SERVER-42902 Update the MR response formatting code to run on a pipeline

10 files changed, 222 insertions, 268 deletions

diff --git a/src/mongo/db/commands/SConscript b/src/mongo/db/commands/SConscript
index a8402d10327..8351ec93f75 100644
--- a/src/mongo/db/commands/SConscript
+++ b/src/mongo/db/commands/SConscript
@@ -394,9 +394,9 @@ env.Library(
         '$BUILD_DIR/mongo/db/dbhelpers',
         '$BUILD_DIR/mongo/db/exec/stagedebug_cmd',
         '$BUILD_DIR/mongo/db/index_builds_coordinator_interface',
-        '$BUILD_DIR/mongo/db/query/mr_response_formatter',
         '$BUILD_DIR/mongo/db/pipeline/mongo_process_interface',
         '$BUILD_DIR/mongo/db/pipeline/pipeline',
+        '$BUILD_DIR/mongo/db/query/map_reduce_output_format',
         '$BUILD_DIR/mongo/db/repl/dbcheck',
         '$BUILD_DIR/mongo/db/repl/oplog',
         '$BUILD_DIR/mongo/db/repl/repl_coordinator_interface',
diff --git a/src/mongo/db/commands/map_reduce_agg.cpp b/src/mongo/db/commands/map_reduce_agg.cpp
index 840618ce9d1..c94116a3934 100644
--- a/src/mongo/db/commands/map_reduce_agg.cpp
+++ b/src/mongo/db/commands/map_reduce_agg.cpp
@@ -35,11 +35,12 @@
 #include "mongo/db/commands/map_reduce_agg.h"
 #include "mongo/db/commands/map_reduce_gen.h"
 #include "mongo/db/db_raii.h"
+#include "mongo/db/namespace_string.h"
 #include "mongo/db/pipeline/document_source.h"
 #include "mongo/db/pipeline/expression_context.h"
 #include "mongo/db/pipeline/pipeline.h"
 #include "mongo/db/pipeline/pipeline_d.h"
-#include "mongo/db/query/mr_response_formatter.h"
+#include "mongo/db/query/map_reduce_output_format.h"
 #include "mongo/util/intrusive_counter.h"
 
 namespace mongo {
@@ -95,8 +96,31 @@ bool runAggregationMapReduce(OperationContext* opCtx,
                              const BSONObj& cmd,
                              std::string& errmsg,
                              BSONObjBuilder& result) {
+    auto exhaustPipelineIntoBSONArray = [](auto&& pipeline) {
+        BSONArrayBuilder bab;
+        while (auto&& doc = pipeline->getNext())
+            bab.append(doc->toBson());
+        return bab.arr();
+    };
+
     auto parsedMr = MapReduce::parse(IDLParserErrorContext("MapReduce"), cmd);
-    [[maybe_unused]] auto pipe = translateFromMR(parsedMr, makeExpressionContext(opCtx, parsedMr));
+    bool inMemory = parsedMr.getOutOptions().getOutputType() == OutputType::InMemory;
+
+    auto pipe = translateFromMR(parsedMr, makeExpressionContext(opCtx, parsedMr));
+
+    if (inMemory)
+        map_reduce_output_format::appendInlineResponse(exhaustPipelineIntoBSONArray(pipe),
+                                                       parsedMr.getVerbose().get_value_or(false),
+                                                       false,
+                                                       &result);
+    else
+        map_reduce_output_format::appendOutResponse(
+            NamespaceString(parsedMr.getOutOptions().getDatabaseName(),
+                            parsedMr.getOutOptions().getCollectionName()),
+            boost::get_optional_value_or(parsedMr.getVerbose(), false),
+            false,
+            &result);
+
     return true;
 }
 
diff --git a/src/mongo/db/commands/map_reduce_agg.h b/src/mongo/db/commands/map_reduce_agg.h
index c946f74c380..8ac5d0ead5f 100644
--- a/src/mongo/db/commands/map_reduce_agg.h
+++ b/src/mongo/db/commands/map_reduce_agg.h
@@ -27,10 +27,6 @@
  *    it in the license file.
  */
 
