SERVER-18418 Remote command targeter

This change introduces a remote command targeter interface to be used as a
stub to start implementing the targeting logic.

1 files changed, 124 insertions, 0 deletions

diff --git a/src/mongo/client/read_preference.h b/src/mongo/client/read_preference.h
new file mode 100644
index 00000000000..f65818b04bc
--- /dev/null
+++ b/src/mongo/client/read_preference.h
@@ -0,0 +1,124 @@
+/**
+ *    Copyright (C) 2015 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    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 Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the GNU Affero General Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include "mongo/db/json.h"
+
+namespace mongo {
+
+    enum ReadPreference {
+        /**
+         * Read from primary only. All operations produce an error (throw an exception where
+         * applicable) if primary is unavailable. Cannot be combined with tags.
+         */
+        ReadPreference_PrimaryOnly = 0,
+
+        /**
+         * Read from primary if available, otherwise a secondary. Tags will only be applied in the
+         * event that the primary is unavailable and a secondary is read from. In this event only
+         * secondaries matching the tags provided would be read from.
+         */
+        ReadPreference_PrimaryPreferred,
+
+        /**
+         * Read from secondary if available, otherwise error.
+         */
+        ReadPreference_SecondaryOnly,
+
+        /**
+         * Read from a secondary if available, otherwise read from the primary.
+         */
+        ReadPreference_SecondaryPreferred,
+
+        /**
+         * Read from any member.
+         */
+        ReadPreference_Nearest,
+    };
+
+
+    /**
+     * A simple object for representing the list of tags requested by a $readPreference.
+     */
+    class TagSet {
+    public:
+        /**
+         * Creates a TagSet that matches any nodes.
+         *
+         * Do not call during static init.
+         */
+        TagSet();
+
+        /**
+         * Creates a TagSet from a BSONArray of tags.
+         *
+         * @param tags the list of tags associated with this option. This object
+         *     will get a shared copy of the list. Therefore, it is important
+         *     for the the given tag to live longer than the created tag set.
+         */
+        explicit TagSet(const BSONArray& tags) : _tags(tags) {}
+
+        /**
+         * Returns the BSONArray listing all tags that should be accepted.
+         */
+        const BSONArray& getTagBSON() const { return _tags; }
+
+        bool operator==(const TagSet& other) const { return _tags == other._tags; }
+
+    private:
+        BSONArray _tags;
+    };
+
+
+    struct ReadPreferenceSetting {
+        /**
+         * @param pref the read preference mode.
+         * @param tag the tag set. Note that this object will have the
+         *     tag set will have this in a reset state (meaning, this
+         *     object's copy of tag will have the iterator in the initial
+         *     position).
+         */
+        ReadPreferenceSetting(ReadPreference pref, const TagSet& tag)
+            : pref(pref),
+              tags(tag) {
+
+        }
+
+        inline bool equals(const ReadPreferenceSetting& other) const {
+            return (pref == other.pref) && (tags == other.tags);
+        }
+
+        BSONObj toBSON() const;
+
+
+        const ReadPreference pref;
+        const TagSet tags;
+    };
+
+} // namespace mongo