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/**
* Copyright (C) 2018-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/command_can_run_here.h"
#include "mongo/db/commands.h"
#include "mongo/db/query/explain.h"
#include "mongo/util/str.h"
namespace mongo {
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 final : public Command {
public:
CmdExplain() : Command("explain") {}
std::unique_ptr<CommandInvocation> parse(OperationContext* opCtx,
const OpMsgRequest& request) override;
/**
* Running an explain on a secondary requires explicitly setting slaveOk.
*/
AllowedOnSecondary secondaryAllowed(ServiceContext*) const override {
return AllowedOnSecondary::kOptIn;
}
bool maintenanceOk() const override {
return false;
}
bool adminOnly() const override {
return false;
}
std::string help() const override {
return "explain database reads and writes";
}
private:
class Invocation;
};
class CmdExplain::Invocation final : public CommandInvocation {
public:
Invocation(const CmdExplain* explainCommand,
const OpMsgRequest& request,
ExplainOptions::Verbosity verbosity,
std::unique_ptr<OpMsgRequest> innerRequest,
std::unique_ptr<CommandInvocation> innerInvocation)
: CommandInvocation(explainCommand),
_outerRequest{&request},
_dbName{_outerRequest->getDatabase().toString()},
_verbosity{std::move(verbosity)},
_innerRequest{std::move(innerRequest)},
_innerInvocation{std::move(innerInvocation)} {}
void run(OperationContext* opCtx, rpc::ReplyBuilderInterface* result) override {
// Explain is never allowed in multi-document transactions.
const bool inMultiDocumentTransaction = false;
uassert(50746,
"Explain's child command cannot run on this node. "
"Are you explaining a write command on a secondary?",
commandCanRunHere(
opCtx, _dbName, _innerInvocation->definition(), inMultiDocumentTransaction));
_innerInvocation->explain(opCtx, _verbosity, result);
}
void explain(OperationContext* opCtx,
ExplainOptions::Verbosity verbosity,
rpc::ReplyBuilderInterface* result) override {
uasserted(ErrorCodes::IllegalOperation, "Explain cannot explain itself.");
}
NamespaceString ns() const override {
return _innerInvocation->ns();
}
bool supportsWriteConcern() const override {
return false;
}
/**
* 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.
*/
void doCheckAuthorization(OperationContext* opCtx) const override {
_innerInvocation->checkAuthorization(opCtx, *_innerRequest);
}
private:
const CmdExplain* command() const {
return static_cast<const CmdExplain*>(definition());
}
const OpMsgRequest* _outerRequest;
const std::string _dbName;
const NamespaceString _ns;
ExplainOptions::Verbosity _verbosity;
std::unique_ptr<OpMsgRequest> _innerRequest; // Lifespan must enclose that of _innerInvocation.
std::unique_ptr<CommandInvocation> _innerInvocation;
};
std::unique_ptr<CommandInvocation> CmdExplain::parse(OperationContext* opCtx,
const OpMsgRequest& request) {
CommandHelpers::uassertNoDocumentSequences(getName(), request);
std::string dbname = request.getDatabase().toString();
const BSONObj& cmdObj = request.body;
ExplainOptions::Verbosity verbosity = uassertStatusOK(ExplainOptions::parseCmdBSON(cmdObj));
uassert(ErrorCodes::BadValue,
"explain command requires a nested object",
cmdObj.firstElement().type() == Object);
auto explainedObj = cmdObj.firstElement().Obj();
if (auto innerDb = explainedObj["$db"]) {
uassert(ErrorCodes::InvalidNamespace,
str::stream() << "Mismatched $db in explain command. Expected " << dbname
<< " but got " << innerDb.checkAndGetStringData(),
innerDb.checkAndGetStringData() == dbname);
}
auto explainedCommand = CommandHelpers::findCommand(explainedObj.firstElementFieldName());
uassert(ErrorCodes::CommandNotFound,
str::stream() << "Explain failed due to unknown command: "
<< explainedObj.firstElementFieldName(),
explainedCommand);
auto innerRequest =
std::make_unique<OpMsgRequest>(OpMsgRequest::fromDBAndBody(dbname, explainedObj));
auto innerInvocation = explainedCommand->parse(opCtx, *innerRequest);
return std::make_unique<Invocation>(
this, request, std::move(verbosity), std::move(innerRequest), std::move(innerInvocation));
}
CmdExplain cmdExplain;
} // namespace
} // namespace mongo
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