1 files changed, 99 insertions, 0 deletions
diff --git a/src/post/asset/loader_archive.go b/src/post/asset/loader_archive.go
new file mode 100644
index 0000000..1c8697f
--- /dev/null
+++ b/src/post/asset/loader_archive.go
@@ -0,0 +1,99 @@
+package asset
+
+import (
+	"bytes"
+	"compress/gzip"
+	"errors"
+	"fmt"
+	"io"
+	"io/fs"
+	"strings"
+
+	"github.com/omeid/go-tarfs"
+)
+
+type archiveLoader struct {
+	loader Loader
+}
+
+// NewArchiveLoader wraps an existing Loader in order to support extracting
+// files from within an archive file asset.
+//
+// For example, loading the path `foo.tgz/foo/bar.jpg` will call
+// `Load("foo.tgz")`, load that archive into memory, and serve the file
+// `./foo/bar.jpg` from within the archive.
+func NewArchiveLoader(loader Loader) Loader {
+	return &archiveLoader{loader: loader}
+}
+
+func (l *archiveLoader) Load(path string, into io.Writer, opts LoadOpts) error {
+
+	id, subPath, ok := strings.Cut(strings.TrimPrefix(path, "/"), "/")
+
+	if !ok {
+		return l.loader.Load(path, into, opts)
+	}
+
+	var isGzipped bool
+
+	switch {
+
+	case strings.HasSuffix(id, ".tar.gz"),
+		strings.HasSuffix(id, ".tgz"):
+		isGzipped = true
+
+	case strings.HasSuffix(id, ".tar"):
+		// ok
+
+	default:
+		// unsupported
+		return l.loader.Load(path, into, opts)
+	}
+
+	buf := new(bytes.Buffer)
+
+	if err := l.loader.Load(id, buf, opts); err != nil {
+		return fmt.Errorf("loading archive into buffer: %w", err)
+	}
+
+	var (
+		from io.Reader = buf
+		err  error
+	)
+
+	if isGzipped {
+
+		if from, err = gzip.NewReader(from); err != nil {
+			return fmt.Errorf("decompressing archive asset with id %q: %w", id, err)
+		}
+	}
+
+	tarFS, err := tarfs.New(from)
+
+	if err != nil {
+		return fmt.Errorf("reading archive asset with id %q as fs: %w", id, err)
+	}
+
+	f, err := tarFS.Open(subPath)
+
+	if errors.Is(err, fs.ErrExist) {
+		return ErrNotFound
+
+	} else if err != nil {
+		return fmt.Errorf(
+			"opening path %q from archive asset with id %q as fs: %w",
+			subPath, id, err,
+		)
+	}
+
+	defer f.Close()
+
+	if _, err = io.Copy(into, f); err != nil {
+		return fmt.Errorf(
+			"reading %q from archive asset with id %q as fs: %w",
+			subPath, id, err,
+		)
+	}
+
+	return nil
+}