-#include "mongo/bson/bsonobj.h"
-#include "mongo/bson/bsonobjbuilder.h"
-#include "mongo/db/operation_context.h"
-
 namespace mongo {
 
 bool runAggregationMapReduce(OperationContext* opCtx,
@@ -38,4 +34,5 @@ bool runAggregationMapReduce(OperationContext* opCtx,
                              const BSONObj& cmd,
                              std::string& errmsg,
                              BSONObjBuilder& result);
+
 }  // namespace mongo
diff --git a/src/mongo/db/query/SConscript b/src/mongo/db/query/SConscript
index 0260575ec37..ef3c6075095 100644
--- a/src/mongo/db/query/SConscript
+++ b/src/mongo/db/query/SConscript
@@ -104,9 +104,9 @@ env.Library(
 )
 
 env.Library(
-    target='mr_response_formatter',
+    target='map_reduce_output_format',
     source=[
-        'mr_response_formatter.cpp'
+        'map_reduce_output_format.cpp',
     ],
     LIBDEPS=[
         '$BUILD_DIR/mongo/base',
@@ -250,7 +250,7 @@ env.CppUnitTest(
         "killcursors_request_test.cpp",
         "killcursors_response_test.cpp",
         "lru_key_value_test.cpp",
-        "mr_response_formatter_test.cpp",
+        'map_reduce_output_format_test.cpp',
         "parsed_distinct_test.cpp",
         "parsed_projection_test.cpp",
         "plan_cache_indexability_test.cpp",
@@ -284,7 +284,7 @@ env.CppUnitTest(
         "command_request_response",
         "explain_options",
         "hint_parser",
-        "mr_response_formatter",
+        "map_reduce_output_format",
         "query_common",
         "query_planner",
         "query_planner_test_fixture",
diff --git a/src/mongo/db/query/map_reduce_output_format.cpp b/src/mongo/db/query/map_reduce_output_format.cpp
new file mode 100644
index 00000000000..c3c9859a423
--- /dev/null
+++ b/src/mongo/db/query/map_reduce_output_format.cpp
@@ -0,0 +1,90 @@
+/**
+ *    Copyright (C) 2019-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    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
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/db/query/map_reduce_output_format.h"
+
+namespace mongo::map_reduce_output_format {
+
+namespace {
+
+void appendMetadataFields(bool verbose, bool inMongos, BSONObjBuilder* resultBuilder) {
+    // TODO: SERVER-42644 Build stats (encapsulate in functions!).
+    if (inMongos)
+        resultBuilder->append("counts",
+                              BSON("input" << 0 << "emit" << 0 << "reduce" << 0 << "output" << 0));
+
+    resultBuilder->append("timeMillis", 0);
+
+    if (verbose) {
+        auto&& timingField = inMongos
+            ? BSON("shardProcessing" << 0 << "postProcessing" << 0)
+            : BSON("mapTime" << 0 << "emitLoop" << 0 << "reduceTime" << 0 << "total" << 0);
+        resultBuilder->append("timing", timingField);
+    }
+
+    if (inMongos) {
+        resultBuilder->append(
+            "shardCounts",
+            BSON("shard-conn-string"
+                 << BSON("input" << 0 << "emit" << 0 << "reduce" << 0 << "output" << 0)));
+        resultBuilder->append("postProcessCounts",
+                              BSON("merging-shard-conn-string"
+                                   << BSON("input" << 0 << "reduce" << 0 << "output" << 0)));
+    } else {
+        resultBuilder->append("counts",
+                              BSON("input" << 0 << "emit" << 0 << "reduce" << 0 << "output" << 0));
+    }
+
+    resultBuilder->append("ok", 1);
+}
+
+}  // namespace
+
+void appendInlineResponse(BSONArray&& documents,
+                          bool verbose,
+                          bool inMongos,
+                          BSONObjBuilder* resultBuilder) {
+    resultBuilder->appendArray("results", documents);
+    appendMetadataFields(verbose, inMongos, resultBuilder);
+}
+
+void appendOutResponse(NamespaceString outCollNss,
+                       bool verbose,
+                       bool inMongos,
+                       BSONObjBuilder* resultBuilder) {
+    if (outCollNss.db().empty())
+        resultBuilder->append("result", outCollNss.coll());
+    else
+        resultBuilder->append("result",
+                              BSON("db" << outCollNss.db() << "collection" << outCollNss.coll()));
+    appendMetadataFields(verbose, inMongos, resultBuilder);
+}
+}  // namespace mongo::map_reduce_output_format
diff --git a/src/mongo/db/query/map_reduce_output_format.h b/src/mongo/db/query/map_reduce_output_format.h
new file mode 100644
index 00000000000..eff91ae14e3
--- /dev/null
+++ b/src/mongo/db/query/map_reduce_output_format.h
@@ -0,0 +1,63 @@
+/**
+ *    Copyright (C) 2019-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    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
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include "mongo/bson/bsonobjbuilder.h"
+#include "mongo/db/namespace_string.h"
+
+/**
+ * Formats Aggregation Pipeline results as legacy mapReduce output.
+ */
+namespace mongo::map_reduce_output_format {
+
+/**
+ * Appends fields to 'resultBuilder' as if 'documents' was a response from the mapReduce command
+ * with inline output. 'verbose' causes extra fields to be appended to the response in accordance
+ * with the verbose option on the mapReduce command. 'inMongos' indicates that we are using the
+ * format that was historically sent from mongos. If it isn't set, we will use the mongod format.
+ */
+void appendInlineResponse(BSONArray&& documents,
+                          bool verbose,
+                          bool inMongos,
+                          BSONObjBuilder* resultBuilder);
+
+/**
+ * Appends fields to 'resultBuilder' to formulate a response that would be given if the mapReduce
+ * command had written output to the collection named by 'outCollNss'. 'verbose' causes extra fields
+ * to be appended to the response in accordance with the verbose option on the mapReduce command.
+ * 'inMongos' indicates that we are using the format that was historically sent from mongos. If it
+ * isn't set, we will use the mongod format.
+ */
+void appendOutResponse(NamespaceString outCollNss,
+                       bool verbose,
+                       bool inMongos,
+                       BSONObjBuilder* resultBuilder);
+
+}  // namespace mongo::map_reduce_output_format
diff --git a/src/mongo/db/query/mr_response_formatter_test.cpp b/src/mongo/db/query/map_reduce_output_format_test.cpp
index cf0bebc706a..06460770eb2 100644
--- a/src/mongo/db/query/mr_response_formatter_test.cpp
+++ b/src/mongo/db/query/map_reduce_output_format_test.cpp
@@ -33,25 +33,18 @@
 #include "mongo/bson/bsonobjbuilder.h"
 #include "mongo/db/json.h"
 #include "mongo/db/namespace_string.h"
-#include "mongo/db/query/cursor_response.h"
-#include "mongo/db/query/mr_response_formatter.h"
+#include "mongo/db/query/map_reduce_output_format.h"
 #include "mongo/unittest/unittest.h"
 
