* Unit test for SR 2PC

* Removed redundant data class
* Introduced const_buffer and mutable_buffer
* Transaction context and client context interface refactoring

include/wsrep/buffer.hpp

@@ -5,27 +5,52 @@
 #ifndef WSREP_BUFFER_HPP
 #define WSREP_BUFFER_HPP
 
+#include <vector>
+
 namespace wsrep
 {
-    class buffer
+    class const_buffer
     {
     public:
-        buffer()
+        const_buffer()
             : ptr_()
             , size_()
         { }
-        buffer(const void* ptr, size_t size)
+
+        const_buffer(const void* ptr, size_t size)
             : ptr_(ptr)
             , size_(size)
         { }
 
         const void* ptr() const { return ptr_; }
+        const void* data() const { return ptr_; }
         size_t size() const { return size_; }
 
     private:
+        // const_buffer(const const_buffer&);
+        // const_buffer& operator=(const const_buffer&);
         const void* ptr_;
         size_t size_;
     };
+
+
+    class mutable_buffer
+    {
+    public:
+        mutable_buffer()
+            : buffer_()
+        { }
+
+        void push_back(const char* begin, const char* end)
+        {
+            buffer_.insert(buffer_.end(), begin, end);
+        }
+        const char* data() const { return &buffer_[0]; }
+        size_t size() const { return buffer_.size(); }
+    private:
+        std::vector<char> buffer_;
+    };
+
 }
 
 #endif // WSREP_BUFFER_HPP