rgw: add basic infrastructure for decorators over RGWStreamIOBase.

Signed-off-by: Radoslaw Zarzynski <rzarzynski@mirantis.com>

diff --git a/src/rgw/rgw_client_io_decoimpl.h b/src/rgw/rgw_client_io_decoimpl.h
new file mode 100644 (file)
index 0000000..f727033
--- /dev/null
+++ b/src/rgw/rgw_client_io_decoimpl.h
@@ -0,0 +1,89 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+
+#ifndef CEPH_RGW_CLIENT_IO_DECOIMPL_H
+#define CEPH_RGW_CLIENT_IO_DECOIMPL_H
+
+#include <type_traits>
+
+#include "rgw_common.h"
+#include "rgw_client_io.h"
+
+/* Abstract decorator over any implementation of RGWStreamIOEngine. */
+template <typename DecorateeT>
+class RGWDecoratedStreamIO : public RGWStreamIOEngine {
+  template<typename T> friend class RGWDecoratedStreamIO;
+
+  typedef typename std::remove_pointer<DecorateeT>::type DerefedDecorateeT;
+
+  static_assert(std::is_base_of<RGWStreamIOEngine, DerefedDecorateeT>::value,
+                "DecorateeT must be a subclass of RGWStreamIOEngine");
+
+  DecorateeT decoratee;
+
+  /* There is an indirection layer over accessing decoratee to share the same
+   * code base between dynamic and static decorators. The difference is about
+   * what we store internally: pointer to a decorated object versus the whole
+   * object itself. */
+  template <typename T = void,
+            typename std::enable_if<
+    std::is_pointer<DecorateeT>::value, T>::type* = nullptr>
+  DerefedDecorateeT& get_decoratee() {
+    return *decoratee;
+  }
+
+  template <typename T = void,
+            typename std::enable_if<
+    ! std::is_pointer<DecorateeT>::value, T>::type* = nullptr>
+  DerefedDecorateeT& get_decoratee() {
+    return decoratee;
+  }
+
+protected:
+  void init_env(CephContext *cct) override {
+    return get_decoratee().init_env(cct);
+  }
+
+  int read_data(char* const buf, const int max) override {
+    return get_decoratee().read_data(buf, max);
+  }
+
+  int write_data(const char* const buf, const int len) override {
+    return get_decoratee().write_data(buf, len);
+  }
+
+public:
+  RGWDecoratedStreamIO(const DecorateeT& decoratee)
+    : decoratee(decoratee) {
+  }
+
+  int send_status(const int status, const char* const status_name) override {
+    return get_decoratee().send_status(status, status_name);
+  }
+
+  int send_100_continue() override {
+    return get_decoratee().send_100_continue();
+  }
+
+  int send_content_length(const uint64_t len) override {
+    return get_decoratee().send_content_length(len);
+  }
+
+  int complete_header() override {
+    return get_decoratee().complete_header();
+  }
+
+  void flush() override {
+    return get_decoratee().flush();
+  }
+
+  RGWEnv& get_env() override {
+    return get_decoratee().get_env();
+  }
+
+  int complete_request() override {
+    return get_decoratee().complete_request();
+  }
+};
+
+#endif /* CEPH_RGW_CLIENT_IO_DECOIMPL_H */