-
-// TODO: SERVER-42644 Update for processing stats from aggregation.
-
 namespace mongo {
 namespace {
 
-const NamespaceString testNss("", "mr_response_formatter");
-const NamespaceString testNssWithDb("db.mr_response_formatter");
-const CursorId testCursor(0);
-
-TEST(MapReduceResponseFormatter, FormatInlineMapReduceResponse) {
-    CursorResponse cr(testNss, testCursor, {BSON("a" << 1), BSON("b" << 1)});
-    MapReduceResponseFormatter formatter(std::move(cr), boost::none, false);
+TEST(MapReduceOutputFormat, FormatInlineMapReduceResponse) {
+    BSONArrayBuilder documents;
+    documents.append(BSON("a" << 1));
+    documents.append(BSON("b" << 1));
     BSONObjBuilder builder;
-    formatter.appendAsMapReduceResponse(&builder);
+    map_reduce_output_format::appendInlineResponse(documents.arr(), false, false, &builder);
     ASSERT_BSONOBJ_EQ(fromjson("{results: [{a: 1}, {b: 1}],"
                                "timeMillis: 0,"
                                "counts: {input: 0, emit: 0, reduce: 0, output: 0},"
@@ -59,11 +52,10 @@ TEST(MapReduceResponseFormatter, FormatInlineMapReduceResponse) {
                       builder.obj());
 }
 
