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moby--moby/layer/empty.go
John Howard 0380fbff37 LCOW: API: Add platform to /images/create and /build
Signed-off-by: John Howard <jhoward@microsoft.com>

This PR has the API changes described in https://github.com/moby/moby/issues/34617.
Specifically, it adds an HTTP header "X-Requested-Platform" which is a JSON-encoded
OCI Image-spec `Platform` structure.

In addition, it renames (almost all) uses of a string variable platform (and associated)
methods/functions to os. This makes it much clearer to disambiguate with the swarm
"platform" which is really os/arch. This is a stepping stone to getting the daemon towards
fully multi-platform/arch-aware, and makes it clear when "operating system" is being
referred to rather than "platform" which is misleadingly used - sometimes in the swarm
meaning, but more often as just the operating system.
2017-10-06 11:44:18 -07:00

65 lines
1.4 KiB
Go

package layer
import (
"archive/tar"
"bytes"
"fmt"
"io"
"io/ioutil"
)
// DigestSHA256EmptyTar is the canonical sha256 digest of empty tar file -
// (1024 NULL bytes)
const DigestSHA256EmptyTar = DiffID("sha256:5f70bf18a086007016e948b04aed3b82103a36bea41755b6cddfaf10ace3c6ef")
type emptyLayer struct{}
// EmptyLayer is a layer that corresponds to empty tar.
var EmptyLayer = &emptyLayer{}
func (el *emptyLayer) TarStream() (io.ReadCloser, error) {
buf := new(bytes.Buffer)
tarWriter := tar.NewWriter(buf)
tarWriter.Close()
return ioutil.NopCloser(buf), nil
}
func (el *emptyLayer) TarStreamFrom(p ChainID) (io.ReadCloser, error) {
if p == "" {
return el.TarStream()
}
return nil, fmt.Errorf("can't get parent tar stream of an empty layer")
}
func (el *emptyLayer) ChainID() ChainID {
return ChainID(DigestSHA256EmptyTar)
}
func (el *emptyLayer) DiffID() DiffID {
return DigestSHA256EmptyTar
}
func (el *emptyLayer) Parent() Layer {
return nil
}
func (el *emptyLayer) Size() (size int64, err error) {
return 0, nil
}
func (el *emptyLayer) DiffSize() (size int64, err error) {
return 0, nil
}
func (el *emptyLayer) Metadata() (map[string]string, error) {
return make(map[string]string), nil
}
func (el *emptyLayer) OS() OS {
return ""
}
// IsEmpty returns true if the layer is an EmptyLayer
func IsEmpty(diffID DiffID) bool {
return diffID == DigestSHA256EmptyTar
}