internal/pkg: decompress xz streams

This uses a port of the public domain xz implementation.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pkg/compress.go

@@ -7,6 +7,7 @@ import (
 	"io"
 	"os"
 
+	"hakurei.app/internal/xz"
 	"hakurei.app/internal/zstd"
 )
 
@@ -17,6 +18,8 @@ const (
 	Bzip2
 	// Zstd denotes a stream compressed via [zstd].
 	Zstd
+	// XZ denotes a stream compressed via [xz].
+	XZ
 )
 
 // A decompressArtifact is a [FileArtifact] decompressing a backing
@@ -127,6 +130,17 @@ func (a *decompressArtifact) Cure(r *RContext) (io.ReadCloser, error) {
 			io.Closer
 		}{zstd.NewReader(br), br}, nil
 
+	case XZ:
+		var _dr io.Reader
+		if _dr, err = xz.NewReader(br, 0); err != nil {
+			_ = br.Close()
+			return nil, err
+		}
+		return struct {
+			io.Reader
+			io.Closer
+		}{_dr, br}, nil
+
 	default:
 		return nil, os.ErrInvalid
 	}