found failing case for multipacket

tcp/conn.go

@@ -69,6 +69,8 @@ func (conn *Conn) State() State { return conn.h.State() }
 // and available to read via a [Conn.Read] call.
 func (conn *Conn) BufferedInput() int { return conn.h.BufferedInput() }
 
+func (conn *Conn) AvailableInput() int { return conn.h.FreeRx() }
+
 // AvailableOutput returns amount of bytes available to write to output
 // before [Conn.Write] returns an error due to insufficient space to store outgoing data.
 func (conn *Conn) AvailableOutput() int { return conn.h.AvailableOutput() }

tcp/handler.go

@@ -290,6 +290,11 @@ func (h *Handler) FreeTx() int {
 	return h.bufTx.Free()
 }
 
+// FreeRx returns the amount of space free in the receive buffer.
+func (h *Handler) FreeRx() int {
+	return h.bufRx.Free()
+}
+
 // SizeRx returns the size of the TCP receive ring buffer.
 func (h *Handler) SizeRx() int {
 	return h.bufRx.Size()