More refactoring.

Change-Id: Iaf937feb0486d2f008a47584c0a75edccbde2b34

src/nt_raw_istream.cpp

@@ -7,9 +7,22 @@
 
 #include "nt_raw_istream.h"
 
+#include <cstring>
+
 using namespace NtImpl;
 
 void
 raw_istream::anchor()
 {
 }
+
+bool
+raw_mem_istream::read(void *data, std::size_t len)
+{
+    if (len > m_left)
+        return false;
+    std::memcpy(data, m_cur, len);
+    m_cur += len;
+    m_left -= len;
+    return true;
+}