buffer_input_stream: make it possible to specify chunk size

This will allow to force input stream to return its data
in chunks of a specified size.

Signed-off-by: Piotr Jastrzebski <piotr@scylladb.com>

utils/buffer_input_stream.cc

@@ -20,6 +20,7 @@
  */
 
 #include "buffer_input_stream.hh"
+#include "limiting_data_source.hh"
 
 using namespace seastar;
 
@@ -45,6 +46,13 @@ public:
 };
 
 input_stream<char> make_buffer_input_stream(temporary_buffer<char>&& buf) {
-    return input_stream<char>{
-        data_source{std::make_unique<buffer_data_source_impl>(std::move(buf))}};
+    return input_stream < char > {
+        data_source{std::make_unique<buffer_data_source_impl>(std::move(buf))}
+    };
+}
+
+input_stream<char> make_buffer_input_stream(temporary_buffer<char>&& buf,
+                                            seastar::noncopyable_function<size_t()>&& limit_generator) {
+    auto res = data_source{std::make_unique<buffer_data_source_impl>(std::move(buf))};
+    return input_stream < char > { make_limiting_data_source(std::move(res), std::move(limit_generator)) };
 }

utils/buffer_input_stream.hh

@@ -23,6 +23,7 @@
 
 #include <seastar/core/iostream.hh>
 #include <seastar/core/temporary_buffer.hh>
+#include <seastar/util/noncopyable_function.hh>
 #include "seastarx.hh"
 
 /// \brief Creates an input_stream to read from a supplied buffer
@@ -30,3 +31,11 @@
 /// \param buf Buffer to return from the stream while reading
 /// \return resulting input stream
 input_stream<char> make_buffer_input_stream(temporary_buffer<char>&& buf);
+
+/// \brief Creates an input_stream to read from a supplied buffer
+///
+/// \param buf Buffer to return from the stream while reading
+/// \param limit_generator Generates limits of chunk sizes
+/// \return resulting input stream
+input_stream<char> make_buffer_input_stream(temporary_buffer<char>&& buf,
+                                            seastar::noncopyable_function<size_t()>&& limit_generator);