SERVER-27438 Prevent mongos from dropping legacy $comment meta-operator

Closes #1135

Signed-off-by: James Wahlin <james.wahlin@10gen.com>

3 files changed, 59 insertions, 2 deletions

diff --git a/src/mongo/db/query/query_request.cpp b/src/mongo/db/query/query_request.cpp
index 821282f78eb..b0f1334de8d 100644
--- a/src/mongo/db/query/query_request.cpp
+++ b/src/mongo/db/query/query_request.cpp
@@ -37,6 +37,7 @@
 #include "mongo/db/dbmessage.h"
 #include "mongo/db/namespace_string.h"
 #include "mongo/db/repl/read_concern_args.h"
+#include "mongo/stdx/memory.h"
 #include "mongo/util/assert_util.h"
 #include "mongo/util/mongoutils/str.h"
 
@@ -113,7 +114,7 @@ QueryRequest::QueryRequest(NamespaceString nss) : _nss(std::move(nss)) {}
 StatusWith<unique_ptr<QueryRequest>> QueryRequest::makeFromFindCommand(NamespaceString nss,
                                                                        const BSONObj& cmdObj,
                                                                        bool isExplain) {
-    unique_ptr<QueryRequest> qr(new QueryRequest(std::move(nss)));
+    auto qr = stdx::make_unique<QueryRequest>(nss);
     qr->_explain = isExplain;
 
     // Parse the command BSON by looping through one element at a time.
@@ -702,7 +703,7 @@ bool QueryRequest::isQueryIsolated(const BSONObj& query) {
 
 // static
 StatusWith<unique_ptr<QueryRequest>> QueryRequest::fromLegacyQueryMessage(const QueryMessage& qm) {
-    unique_ptr<QueryRequest> qr(new QueryRequest(NamespaceString(qm.ns)));
+    auto qr = stdx::make_unique<QueryRequest>(NamespaceString(qm.ns));
 
     Status status = qr->init(qm.ntoskip, qm.ntoreturn, qm.queryOptions, qm.query, qm.fields, true);
     if (!status.isOK()) {
@@ -712,6 +713,22 @@ StatusWith<unique_ptr<QueryRequest>> QueryRequest::fromLegacyQueryMessage(const
     return std::move(qr);
 }
 
+StatusWith<unique_ptr<QueryRequest>> QueryRequest::fromLegacyQueryForTest(NamespaceString nss,
+                                                                          const BSONObj& queryObj,
+                                                                          const BSONObj& proj,
+                                                                          int ntoskip,
+                                                                          int ntoreturn,
+                                                                          int queryOptions) {
+    auto qr = stdx::make_unique<QueryRequest>(nss);
+
+    Status status = qr->init(ntoskip, ntoreturn, queryOptions, queryObj, proj, true);
+    if (!status.isOK()) {
+        return status;
+    }
+
+    return std::move(qr);
+}
+
 Status QueryRequest::init(int ntoskip,
                           int ntoreturn,
                           int queryOptions,
@@ -862,6 +879,13 @@ Status QueryRequest::initFullQuery(const BSONObj& top) {
                     return maxTimeMS.getStatus();
                 }
                 _maxTimeMS = maxTimeMS.getValue();
+            } else if (str::equals("comment", name)) {
+                // Legacy $comment can be any BSON element. Convert to string if it isn't already.
+                if (e.type() == BSONType::String) {
+                    _comment = e.str();
+                } else {
+                    _comment = e.toString(false);
+                }
             }
         }
     }
diff --git a/src/mongo/db/query/query_request.h b/src/mongo/db/query/query_request.h
index 01d356a5837..376d5ece98c 100644
--- a/src/mongo/db/query/query_request.h
+++ b/src/mongo/db/query/query_request.h
@@ -393,6 +393,16 @@ public:
      */
     static StatusWith<std::unique_ptr<QueryRequest>> fromLegacyQueryMessage(const QueryMessage& qm);
 
+    /**
+     * Parse the provided legacy query object and parameters to construct a QueryRequest.
+     */
+    static StatusWith<std::unique_ptr<QueryRequest>> fromLegacyQueryForTest(NamespaceString nss,
+                                                                            const BSONObj& queryObj,
+                                                                            const BSONObj& proj,
+                                                                            int ntoskip,
+                                                                            int ntoreturn,
+                                                                            int queryOptions);
+
 private:
     Status init(int ntoskip,
                 int ntoreturn,
diff --git a/src/mongo/db/query/query_request_test.cpp b/src/mongo/db/query/query_request_test.cpp
index b8e45d810e4..bd40a94ef33 100644
--- a/src/mongo/db/query/query_request_test.cpp
+++ b/src/mongo/db/query/query_request_test.cpp
@@ -1304,5 +1304,28 @@ TEST(QueryRequestTest, ConvertToAggregationWithCollationSucceeds) {
     ASSERT_BSONOBJ_EQ(ar.getValue().getCollation(), BSON("f" << 1));
 }
 
+TEST(QueryRequestTest, ParseFromLegacyObjMetaOpComment) {
+    BSONObj queryObj = fromjson(
+        "{$query: {a: 1},"
+        "$comment: {b: 2, c: {d: 'ParseFromLegacyObjMetaOpComment'}}}");
+    const NamespaceString nss("test.testns");
+    unique_ptr<QueryRequest> qr(
+        assertGet(QueryRequest::fromLegacyQueryForTest(nss, queryObj, BSONObj(), 0, 0, 0)));
+
+    // Ensure that legacy comment meta-operator is parsed to a string comment
+    ASSERT_EQ(qr->getComment(), "{ b: 2, c: { d: \"ParseFromLegacyObjMetaOpComment\" } }");
+}
+
+TEST(QueryRequestTest, ParseFromLegacyStringMetaOpComment) {
+    BSONObj queryObj = fromjson(
+        "{$query: {a: 1},"
+        "$comment: 'ParseFromLegacyStringMetaOpComment'}");
+    const NamespaceString nss("test.testns");
+    unique_ptr<QueryRequest> qr(
+        assertGet(QueryRequest::fromLegacyQueryForTest(nss, queryObj, BSONObj(), 0, 0, 0)));
+
+    ASSERT_EQ(qr->getComment(), "ParseFromLegacyStringMetaOpComment");
+}
+
 }  // namespace mongo
 }  // namespace