/**
 *    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.
 */

#define MONGO_LOG_DEFAULT_COMPONENT ::mongo::logger::LogComponent::kCommand

#include "mongo/platform/basic.h"

#include "mongo/db/commands.h"

#include <string>
#include <vector>

#include "mongo/bson/mutable/algorithm.h"
#include "mongo/bson/mutable/document.h"
#include "mongo/bson/timestamp.h"
#include "mongo/bson/util/bson_extract.h"
#include "mongo/db/audit.h"
#include "mongo/db/auth/action_set.h"
#include "mongo/db/auth/action_type.h"
#include "mongo/db/auth/authorization_manager.h"
#include "mongo/db/auth/authorization_session.h"
#include "mongo/db/auth/privilege.h"
#include "mongo/db/client.h"
#include "mongo/db/command_generic_argument.h"
#include "mongo/db/commands/test_commands_enabled.h"
#include "mongo/db/curop.h"
#include "mongo/db/jsobj.h"
#include "mongo/db/namespace_string.h"
#include "mongo/rpc/factory.h"
#include "mongo/rpc/metadata/client_metadata_ismaster.h"
#include "mongo/rpc/op_msg_rpc_impls.h"
#include "mongo/rpc/protocol.h"
#include "mongo/rpc/write_concern_error_detail.h"
#include "mongo/s/stale_exception.h"
#include "mongo/util/fail_point_service.h"
#include "mongo/util/invariant.h"
#include "mongo/util/log.h"
#include "mongo/util/str.h"

namespace mongo {

using logger::LogComponent;

namespace {

const char kWriteConcernField[] = "writeConcern";
const WriteConcernOptions kMajorityWriteConcern(
    WriteConcernOptions::kMajority,
    // Note: Even though we're setting UNSET here, kMajority implies JOURNAL if journaling is
    // supported by the mongod.
    WriteConcernOptions::SyncMode::UNSET,
    WriteConcernOptions::kWriteConcernTimeoutUserCommand);

// Returns true if found to be authorized, false if undecided. Throws if unauthorized.
bool checkAuthorizationImplPreParse(OperationContext* opCtx,
                                    const Command* command,
                                    const OpMsgRequest& request) {
    auto client = opCtx->getClient();
    if (client->isInDirectClient())
        return true;
    uassert(ErrorCodes::Unauthorized,
            str::stream() << command->getName() << " may only be run against the admin database.",
            !command->adminOnly() || request.getDatabase() == NamespaceString::kAdminDb);

    auto authzSession = AuthorizationSession::get(client);
    if (!authzSession->getAuthorizationManager().isAuthEnabled()) {
        // Running without auth, so everything should be allowed except remotely invoked
        // commands that have the 'localHostOnlyIfNoAuth' restriction.
        uassert(ErrorCodes::Unauthorized,
                str::stream() << command->getName()
                              << " must run from localhost when running db without auth",
                !command->adminOnly() || !command->localHostOnlyIfNoAuth() ||
                    client->getIsLocalHostConnection());
        return true;  // Blanket authorization: don't need to check anything else.
    }
    if (authzSession->isUsingLocalhostBypass())
        return false;  // Still can't decide on auth because of the localhost bypass.
    uassert(ErrorCodes::Unauthorized,
            str::stream() << "command " << command->getName() << " requires authentication",
            !command->requiresAuth() || authzSession->isAuthenticated());
    return false;
}

// The command names that are allowed in a multi-document transaction.
const StringMap<int> txnCmdWhitelist = {{"abortTransaction", 1},
                                        {"aggregate", 1},
                                        {"commitTransaction", 1},
                                        {"coordinateCommitTransaction", 1},
                                        {"delete", 1},
                                        {"distinct", 1},
                                        {"find", 1},
                                        {"findandmodify", 1},
                                        {"findAndModify", 1},
                                        {"geoSearch", 1},
                                        {"getMore", 1},
                                        {"insert", 1},
                                        {"killCursors", 1},
                                        {"prepareTransaction", 1},
                                        {"update", 1}};