-TEST(MapReduceResponseFormatter, FormatEmptyInlineMapReduceResponse) {
-    CursorResponse cr(testNss, testCursor, {});
-    MapReduceResponseFormatter formatter(std::move(cr), boost::none, false);
+TEST(MapReduceOutputFormat, FormatEmptyInlineMapReduceResponse) {
+    BSONArrayBuilder documents;
     BSONObjBuilder builder;
-    formatter.appendAsMapReduceResponse(&builder);
+    map_reduce_output_format::appendInlineResponse(documents.arr(), false, false, &builder);
     ASSERT_BSONOBJ_EQ(fromjson("{results: [],"
                                "timeMillis: 0,"
                                "counts: {input: 0, emit: 0, reduce: 0, output: 0},"
@@ -71,36 +63,30 @@ TEST(MapReduceResponseFormatter, FormatEmptyInlineMapReduceResponse) {
                       builder.obj());
 }
 
-TEST(MapReduceResponseFormatter, FormatNonInlineMapReduceResponseWithoutDb) {
-    CursorResponse cr(testNss, testCursor, {});
-    MapReduceResponseFormatter formatter(std::move(cr), testNss, false);
+TEST(MapReduceOutputFormat, FormatNonInlineMapReduceResponseWithoutDb) {
     BSONObjBuilder builder;
-    formatter.appendAsMapReduceResponse(&builder);
-    ASSERT_BSONOBJ_EQ(fromjson("{result: \"mr_response_formatter\","
+    map_reduce_output_format::appendOutResponse(NamespaceString("", "c"), false, false, &builder);
+    ASSERT_BSONOBJ_EQ(fromjson("{result: \"c\","
                                "timeMillis: 0,"
                                "counts: {input: 0, emit: 0, reduce: 0, output: 0},"
                                "ok: 1}"),
                       builder.obj());
 }
 
-TEST(MapReduceResponseFormatter, FormatNonInlineMapReduceResponseWithDb) {
-    CursorResponse cr(testNss, testCursor, {});
-    MapReduceResponseFormatter formatter(std::move(cr), testNssWithDb, false);
+TEST(MapReduceOutputFormat, FormatNonInlineMapReduceResponseWithDb) {
     BSONObjBuilder builder;
-    formatter.appendAsMapReduceResponse(&builder);
-    ASSERT_BSONOBJ_EQ(fromjson("{result: {db: \"db\", collection: \"mr_response_formatter\"},"
+    map_reduce_output_format::appendOutResponse(NamespaceString("db", "c"), false, false, &builder);
+    ASSERT_BSONOBJ_EQ(fromjson("{result: {db: \"db\", collection: \"c\"},"
                                "timeMillis: 0,"
                                "counts: {input: 0, emit: 0, reduce: 0, output: 0},"
                                "ok: 1}"),
                       builder.obj());
 }
 
-TEST(MapReduceResponseFormatter, FormatVerboseMapReduceResponse) {
-    CursorResponse cr(testNss, testCursor, {});
-    MapReduceResponseFormatter formatter(std::move(cr), testNss, true);
+TEST(MapReduceOutputFormat, FormatVerboseMapReduceResponse) {
     BSONObjBuilder builder;
-    formatter.appendAsMapReduceResponse(&builder);
-    ASSERT_BSONOBJ_EQ(fromjson("{result: \"mr_response_formatter\","
+    map_reduce_output_format::appendOutResponse(NamespaceString("", "c"), true, false, &builder);
+    ASSERT_BSONOBJ_EQ(fromjson("{result: \"c\","
                                "timeMillis: 0,"
                                "timing: {mapTime: 0, emitLoop: 0, reduceTime: 0, total: 0},"
                                "counts: {input: 0, emit: 0, reduce: 0, output: 0},"
@@ -108,11 +94,12 @@ TEST(MapReduceResponseFormatter, FormatVerboseMapReduceResponse) {
                       builder.obj());
 }
 
