1
0
Fork 0
mirror of https://github.com/moby/moby.git synced 2022-11-09 12:21:53 -05:00
moby--moby/daemon/image_delete.go
David Calavera a793564b25 Remove static errors from errors package.
Moving all strings to the errors package wasn't a good idea after all.

Our custom implementation of Go errors predates everything that's nice
and good about working with errors in Go. Take as an example what we
have to do to get an error message:

```go
func GetErrorMessage(err error) string {
	switch err.(type) {
	case errcode.Error:
		e, _ := err.(errcode.Error)
		return e.Message

	case errcode.ErrorCode:
		ec, _ := err.(errcode.ErrorCode)
		return ec.Message()

	default:
		return err.Error()
	}
}
```

This goes against every good practice for Go development. The language already provides a simple, intuitive and standard way to get error messages, that is calling the `Error()` method from an error. Reinventing the error interface is a mistake.

Our custom implementation also makes very hard to reason about errors, another nice thing about Go. I found several (>10) error declarations that we don't use anywhere. This is a clear sign about how little we know about the errors we return. I also found several error usages where the number of arguments was different than the parameters declared in the error, another clear example of how difficult is to reason about errors.

Moreover, our custom implementation didn't really make easier for people to return custom HTTP status code depending on the errors. Again, it's hard to reason about when to set custom codes and how. Take an example what we have to do to extract the message and status code from an error before returning a response from the API:

```go
	switch err.(type) {
	case errcode.ErrorCode:
		daError, _ := err.(errcode.ErrorCode)
		statusCode = daError.Descriptor().HTTPStatusCode
		errMsg = daError.Message()

	case errcode.Error:
		// For reference, if you're looking for a particular error
		// then you can do something like :
		//   import ( derr "github.com/docker/docker/errors" )
		//   if daError.ErrorCode() == derr.ErrorCodeNoSuchContainer { ... }

		daError, _ := err.(errcode.Error)
		statusCode = daError.ErrorCode().Descriptor().HTTPStatusCode
		errMsg = daError.Message

	default:
		// This part of will be removed once we've
		// converted everything over to use the errcode package

		// FIXME: this is brittle and should not be necessary.
		// If we need to differentiate between different possible error types,
		// we should create appropriate error types with clearly defined meaning
		errStr := strings.ToLower(err.Error())
		for keyword, status := range map[string]int{
			"not found":             http.StatusNotFound,
			"no such":               http.StatusNotFound,
			"bad parameter":         http.StatusBadRequest,
			"conflict":              http.StatusConflict,
			"impossible":            http.StatusNotAcceptable,
			"wrong login/password":  http.StatusUnauthorized,
			"hasn't been activated": http.StatusForbidden,
		} {
			if strings.Contains(errStr, keyword) {
				statusCode = status
				break
			}
		}
	}
```

You can notice two things in that code:

1. We have to explain how errors work, because our implementation goes against how easy to use Go errors are.
2. At no moment we arrived to remove that `switch` statement that was the original reason to use our custom implementation.

This change removes all our status errors from the errors package and puts them back in their specific contexts.
IT puts the messages back with their contexts. That way, we know right away when errors used and how to generate their messages.
It uses custom interfaces to reason about errors. Errors that need to response with a custom status code MUST implementent this simple interface:

```go
type errorWithStatus interface {
	HTTPErrorStatusCode() int
}
```

This interface is very straightforward to implement. It also preserves Go errors real behavior, getting the message is as simple as using the `Error()` method.

I included helper functions to generate errors that use custom status code in `errors/errors.go`.

By doing this, we remove the hard dependency we have eeverywhere to our custom errors package. Yes, you can use it as a helper to generate error, but it's still very easy to generate errors without it.

