path: root/src/mongo/db/pipeline/variables.cpp

/**
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 *    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.
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 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    Server Side Public License for more details.
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 *    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>.
 *
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 *    code of portions of this program with the OpenSSL library under certain
 *    conditions as described in each individual source file and distribute
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 *    all of the code used other than as permitted herein. If you modify file(s)
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#include "mongo/db/pipeline/variables.h"
#include "mongo/bson/bsonobj.h"
#include "mongo/db/client.h"
#include "mongo/db/pipeline/expression.h"
#include "mongo/db/pipeline/variable_validation.h"
#include "mongo/db/vector_clock.h"
#include "mongo/platform/basic.h"
#include "mongo/platform/random.h"
#include "mongo/util/str.h"
#include "mongo/util/time_support.h"

namespace mongo {

using namespace std::string_literals;

constexpr Variables::Id Variables::kRootId;
constexpr Variables::Id Variables::kRemoveId;

const StringMap<Variables::Id> Variables::kBuiltinVarNameToId = {{"ROOT", kRootId},
                                                                 {"REMOVE", kRemoveId},
                                                                 {"NOW", kNowId},
                                                                 {"CLUSTER_TIME", kClusterTimeId},
                                                                 {"JS_SCOPE", kJsScopeId},
                                                                 {"IS_MR", kIsMapReduceId}};

const std::map<Variables::Id, std::string> Variables::kIdToBuiltinVarName = {
    {kRootId, "ROOT"},
    {kRemoveId, "REMOVE"},
    {kNowId, "NOW"},
    {kClusterTimeId, "CLUSTER_TIME"},
    {kJsScopeId, "JS_SCOPE"},
    {kIsMapReduceId, "IS_MR"}};

const std::map<StringData, std::function<void(const Value&)>> Variables::kSystemVarValidators = {
    {"NOW"_sd,
     [](const auto& value) {
         uassert(ErrorCodes::TypeMismatch,
                 str::stream() << "$$NOW must have a date value, found "
                               << typeName(value.getType()),
                 value.getType() == BSONType::Date);
     }},
    {"CLUSTER_TIME"_sd,
     [](const auto& value) {
         uassert(ErrorCodes::TypeMismatch,
                 str::stream() << "$$CLUSTER_TIME must have a timestamp value, found "
                               << typeName(value.getType()),
                 value.getType() == BSONType::bsonTimestamp);
     }},
    {"JS_SCOPE"_sd,
     [](const auto& value) {
         uassert(ErrorCodes::TypeMismatch,
                 str::stream() << "$$JS_SCOPE must have an object value, found "
                               << typeName(value.getType()),
                 value.getType() == BSONType::Object);
     }},
    {"IS_MR"_sd, [](const auto& value) {
         uassert(ErrorCodes::TypeMismatch,
                 str::stream() << "$$IS_MR must have a bool value, found "
                               << typeName(value.getType()),
                 value.getType() == BSONType::Bool);
     }}};

void Variables::setValue(Id id, const Value& value, bool isConstant) {
    uassert(17199, "can't use Variables::setValue to set a reserved builtin variable", id >= 0);

    // If a value has already been set for 'id', and that value was marked as constant, then it
    // is illegal to modify.
    invariant(!hasConstantValue(id));
    _letParametersMap[id] = {value, isConstant};
}

void Variables::setValue(Variables::Id id, const Value& value) {
    const bool isConstant = false;
    setValue(id, value, isConstant);
}

void Variables::setConstantValue(Variables::Id id, const Value& value) {
    const bool isConstant = true;
    setValue(id, value, isConstant);
}

Value Variables::getUserDefinedValue(Variables::Id id) const {
    invariant(isUserDefinedVariable(id));

    auto it = _letParametersMap.find(id);
    uassert(40434, str::stream() << "Undefined variable id: " << id, it != _letParametersMap.end());
    return it->second.value;
}

Value Variables::getValue(Id id, const Document& root) const {
    if (id < 0) {
        // This is a reserved id for a builtin variable.
        switch (id) {
            case Variables::kRootId:
                return Value(root);
            case Variables::kRemoveId:
                return Value();
            case Variables::kNowId:
            case Variables::kClusterTimeId:
                if (auto it = _runtimeConstantsMap.find(id); it != _runtimeConstantsMap.end()) {
                    return it->second;
                }
                uasserted(51144,
                          str::stream() << "Builtin variable '$$" << getBuiltinVariableName(id)
                                        << "' is not available");
                MONGO_UNREACHABLE;
            case Variables::kJsScopeId:
                uasserted(4631100, "Use of undefined variable '$$JS_SCOPE'.");
            case Variables::kIsMapReduceId:
                uasserted(4631101, "Use of undefined variable '$$IS_MR'.");
            default:
                MONGO_UNREACHABLE;
        }
    }

    return getUserDefinedValue(id);
}

Document Variables::getDocument(Id id, const Document& root) const {
    if (id == Variables::kRootId) {
        // For the common case of ROOT, avoid round-tripping through Value.
        return root;
    }

    const Value var = getValue(id, root);
    if (var.getType() == Object)
        return var.getDocument();

