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/**
* Copyright (C) 2014 MongoDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* 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
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* 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 GNU Affero General 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/commands.h"
#include "mongo/db/query/explain.h"
#include "mongo/db/repl/replication_coordinator_global.h"
#include "mongo/rpc/metadata/server_selection_metadata.h"
#include "mongo/util/mongoutils/str.h"
namespace mongo {
using std::string;
namespace {
/**
* The explain command is used to generate explain output for any read or write operation which has
* a query component (e.g. find, count, update, remove, distinct, etc.).
*
* The explain command takes as its argument a nested object which specifies the command to
* explain, and a verbosity indicator. For example:
*
* {explain: {count: "coll", query: {foo: "bar"}}, verbosity: "executionStats"}
*
* This command like a dispatcher: it just retrieves a pointer to the nested command and invokes
* its explain() implementation.
*/
class CmdExplain : public Command {
public:
CmdExplain() : Command("explain") {}
/**
* Running an explain on a secondary requires explicitly setting slaveOk.
*/
virtual bool slaveOk() const {
return false;
}
virtual bool slaveOverrideOk() const {
return true;
}
virtual bool maintenanceOk() const {
return false;
}
virtual bool adminOnly() const {
return false;
}
virtual void help(std::stringstream& help) const {
help << "explain database reads and writes";
}
/**
* You are authorized to run an explain if you are authorized to run
* the command that you are explaining. The auth check is performed recursively
* on the nested command.
*/
virtual Status checkAuthForCommand(ClientBasic* client,
const std::string& dbname,
const BSONObj& cmdObj) {
if (Object != cmdObj.firstElement().type()) {
return Status(ErrorCodes::BadValue, "explain command requires a nested object");
}
BSONObj explainObj = cmdObj.firstElement().Obj();
Command* commToExplain = Command::findCommand(explainObj.firstElementFieldName());
if (NULL == commToExplain) {
mongoutils::str::stream ss;
ss << "unknown command: " << explainObj.firstElementFieldName();
return Status(ErrorCodes::CommandNotFound, ss);
}
return commToExplain->checkAuthForCommand(client, dbname, explainObj);
}
virtual bool run(OperationContext* txn,
const std::string& dbname,
BSONObj& cmdObj,
int options,
std::string& errmsg,
BSONObjBuilder& result) {
ExplainCommon::Verbosity verbosity;
Status parseStatus = ExplainCommon::parseCmdBSON(cmdObj, &verbosity);
if (!parseStatus.isOK()) {
return appendCommandStatus(result, parseStatus);
}
// This is the nested command which we are explaining.
BSONObj explainObj = cmdObj.firstElement().Obj();
Command* commToExplain = Command::findCommand(explainObj.firstElementFieldName());
if (NULL == commToExplain) {
mongoutils::str::stream ss;
ss << "Explain failed due to unknown command: " << explainObj.firstElementFieldName();
Status explainStatus(ErrorCodes::CommandNotFound, ss);
return appendCommandStatus(result, explainStatus);
}
// Check whether the child command is allowed to run here. TODO: this logic is
// copied from Command::execCommand and should be abstracted. Until then, make
// sure to keep it up to date.
repl::ReplicationCoordinator* replCoord = repl::getGlobalReplicationCoordinator();
bool iAmPrimary = replCoord->canAcceptWritesForDatabase(dbname);
bool commandCanRunOnSecondary = commToExplain->slaveOk();
bool commandIsOverriddenToRunOnSecondary = commToExplain->slaveOverrideOk() &&
rpc::ServerSelectionMetadata::get(txn).canRunOnSecondary();
bool iAmStandalone = !txn->writesAreReplicated();
const bool canRunHere = iAmPrimary || commandCanRunOnSecondary ||
commandIsOverriddenToRunOnSecondary || iAmStandalone;
if (!canRunHere) {
mongoutils::str::stream ss;
ss << "Explain's child command cannot run on this node. "
<< "Are you explaining a write command on a secondary?";
appendCommandStatus(result, false, ss);
return false;
}
// Actually call the nested command's explain(...) method.
Status explainStatus = commToExplain->explain(
txn, dbname, explainObj, verbosity, rpc::ServerSelectionMetadata::get(txn), &result);
if (!explainStatus.isOK()) {
return appendCommandStatus(result, explainStatus);
}
return true;
}
} cmdExplain;
} // namespace
} // namespace mongo
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