Please, read this fantastic blog post about errors in Go: http://dave.cheney.net/2014/12/24/inspecting-errors

Signed-off-by: David Calavera <david.calavera@gmail.com>
2016-02-26 15:49:09 -05:00

371 lines
13 KiB
Go

package daemon
import (
"fmt"
"strings"
"github.com/docker/docker/container"
"github.com/docker/docker/errors"
"github.com/docker/docker/image"
"github.com/docker/docker/pkg/stringid"
"github.com/docker/docker/reference"
"github.com/docker/engine-api/types"
)
type conflictType int
const (
conflictDependentChild conflictType = (1 << iota)
conflictRunningContainer
conflictActiveReference
conflictStoppedContainer
conflictHard = conflictDependentChild | conflictRunningContainer
conflictSoft = conflictActiveReference | conflictStoppedContainer
)
// ImageDelete deletes the image referenced by the given imageRef from this
// daemon. The given imageRef can be an image ID, ID prefix, or a repository
// reference (with an optional tag or digest, defaulting to the tag name
// "latest"). There is differing behavior depending on whether the given
// imageRef is a repository reference or not.
//
// If the given imageRef is a repository reference then that repository
// reference will be removed. However, if there exists any containers which
// were created using the same image reference then the repository reference
// cannot be removed unless either there are other repository references to the
// same image or force is true. Following removal of the repository reference,
// the referenced image itself will attempt to be deleted as described below
// but quietly, meaning any image delete conflicts will cause the image to not
// be deleted and the conflict will not be reported.
//
// There may be conflicts preventing deletion of an image and these conflicts
// are divided into two categories grouped by their severity:
//
// Hard Conflict:
// - a pull or build using the image.
// - any descendant image.
// - any running container using the image.
//
// Soft Conflict:
// - any stopped container using the image.
// - any repository tag or digest references to the image.
//
// The image cannot be removed if there are any hard conflicts and can be
// removed if there are soft conflicts only if force is true.
//
// If prune is true, ancestor images will each attempt to be deleted quietly,
// meaning any delete conflicts will cause the image to not be deleted and the
// conflict will not be reported.
//
// FIXME: remove ImageDelete's dependency on Daemon, then move to the graph
// package. This would require that we no longer need the daemon to determine
// whether images are being used by a stopped or running container.
func (daemon *Daemon) ImageDelete(imageRef string, force, prune bool) ([]types.ImageDelete, error) {
records := []types.ImageDelete{}
imgID, err := daemon.GetImageID(imageRef)
if err != nil {
return nil, daemon.imageNotExistToErrcode(err)
}
repoRefs := daemon.referenceStore.References(imgID)
var removedRepositoryRef bool
if !isImageIDPrefix(imgID.String(), imageRef) {
// A repository reference was given and should be removed
// first. We can only remove this reference if either force is
// true, there are multiple repository references to this
// image, or there are no containers using the given reference.
if !(force || len(repoRefs) > 1) {
if container := daemon.getContainerUsingImage(imgID); container != nil {
// If we removed the repository reference then
// this image would remain "dangling" and since
// we really want to avoid that the client must
// explicitly force its removal.
err := fmt.Errorf("conflict: unable to remove repository reference %q (must force) - container %s is using its referenced image %s", imageRef, stringid.TruncateID(container.ID), stringid.TruncateID(imgID.String()))
return nil, errors.NewRequestConflictError(err)
}
}
parsedRef, err := reference.ParseNamed(imageRef)
if err != nil {
return nil, err
}
parsedRef, err = daemon.removeImageRef(parsedRef)
if err != nil {
return nil, err
}
untaggedRecord := types.ImageDelete{Untagged: parsedRef.String()}
daemon.LogImageEvent(imgID.String(), imgID.String(), "untag")
records = append(records, untaggedRecord)
repoRefs = daemon.referenceStore.References(imgID)
// If this is a tag reference and all the remaining references
// to this image are digest references, delete the remaining
// references so that they don't prevent removal of the image.