    return Document();
}

const RuntimeConstants& Variables::getRuntimeConstants() const {
    invariant(_runtimeConstants);
    return *_runtimeConstants;
}

void Variables::setRuntimeConstants(const RuntimeConstants& constants) {
    invariant(!_runtimeConstants);
    _runtimeConstantsMap[kNowId] = Value(constants.getLocalNow());
    // We use a null Timestamp to indicate that the clusterTime is not available; this can happen if
    // the logical clock is not running. We do not use boost::optional because this would allow the
    // IDL to serialize a RuntimConstants without clusterTime, which should always be an error.
    if (!constants.getClusterTime().isNull()) {
        _runtimeConstantsMap[kClusterTimeId] = Value(constants.getClusterTime());
    }

    if (constants.getJsScope()) {
        _runtimeConstantsMap[kJsScopeId] = Value(constants.getJsScope().get());
    }
    if (constants.getIsMapReduce()) {
        _runtimeConstantsMap[kIsMapReduceId] = Value(constants.getIsMapReduce().get());
    }
    _runtimeConstants = constants;
}

void Variables::setDefaultRuntimeConstants(OperationContext* opCtx) {
    setRuntimeConstants(Variables::generateRuntimeConstants(opCtx));
}

void Variables::seedVariablesWithLetParameters(ExpressionContext* const expCtx,
                                               const BSONObj letParams) {
    for (auto&& elem : letParams) {
        variableValidation::validateNameForUserWrite(elem.fieldName());
        auto expr = Expression::parseOperand(expCtx, elem, expCtx->variablesParseState);

        uassert(4890500,
                "Command let Expression tried to access a field, but this is not allowed because "
                "Command let Expressions run before the query examines any documents.",
                expr->getDependencies().hasNoRequirements());
        Value value = expr->evaluate(Document{}, &expCtx->variables);

        const auto sysVarName = [&]() -> boost::optional<StringData> {
            // ROOT and REMOVE are excluded since they're not constants.
            auto name = elem.fieldNameStringData();
            if (auto it = kSystemVarValidators.find(name); it != kSystemVarValidators.end()) {
                auto&& [ignore, validator] = *it;
                validator(value);
                return name;
            }
            return boost::none;
        }();
        if (sysVarName) {
            if (!(sysVarName == "CLUSTER_TIME"_sd && value.getTimestamp().isNull())) {
                // Avoid populating a value for CLUSTER_TIME if the value is null.
                _runtimeConstantsMap[kBuiltinVarNameToId.at(*sysVarName)] = value;
            }
        } else {
            setConstantValue(expCtx->variablesParseState.defineVariable(elem.fieldName()), value);
        }
    }
}

RuntimeConstants Variables::generateRuntimeConstants(OperationContext* opCtx) {
    // On a standalone, the clock may not be running and $$CLUSTER_TIME is unavailable. If the
    // logical clock is available, set the clusterTime in the runtime constants. Otherwise, the
    // clusterTime is set to the null Timestamp.
    if (opCtx->getClient()) {
        if (const auto vectorClock = VectorClock::get(opCtx)) {
            const auto now = vectorClock->getTime();
            if (now.clusterTime() != LogicalTime::kUninitialized) {
                return {Date_t::now(), now.clusterTime().asTimestamp()};
            }
        }
    }
    return {Date_t::now(), Timestamp()};
}

void Variables::copyToExpCtx(const VariablesParseState& vps, ExpressionContext* expCtx) const {
    expCtx->variables = *this;
    expCtx->variablesParseState = vps.copyWith(expCtx->variables.useIdGenerator());
}

Variables::Id VariablesParseState::defineVariable(StringData name) {
    // Caller should have validated before hand by using variableValidationvalidateNameForUserWrite.
    massert(17275,
            "Can't redefine a non-user-writable variable",
            Variables::kBuiltinVarNameToId.find(name) == Variables::kBuiltinVarNameToId.end());

    Variables::Id id = _idGenerator->generateId();
    invariant(id > _lastSeen);

    _variables[name] = _lastSeen = id;
    return id;
}

Variables::Id VariablesParseState::getVariable(StringData name) const {
    auto it = _variables.find(name);
    if (it != _variables.end()) {
        // Found a user-defined variable.
        return it->second;
    }

    it = Variables::kBuiltinVarNameToId.find(name);
    if (it != Variables::kBuiltinVarNameToId.end()) {
        // This is a builtin variable.
        return it->second;
    }

    // If we didn't find either a user-defined or builtin variable, then we reject everything other
    // than CURRENT. If this is CURRENT, then we treat it as equivalent to ROOT.
    uassert(17276, str::stream() << "Use of undefined variable: " << name, name == "CURRENT");
    return Variables::kRootId;
}

std::set<Variables::Id> VariablesParseState::getDefinedVariableIDs() const {
    std::set<Variables::Id> ids;

    for (auto&& keyId : _variables) {
        ids.insert(keyId.second);
    }

    return ids;
}

BSONObj VariablesParseState::serializeUserVariables(const Variables& vars) const {
    auto bob = BSONObjBuilder{};
    for (auto&& [var_name, id] : _variables)
        if (vars.hasValue(id))
            bob << var_name << vars.getValue(id);
    return bob.obj();
}
}  // namespace mongo