manifest: add xz pipeline for compressing ostree images

The XZ pipeline is added explicitly for ostree raw images for now.
It should be changed to support compressing general raw images as well.

Co-Authored-By: Ondřej Budai <ondrej@budai.cz>

internal/manifest/xz.go

@@ -0,0 +1,53 @@
+package manifest
+
+import (
+	"github.com/osbuild/osbuild-composer/internal/artifact"
+	"github.com/osbuild/osbuild-composer/internal/osbuild"
+)
+
+// The XZ pipeline compresses a raw image file using xz.
+type XZ struct {
+	Base
+	Filename string
+
+	imgPipeline *RawOSTreeImage
+}
+
+// NewXZ creates a new XZ pipeline. imgPipeline is the pipeline producing the
+// raw image. Filename is the name of the produced archive.
+func NewXZ(m *Manifest,
+	buildPipeline *Build,
+	imgPipeline *RawOSTreeImage) *XZ {
+	p := &XZ{
+		Base:        NewBase(m, "xz", buildPipeline),
+		imgPipeline: imgPipeline,
+		Filename:    "image.xz",
+	}
+	if imgPipeline.Base.manifest != m {
+		panic("live image pipeline from different manifest")
+	}
+	buildPipeline.addDependent(p)
+	m.addPipeline(p)
+	return p
+}
+
+func (p *XZ) serialize() osbuild.Pipeline {
+	pipeline := p.Base.serialize()
+
+	pipeline.AddStage(osbuild.NewXzStage(
+		osbuild.NewXzStageOptions(p.Filename),
+		osbuild.NewFilesInputs(osbuild.NewFilesInputReferencesPipeline(p.imgPipeline.Name(), p.imgPipeline.Filename)),
+	))
+
+	return pipeline
+}
+
+func (p *XZ) getBuildPackages() []string {
+	return []string{"xz"}
+}
+
+func (p *XZ) Export() *artifact.Artifact {
+	p.Base.export = true
+	mimeType := "application/xz"
+	return artifact.New(p.Name(), p.Filename, &mimeType)
+}