// The commands that can be run on the 'admin' database in multi-document transactions.
const StringMap<int> txnAdminCommands = {{"abortTransaction", 1},
                                         {"commitTransaction", 1},
                                         {"coordinateCommitTransaction", 1},
                                         {"prepareTransaction", 1}};

}  // namespace


//////////////////////////////////////////////////////////////
// CommandHelpers

BSONObj CommandHelpers::runCommandDirectly(OperationContext* opCtx, const OpMsgRequest& request) {
    auto command = globalCommandRegistry()->findCommand(request.getCommandName());
    invariant(command);
    rpc::OpMsgReplyBuilder replyBuilder;
    std::unique_ptr<CommandInvocation> invocation;
    try {
        invocation = command->parse(opCtx, request);
        invocation->run(opCtx, &replyBuilder);
        auto body = replyBuilder.getBodyBuilder();
        CommandHelpers::extractOrAppendOk(body);
    } catch (const StaleConfigException&) {
        // These exceptions are intended to be handled at a higher level.
        throw;
    } catch (const DBException& ex) {
        if (ex.code() == ErrorCodes::Unauthorized) {
            CommandHelpers::auditLogAuthEvent(opCtx, invocation.get(), request, ex.code());
        }
        auto body = replyBuilder.getBodyBuilder();
        body.resetToEmpty();
        appendCommandStatusNoThrow(body, ex.toStatus());
    }
    return replyBuilder.releaseBody();
}

void CommandHelpers::auditLogAuthEvent(OperationContext* opCtx,
                                       const CommandInvocation* invocation,
                                       const OpMsgRequest& request,
                                       ErrorCodes::Error err) {
    class Hook final : public audit::CommandInterface {
    public:
        explicit Hook(const CommandInvocation* invocation, const NamespaceString* nss)
            : _invocation(invocation), _nss(nss) {}

        void snipForLogging(mutablebson::Document* cmdObj) const override {
            if (_invocation) {
                _invocation->definition()->snipForLogging(cmdObj);
            }
        }

        StringData sensitiveFieldName() const override {
            if (_invocation) {
                return _invocation->definition()->sensitiveFieldName();
            }
            return StringData{};
        }

        StringData getName() const override {
            if (!_invocation) {
                return "Error"_sd;
            }
            return _invocation->definition()->getName();
        }

        NamespaceString ns() const override {
            return *_nss;
        }

        bool redactArgs() const override {
            return !_invocation;
        }

    private:
        const CommandInvocation* _invocation;
        const NamespaceString* _nss;
    };

    NamespaceString nss = invocation ? invocation->ns() : NamespaceString(request.getDatabase());
    audit::logCommandAuthzCheck(opCtx->getClient(), request, Hook(invocation, &nss), err);
}

void CommandHelpers::uassertNoDocumentSequences(StringData commandName,
                                                const OpMsgRequest& request) {
    uassert(40472,
            str::stream() << "The " << commandName
                          << " command does not support document sequences.",
            request.sequences.empty());
}

std::string CommandHelpers::parseNsFullyQualified(const BSONObj& cmdObj) {
    BSONElement first = cmdObj.firstElement();
    uassert(ErrorCodes::BadValue,
            str::stream() << "collection name has invalid type " << typeName(first.type()),
            first.canonicalType() == canonicalizeBSONType(mongo::String));
    const NamespaceString nss(first.valueStringData());
    uassert(ErrorCodes::InvalidNamespace,
            str::stream() << "Invalid namespace specified '" << nss.ns() << "'",
            nss.isValid());
    return nss.ns();
}

