Replace stdx::optional and stdx::string_view with the C++ std
counterparts.
Some instances of boost::variant were also replaced with std::variant,
namely those that called seastar::visit.
Scylla now requires GCC 8 to compile.
Signed-off-by: Duarte Nunes <duarte@scylladb.com>
Message-Id: <20190108111141.5369-1-duarte@scylladb.com>
sprint() recently became more strict, throwing on sprint("%s", 5). Replace
with the more modern format().
Mechanically converted with https://github.com/avikivity/unsprint.
The logic responsible for reading requests was operating on
temporary_buffer<char> and bytes_view. This required all request
messages to be linearised to a contiguous buffer, possibly causing large
allocations. Changing to fragmented_temporary_buffer mostly alleviates this
problem unless the reader code explicitly asks for a contiguous bytes_view.
