1 files changed, 115 insertions, 0 deletions
diff --git a/src/mongo/db/ops/log_builder.cpp b/src/mongo/db/ops/log_builder.cpp
new file mode 100644
index 00000000000..cde2668f1ca
--- /dev/null
+++ b/src/mongo/db/ops/log_builder.cpp
@@ -0,0 +1,115 @@
+/**
+ *    Copyright (C) 2013 10gen 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/>.
+ */
+
+#include "mongo/db/ops/log_builder.h"
+
+namespace mongo {
+
+    using mutablebson::Document;
+    using mutablebson::Element;
+
+    namespace {
+        const char kSet[] = "$set";
+        const char kUnset[] = "$unset";
+    } // namespace
+
+    inline Status LogBuilder::addToSection(Element newElt,
+                                           Element* section,
+                                           const char* sectionName) {
+
+        // If we don't already have this section, try to create it now.
+        if (!section->ok()) {
+
+            // If we already have object replacement data, we can't also have section entries.
+            if (hasObjectReplacement())
+                return Status(
+                    ErrorCodes::IllegalOperation,
+                    "LogBuilder: Invalid attempt to add a $set/$unset entry"
+                    "to a log with an existing object replacement");
+
+            Document& doc = _logRoot.getDocument();
+
+            // We should not already have an element with the section name under the root.
+            dassert(_logRoot[sectionName] == doc.end());
+
+            // Construct a new object element to represent this section in the log.
+            const Element newElement = doc.makeElementObject(sectionName);
+            if (!newElement.ok())
+                return Status(ErrorCodes::InternalError,
+                              "LogBuilder: failed to construct Object Element for $set/$unset");
+
+            // Enqueue the new section under the root, and record it as our out parameter.
+            Status result = _logRoot.pushBack(newElement);
+            if (!result.isOK())
+                return result;
+            *section = newElement;
+
+            // Invalidate attempts to add an object replacement, now that we have a named
+            // section under the root.
+            _objectReplacementAccumulator = doc.end();
+        }
+
+        // Whatever transpired, we should now have an ok accumulator for the section, and not
+        // have a replacement accumulator.
+        dassert(section->ok());
+        dassert(!_objectReplacementAccumulator.ok());
+
+        // Enqueue the provided element to the section and propagate the result.
+        return section->pushBack(newElt);
+    }
+
+    Status LogBuilder::addToSets(Element elt) {
+        return addToSection(elt, &_setAccumulator, kSet);
+    }
+
+    Status LogBuilder::addToUnsets(Element elt) {
+        return addToSection(elt, &_unsetAccumulator, kUnset);
+    }
+
+    Status LogBuilder::getReplacementObject(Element* outElt) {
+
+        // If the replacement accumulator is not ok, we must have started a $set or $unset
+        // already, so an object replacement is not permitted.
+        if (!_objectReplacementAccumulator.ok()) {
+            dassert(_setAccumulator.ok() || _unsetAccumulator.ok());
+            return Status(
+                ErrorCodes::IllegalOperation,
+                "LogBuilder: Invalid attempt to obtain the object replacement slot "
+                "for a log containing $set or $unset entries");
+        }
+
+        if (hasObjectReplacement())
+            return Status(
+                ErrorCodes::IllegalOperation,
+                "LogBuilder: Invalid attempt to acquire the replacement object "
+                "in a log with existing object replacement data");
+
+        // OK to enqueue object replacement items.
+        *outElt = _objectReplacementAccumulator;
+        return Status::OK();
+    }
+
+    inline bool LogBuilder::hasObjectReplacement() const {
+        if (!_objectReplacementAccumulator.ok())
+            return false;
+
+        dassert(!_setAccumulator.ok());
+        dassert(!_unsetAccumulator.ok());
+
+        return _objectReplacementAccumulator.hasChildren();
+    }
+
+} // namespace mongo