NamespaceString CommandHelpers::parseNsCollectionRequired(StringData dbname,
                                                          const BSONObj& cmdObj) {
    // Accepts both BSON String and Symbol for collection name per SERVER-16260
    // TODO(kangas) remove Symbol support in MongoDB 3.0 after Ruby driver audit
    BSONElement first = cmdObj.firstElement();
    const bool isUUID = (first.canonicalType() == canonicalizeBSONType(mongo::BinData) &&
                         first.binDataType() == BinDataType::newUUID);
    uassert(ErrorCodes::InvalidNamespace,
            str::stream() << "Collection name must be provided. UUID is not valid in this "
                          << "context",
            !isUUID);
    uassert(ErrorCodes::InvalidNamespace,
            str::stream() << "collection name has invalid type " << typeName(first.type()),
            first.canonicalType() == canonicalizeBSONType(mongo::String));
    const NamespaceString nss(dbname, first.valueStringData());
    uassert(ErrorCodes::InvalidNamespace,
            str::stream() << "Invalid namespace specified '" << nss.ns() << "'",
            nss.isValid());
    return nss;
}

NamespaceStringOrUUID CommandHelpers::parseNsOrUUID(StringData dbname, const BSONObj& cmdObj) {
    BSONElement first = cmdObj.firstElement();
    if (first.type() == BinData && first.binDataType() == BinDataType::newUUID) {
        return {dbname.toString(), uassertStatusOK(UUID::parse(first))};
    } else {
        // Ensure collection identifier is not a Command
        const NamespaceString nss(parseNsCollectionRequired(dbname, cmdObj));
        uassert(ErrorCodes::InvalidNamespace,
                str::stream() << "Invalid collection name specified '" << nss.ns(),
                !(nss.ns().find('$') != std::string::npos && nss.ns() != "local.oplog.$main"));
        return nss;
    }
}

std::string CommandHelpers::parseNsFromCommand(StringData dbname, const BSONObj& cmdObj) {
    BSONElement first = cmdObj.firstElement();
    if (first.type() != mongo::String)
        return dbname.toString();
    return str::stream() << dbname << '.' << cmdObj.firstElement().valueStringData();
}

ResourcePattern CommandHelpers::resourcePatternForNamespace(const std::string& ns) {
    if (!NamespaceString::validCollectionComponent(ns)) {
        return ResourcePattern::forDatabaseName(ns);
    }
    return ResourcePattern::forExactNamespace(NamespaceString(ns));
}

Command* CommandHelpers::findCommand(StringData name) {
    return globalCommandRegistry()->findCommand(name);
}

bool CommandHelpers::appendCommandStatusNoThrow(BSONObjBuilder& result, const Status& status) {
    appendSimpleCommandStatus(result, status.isOK(), status.reason());
    BSONObj tmp = result.asTempObj();
    if (!status.isOK() && !tmp.hasField("code")) {
        result.append("code", status.code());
        result.append("codeName", ErrorCodes::errorString(status.code()));
    }
    if (auto extraInfo = status.extraInfo()) {
        extraInfo->serialize(&result);
    }
    return status.isOK();
}

void CommandHelpers::appendSimpleCommandStatus(BSONObjBuilder& result,
                                               bool ok,
                                               const std::string& errmsg) {
    BSONObj tmp = result.asTempObj();
    bool have_ok = tmp.hasField("ok");
    bool need_errmsg = !ok && !tmp.hasField("errmsg");

    if (!have_ok)
        result.append("ok", ok ? 1.0 : 0.0);

    if (need_errmsg) {
        result.append("errmsg", errmsg);
    }
}

bool CommandHelpers::extractOrAppendOk(BSONObjBuilder& reply) {
    if (auto okField = reply.asTempObj()["ok"]) {
        // If ok is present, use its truthiness.
        return okField.trueValue();
    }
    // Missing "ok" field is an implied success.
    CommandHelpers::appendSimpleCommandStatus(reply, true);
    return true;
}

void CommandHelpers::appendCommandWCStatus(BSONObjBuilder& result,
                                           const Status& awaitReplicationStatus,
                                           const WriteConcernResult& wcResult) {
    if (!awaitReplicationStatus.isOK() && !result.hasField("writeConcernError")) {
        WriteConcernErrorDetail wcError;
        wcError.setStatus(awaitReplicationStatus);
        if (wcResult.wTimedOut) {
            wcError.setErrInfo(BSON("wtimeout" << true));
        }
        result.append("writeConcernError", wcError.toBSON());
    }
}

