Define tcpip.Payloader in terms of io.Reader

Fixes #1509.

PiperOrigin-RevId: 353295589

1 files changed, 13 insertions, 7 deletions

diff --git a/pkg/usermem/usermem.go b/pkg/usermem/usermem.go
index 79db8895b..dc2571154 100644
--- a/pkg/usermem/usermem.go
+++ b/pkg/usermem/usermem.go
@@ -517,28 +517,29 @@ func (s IOSequence) CopyInTo(ctx context.Context, dst safemem.Writer) (int64, er
 // Reader returns an io.Reader that reads from s. Reads beyond the end of s
 // return io.EOF. The preconditions that apply to s.CopyIn also apply to the
 // returned io.Reader.Read.
-func (s IOSequence) Reader(ctx context.Context) io.Reader {
-	return &ioSequenceReadWriter{ctx, s}
+func (s IOSequence) Reader(ctx context.Context) *IOSequenceReadWriter {
+	return &IOSequenceReadWriter{ctx, s}
 }
 
 // Writer returns an io.Writer that writes to s. Writes beyond the end of s
 // return ErrEndOfIOSequence. The preconditions that apply to s.CopyOut also
 // apply to the returned io.Writer.Write.
-func (s IOSequence) Writer(ctx context.Context) io.Writer {
-	return &ioSequenceReadWriter{ctx, s}
+func (s IOSequence) Writer(ctx context.Context) *IOSequenceReadWriter {
+	return &IOSequenceReadWriter{ctx, s}
 }
 
 // ErrEndOfIOSequence is returned by IOSequence.Writer().Write() when
 // attempting to write beyond the end of the IOSequence.
 var ErrEndOfIOSequence = errors.New("write beyond end of IOSequence")
 
-type ioSequenceReadWriter struct {
+// IOSequenceReadWriter implements io.Reader and io.Writer for an IOSequence.
+type IOSequenceReadWriter struct {
 	ctx context.Context
 	s   IOSequence
 }
 
 // Read implements io.Reader.Read.
-func (rw *ioSequenceReadWriter) Read(dst []byte) (int, error) {
+func (rw *IOSequenceReadWriter) Read(dst []byte) (int, error) {
 	n, err := rw.s.CopyIn(rw.ctx, dst)
 	rw.s = rw.s.DropFirst(n)
 	if err == nil && rw.s.NumBytes() == 0 {
@@ -547,8 +548,13 @@ func (rw *ioSequenceReadWriter) Read(dst []byte) (int, error) {
 	return n, err
 }
 
+// Len implements tcpip.Payloader.
+func (rw *IOSequenceReadWriter) Len() int {
+	return int(rw.s.NumBytes())
+}
+
 // Write implements io.Writer.Write.
-func (rw *ioSequenceReadWriter) Write(src []byte) (int, error) {
+func (rw *IOSequenceReadWriter) Write(src []byte) (int, error) {
 	n, err := rw.s.CopyOut(rw.ctx, src)
 	rw.s = rw.s.DropFirst(n)
 	if err == nil && n < len(src) {