CDRIVER-4309: always use count command for estimatedDocumentCount (#984)

* always use count command for estimatedDocumentCount

* Update spec tests for estimatedDocumentCount

Synced with mongodb/specifications@021cbc8

Includes some test changes for CDRIVER-4063 and CDRIVER-4330

* Ignore "ns not found" error for dropCollection operations

This requires setting MONGOC_ERROR_API_VERSION_2 on clients under test. It was previously only set on the internal client.

* Skip comment option tests pending CDRIVER-4199

Author: jmikola

src/libmongoc/src/mongoc/mongoc-collection.c

@@ -790,57 +790,6 @@ mongoc_collection_count_with_opts (
    RETURN (ret);
 }
 
-/* --------------------------------------------------------------------------
- *
- * _make_aggregate_for_edc --
- *
- *       Construct an aggregate pipeline with the following form:
- *
- *
- *       { pipeline: [
- *           { $collStats: { count: {} } },
- *           { $group: { _id: 1, n: { $sum: $count } } },
- *         ]
- *       }
- *
- *--------------------------------------------------------------------------
- */
-static void
-_make_aggregate_for_edc (const mongoc_collection_t *coll, bson_t *out)
-{
-   bson_t pipeline;
-   bson_t coll_stats_stage;
-   bson_t coll_stats_stage_doc;
-   bson_t group_stage;
-   bson_t group_stage_doc;
-   bson_t sum;
-   bson_t cursor_empty;
-   bson_t empty;
-
-   BSON_APPEND_UTF8 (out, "aggregate", coll->collection);
-   BSON_APPEND_DOCUMENT_BEGIN (out, "cursor", &cursor_empty);
-   bson_append_document_end (out, &cursor_empty);
-   BSON_APPEND_ARRAY_BEGIN (out, "pipeline", &pipeline);
-
-   BSON_APPEND_DOCUMENT_BEGIN (&pipeline, "0", &coll_stats_stage);
-   BSON_APPEND_DOCUMENT_BEGIN (
-      &coll_stats_stage, "$collStats", &coll_stats_stage_doc);
-   BSON_APPEND_DOCUMENT_BEGIN (&coll_stats_stage_doc, "count", &empty);
-   bson_append_document_end (&coll_stats_stage_doc, &empty);
-   bson_append_document_end (&coll_stats_stage, &coll_stats_stage_doc);
-   bson_append_document_end (&pipeline, &coll_stats_stage);
-
-   BSON_APPEND_DOCUMENT_BEGIN (&pipeline, "1", &group_stage);
-   BSON_APPEND_DOCUMENT_BEGIN (&group_stage, "$group", &group_stage_doc);
-   BSON_APPEND_INT32 (&group_stage_doc, "_id", 1);
-   BSON_APPEND_DOCUMENT_BEGIN (&group_stage_doc, "n", &sum);
-   BSON_APPEND_UTF8 (&sum, "$sum", "$count");
-   bson_append_document_end (&group_stage_doc, &sum);
-   bson_append_document_end (&group_stage, &group_stage_doc);
-   bson_append_document_end (&pipeline, &group_stage);
-   bson_append_array_end (out, &pipeline);
-}
-
 int64_t
 mongoc_collection_estimated_document_count (
    mongoc_collection_t *coll,
@@ -878,48 +827,23 @@ mongoc_collection_estimated_document_count (
    }
 
    reply_ptr = reply ? reply : &reply_local;
-   if (server_stream->sd->max_wire_version < WIRE_VERSION_4_9) {
-      /* On < 4.9, use actual count command for estimatedDocumentCount */
-      BSON_APPEND_UTF8 (&cmd, "count", coll->collection);
-      ret = _mongoc_client_command_with_opts (coll->client,
-                                              coll->db,
-                                              &cmd,
-                                              MONGOC_CMD_READ,
-                                              opts,
-                                              MONGOC_QUERY_NONE,
-                                              read_prefs,
-                                              coll->read_prefs,
-                                              coll->read_concern,
-                                              coll->write_concern,
-                                              reply_ptr,
-                                              error);
-      if (ret) {
-         if (bson_iter_init_find (&iter, reply_ptr, "n")) {
-            count = bson_iter_as_int64 (&iter);
-         }
-      }
-   } else {
-      /* On >= 4.9, use aggregate with collStats for estimatedDocumentCount */
-      _make_aggregate_for_edc (coll, &cmd);
-      ret = mongoc_collection_read_command_with_opts (
-         coll, &cmd, read_prefs, opts, reply_ptr, error);
-
-      if (!ret && error->code == MONGOC_ERROR_COLLECTION_DOES_NOT_EXIST) {
-         /* Collection does not exist. From spec: return 0 but no err:
-          * https://github.com/mongodb/specifications/blob/master/source/crud/crud.rst#estimateddocumentcount
-          */
-         if (reply) {
-            bson_reinit (reply);
-         }
-         memset (error, 0, sizeof *error);
-         count = 0;
-         GOTO (done);
-      }
-      if (ret && bson_iter_init (&iter, reply_ptr)) {
-         if (bson_iter_find_descendant (
-                &iter, "cursor.firstBatch.0.n", &iter)) {
-            count = bson_iter_as_int64 (&iter);
-         }
+
+   BSON_APPEND_UTF8 (&cmd, "count", coll->collection);
+   ret = _mongoc_client_command_with_opts (coll->client,
+                                           coll->db,
+                                           &cmd,
+                                           MONGOC_CMD_READ,
+                                           opts,
+                                           MONGOC_QUERY_NONE,
+                                           read_prefs,
+                                           coll->read_prefs,
+                                           coll->read_concern,
+                                           coll->write_concern,
+                                           reply_ptr,
+                                           error);
+   if (ret) {
+      if (bson_iter_init_find (&iter, reply_ptr, "n")) {
+         count = bson_iter_as_int64 (&iter);
       }
    }
 

src/libmongoc/tests/json/crud/unified/aggregate-out-readConcern.json

@@ -1,13 +1,14 @@
 {
   "description": "aggregate-out-readConcern",
-  "schemaVersion": "1.0",
+  "schemaVersion": "1.4",
   "runOnRequirements": [
     {
       "minServerVersion": "4.1.0",
       "topologies": [
         "replicaset",
         "sharded"
-      ]
+      ],
+      "serverless": "forbid"
     }
   ],
   "createEntities": [