BSONObj CommandHelpers::appendPassthroughFields(const BSONObj& cmdObjWithPassthroughFields,
                                                const BSONObj& request) {
    BSONObjBuilder b;
    b.appendElements(request);
    for (const auto& elem : filterCommandRequestForPassthrough(cmdObjWithPassthroughFields)) {
        const auto name = elem.fieldNameStringData();
        if (isGenericArgument(name) && !request.hasField(name)) {
            b.append(elem);
        }
    }
    return b.obj();
}

BSONObj CommandHelpers::appendMajorityWriteConcern(const BSONObj& cmdObj) {
    WriteConcernOptions newWC = kMajorityWriteConcern;

    if (cmdObj.hasField(kWriteConcernField)) {
        auto wc = cmdObj.getField(kWriteConcernField);
        // The command has a writeConcern field and it's majority, so we can
        // return it as-is.
        if (wc["w"].ok() && wc["w"].str() == "majority") {
            return cmdObj;
        }

        if (wc["wtimeout"].ok()) {
            // They set a timeout, but aren't using majority WC. We want to use their
            // timeout along with majority WC.
            newWC = WriteConcernOptions(WriteConcernOptions::kMajority,
                                        WriteConcernOptions::SyncMode::UNSET,
                                        wc["wtimeout"].Number());
        }
    }

    // Append all original fields except the writeConcern field to the new command.
    BSONObjBuilder cmdObjWithWriteConcern;
    for (const auto& elem : cmdObj) {
        const auto name = elem.fieldNameStringData();
        if (name != "writeConcern" && !cmdObjWithWriteConcern.hasField(name)) {
            cmdObjWithWriteConcern.append(elem);
        }
    }

    // Finally, add the new write concern.
    cmdObjWithWriteConcern.append(kWriteConcernField, newWC.toBSON());
    return cmdObjWithWriteConcern.obj();
}

BSONObj CommandHelpers::filterCommandRequestForPassthrough(const BSONObj& cmdObj) {
    BSONObjIterator cmdIter(cmdObj);
    BSONObjBuilder bob;
    filterCommandRequestForPassthrough(&cmdIter, &bob);
    return bob.obj();
}

void CommandHelpers::filterCommandRequestForPassthrough(BSONObjIterator* cmdIter,
                                                        BSONObjBuilder* requestBuilder) {
    while (cmdIter->more()) {
        auto elem = cmdIter->next();
        const auto name = elem.fieldNameStringData();
        if (name == "$readPreference") {
            BSONObjBuilder(requestBuilder->subobjStart("$queryOptions")).append(elem);
            continue;
        }
        if (isRequestStripArgument(name))
            continue;
        requestBuilder->append(elem);
    }
}

void CommandHelpers::filterCommandReplyForPassthrough(const BSONObj& cmdObj,
                                                      BSONObjBuilder* output) {
    for (auto elem : cmdObj) {
        const auto name = elem.fieldNameStringData();
        if (isReplyStripArgument(name))
            continue;
        output->append(elem);
    }
}

BSONObj CommandHelpers::filterCommandReplyForPassthrough(const BSONObj& cmdObj) {
    BSONObjBuilder bob;
    filterCommandReplyForPassthrough(cmdObj, &bob);
    return bob.obj();
}

bool CommandHelpers::isHelpRequest(const BSONElement& helpElem) {
    return !helpElem.eoo() && helpElem.trueValue();
}

bool CommandHelpers::uassertShouldAttemptParse(OperationContext* opCtx,
                                               const Command* command,
                                               const OpMsgRequest& request) {
    try {
        return checkAuthorizationImplPreParse(opCtx, command, request);
    } catch (const ExceptionFor<ErrorCodes::Unauthorized>& e) {
        CommandHelpers::auditLogAuthEvent(opCtx, nullptr, request, e.code());
        throw;
    }
}


