SERVER-43578 M/R Agg: Reject mapreduce command sent to mongos which is expected to drop and re-shard the output collection

3 files changed, 35 insertions, 0 deletions

diff --git a/src/mongo/db/commands/map_reduce_agg_test.cpp b/src/mongo/db/commands/map_reduce_agg_test.cpp
index 98a237d7d3f..8cdbbe439a3 100644
--- a/src/mongo/db/commands/map_reduce_agg_test.cpp
+++ b/src/mongo/db/commands/map_reduce_agg_test.cpp
@@ -267,5 +267,28 @@ TEST(MapReduceAggTest, testSourceDestinationCollectionsNotEqualMergeDoesNotFail)
     ASSERT_DOES_NOT_THROW(map_reduce_common::translateFromMR(mr, expCtx));
 }
 
+TEST(MapReduceAggTest, testShardedTrueWithReplaceActionFailsOnMongos) {
+    auto nss = NamespaceString{"db", "coll"};
+    auto mr = MapReduce{
+        nss,
+        MapReduceJavascriptCode{mapJavascript.toString()},
+        MapReduceJavascriptCode{reduceJavascript.toString()},
+        MapReduceOutOptions{boost::make_optional("db"s), "coll2", OutputType::Replace, true}};
+    boost::intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest(nss));
+    expCtx->inMongos = true;
+    ASSERT_THROWS_CODE(map_reduce_common::translateFromMR(mr, expCtx), DBException, 31327);
+}
+
+TEST(MapReduceAggTest, testShardedTrueWithReplaceActionDoesNotFailOnMongod) {
+    auto nss = NamespaceString{"db", "coll"};
+    auto mr = MapReduce{
+        nss,
+        MapReduceJavascriptCode{mapJavascript.toString()},
+        MapReduceJavascriptCode{reduceJavascript.toString()},
+        MapReduceOutOptions{boost::make_optional("db"s), "coll2", OutputType::Replace, true}};
+    boost::intrusive_ptr<ExpressionContextForTest> expCtx(new ExpressionContextForTest(nss));
+    ASSERT_DOES_NOT_THROW(map_reduce_common::translateFromMR(mr, expCtx));
+}
+
 }  // namespace
 }  // namespace mongo
diff --git a/src/mongo/db/commands/map_reduce_out_options.h b/src/mongo/db/commands/map_reduce_out_options.h
index b7d25fd7840..d62f632dae8 100644
--- a/src/mongo/db/commands/map_reduce_out_options.h
+++ b/src/mongo/db/commands/map_reduce_out_options.h
@@ -94,6 +94,10 @@ public:
         return _databaseName;
     }
 
+    const bool isSharded() const {
+        return _sharded;
+    }
+
 private:
     boost::optional<std::string> _databaseName;
     std::string _collectionName;
diff --git a/src/mongo/db/commands/mr_common.cpp b/src/mongo/db/commands/mr_common.cpp
index 8eece3727a0..16269873593 100644
--- a/src/mongo/db/commands/mr_common.cpp
+++ b/src/mongo/db/commands/mr_common.cpp
@@ -331,6 +331,14 @@ std::unique_ptr<Pipeline, PipelineDeleter> translateFromMR(
                 shardKey == std::set<FieldPath>{FieldPath("_id"s)});
     }
 
+    // If sharded option is set to true and the replace action is specified, verify that this isn't
+    // running on mongos.
+    if (outType == OutputType::Replace && parsedMr.getOutOptions().isSharded()) {
+        uassert(31327,
+                "Cannot replace output collection when specifying sharded: true",
+                !expCtx->inMongos);
+    }
+
     // TODO: It would be good to figure out what kind of errors this would produce in the Status.
     // It would be better not to produce something incomprehensible out of an internal translation.
     auto pipeline = uassertStatusOK(Pipeline::create(