-TEST(MapReduceResponseFormatter, FormatInlineClusterMapReduceResponse) {
-    CursorResponse cr(testNss, testCursor, {BSON("a" << 1), BSON("b" << 1)});
-    MapReduceResponseFormatter formatter(std::move(cr), boost::none, false);
+TEST(MapReduceOutputFormat, FormatInlineClusterMapReduceResponse) {
+    BSONArrayBuilder documents;
+    documents.append(BSON("a" << 1));
+    documents.append(BSON("b" << 1));
     BSONObjBuilder builder;
-    formatter.appendAsClusterMapReduceResponse(&builder);
+    map_reduce_output_format::appendInlineResponse(documents.arr(), false, true, &builder);
     ASSERT_BSONOBJ_EQ(fromjson("{results: [{a: 1}, {b: 1}], "
                                "counts: {input: 0, emit: 0, reduce: 0, output: 0}, "
                                "timeMillis: 0, "
@@ -124,11 +111,10 @@ TEST(MapReduceResponseFormatter, FormatInlineClusterMapReduceResponse) {
                       builder.obj());
 }
 
-TEST(MapReduceResponseFormatter, FormatEmptyInlineClusterMapReduceResponseWithoutDb) {
-    CursorResponse cr(testNss, testCursor, {});
-    MapReduceResponseFormatter formatter(std::move(cr), boost::none, false);
+TEST(MapReduceOutputFormat, FormatEmptyInlineClusterMapReduceResponse) {
+    BSONArrayBuilder documents;
     BSONObjBuilder builder;
-    formatter.appendAsClusterMapReduceResponse(&builder);
+    map_reduce_output_format::appendInlineResponse(documents.arr(), false, true, &builder);
     ASSERT_BSONOBJ_EQ(fromjson("{results: [],"
                                "counts: {input: 0, emit: 0, reduce: 0, output: 0},"
                                "timeMillis: 0,"
@@ -140,12 +126,10 @@ TEST(MapReduceResponseFormatter, FormatEmptyInlineClusterMapReduceResponseWithou
                       builder.obj());
 }
 
-TEST(MapReduceResponseFormatter, FormatNonInlineClusterMapReduceResponseWithDb) {
-    CursorResponse cr(testNss, testCursor, {});
-    MapReduceResponseFormatter formatter(std::move(cr), testNssWithDb, false);
+TEST(MapReduceOutputFormat, FormatNonInlineClusterMapReduceResponseWithoutDb) {
     BSONObjBuilder builder;
-    formatter.appendAsClusterMapReduceResponse(&builder);
-    ASSERT_BSONOBJ_EQ(fromjson("{result: {db: \"db\", collection: \"mr_response_formatter\"},"
+    map_reduce_output_format::appendOutResponse(NamespaceString("", "c"), false, true, &builder);
+    ASSERT_BSONOBJ_EQ(fromjson("{result: \"c\","
                                "counts: {input: 0, emit: 0, reduce: 0, output: 0},"
                                "timeMillis: 0,"
                                "shardCounts: {"
@@ -156,12 +140,10 @@ TEST(MapReduceResponseFormatter, FormatNonInlineClusterMapReduceResponseWithDb)
                       builder.obj());
 }
 
