path: root/src/mongo/db/pipeline/value_internal.h

/**
 *    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.
 */

#pragma once

#include <algorithm>
#include <boost/intrusive_ptr.hpp>

#include "mongo/base/static_assert.h"
#include "mongo/bson/bsonmisc.h"
#include "mongo/bson/bsonobj.h"
#include "mongo/bson/bsontypes.h"
#include "mongo/bson/oid.h"
#include "mongo/bson/timestamp.h"
#include "mongo/util/debug_util.h"
#include "mongo/util/intrusive_counter.h"


namespace mongo {
class Document;
class DocumentStorage;
class Value;

// TODO: a MutableVector, similar to MutableDocument
/// A heap-allocated reference-counted std::vector
class RCVector : public RefCountable {
public:
    RCVector() {}
    RCVector(std::vector<Value> v) : vec(std::move(v)) {}
    std::vector<Value> vec;
};

class RCCodeWScope : public RefCountable {
public:
    RCCodeWScope(const std::string& str, BSONObj obj) : code(str), scope(obj.getOwned()) {}
    const std::string code;
    const BSONObj scope;  // Not worth converting to Document for now
};

class RCDBRef : public RefCountable {
public:
    RCDBRef(const std::string& str, const OID& o) : ns(str), oid(o) {}
    const std::string ns;
    const OID oid;
};

class RCDecimal : public RefCountable {
public:
    RCDecimal(const Decimal128& decVal) : decimalValue(decVal) {}
    const Decimal128 decimalValue;
};

class ValueStorage {
public:
    // Note: it is important the memory is zeroed out (by calling zero()) at the start of every
    // constructor. Much code relies on every byte being predictably initialized to zero.

    // This is a "missing" Value
    ValueStorage() {
        zero();
        type = EOO;
    }

    explicit ValueStorage(BSONType t) {
        zero();
        type = t;
    }
    ValueStorage(BSONType t, int i) {
        zero();
        type = t;
        intValue = i;
    }
    ValueStorage(BSONType t, long long l) {
        zero();
        type = t;
        longValue = l;
    }
    ValueStorage(BSONType t, double d) {
        zero();
        type = t;
        doubleValue = d;
    }
    ValueStorage(BSONType t, const Decimal128& d) {
        zero();
        type = t;
        putDecimal(d);
    }
    ValueStorage(BSONType t, Timestamp r) {
        zero();
        type = t;
        timestampValue = r.asULL();
    }
    ValueStorage(BSONType t, bool b) {
        zero();
        type = t;
        boolValue = b;
    }
    ValueStorage(BSONType t, const Document& d) {
        zero();
        type = t;
        putDocument(d);
    }
    ValueStorage(BSONType t, const RCVector* a) {
        zero();
        type = t;
        putVector(a);
    }
    ValueStorage(BSONType t, StringData s) {
        zero();
        type = t;
        putString(s);
    }
    ValueStorage(BSONType t, const BSONBinData& bd) {
        zero();
        type = t;
        putBinData(bd);
    }
    ValueStorage(BSONType t, const BSONRegEx& re) {
        zero();
        type = t;
        putRegEx(re);
    }
    ValueStorage(BSONType t, const BSONCodeWScope& cs) {
        zero();
        type = t;
        putCodeWScope(cs);
    }
    ValueStorage(BSONType t, const BSONDBRef& dbref) {
        zero();
        type = t;
        putDBRef(dbref);
    }

    ValueStorage(BSONType t, const OID& o) {
        zero();
        type = t;
        memcpy(&oid, o.view().view(), OID::kOIDSize);
    }

    ValueStorage(const ValueStorage& rhs) {
        memcpy(this, &rhs, sizeof(*this));
        memcpyed();
    }

    ValueStorage(ValueStorage&& rhs) noexcept {
        memcpy(this, &rhs, sizeof(*this));
        rhs.zero();  // Reset rhs to the missing state. TODO consider only doing this if refCounter.
    }

