ability to store and retrieve envelopes

include/amqpcpp/envelope.h

@@ -4,7 +4,7 @@
  *  When you send or receive a message to the rabbitMQ server, it is encapsulated
  *  in an envelope that contains additional meta information as well.
  *
- *  @copyright 2014 - 2017 Copernica BV
+ *  @copyright 2014 - 2020 Copernica BV
  */
 
 /**
@@ -24,6 +24,10 @@ namespace AMQP {
 
 /**
  *  Class definition
+ *  The envelope extends from MetaData, although this is conceptually not entirely
+ *  correct: and envelope _holds_ meta data and a body, so it would have been more
+ *  correct to make the MetaData instance a member. But by extending we automatically
+ *  make all meta-data properties accesible.
  */
 class Envelope : public MetaData
 {
@@ -43,18 +47,29 @@ protected:
 public:
     /**
      *  Constructor
-     *
      *  The data buffer that you pass to this constructor must be valid during
      *  the lifetime of the Envelope object.
-     *
      *  @param  body
      *  @param  size
      */
     Envelope(const char *body, uint64_t size) : MetaData(), _body(body), _bodySize(size) {}
 
+    /**
+     *  Read envelope frmo an input-buffer
+     *  This method is the counterpart of the Envelope::fill() method, and is not used
+     *  by the library itself, but might be useful for applications that want to store
+     *  envelopes.
+     *  @param  frame
+     */
+    Envelope(InBuffer &buffer) : MetaData(buffer)
+    {
+        // extract the properties
+        _bodySize = buffer.nextUint64();
+        _body = buffer.nextData(_bodySize);
+    }
+
     /**
      *  Disabled copy constructor
-     *
      *  @param  envelope    the envelope to copy
      */
     Envelope(const Envelope &envelope) = delete;
@@ -81,6 +96,34 @@ public:
     {
         return _bodySize;
     }
+    
+    /**
+     *  Size of the envelope, this is the size of the meta+data plus the number of bytes
+     *  required to store the size of the body + the actual body. This method is not used
+     *  by the AMQP-CPP library, but could be useful if you feel the need to store 
+     *  @return size_t
+     */
+    size_t size() const
+    {
+        // this is the size of the meta-data + the size of the body 
+        return MetaData::size() + _bodySize + sizeof(uint64_t);
+    }
+    
+    /**
+     *  Fill an output buffer
+     *  This method is not used by this library, but could be useful if you want to store
+     *  the meta-data + message contents (
+     *  @param  buffer
+     */
+    void fill(OutBuffer &buffer) const
+    {
+        // first we store the meta-data
+        MetaData::fill(buffer);
+        
+        // now the size of the message body + the actual body
+        buffer.add(_bodySize);
+        buffer.add(_body, _bodySize);
+    }
 };
 
 /**