1 files changed, 151 insertions, 0 deletions
diff --git a/pkg/compress.go b/pkg/compress.go
new file mode 100644
index 00000000..22f990f1
--- /dev/null
+++ b/pkg/compress.go
@@ -0,0 +1,151 @@
+package pkg
+
+import (
+	"compress/bzip2"
+	"compress/gzip"
+	"fmt"
+	"io"
+	"os"
+
+	"hakurei.app/internal/xz"
+	"hakurei.app/internal/zstd"
+)
+
+const (
+	// Gzip denotes a stream compressed via [gzip].
+	Gzip = iota
+	// Bzip2 denotes a stream compressed via [bzip2].
+	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
+// [FileArtifact] stream.
+type decompressArtifact struct {
+	// Caller-supplied backing stream.
+	f Artifact
+	// Compression on top of the stream.
+	compress uint32
+}
+
+var _ FileArtifact = new(decompressArtifact)
+var _ CuresExempt = new(decompressArtifact)
+
+// decompressArtifactNamed embeds decompressArtifact for a [fmt.Stringer] stream.
+type decompressArtifactNamed struct {
+	decompressArtifact
+	// Copied from decompressArtifact.f.
+	name string
+}
+
+var _ fmt.Stringer = new(decompressArtifactNamed)
+
+// NewDecompress returns a [FileArtifact] decompressing the supplied [Artifact].
+func NewDecompress(a Artifact, compress uint32) FileArtifact {
+	da := decompressArtifact{a, compress}
+	if s, ok := a.(fmt.Stringer); ok {
+		if name := s.String(); name != "" {
+			return &decompressArtifactNamed{da, name}
+		}
+	}
+	return &da
+}
+
+// String returns the name of the underlying [Artifact] prefixed with decompress.
+func (a *decompressArtifactNamed) String() string { return "decompress-" + a.name }
+
+// Kind returns the hardcoded [Kind] constant.
+func (a *decompressArtifact) Kind() Kind { return KindDecompress }
+
+// Params writes value of compression enum.
+func (a *decompressArtifact) Params(ctx *IContext) { ctx.WriteUint32(a.compress) }
+
+func init() {
+	register(KindDecompress, func(r *IRReader) Artifact {
+		a := NewDecompress(r.Next(), r.ReadUint32())
+		if _, ok := r.Finalise(); ok {
+			panic(ErrUnexpectedChecksum)
+		}
+		return a
+	})
+}
+
+// Inputs returns a slice containing the backing file.
+func (a *decompressArtifact) Inputs() []Artifact {
+	return []Artifact{a.f}
+}
+
+// IsExclusive returns false: decompressor is fully sequential.
+func (a *decompressArtifact) IsExclusive() bool { return false }
+
+// compoundCloser is an [io.ReadCloser] with an additional [io.Closer] attached.
+type compoundCloser struct {
+	io.ReadCloser
+	c io.Closer
+}
+
+// Close closes [io.ReadCloser] and the additional [io.Closer]. It returns the
+// non-nil error returned by the underlying [io.ReadCloser], otherwise it
+// returns the error returned by the additional [io.Closer].
+func (c compoundCloser) Close() error {
+	err := c.ReadCloser.Close()
+	if _err := c.c.Close(); err == nil {
+		err = _err
+	}
+	return err
+}
+
+// IsExecutable returns false.
+func (*decompressArtifact) IsExecutable() bool { return false }
+
+// Cure returns a decompressor [io.ReadCloser].
+func (a *decompressArtifact) Cure(r *RContext) (io.ReadCloser, error) {
+	sr, err := r.Open(a.f)
+	if err != nil {
+		return nil, err
+	}
+	br := r.cache.getReaderRC(sr)
+
+	var dr io.ReadCloser
+	switch a.compress {
+	case Gzip:
+		if dr, err = gzip.NewReader(br); err != nil {
+			_ = br.Close()
+			return nil, err
+		}
+		return compoundCloser{dr, br}, nil
+
+	case Bzip2:
+		return struct {
+			io.Reader
+			io.Closer
+		}{bzip2.NewReader(br), br}, nil
+
+	case Zstd:
+		return struct {
+			io.Reader
+			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
+	}
+}
+
+// CuresExempt exempts the cheap [KindDecompress] implementation often part of
+// a [FileArtifact] pipeline.
+func (*decompressArtifact) CuresExempt() {}