if _, isCanonical := parsedRef.(reference.Canonical); !isCanonical {
foundTagRef := false
for _, repoRef := range repoRefs {
if _, repoRefIsCanonical := repoRef.(reference.Canonical); !repoRefIsCanonical {
foundTagRef = true
break
}
}
if !foundTagRef {
for _, repoRef := range repoRefs {
if _, err := daemon.removeImageRef(repoRef); err != nil {
return records, err
}
untaggedRecord := types.ImageDelete{Untagged: repoRef.String()}
records = append(records, untaggedRecord)
}
repoRefs = []reference.Named{}
}
}
// If it has remaining references then the untag finished the remove
if len(repoRefs) > 0 {
return records, nil
}
removedRepositoryRef = true
} else {
// If an ID reference was given AND there is exactly one
// repository reference to the image then we will want to
// remove that reference.
// FIXME: Is this the behavior we want?
if len(repoRefs) == 1 {
c := conflictHard
if !force {
c |= conflictSoft &^ conflictActiveReference
}
if conflict := daemon.checkImageDeleteConflict(imgID, c); conflict != nil {
return nil, conflict
}
parsedRef, err := daemon.removeImageRef(repoRefs[0])
if err != nil {
return nil, err
}
untaggedRecord := types.ImageDelete{Untagged: parsedRef.String()}
daemon.LogImageEvent(imgID.String(), imgID.String(), "untag")
records = append(records, untaggedRecord)
}
}
return records, daemon.imageDeleteHelper(imgID, &records, force, prune, removedRepositoryRef)
}
// isImageIDPrefix returns whether the given possiblePrefix is a prefix of the
// given imageID.
func isImageIDPrefix(imageID, possiblePrefix string) bool {
if strings.HasPrefix(imageID, possiblePrefix) {
return true
}
if i := strings.IndexRune(imageID, ':'); i >= 0 {
return strings.HasPrefix(imageID[i+1:], possiblePrefix)
}
return false
}
// getContainerUsingImage returns a container that was created using the given
// imageID. Returns nil if there is no such container.
func (daemon *Daemon) getContainerUsingImage(imageID image.ID) *container.Container {
return daemon.containers.First(func(c *container.Container) bool {
return c.ImageID == imageID
})
}
// removeImageRef attempts to parse and remove the given image reference from
// this daemon's store of repository tag/digest references. The given
// repositoryRef must not be an image ID but a repository name followed by an
// optional tag or digest reference. If tag or digest is omitted, the default
// tag is used. Returns the resolved image reference and an error.
func (daemon *Daemon) removeImageRef(ref reference.Named) (reference.Named, error) {
ref = reference.WithDefaultTag(ref)
// Ignore the boolean value returned, as far as we're concerned, this
// is an idempotent operation and it's okay if the reference didn't
// exist in the first place.
_, err := daemon.referenceStore.Delete(ref)
return ref, err
}
// removeAllReferencesToImageID attempts to remove every reference to the given
// imgID from this daemon's store of repository tag/digest references. Returns
// on the first encountered error. Removed references are logged to this
// daemon's event service. An "Untagged" types.ImageDelete is added to the
// given list of records.
func (daemon *Daemon) removeAllReferencesToImageID(imgID image.ID, records *[]types.ImageDelete) error {
imageRefs := daemon.referenceStore.References(imgID)
for _, imageRef := range imageRefs {
parsedRef, err := daemon.removeImageRef(imageRef)
if err != nil {
return err
}
untaggedRecord := types.ImageDelete{Untagged: parsedRef.String()}
daemon.LogImageEvent(imgID.String(), imgID.String(), "untag")
*records = append(*records, untaggedRecord)
}
return nil
}
// ImageDeleteConflict holds a soft or hard conflict and an associated error.
// Implements the error interface.
type imageDeleteConflict struct {
hard bool
used bool
imgID image.ID
message string
}
func (idc *imageDeleteConflict) Error() string {
var forceMsg string
if idc.hard {
forceMsg = "cannot be forced"
} else {
forceMsg = "must be forced"
}
return fmt.Sprintf("conflict: unable to delete %s (%s) - %s", stringid.TruncateID(idc.imgID.String()), forceMsg, idc.message)
}
// imageDeleteHelper attempts to delete the given image from this daemon. If
// the image has any hard delete conflicts (child images or running containers
// using the image) then it cannot be deleted. If the image has any soft delete
// conflicts (any tags/digests referencing the image or any stopped container