-TEST(MapReduceResponseFormatter, FormatNonInlineClusterMapReduceResponse) {
-    CursorResponse cr(testNss, testCursor, {});
-    MapReduceResponseFormatter formatter(std::move(cr), testNss, false);
+TEST(MapReduceOutputFormat, FormatNonInlineClusterMapReduceResponseWithDb) {
     BSONObjBuilder builder;
-    formatter.appendAsClusterMapReduceResponse(&builder);
-    ASSERT_BSONOBJ_EQ(fromjson("{result: \"mr_response_formatter\","
+    map_reduce_output_format::appendOutResponse(NamespaceString("db", "c"), false, true, &builder);
+    ASSERT_BSONOBJ_EQ(fromjson("{result: {db: \"db\", collection: \"c\"},"
                                "counts: {input: 0, emit: 0, reduce: 0, output: 0},"
                                "timeMillis: 0,"
                                "shardCounts: {"
@@ -172,12 +154,10 @@ TEST(MapReduceResponseFormatter, FormatNonInlineClusterMapReduceResponse) {
                       builder.obj());
 }
 
-TEST(MapReduceResponseFormatter, FormatVerboseClusterMapReduceResponse) {
-    CursorResponse cr(testNss, testCursor, {});
-    MapReduceResponseFormatter formatter(std::move(cr), testNss, true);
+TEST(MapReduceOutputFormat, FormatVerboseClusterMapReduceResponse) {
     BSONObjBuilder builder;
-    formatter.appendAsClusterMapReduceResponse(&builder);
-    ASSERT_BSONOBJ_EQ(fromjson("{result: \"mr_response_formatter\","
+    map_reduce_output_format::appendOutResponse(NamespaceString("", "c"), true, true, &builder);
+    ASSERT_BSONOBJ_EQ(fromjson("{result: \"c\","
                                "counts: {input: 0, emit: 0, reduce: 0, output: 0},"
                                "timeMillis: 0,"
                                "timing: {shardProcessing: 0, postProcessing: 0},"
diff --git a/src/mongo/db/query/mr_response_formatter.cpp b/src/mongo/db/query/mr_response_formatter.cpp
deleted file mode 100644
index f7b5edc95f7..00000000000
--- a/src/mongo/db/query/mr_response_formatter.cpp
+++ /dev/null
@@ -1,105 +0,0 @@
-/**
- *    Copyright (C) 2019-present MongoDB, Inc.
- *
- *    This program is free software: you can redistribute it and/or modify
- *    it under the terms of the Server Side Public License, version 1,
- *    as published by MongoDB, Inc.
- *
- *    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
- *    Server Side Public License for more details.
- *
- *    You should have received a copy of the Server Side Public License
- *    along with this program. If not, see
- *    <http://www.mongodb.com/licensing/server-side-public-license>.
- *
- *    As a special exception, the copyright holders give permission to link the
- *    code of portions of this program with the OpenSSL library under certain
- *    conditions as described in each individual source file and distribute
- *    linked combinations including the program with the OpenSSL library. You
- *    must comply with the Server Side Public License in all respects for
- *    all of the code used other than as permitted herein. If you modify file(s)
- *    with this exception, you may extend this exception to your version of the
- *    file(s), but you are not obligated to do so. If you do not wish to do so,
- *    delete this exception statement from your version. If you delete this
- *    exception statement from all source files in the program, then also delete
- *    it in the license file.
- */
-
-#include "mongo/platform/basic.h"
-
-#include "mongo/db/query/mr_response_formatter.h"
-
-namespace mongo {
-
-MapReduceResponseFormatter::MapReduceResponseFormatter(CursorResponse aggregationResponse,
-                                                       boost::optional<NamespaceString> outCollNss,
-                                                       bool verbose)
-    : _response(std::move(aggregationResponse)),
-      _outCollNss(std::move(outCollNss)),
-      _verbose(verbose) {}
-
-void MapReduceResponseFormatter::appendResultsField(BSONObjBuilder* resultBuilder) {
-    if (_outCollNss) {
-        if (_outCollNss->db().empty()) {
