server(filesystem): allow decompressing individual files

Implements logic for handling a file that is compressed but isn't an archive.

Fixes https://github.com/pterodactyl/panel/issues/5034

Signed-off-by: Matthew Penner <me@matthewp.io>

server/filesystem/archiverext/compressed.go

@@ -0,0 +1,100 @@
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: Copyright (c) 2016 Matthew Holt
+
+// Code in this file was derived from
+// https://github.com/mholt/archiver/blob/v4.0.0-alpha.8/fs.go
+//
+// These modifications were necessary to allow us to use an already open file
+// with archiver.FileFS.
+
+package archiverext
+
+import (
+	"io"
+	"io/fs"
+
+	"github.com/mholt/archiver/v4"
+)
+
+// FileFS allows accessing a file on disk using a consistent file system interface.
+// The value should be the path to a regular file, not a directory. This file will
+// be the only entry in the file system and will be at its root. It can be accessed
+// within the file system by the name of "." or the filename.
+//
+// If the file is compressed, set the Compression field so that reads from the
+// file will be transparently decompressed.
+type FileFS struct {
+	// File is the compressed file backing the FileFS.
+	File fs.File
+
+	// If file is compressed, setting this field will
+	// transparently decompress reads.
+	Compression archiver.Decompressor
+}
+
+// Open opens the named file, which must be the file used to create the file system.
+func (f FileFS) Open(name string) (fs.File, error) {
+	if err := f.checkName(name, "open"); err != nil {
+		return nil, err
+	}
+	if f.Compression == nil {
+		return f.File, nil
+	}
+	r, err := f.Compression.OpenReader(f.File)
+	if err != nil {
+		return nil, err
+	}
+	return compressedFile{f.File, r}, nil
+}
+
+// ReadDir returns a directory listing with the file as the singular entry.
+func (f FileFS) ReadDir(name string) ([]fs.DirEntry, error) {
+	if err := f.checkName(name, "stat"); err != nil {
+		return nil, err
+	}
+	info, err := f.Stat(name)
+	if err != nil {
+		return nil, err
+	}
+	return []fs.DirEntry{fs.FileInfoToDirEntry(info)}, nil
+}
+
+// Stat stats the named file, which must be the file used to create the file system.
+func (f FileFS) Stat(name string) (fs.FileInfo, error) {
+	if err := f.checkName(name, "stat"); err != nil {
+		return nil, err
+	}
+	return f.File.Stat()
+}
+
+func (f FileFS) checkName(name, op string) error {
+	if !fs.ValidPath(name) {
+		return &fs.PathError{Op: "open", Path: name, Err: fs.ErrInvalid}
+	}
+	// TODO: we may need better name validation.
+	if name != "." {
+		return &fs.PathError{Op: op, Path: name, Err: fs.ErrNotExist}
+	}
+	return nil
+}
+
+// compressedFile is an fs.File that specially reads
+// from a decompression reader, and which closes both
+// that reader and the underlying file.
+type compressedFile struct {
+	fs.File
+	decomp io.ReadCloser
+}
+
+func (cf compressedFile) Read(p []byte) (int, error) {
+	return cf.decomp.Read(p)
+}
+
+func (cf compressedFile) Close() error {
+	err := cf.File.Close()
+	err2 := cf.decomp.Close()
+	if err2 != nil && err == nil {
+		err = err2
+	}
+	return err
+}

server/filesystem/compress.go

@@ -16,6 +16,7 @@ import (
 	"github.com/mholt/archiver/v4"
 
 	"github.com/pterodactyl/wings/internal/ufs"
+	"github.com/pterodactyl/wings/server/filesystem/archiverext"
 )
 
 // CompressFiles compresses all the files matching the given paths in the
@@ -85,11 +86,12 @@ func (fs *Filesystem) archiverFileSystem(ctx context.Context, p string) (iofs.FS
 			return zip.NewReader(f, info.Size())
 		case archiver.Archival:
 			return archiver.ArchiveFS{Stream: io.NewSectionReader(f, 0, info.Size()), Format: ff, Context: ctx}, nil
+		case archiver.Compression:
+			return archiverext.FileFS{File: f, Compression: ff}, nil
 		}
 	}
-
 	_ = f.Close()
-	return nil, nil
+	return nil, archiver.ErrNoMatch
 }
 
 // SpaceAvailableForDecompression looks through a given archive and determines