sandbox: move out of internal

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

sandbox/seccomp/export.go

@@ -0,0 +1,58 @@
+package seccomp
+
+import (
+	"os"
+	"runtime"
+	"sync"
+)
+
+type exporter struct {
+	opts SyscallOpts
+	r, w *os.File
+
+	prepareOnce sync.Once
+	prepareErr  error
+	closeOnce   sync.Once
+	closeErr    error
+	exportErr   <-chan error
+}
+
+func (e *exporter) prepare() error {
+	e.prepareOnce.Do(func() {
+		if r, w, err := os.Pipe(); err != nil {
+			e.prepareErr = err
+			return
+		} else {
+			e.r, e.w = r, w
+		}
+
+		ec := make(chan error, 1)
+		go func(fd uintptr) {
+			ec <- buildFilter(int(fd), e.opts)
+			close(ec)
+			_ = e.closeWrite()
+			runtime.KeepAlive(e.w)
+		}(e.w.Fd())
+		e.exportErr = ec
+		runtime.SetFinalizer(e, (*exporter).closeWrite)
+	})
+	return e.prepareErr
+}
+
+func (e *exporter) closeWrite() error {
+	e.closeOnce.Do(func() {
+		if e.w == nil {
+			panic("closeWrite called on invalid exporter")
+		}
+		e.closeErr = e.w.Close()
+
+		// no need for a finalizer anymore
+		runtime.SetFinalizer(e, nil)
+	})
+
+	return e.closeErr
+}
+
+func newExporter(opts SyscallOpts) *exporter {
+	return &exporter{opts: opts}
+}