server(filesystem): rebuild everything imaginable

This wonderfully large commit replaces basically everything under the
`server/filesystem` package, re-implementing essentially everything.

This is related to
https://github.com/pterodactyl/wings/security/advisories/GHSA-494h-9924-xww9

If any vulnerabilities related to symlinks persist after this commit, I
will be very upset.

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

server/backup/backup.go

@@ -16,6 +16,7 @@ import (
 
 	"github.com/pterodactyl/wings/config"
 	"github.com/pterodactyl/wings/remote"
+	"github.com/pterodactyl/wings/server/filesystem"
 )
 
 var format = archiver.CompressedArchive{
@@ -46,7 +47,7 @@ type BackupInterface interface {
 	WithLogContext(map[string]interface{})
 	// Generate creates a backup in whatever the configured source for the
 	// specific implementation is.
-	Generate(context.Context, string, string) (*ArchiveDetails, error)
+	Generate(context.Context, *filesystem.Filesystem, string) (*ArchiveDetails, error)
 	// Ignored returns the ignored files for this backup instance.
 	Ignored() string
 	// Checksum returns a SHA1 checksum for the generated backup.

server/backup/backup_local.go

@@ -59,10 +59,10 @@ func (b *LocalBackup) WithLogContext(c map[string]interface{}) {
 
 // Generate generates a backup of the selected files and pushes it to the
 // defined location for this instance.
-func (b *LocalBackup) Generate(ctx context.Context, basePath, ignore string) (*ArchiveDetails, error) {
+func (b *LocalBackup) Generate(ctx context.Context, fsys *filesystem.Filesystem, ignore string) (*ArchiveDetails, error) {
 	a := &filesystem.Archive{
-		BasePath: basePath,
-		Ignore:   ignore,
+		Filesystem: fsys,
+		Ignore:     ignore,
 	}
 
 	b.log().WithField("path", b.Path()).Info("creating backup for server")

server/backup/backup_s3.go

@@ -48,12 +48,12 @@ func (s *S3Backup) WithLogContext(c map[string]interface{}) {
 
 // Generate creates a new backup on the disk, moves it into the S3 bucket via
 // the provided presigned URL, and then deletes the backup from the disk.
-func (s *S3Backup) Generate(ctx context.Context, basePath, ignore string) (*ArchiveDetails, error) {
+func (s *S3Backup) Generate(ctx context.Context, fsys *filesystem.Filesystem, ignore string) (*ArchiveDetails, error) {
 	defer s.Remove()
 
 	a := &filesystem.Archive{
-		BasePath: basePath,
-		Ignore:   ignore,
+		Filesystem: fsys,
+		Ignore:     ignore,
 	}
 
 	s.log().WithField("path", s.Path()).Info("creating backup for server")