the given image's filesystem layer.
// The archive is stored on disk and will be automatically deleted as soon as has been read.
// If output is not nil, a human-readable progress bar will be written to it.
// FIXME: does this belong in Graph? How about MktempFile, let the caller use it for archives?
func (graph *Graph) TempLayerArchive(id string, compression Compression, output io.Writer) (*TempArchive, error) {
image, err := graph.Get(id)
if err != nil {
return nil, err
}
tmp, err := graph.tmp()
if err != nil {
return nil, err
}
archive, err := image.TarLayer(compression)
if err != nil {
return nil, err
}
return NewTempArchive(ProgressReader(ioutil.NopCloser(archive), 0, output, "Buffering to disk %v/%v (%v)"), tmp.Root)
}
// Mktemp creates a temporary sub-directory inside the graph's filesystem.
func (graph *Graph) Mktemp(id string) (string, error) {
if id == "" {
id = GenerateId()
}
tmp, err := graph.tmp()
if err != nil {
return "", fmt.Errorf("Couldn't create temp: %s", err)
}
if tmp.Exists(id) {
return "", fmt.Errorf("Image %d already exists", id)
}
return tmp.imageRoot(id), nil
}
func (graph *Graph) tmp() (*Graph, error) {
return NewGraph(path.Join(graph.Root, ":tmp:"))
}
// Check if given error is "not empty".
// Note: this is the way golang does it internally with os.IsNotExists.
func isNotEmpty(err error) bool {
switch pe := err.(type) {
case nil:
return false
case *os.PathError:
err = pe.Err
case *os.LinkError:
err = pe.Err
}
return strings.Contains(err.Error(), " not empty")
}
// Delete atomically removes an image from the graph.
func (graph *Graph) Delete(name string) error {
id, err := graph.idIndex.Get(name)
if err != nil {
return err
}
tmp, err := graph.Mktemp("")
if err != nil {
return err
}
graph.idIndex.Delete(id)
err = os.Rename(graph.imageRoot(id), tmp)
if err != nil {
return err
}
return os.RemoveAll(tmp)
}
// Map returns a list of all images in the graph, addressable by ID.
func (graph *Graph) Map() (map[string]*Image, error) {
// FIXME: this should replace All()
all, err := graph.All()
if err != nil {
return nil, err
}
images := make(map[string]*Image, len(all))
for _, image := range all {
images[image.Id] = image
}
return images, nil
}
// All returns a list of all images in the graph.
func (graph *Graph) All() ([]*Image, error) {
var images []*Image
err := graph.WalkAll(func(image *Image) {
images = append(images, image)
})
return images, err
}
// WalkAll iterates over each image in the graph, and passes it to a handler.
// The walking order is undetermined.
func (graph *Graph) WalkAll(handler func(*Image)) error {
files, err := ioutil.ReadDir(graph.Root)
if err != nil {
return err
}
for _, st := range files {
if img, err := graph.Get(st.Name()); err != nil {
// Skip image
continue
} else if handler != nil {
handler(img)
}
}
return nil
}
// ByParent returns a lookup table of images by their parent.
// If an image of id ID has 3 children images, then the value for key ID
// will be a list of 3 images.
// If an image has no children, it will not have an entry in the table.
func (graph *Graph) ByParent() (map[string][]*Image, error) {
byParent := make(map[string][]*Image)
err := graph.WalkAll(func(image *Image) {
image, err := graph.Get(image.Parent)
if err != nil {
return
}
if children, exists := byParent[image.Parent]; exists {
byParent[image.Parent] = []*Image{image}
} else {
byParent[image.Parent] = append(children, image)
}
})
return byParent, err
}
// Heads returns all heads in the graph, keyed by id.
// A head is an image which is not the parent of another image in the graph.
func (graph *Graph) Heads() (map[string]*Image, error) {
heads := make(map[string]*Image)
byParent, err := graph.ByParent()
if err != nil {
return nil, err
}
err = graph.WalkAll(func(image *Image) {
// If it's not in the byParent lookup table, then
// it's not a parent -> so it's a head!
if _, exists := byParent[image.Id]; !exists {
heads[image.Id] = image
}
})
return heads, err
}
func (graph *Graph) imageRoot(id string) string {
return path.Join(graph.Root, id)
}