fix: reintroduce support for 2.6 listIndexes

Author: mbroadst

lib/operations/list_indexes.js

@@ -6,6 +6,7 @@ const defineAspects = require('./operation').defineAspects;
 const maxWireVersion = require('../core/utils').maxWireVersion;
 
 const LIST_INDEXES_WIRE_VERSION = 3;
+const SUPPORTS_FIND_COMMAND = 4;
 
 class ListIndexesOperation extends CommandOperationV2 {
   constructor(collection, options) {
@@ -16,7 +17,8 @@ class ListIndexesOperation extends CommandOperationV2 {
   }
 
   execute(server, callback) {
-    if (maxWireVersion(server) >= LIST_INDEXES_WIRE_VERSION) {
+    const serverWireVersion = maxWireVersion(server);
+    if (serverWireVersion >= LIST_INDEXES_WIRE_VERSION) {
       const cursor = this.options.batchSize ? { batchSize: this.options.batchSize } : {};
       super.executeCommand(
         server,
@@ -29,7 +31,18 @@ class ListIndexesOperation extends CommandOperationV2 {
 
     const systemIndexesNS = this.collectionNamespace.withCollection('system.indexes').toString();
     const collectionNS = this.collectionNamespace.toString();
-    super.executeCommand(server, { find: systemIndexesNS, query: { ns: collectionNS } }, callback);
+
+    if (serverWireVersion >= SUPPORTS_FIND_COMMAND) {
+      super.executeCommand(
+        server,
+        { find: systemIndexesNS, query: { ns: collectionNS } },
+        callback
+      );
+      return;
+    }
+
+    // fall back to running a query
+    server.query(systemIndexesNS, { query: { ns: collectionNS } }, {}, this.options, callback);
   }
 }