Revert "SERVER-58566 Clean up remaining OP_QUERY code" due to a wrong author info

This reverts commit 3b293a78b0e24c5497464c3979daddfa0792bb55.

2 files changed, 97 insertions, 27 deletions

diff --git a/src/mongo/shell/explain_query.js b/src/mongo/shell/explain_query.js
index 453751d88de..b4935fd07d4 100644
--- a/src/mongo/shell/explain_query.js
+++ b/src/mongo/shell/explain_query.js
@@ -9,6 +9,37 @@ var DBExplainQuery = (function() {
     //
 
     /**
+     * In 2.6 and before, .explain(), .explain(false), or .explain(<falsy value>) instructed the
+     * shell to reduce the explain verbosity by removing certain fields from the output. This
+     * is implemented here for backwards compatibility.
+     */
+    function removeVerboseFields(obj) {
+        if (typeof (obj) !== "object") {
+            return;
+        }
+
+        delete obj.allPlans;
+        delete obj.oldPlan;
+        delete obj.stats;
+
+        if (typeof (obj.length) === "number") {
+            for (var i = 0; i < obj.length; i++) {
+                removeVerboseFields(obj[i]);
+            }
+        }
+
+        if (obj.shards) {
+            for (var key in obj.shards) {
+                removeVerboseFields(obj.shards[key]);
+            }
+        }
+
+        if (obj.clauses) {
+            removeVerboseFields(obj.clauses);
+        }
+    }
+
+    /**
      * Many of the methods of an explain query just pass through to the underlying
      * non-explained DBQuery. Use this to generate a function which calls function 'name' on
      * 'destObj' and then returns this.
@@ -20,6 +51,28 @@ var DBExplainQuery = (function() {
         };
     }
 
+    /**
+     * Where possible, the explain query will be sent to the server as an explain command.
+     * However, if one of the nodes we are talking to (either a standalone or a shard in
+     * a sharded cluster) is of a version that doesn't have the explain command, we will
+     * use this function to fall back on the $explain query option.
+     */
+    function explainWithLegacyQueryOption(explainQuery) {
+        // The wire protocol version indicates that the server does not have the explain
+        // command. Add $explain to the query and send it to the server.
+        var clone = explainQuery._query.clone();
+        clone._addSpecial("$explain", true);
+        var result = clone.next();
+
+        // Remove some fields from the explain if verbosity is
+        // just "queryPlanner".
+        if ("queryPlanner" === explainQuery._verbosity) {
+            removeVerboseFields(result);
+        }
+
+        return Explainable.throwOrReturn(result);
+    }
+
     function constructor(query, verbosity) {
         //
         // Private vars.
@@ -83,35 +136,47 @@ var DBExplainQuery = (function() {
             // Explain always gets pretty printed.
             this._query._prettyShell = true;
 
-            // Convert this explain query into an explain command, and send the command to
-            // the server.
-            var innerCmd;
-            if (this._isCount) {
-                // True means to always apply the skip and limit values.
-                innerCmd = this._query._convertToCountCmd(this._applySkipLimit);
+            if (this._mongo.hasExplainCommand()) {
+                // The wire protocol version indicates that the server has the explain command.
+                // Convert this explain query into an explain command, and send the command to
+                // the server.
+                var innerCmd;
+                if (this._isCount) {
+                    // True means to always apply the skip and limit values.
+                    innerCmd = this._query._convertToCountCmd(this._applySkipLimit);
+                } else {
+                    var canAttachReadPref = false;
+                    innerCmd = this._query._convertToCommand(canAttachReadPref);
+                }
+
+                var explainCmd = {explain: innerCmd};
+                explainCmd["verbosity"] = this._verbosity;
+                // If "maxTimeMS" is set on innerCmd, it needs to be propagated to the top-level
+                // of explainCmd so that it has the intended effect.
+                if (innerCmd.hasOwnProperty("maxTimeMS")) {
+                    explainCmd.maxTimeMS = innerCmd.maxTimeMS;
+                }
+
+                var explainDb = this._query._db;
+
+                if ("$readPreference" in this._query._query) {
+                    var prefObj = this._query._query.$readPreference;
+                    explainCmd = explainDb._attachReadPreferenceToCommand(explainCmd, prefObj);
+                }
+
+                var explainResult =
+                    explainDb.runReadCommand(explainCmd, null, this._query._options);
+
+                if (!explainResult.ok && explainResult.code === ErrorCodes.CommandNotFound) {
+                    // One of the shards doesn't have the explain command available. Retry using
+                    // the legacy $explain format, which should be supported by all shards.
+                    return explainWithLegacyQueryOption(this);
+                }
+
+                return Explainable.throwOrReturn(explainResult);
             } else {
-                var canAttachReadPref = false;
-                innerCmd = this._query._convertToCommand(canAttachReadPref);
+                return explainWithLegacyQueryOption(this);
             }
-
-            var explainCmd = {explain: innerCmd};
-            explainCmd["verbosity"] = this._verbosity;
-            // If "maxTimeMS" is set on innerCmd, it needs to be propagated to the top-level
-            // of explainCmd so that it has the intended effect.
-            if (innerCmd.hasOwnProperty("maxTimeMS")) {
-                explainCmd.maxTimeMS = innerCmd.maxTimeMS;
-            }
-
-            var explainDb = this._query._db;
-
-            if ("$readPreference" in this._query._query) {
-                var prefObj = this._query._query.$readPreference;
-                explainCmd = explainDb._attachReadPreferenceToCommand(explainCmd, prefObj);
-            }
-
-            var explainResult = explainDb.runReadCommand(explainCmd, null, this._query._options);
-
-            return Explainable.throwOrReturn(explainResult);
         };
 
         this.next = function() {
diff --git a/src/mongo/shell/mongo.js b/src/mongo/shell/mongo.js
index 7146fd8670a..cf05337eead 100644
--- a/src/mongo/shell/mongo.js
+++ b/src/mongo/shell/mongo.js
@@ -418,6 +418,11 @@ connect = function(url, user, pass, apiParameters) {
     return db;
 };
 
+Mongo.prototype.hasExplainCommand = function() {
+    var hasExplain = (this.getMinWireVersion() <= 3 && 3 <= this.getMaxWireVersion());
+    return hasExplain;
+};
+
 //
 // Write Concern can be set at the connection level, and is used for all write operations unless
 // overridden at the collection level.