Status CommandHelpers::canUseTransactions(StringData dbName, StringData cmdName) {
    if (cmdName == "count"_sd) {
        return {ErrorCodes::OperationNotSupportedInTransaction,
                "Cannot run 'count' in a multi-document transaction. Please see "
                "http://dochub.mongodb.org/core/transaction-count for a recommended alternative."};
    }

    if (txnCmdWhitelist.find(cmdName) == txnCmdWhitelist.cend()) {
        return {ErrorCodes::OperationNotSupportedInTransaction,
                str::stream() << "Cannot run '" << cmdName << "' in a multi-document transaction."};
    }

    if (dbName == "config"_sd || dbName == "local"_sd ||
        (dbName == "admin"_sd && txnAdminCommands.find(cmdName) == txnAdminCommands.cend())) {
        return {ErrorCodes::OperationNotSupportedInTransaction,
                str::stream() << "Cannot run command against the '" << dbName
                              << "' database in a transaction"};
    }

    return Status::OK();
}

constexpr StringData CommandHelpers::kHelpFieldName;

MONGO_FAIL_POINT_DEFINE(failCommand);
MONGO_FAIL_POINT_DEFINE(waitInCommandMarkKillOnClientDisconnect);

bool CommandHelpers::shouldActivateFailCommandFailPoint(const BSONObj& data,
                                                        StringData cmdName,
                                                        Client* client) {
    if (cmdName == "configureFailPoint"_sd)  // Banned even if in failCommands.
        return false;

    if (data.hasField("threadName") &&
        (client->desc() !=
         data.getStringField(
             "threadName"))) {  // only activate failpoint on thread from certain client
        return false;
    }

    if (client->session() && (client->session()->getTags() & transport::Session::kInternalClient)) {
        if (!data.hasField("failInternalCommands") || !data.getBoolField("failInternalCommands")) {
            return false;
        }
    }

    for (auto&& failCommand : data.getObjectField("failCommands")) {
        if (failCommand.type() == String && failCommand.valueStringData() == cmdName) {
            return true;
        }
    }

    return false;
}

void CommandHelpers::evaluateFailCommandFailPoint(OperationContext* opCtx, StringData commandName) {
    bool closeConnection, hasErrorCode;
    long long errorCode;

    MONGO_FAIL_POINT_BLOCK_IF(failCommand, data, [&](const BSONObj& data) {
        closeConnection = data.hasField("closeConnection") &&
            bsonExtractBooleanField(data, "closeConnection", &closeConnection).isOK() &&
            closeConnection;
        hasErrorCode = data.hasField("errorCode") &&
            bsonExtractIntegerField(data, "errorCode", &errorCode).isOK();

        return shouldActivateFailCommandFailPoint(data, commandName, opCtx->getClient()) &&
            (closeConnection || hasErrorCode);
    }) {
        if (closeConnection) {
            opCtx->getClient()->session()->end();
            log() << "Failing command '" << commandName
                  << "' via 'failCommand' failpoint. Action: closing connection.";
            uasserted(50985, "Failing command due to 'failCommand' failpoint");
        }

        if (hasErrorCode) {
            log() << "Failing command '" << commandName
                  << "' via 'failCommand' failpoint. Action: returning error code " << errorCode
                  << ".";
            uasserted(ErrorCodes::Error(errorCode),
                      "Failing command due to 'failCommand' failpoint");
        }
    }
}

void CommandHelpers::handleMarkKillOnClientDisconnect(OperationContext* opCtx,
                                                      bool shouldMarkKill) {
    if (opCtx->getClient()->isInDirectClient()) {
        return;
    }

