SFINAE for choosing 'write' overload

deanberris · deanberris · commit ddc8bdf03eda · 2011-01-30T00:31:18.000+08:00
Aside from adding an additional clarification in the documentation for
the macro defining the size of a page, this change makes the user-facing
'write' implementation use SFINAE to choose whether to deal with the
buffer provided as a buffer that doesn't need to be copied (derives from
Boost.Asio's const_buffer type) or whether it's something that needs to
be copied (in the case of any other range).

In the future there should be other overloads which deal with explicit
Boost.Range iterator ranges, and maybe specific types.
diff --git a/boost/network/protocol/http/server/async_connection.hpp b/boost/network/protocol/http/server/async_connection.hpp
@@ -24,6 +24,7 @@
 #include <boost/utility/typed_in_place_factory.hpp>
 #include <boost/thread/locks.hpp>
 #include <boost/thread/recursive_mutex.hpp>
+#include <boost/utility/enable_if.hpp>
 #include <list>
 #include <vector>
 #include <iterator>
@@ -35,6 +36,10 @@
  *  This is the maximum size though and Boost.Asio's internal representation
  *  of a streambuf would make appropriate decisions on how big a buffer
  *  is to begin with.
+ *
+ *  This kinda assumes that a page is by default 4096. Since we're using
+ *  the default allocator with the static buffers, it's not guaranteed that
+ *  the static buffers will be page-aligned when they are allocated.
  */
 #define BOOST_NETWORK_HTTP_SERVER_CONNECTION_HEADER_BUFFER_MAX_SIZE 4096
 #endif /* BOOST_NETWORK_HTTP_SERVER_CONNECTION_HEADER_BUFFER_MAX_SIZE */
@@ -211,14 +216,16 @@ namespace boost { namespace network { namespace http {
         }
 
         template <class Range, class Callback>
-        void write(Range const & range, Callback const & callback) {
+        typename disable_if<is_base_of<asio::const_buffer, Range>, void>::type
+        write(Range const & range, Callback const & callback) {
             lock_guard lock(headers_mutex);
             if (error_encountered) boost::throw_exception(boost::system::system_error(*error_encountered));
             write_impl(boost::make_iterator_range(range), callback);
         }
 
         template <class ConstBufferSeq, class Callback>
-        void write_vec(ConstBufferSeq const & seq, Callback const & callback)
+        typename enable_if<is_base_of<asio::const_buffer, ConstBufferSeq>, void>::type
+        write(ConstBufferSeq const & seq, Callback const & callback)
         {
             write_vec_impl(seq, callback, shared_array_list(), shared_buffers());
         }