-            resultBuilder->append(MapReduceResponseFormatter::kResultField, _outCollNss->coll());
-        } else {
-            resultBuilder->append(
-                MapReduceResponseFormatter::kResultField,
-                BSON(kDbField << _outCollNss->db() << kCollectionField << _outCollNss->coll()));
-        }
-    } else {
-        BSONArrayBuilder docsBuilder;
-        auto batch = _response.releaseBatch();
-        size_t sizeSoFar = 0;
-        for (auto& doc : batch) {
-            sizeSoFar += doc.objsize();
-            docsBuilder.append(doc);
-        }
-        uassert(ErrorCodes::BSONObjectTooLarge,
-                "too much data for in memory map/reduce",
-                sizeSoFar < BSONObjMaxUserSize);
-        resultBuilder->appendArray(MapReduceResponseFormatter::kResultsField, docsBuilder.arr());
-    }
-}
-
-void MapReduceResponseFormatter::appendAsMapReduceResponse(BSONObjBuilder* resultBuilder) {
-    appendResultsField(resultBuilder);
-    // TODO: SERVER-42644 Build stats.
-    resultBuilder->append(kTimeMillisField, 0);
-    if (_verbose) {
-        resultBuilder->append(kTimingField,
-                              BSON(kMapTimeField << 0 << kEmitLoopField << 0 << kReduceTimeField
-                                                 << 0 << kTotalField << 0));
-    }
-
-    resultBuilder->append(
-        kCountsfield,
-        BSON(kInputField << 0 << kEmitField << 0 << kReduceField << 0 << kOutputField << 0));
-    resultBuilder->append(kOkField, 1);
-}
-
-void MapReduceResponseFormatter::appendAsClusterMapReduceResponse(BSONObjBuilder* resultBuilder) {
-    appendResultsField(resultBuilder);
-    // TODO: SERVER-42644 Build stats.
-    resultBuilder->append(
-        kCountsfield,
-        BSON(kInputField << 0 << kEmitField << 0 << kReduceField << 0 << kOutputField << 0));
-    resultBuilder->append(kTimeMillisField, 0);
-
-    if (_verbose) {
-        resultBuilder->append(kTimingField,
-                              BSON(kShardProcessingField << 0 << kPostProcessing << 0));
-    }
-
-    resultBuilder->append(
-        kShardCountsfield,
-        BSON("shard-conn-string" << BSON(kInputField << 0 << kEmitField << 0 << kReduceField << 0
-                                                     << kOutputField << 0)));
-    resultBuilder->append(kPostProcessCountsField,
-                          BSON("merging-shard-conn-string" << BSON(
-                                   kInputField << 0 << kReduceField << 0 << kOutputField << 0)));
-    resultBuilder->append(kOkField, 1);
-}
-}  // namespace mongo
diff --git a/src/mongo/db/query/mr_response_formatter.h b/src/mongo/db/query/mr_response_formatter.h
deleted file mode 100644
index 46e5cc2d334..00000000000
--- a/src/mongo/db/query/mr_response_formatter.h
+++ /dev/null
@@ -1,90 +0,0 @@
-/**
- *    Copyright (C) 2019-present MongoDB, Inc.
- *
- *    This program is free software: you can redistribute it and/or modify
- *    it under the terms of the Server Side Public License, version 1,
- *    as published by MongoDB, Inc.
- *
- *    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
- *    Server Side Public License for more details.
- *
- *    You should have received a copy of the Server Side Public License
- *    along with this program. If not, see
- *    <http://www.mongodb.com/licensing/server-side-public-license>.
- *
- *    As a special exception, the copyright holders give permission to link the
- *    code of portions of this program with the OpenSSL library under certain
- *    conditions as described in each individual source file and distribute
- *    linked combinations including the program with the OpenSSL library. You
- *    must comply with the Server Side Public License in all respects for
- *    all of the code used other than as permitted herein. If you modify file(s)
- *    with this exception, you may extend this exception to your version of the
- *    file(s), but you are not obligated to do so. If you do not wish to do so,
