[frontend] Adds generic XrdCtaStream class

All "cta-admin ... ls" commands will now use the streaming interface.
The XrdCtaStream class provides a common API.

xroot_plugins/XrdCtaStream.hpp

+/*!
+ * @project        The CERN Tape Archive (CTA)
+ * @brief          CTA Frontend stream implementation for cta-admin commands
+ * @copyright      Copyright 2019 CERN
+ * @license        This program is free software: you can redistribute it and/or modify
+ *                 it under the terms of the GNU General Public License as published by
+ *                 the Free Software Foundation, either version 3 of the License, or
+ *                 (at your option) any later version.
+ *
+ *                 This program is distributed in the hope that it will be useful,
+ *                 but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *                 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *                 GNU General Public License for more details.
+ *
+ *                 You should have received a copy of the GNU General Public License
+ *                 along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <XrdSsiPbOStreamBuffer.hpp>
+#include <catalogue/Catalogue.hpp>
+#include <scheduler/Scheduler.hpp>
+
+
+
+namespace cta { namespace xrd {
+
+/*!
+ * Virtual stream object
+ */
+class XrdCtaStream : public XrdSsiStream
+{
+public:
+  XrdCtaStream(const cta::admin::AdminCmd &admincmd, cta::catalogue::Catalogue &catalogue, cta::scheduler::Scheduler &scheduler)
+    XrdSsiStream(XrdSsiStream::isActive),
+    m_catalogue(catalogue),
+    m_scheduler(scheduler)
+  {
+    XrdSsiPb::Log::Msg(XrdSsiPb::Log::DEBUG, LOG_SUFFIX, "XrdCtaStream() constructor");
+  }
+
+  virtual ~ArchiveFileLsStream() {
+    XrdSsiPb::Log::Msg(XrdSsiPb::Log::DEBUG, LOG_SUFFIX, "~XrdCtaStream() destructor");
+  }
+
+  /*!
+   * Synchronously obtain data from an active stream
+   *
+   * Active streams can only exist on the server-side. This XRootD SSI Stream class is marked as an
+   * active stream in the constructor.
+   *
+   * @param[out]       eInfo   The object to receive any error description.
+   * @param[in,out]    dlen    input:  the optimal amount of data wanted (this is a hint)
+   *                           output: the actual amount of data returned in the buffer.
+   * @param[in,out]    last    input:  should be set to false.
+   *                           output: if true it indicates that no more data remains to be returned
+   *                                   either for this call or on the next call.
+   *
+   * @return    Pointer to the Buffer object that contains a pointer to the the data (see below). The
+   *            buffer must be returned to the stream using Buffer::Recycle(). The next member is usable.
+   * @retval    0    No more data remains or an error occurred:
+   *                 last = true:  No more data remains.
+   *                 last = false: A fatal error occurred, eRef has the reason.
+   */
+  virtual Buffer *GetBuff(XrdSsiErrInfo &eInfo, int &dlen, bool &last) override {
+    XrdSsiPb::Log::Msg(XrdSsiPb::Log::DEBUG, LOG_SUFFIX, "GetBuff(): XrdSsi buffer fill request (", dlen, " bytes)");
+
+    XrdSsiPb::OStreamBuffer<Data> *streambuf;
+
+    try {
+      if(isDone()) {
+        // Nothing more to send, close the stream
+        last = true;
+        return nullptr;
+      }
+
+      streambuf = new XrdSsiPb::OStreamBuffer<Data>(dlen);
+
+      dlen = fillBuffer(streambuf);
+
+      XrdSsiPb::Log::Msg(XrdSsiPb::Log::DEBUG, LOG_SUFFIX, "GetBuff(): Returning buffer with ", dlen, " bytes of data.");
+    } catch(cta::exception::Exception &ex) {
+      std::ostringstream errMsg;
+      errMsg << __FUNCTION__ << " failed: Caught CTA exception: " << ex.what();
+      eInfo.Set(errMsg.str().c_str(), ECANCELED);
+      delete streambuf;
+    } catch(std::exception &ex) {
+      std::ostringstream errMsg;
+      errMsg << __FUNCTION__ << " failed: " << ex.what();
+      eInfo.Set(errMsg.str().c_str(), ECANCELED);
+      delete streambuf;
+    } catch(...) {
+      std::ostringstream errMsg;
+      errMsg << __FUNCTION__ << " failed: Caught an unknown exception";
+      eInfo.Set(errMsg.str().c_str(), ECANCELED);
+      delete streambuf;
+    }
+    return streambuf;
+  }
+
+  /*!
+   * Returns true if there is nothing more to send (i.e. we can close the stream)
+   */
+  bool isDone() const = 0;
+
+  /*!
+   * Fills the stream buffer
+   */
+  int fillBuffer(XrdSsiPb::OStreamBuffer<Data> *streambuf) = 0;
+
+protected:
+  cta::catalogue::Catalogue &m_catalogue;                 //!< Reference to CTA Catalogue
+  cta::scheduler::Scheduler &m_scheduler;                 //!< Reference to CTA Scheduler
+
+private:
+  static constexpr const char* const LOG_SUFFIX  = "XrdCtaStream";    //!< Identifier for log messages
+};
+
+}} // namespace cta::xrd