    if (shouldMarkKill) {
        opCtx->markKillOnClientDisconnect();
    }

    MONGO_FAIL_POINT_BLOCK_IF(
        waitInCommandMarkKillOnClientDisconnect, options, [&](const BSONObj& obj) {
            const auto& clientMetadata =
                ClientMetadataIsMasterState::get(opCtx->getClient()).getClientMetadata();

            return clientMetadata && (clientMetadata->getApplicationName() == obj["appName"].str());
        }) {
        MONGO_FAIL_POINT_PAUSE_WHILE_SET_OR_INTERRUPTED(opCtx,
                                                        waitInCommandMarkKillOnClientDisconnect);
    }
}

//////////////////////////////////////////////////////////////
// CommandInvocation

CommandInvocation::~CommandInvocation() = default;

void CommandInvocation::checkAuthorization(OperationContext* opCtx,
                                           const OpMsgRequest& request) const {
    // Always send an authorization event to audit log, even if OK.
    // Not using a scope guard because auditLogAuthEvent could conceivably throw.
    try {
        const Command* c = definition();
        if (checkAuthorizationImplPreParse(opCtx, c, request)) {
            // Blanket authorization: don't need to check anything else.
        } else {
            try {
                doCheckAuthorization(opCtx);
            } catch (const ExceptionFor<ErrorCodes::Unauthorized>&) {
                namespace mmb = mutablebson;
                mmb::Document cmdToLog(request.body, mmb::Document::kInPlaceDisabled);
                c->snipForLogging(&cmdToLog);
                auto dbname = request.getDatabase();
                uasserted(ErrorCodes::Unauthorized,
                          str::stream() << "not authorized on " << dbname << " to execute command "
                                        << redact(cmdToLog.getObject()));
            }
        }
    } catch (const DBException& e) {
        log(LogComponent::kAccessControl) << e.toStatus();
        CommandHelpers::auditLogAuthEvent(opCtx, this, request, e.code());
        throw;
    }
    CommandHelpers::auditLogAuthEvent(opCtx, this, request, ErrorCodes::OK);
}

//////////////////////////////////////////////////////////////
// Command

class BasicCommand::Invocation final : public CommandInvocation {
public:
    Invocation(OperationContext*, const OpMsgRequest& request, BasicCommand* command)
        : CommandInvocation(command),
          _command(command),
          _request(&request),
          _dbName(_request->getDatabase().toString()) {}

private:
    void run(OperationContext* opCtx, rpc::ReplyBuilderInterface* result) override {
        BSONObjBuilder bob = result->getBodyBuilder();
        bool ok = _command->run(opCtx, _dbName, _request->body, bob);
        if (!ok)
            CommandHelpers::appendSimpleCommandStatus(bob, ok);
    }

    void explain(OperationContext* opCtx,
                 ExplainOptions::Verbosity verbosity,
                 rpc::ReplyBuilderInterface* result) override {
        uassertStatusOK(_command->explain(opCtx, *_request, verbosity, result));
    }

    NamespaceString ns() const override {
        return NamespaceString(_command->parseNs(_dbName, cmdObj()));
    }

    bool supportsWriteConcern() const override {
        return _command->supportsWriteConcern(cmdObj());
    }

    bool supportsReadConcern(repl::ReadConcernLevel level) const override {
        return _command->supportsReadConcern(_dbName, cmdObj(), level);
    }

    bool allowsAfterClusterTime() const override {
        return _command->allowsAfterClusterTime(cmdObj());
    }

    bool canIgnorePrepareConflicts() const override {
        return _command->canIgnorePrepareConflicts();
    }

    void doCheckAuthorization(OperationContext* opCtx) const override {
        uassertStatusOK(_command->checkAuthForOperation(
            opCtx, _request->getDatabase().toString(), _request->body));
    }

    const BSONObj& cmdObj() const {
        return _request->body;
    }

    BasicCommand* const _command;
    const OpMsgRequest* const _request;
    const std::string _dbName;
};

