added poseidon with aws to k8s changes

pkg/nullio/nullio.go

@@ -0,0 +1,43 @@
+package nullio
+
+import (
+	"context"
+	"fmt"
+	"io"
+)
+
+// Reader is a struct that implements the io.Reader interface.
+// Read does not return when called until the context is done. It is used to avoid reading anything and returning io.EOF
+// before the context has finished.
+// For example the reader is used by the execution that fetches the stderr stream from Nomad. We do not have a stdin
+// that we want to send to Nomad. But we still have to pass Nomad a reader.
+// Normally readers send an io.EOF as soon as they have nothing more to read. But we want to avoid this, because in that
+// case Nomad will abort (not the execution but) the transmission.
+// Why should the reader not just always return 0, nil? Because Nomad reads in an endless loop and thus a busy waiting
+// is avoided.
+type Reader struct {
+	Ctx context.Context
+}
+
+func (r Reader) Read(_ []byte) (int, error) {
+	if r.Ctx == nil || r.Ctx.Err() != nil {
+		return 0, io.EOF
+	}
+
+	<-r.Ctx.Done()
+	return 0, io.EOF
+}
+
+// ReadWriter implements io.ReadWriter. It does not return from Read and discards everything on Write.
+type ReadWriter struct {
+	Reader
+}
+
+func (rw *ReadWriter) Write(p []byte) (int, error) {
+	n, err := io.Discard.Write(p)
+	if err != nil {
+		return n, fmt.Errorf("error writing to io.Discard: %w", err)
+	} else {
+		return n, nil
+	}
+}