SERVER-29461 check for duplicate fields when serializing OP_MSG

2 files changed, 22 insertions, 1 deletions

diff --git a/src/mongo/util/net/op_msg.cpp b/src/mongo/util/net/op_msg.cpp
index 72b27e7482d..5d451af15f0 100644
--- a/src/mongo/util/net/op_msg.cpp
+++ b/src/mongo/util/net/op_msg.cpp
@@ -32,12 +32,13 @@
 
 #include "mongo/util/net/op_msg.h"
 
+#include <set>
+
 #include "mongo/db/bson/dotted_path_support.h"
 #include "mongo/rpc/object_check.h"
 #include "mongo/util/bufreader.h"
 #include "mongo/util/hex.h"
 #include "mongo/util/log.h"
-#include "mongo/util/string_map.h"
 
 namespace mongo {
 namespace {
@@ -183,7 +184,20 @@ BSONObjBuilder OpMsgBuilder::resumeBody() {
     return BSONObjBuilder(BSONObjBuilder::ResumeBuildingTag(), _buf, _bodyStart);
 }
 
+AtomicBool OpMsgBuilder::disableDupeFieldCheck_forTest{false};
+
 Message OpMsgBuilder::finish() {
+    if (kDebugBuild && !disableDupeFieldCheck_forTest.load()) {
+        std::set<StringData> seenFields;
+        for (auto elem : resumeBody().asTempObj()) {
+            if (!(seenFields.insert(elem.fieldNameStringData()).second)) {
+                severe() << "OP_MSG with duplicate field '" << elem.fieldNameStringData()
+                         << "' : " << redact(resumeBody().asTempObj());
+                fassert(40474, false);
+            }
+        }
+    }
+
     invariant(_state == kBody);
     invariant(_bodyStart);
     invariant(!_openBuilder);
diff --git a/src/mongo/util/net/op_msg.h b/src/mongo/util/net/op_msg.h
index 98b04c1bc20..dc8037146be 100644
--- a/src/mongo/util/net/op_msg.h
+++ b/src/mongo/util/net/op_msg.h
@@ -210,6 +210,13 @@ public:
         _openBuilder = false;
     }
 
+    /**
+     * Set to true in tests that need to be able to generate duplicate top-level fields to see how
+     * the server handles them. Is false by default, although the check only happens in debug
+     * builds.
+     */
+    static AtomicBool disableDupeFieldCheck_forTest;
+
 private:
     friend class DocSequenceBuilder;