Implement the support for adhoc commands

We have two basic example commands. But it’s not entirely finished because
there are some error checks that we don’t do.

ref #2521

src/xmpp/adhoc_commands_handler.hpp

@@ -0,0 +1,56 @@
+#ifndef ADHOC_COMMANDS_HANDLER_HPP
+# define ADHOC_COMMANDS_HANDLER_HPP
+
+/**
+ * Manage a list of available AdhocCommands and the list of ongoing
+ * AdhocCommandSessions.
+ */
+
+#include <xmpp/adhoc_command.hpp>
+#include <xmpp/xmpp_stanza.hpp>
+
+#include <utility>
+#include <string>
+#include <map>
+
+class AdhocCommandsHandler
+{
+public:
+  explicit AdhocCommandsHandler();
+  ~AdhocCommandsHandler();
+  /**
+   * Returns the list of available commands.
+   */
+  const std::map<const std::string, const AdhocCommand>& get_commands() const;
+  /**
+   * Find the requested command, create a new session or use an existing
+   * one, and process the request (provide a new form, an error, or a
+   * result).
+   *
+   * Returns a (moved) XmlNode that will be inserted in the iq response. It
+   * should be a <command/> node containing one or more useful children. If
+   * it contains an <error/> node, the iq response will have an error type.
+   *
+   * Takes a copy of the <command/> node so we can actually edit it and use
+   * it as our return value.
+   */
+  XmlNode&& handle_request(const std::string& executor_jid, XmlNode command_node);
+private:
+  /**
+   * The list of all available commands.
+   */
+  const std::map<const std::string, const AdhocCommand> commands;
+  /**
+   * The list of all currently on-going commands.
+   *
+   * Of the form: {{session_id, owner_jid}, session}.
+   */
+  std::map<std::pair<const std::string, const std::string>, AdhocSession> sessions;
+
+  AdhocCommandsHandler(const AdhocCommandsHandler&) = delete;
+  AdhocCommandsHandler(AdhocCommandsHandler&&) = delete;
+  AdhocCommandsHandler& operator=(const AdhocCommandsHandler&) = delete;
+  AdhocCommandsHandler& operator=(AdhocCommandsHandler&&) = delete;
+};
+
+#endif // ADHOC_COMMANDS_HANDLER_HPP