Move prepare_buffers to prepare_buffer.hpp (API Change)

fix #338

include/beast/core/prepare_buffer.hpp

@@ -9,8 +9,14 @@
 #define BEAST_PREPARE_BUFFER_HPP
 
 #include <beast/config.hpp>
+#include <beast/core/detail/prepare_buffer.hpp>
 #include <boost/asio/buffer.hpp>
 #include <algorithm>
+#include <cstdint>
+#include <iterator>
+#include <stdexcept>
+#include <type_traits>
+#include <utility>
 
 namespace beast {
 
@@ -64,6 +70,34 @@ prepare_buffer(std::size_t n,
         (std::min)(n, buffer_size(buffer)) };
 }
 
+/** Return a shortened buffer sequence.
+
+    This function returns a new buffer sequence which adapts the
+    passed buffer sequence and efficiently presents a shorter subset
+    of the original list of buffers starting with the first byte of
+    the original sequence.
+
+    @param n The maximum number of bytes in the wrapped
+    sequence. If this is larger than the size of passed,
+    buffers, the resulting sequence will represent the
+    entire input sequence.
+
+    @param buffers The buffer sequence to adapt. A copy of
+    the sequence will be made, but ownership of the underlying
+    memory is not transferred.
+*/
+template<class BufferSequence>
+#if BEAST_DOXYGEN
+implementation_defined
+#else
+inline
+detail::prepare_buffers_helper<BufferSequence>
+#endif
+prepare_buffers(std::size_t n, BufferSequence const& buffers)
+{
+    return detail::prepare_buffers_helper<BufferSequence>(n, buffers);
+}
+
 } // beast
 
 #endif