// using the image) then it can only be deleted if force is true. If the delete
// succeeds and prune is true, the parent images are also deleted if they do
// not have any soft or hard delete conflicts themselves. Any deleted images
// and untagged references are appended to the given records. If any error or
// conflict is encountered, it will be returned immediately without deleting
// the image. If quiet is true, any encountered conflicts will be ignored and
// the function will return nil immediately without deleting the image.
func (daemon *Daemon) imageDeleteHelper(imgID image.ID, records *[]types.ImageDelete, force, prune, quiet bool) error {
// First, determine if this image has any conflicts. Ignore soft conflicts
// if force is true.
c := conflictHard
if !force {
c |= conflictSoft
}
if conflict := daemon.checkImageDeleteConflict(imgID, c); conflict != nil {
if quiet && (!daemon.imageIsDangling(imgID) || conflict.used) {
// Ignore conflicts UNLESS the image is "dangling" or not being used in
// which case we want the user to know.
return nil
}
// There was a conflict and it's either a hard conflict OR we are not
// forcing deletion on soft conflicts.
return conflict
}
parent, err := daemon.imageStore.GetParent(imgID)
if err != nil {
// There may be no parent
parent = ""
}
// Delete all repository tag/digest references to this image.
if err := daemon.removeAllReferencesToImageID(imgID, records); err != nil {
return err
}
removedLayers, err := daemon.imageStore.Delete(imgID)
if err != nil {
return err
}
daemon.LogImageEvent(imgID.String(), imgID.String(), "delete")
*records = append(*records, types.ImageDelete{Deleted: imgID.String()})
for _, removedLayer := range removedLayers {
*records = append(*records, types.ImageDelete{Deleted: removedLayer.ChainID.String()})
}
if !prune || parent == "" {
return nil
}
// We need to prune the parent image. This means delete it if there are
// no tags/digests referencing it and there are no containers using it (
// either running or stopped).
// Do not force prunings, but do so quietly (stopping on any encountered
// conflicts).
return daemon.imageDeleteHelper(parent, records, false, true, true)
}
// checkImageDeleteConflict determines whether there are any conflicts
// preventing deletion of the given image from this daemon. A hard conflict is
// any image which has the given image as a parent or any running container
// using the image. A soft conflict is any tags/digest referencing the given
// image or any stopped container using the image. If ignoreSoftConflicts is
// true, this function will not check for soft conflict conditions.
func (daemon *Daemon) checkImageDeleteConflict(imgID image.ID, mask conflictType) *imageDeleteConflict {
// Check if the image has any descendant images.
if mask&conflictDependentChild != 0 && len(daemon.imageStore.Children(imgID)) > 0 {
return &imageDeleteConflict{
hard: true,
imgID: imgID,
message: "image has dependent child images",
}
}
if mask&conflictRunningContainer != 0 {
// Check if any running container is using the image.
running := func(c *container.Container) bool {
return c.IsRunning() && c.ImageID == imgID
}
if container := daemon.containers.First(running); container != nil {
return &imageDeleteConflict{
imgID: imgID,
hard: true,
used: true,
message: fmt.Sprintf("image is being used by running container %s", stringid.TruncateID(container.ID)),
}
}
}
// Check if any repository tags/digest reference this image.
if mask&conflictActiveReference != 0 && len(daemon.referenceStore.References(imgID)) > 0 {
return &imageDeleteConflict{
imgID: imgID,
message: "image is referenced in one or more repositories",
}
}
if mask&conflictStoppedContainer != 0 {
// Check if any stopped containers reference this image.
stopped := func(c *container.Container) bool {
return !c.IsRunning() && c.ImageID == imgID
}
if container := daemon.containers.First(stopped); container != nil {
return &imageDeleteConflict{
imgID: imgID,
used: true,
message: fmt.Sprintf("image is being used by stopped container %s", stringid.TruncateID(container.ID)),
}
}
}
return nil
}
// imageIsDangling returns whether the given image is "dangling" which means
// that there are no repository references to the given image and it has no
// child images.
func (daemon *Daemon) imageIsDangling(imgID image.ID) bool {
return !(len(daemon.referenceStore.References(imgID)) > 0 || len(daemon.imageStore.Children(imgID)) > 0)
}