prepare pdu_stream class for output buffering too

acn/pdu.h

@@ -25,7 +25,7 @@
 
 #include <cstdint>
 #include <functional>
-#include <istream>
+#include <iostream>
 #include <memory>
 #include <vector>
 
@@ -54,30 +54,26 @@ struct pdu_header { virtual ~pdu_header() {} };
 struct pdu_data { virtual ~pdu_data() {} };
 
 
-/**
-    Memory buffer of uint8_t data.
-*/
-class pdu_buffer
-  : public std::basic_streambuf<uint8_t>
-{
-public:
-  pdu_buffer(uint8_t * p, size_t l) { setg(p, p, p + l); };
-  uint8_t * in_ptr() { return gptr(); };
-};
 /**
     Input/Output stream of nested PDU
 */
+
 class pdu_stream
-  : public std::basic_istream<uint8_t>
+  : private std::basic_streambuf<uint8_t>
+  , public std::basic_iostream<uint8_t>
 {
 public:
-  pdu_stream(uint8_t * p, size_t l)
-    : std::basic_istream<uint8_t>(&_buffer)
-    , _buffer(p, l)           { rdbuf(&_buffer); }
-  uint32_t  available() { return _buffer.in_avail(); }
-  uint8_t * data()      { return _buffer.in_ptr(); };
+  pdu_stream(uint8_t * p, std::streamsize l)
+    : std::basic_streambuf<uint8_t>()
+    , std::basic_iostream<uint8_t>(this)
+  {
+    setg(p, p, p + l);
+    setp(p, p + l);
+  }
+  uint32_t  available() { return in_avail(); }
+  uint8_t * data()      { return gptr(); };
   template<typename T> T readType() {
-      if (available() < sizeof(T)) {
+      if (in_avail() < sizeof(T)) {
         setstate(std::ios_base::failbit);
         return 0;
       }
@@ -85,13 +81,10 @@ public:
       auto data = reinterpret_cast<uint8_t*>(&ret);
       for (int i = sizeof(T);  --i >= 0; )
           data[i] = get();
-      if (!available())
+      if (!in_avail())
         setstate(std::ios_base::eofbit);
       return ret;
   }
-
-private:
-  pdu_buffer _buffer;
 };
 using Stream = shared_ptr<pdu_stream>;