- *    delete this exception statement from your version. If you delete this
- *    exception statement from all source files in the program, then also delete
- *    it in the license file.
- */
-
-#pragma once
-
-#include "mongo/platform/basic.h"
-
-#include "mongo/bson/bsonobj.h"
-#include "mongo/bson/bsonobjbuilder.h"
-#include "mongo/db/namespace_string.h"
-#include "mongo/db/query/cursor_response.h"
-
-namespace mongo {
-
-class MapReduceResponseFormatter {
-public:
-    static constexpr StringData kResultField = "result"_sd;
-    static constexpr StringData kResultsField = "results"_sd;
-    static constexpr StringData kDbField = "db"_sd;
-    static constexpr StringData kCollectionField = "collection"_sd;
-    static constexpr StringData kTimeMillisField = "timeMillis"_sd;
-    static constexpr StringData kTimingField = "timing"_sd;
-    static constexpr StringData kMapTimeField = "mapTime"_sd;
-    static constexpr StringData kEmitLoopField = "emitLoop"_sd;
-    static constexpr StringData kReduceTimeField = "reduceTime"_sd;
-    static constexpr StringData kTotalField = "total"_sd;
-    static constexpr StringData kShardProcessingField = "shardProcessing"_sd;
-    static constexpr StringData kPostProcessing = "postProcessing"_sd;
-    static constexpr StringData kCountsfield = "counts"_sd;
-    static constexpr StringData kShardCountsfield = "shardCounts"_sd;
-    static constexpr StringData kInputField = "input"_sd;
-    static constexpr StringData kEmitField = "emit"_sd;
-    static constexpr StringData kReduceField = "reduce"_sd;
-    static constexpr StringData kOutputField = "output"_sd;
-    static constexpr StringData kPostProcessCountsField = "postProcessCounts"_sd;
-    static constexpr StringData kOkField = "ok"_sd;
-
-    MapReduceResponseFormatter(CursorResponse aggregationResponse,
-                               boost::optional<NamespaceString> outCollNss,
-                               bool verbose);
-
-    /*
-     * Appends fields to 'resultBuilder' as if '_response' were a response from the mapReduce
-     * command.
-     */
-    void appendAsMapReduceResponse(BSONObjBuilder* resultBuilder);
-
-    /**
-     * Appends fields to 'resultBuilder' as if '_response' were a response from the cluster
-     * mapReduce command.
-     */
-    void appendAsClusterMapReduceResponse(BSONObjBuilder* resultBuilder);
-
-private:
-    CursorResponse _response;
-    boost::optional<NamespaceString> _outCollNss;
-    bool _verbose;
-
-    /**
-     * Appends the 'result(s)' field to the 'resultBuilder'.
-     */
-    void appendResultsField(BSONObjBuilder* resultBuilder);
-};
-}  // namespace mongo
diff --git a/src/mongo/s/commands/cluster_map_reduce_agg.cpp b/src/mongo/s/commands/cluster_map_reduce_agg.cpp
index 234aaef136a..af2c92807be 100644
--- a/src/mongo/s/commands/cluster_map_reduce_agg.cpp
+++ b/src/mongo/s/commands/cluster_map_reduce_agg.cpp
@@ -33,8 +33,8 @@
 #include "mongo/bson/bsonobjbuilder.h"
 #include "mongo/db/commands.h"
 #include "mongo/db/commands/map_reduce_gen.h"
+#include "mongo/db/query/cursor_response.h"
 #include "mongo/db/query/getmore_request.h"
-#include "mongo/db/query/mr_response_formatter.h"
 #include "mongo/s/commands/cluster_map_reduce_agg.h"
 
 namespace mongo {
@@ -81,14 +81,9 @@ bool runAggregationMapReduce(OperationContext* opCtx,
 
     auto cursorResponse = CursorResponse::parseFromBSONThrowing(aggResult);
     auto completeBatch = getAllAggregationResults(opCtx, dbname, cursorResponse);
-    CursorResponse completeCursor(
+    [[maybe_unused]] CursorResponse completeCursor(
         cursorResponse.getNSS(), cursorResponse.getCursorId(), std::move(completeBatch));
 
-    MapReduceResponseFormatter(
-        std::move(completeCursor),
-        boost::make_optional(!inMemory, NamespaceString(std::move(outDb), std::move(outColl))),
-        boost::get_optional_value_or(mrRequest.getVerbose(), false))
-        .appendAsClusterMapReduceResponse(&result);
     return true;
 }