Command::~Command() = default;

void Command::snipForLogging(mutablebson::Document* cmdObj) const {
    StringData sensitiveField = sensitiveFieldName();
    if (!sensitiveField.empty()) {

        for (mutablebson::Element pwdElement =
                 mutablebson::findFirstChildNamed(cmdObj->root(), sensitiveField);
             pwdElement.ok();
             pwdElement =
                 mutablebson::findElementNamed(pwdElement.rightSibling(), sensitiveField)) {
            uassertStatusOK(pwdElement.setValueString("xxx"));
        }
    }
}


std::unique_ptr<CommandInvocation> BasicCommand::parse(OperationContext* opCtx,
                                                       const OpMsgRequest& request) {
    CommandHelpers::uassertNoDocumentSequences(getName(), request);
    return std::make_unique<Invocation>(opCtx, request, this);
}

Command::Command(StringData name, StringData oldName)
    : _name(name.toString()),
      _commandsExecutedMetric("commands." + _name + ".total", &_commandsExecuted),
      _commandsFailedMetric("commands." + _name + ".failed", &_commandsFailed) {
    globalCommandRegistry()->registerCommand(this, name, oldName);
}

Status BasicCommand::explain(OperationContext* opCtx,
                             const OpMsgRequest& request,
                             ExplainOptions::Verbosity verbosity,
                             rpc::ReplyBuilderInterface* result) const {
    return {ErrorCodes::IllegalOperation, str::stream() << "Cannot explain cmd: " << getName()};
}

Status BasicCommand::checkAuthForOperation(OperationContext* opCtx,
                                           const std::string& dbname,
                                           const BSONObj& cmdObj) const {
    return checkAuthForCommand(opCtx->getClient(), dbname, cmdObj);
}

Status BasicCommand::checkAuthForCommand(Client* client,
                                         const std::string& dbname,
                                         const BSONObj& cmdObj) const {
    std::vector<Privilege> privileges;
    this->addRequiredPrivileges(dbname, cmdObj, &privileges);
    if (AuthorizationSession::get(client)->isAuthorizedForPrivileges(privileges))
        return Status::OK();
    return Status(ErrorCodes::Unauthorized, "unauthorized");
}

void Command::generateHelpResponse(OperationContext* opCtx,
                                   rpc::ReplyBuilderInterface* replyBuilder,
                                   const Command& command) {
    BSONObjBuilder helpBuilder;
    helpBuilder.append("help",
                       str::stream() << "help for: " << command.getName() << " " << command.help());
    replyBuilder->setCommandReply(helpBuilder.obj());
}

bool ErrmsgCommandDeprecated::run(OperationContext* opCtx,
                                  const std::string& db,
                                  const BSONObj& cmdObj,
                                  BSONObjBuilder& result) {
    std::string errmsg;
    auto ok = errmsgRun(opCtx, db, cmdObj, errmsg, result);
    if (!errmsg.empty()) {
        CommandHelpers::appendSimpleCommandStatus(result, ok, errmsg);
    }
    return ok;
}

//////////////////////////////////////////////////////////////
// CommandRegistry

void CommandRegistry::registerCommand(Command* command, StringData name, StringData oldName) {
    for (StringData key : {name, oldName}) {
        if (key.empty()) {
            continue;
        }

        auto result = _commands.try_emplace(key, command);
        invariant(result.second, str::stream() << "command name collision: " << key);
    }
}

Command* CommandRegistry::findCommand(StringData name) const {
    auto it = _commands.find(name);
    if (it == _commands.end())
        return nullptr;
    return it->second;
}

CommandRegistry* globalCommandRegistry() {
    static auto reg = new CommandRegistry();
    return reg;
}

}  // namespace mongo