SERVER-25969 make slaves and secondaries always use BSON 1.1 validation

This allows secondaries and slaves to sync NumberDecimal even while
in featureCompatibilityVersion:"3.2" mode.

1 files changed, 13 insertions, 4 deletions

diff --git a/src/mongo/rpc/object_check.h b/src/mongo/rpc/object_check.h
index c4f999fde20..7c7741ada62 100644
--- a/src/mongo/rpc/object_check.h
+++ b/src/mongo/rpc/object_check.h
@@ -45,10 +45,19 @@ class Status;
 template <>
 struct Validator<BSONObj> {
     inline static BSONVersion enabledBSONVersion() {
-        return serverGlobalParams.featureCompatibilityVersion.load() ==
-                ServerGlobalParams::FeatureCompatibilityVersion_34
-            ? BSONVersion::kV1_1
-            : BSONVersion::kV1_0;
+        // If we're in the primary/master role accepting writes, but our feature compatibility
+        // version is 3.2, then we want to reject insertion of the decimal data type. Therefore, we
+        // perform BSON 1.0 validation.
+        if (serverGlobalParams.featureCompatibility.validateFeaturesAsMaster.load() &&
+            serverGlobalParams.featureCompatibility.version.load() ==
+                ServerGlobalParams::FeatureCompatibility::Version::k32) {
+            return BSONVersion::kV1_0;
+        }
+
+        // Except for the special case above, we want to accept any BSON version which we know
+        // about. For instance, if we are a slave/secondary syncing from a primary/master and we are
+        // in 3.2 feature compatibility mode, we still want to be able to sync NumberDecimal data.
+        return BSONVersion::kV1_1;
     }
 
     inline static Status validateLoad(const char* ptr, size_t length) {