    ~ValueStorage() {
        DEV verifyRefCountingIfShould();
        if (refCounter)
            intrusive_ptr_release(genericRCPtr);
        DEV memset(this, 0xee, sizeof(*this));
    }

    ValueStorage& operator=(const ValueStorage& rhs) {
        // This is designed to be effectively a no-op on self-assign, without needing an explicit
        // check. This requires that rhs's refcount is incremented before ours is released, and that
        // we use memmove rather than memcpy.
        DEV rhs.verifyRefCountingIfShould();
        if (rhs.refCounter)
            intrusive_ptr_add_ref(rhs.genericRCPtr);

        DEV verifyRefCountingIfShould();
        if (refCounter)
            intrusive_ptr_release(genericRCPtr);

        memmove(this, &rhs, sizeof(*this));
        return *this;
    }

    ValueStorage& operator=(ValueStorage&& rhs) noexcept {
        DEV verifyRefCountingIfShould();
        if (refCounter)
            intrusive_ptr_release(genericRCPtr);

        memmove(this, &rhs, sizeof(*this));
        rhs.zero();  // Reset rhs to the missing state. TODO consider only doing this if refCounter.
        return *this;
    }

    void swap(ValueStorage& rhs) {
        // Don't need to update ref-counts because they will be the same in the end
        char temp[sizeof(ValueStorage)];
        memcpy(temp, this, sizeof(*this));
        memcpy(this, &rhs, sizeof(*this));
        memcpy(&rhs, temp, sizeof(*this));
    }

    /// Call this after memcpying to update ref counts if needed
    void memcpyed() const {
        DEV verifyRefCountingIfShould();
        if (refCounter)
            intrusive_ptr_add_ref(genericRCPtr);
    }

    /// These are only to be called during Value construction on an empty Value
    void putString(StringData s);
    void putVector(const RCVector* v);
    void putDocument(const Document& d);
    void putRegEx(const BSONRegEx& re);
    void putBinData(const BSONBinData& bd) {
        putRefCountable(RCString::create(StringData(static_cast<const char*>(bd.data), bd.length)));
        binSubType = bd.type;
    }

    void putDBRef(const BSONDBRef& dbref) {
        putRefCountable(new RCDBRef(dbref.ns.toString(), dbref.oid));
    }

    void putCodeWScope(const BSONCodeWScope& cws) {
        putRefCountable(new RCCodeWScope(cws.code.toString(), cws.scope));
    }

    void putDecimal(const Decimal128& d) {
        putRefCountable(new RCDecimal(d));
    }

    void putRefCountable(boost::intrusive_ptr<const RefCountable> ptr) {
        genericRCPtr = ptr.get();

        if (genericRCPtr) {
            intrusive_ptr_add_ref(genericRCPtr);
            refCounter = true;
        }
        DEV verifyRefCountingIfShould();
    }

    StringData getString() const {
        if (shortStr) {
            return StringData(shortStrStorage, shortStrSize);
        } else {
            dassert(typeid(*genericRCPtr) == typeid(const RCString));
            const RCString* stringPtr = static_cast<const RCString*>(genericRCPtr);
            return StringData(stringPtr->c_str(), stringPtr->size());
        }
    }

    const std::vector<Value>& getArray() const {
        dassert(typeid(*genericRCPtr) == typeid(const RCVector));
        const RCVector* arrayPtr = static_cast<const RCVector*>(genericRCPtr);
        return arrayPtr->vec;
    }

    boost::intrusive_ptr<const RCCodeWScope> getCodeWScope() const {
        dassert(typeid(*genericRCPtr) == typeid(const RCCodeWScope));
        return static_cast<const RCCodeWScope*>(genericRCPtr);
    }

    boost::intrusive_ptr<const RCDBRef> getDBRef() const {
        dassert(typeid(*genericRCPtr) == typeid(const RCDBRef));
        return static_cast<const RCDBRef*>(genericRCPtr);
    }

    Decimal128 getDecimal() const {
        dassert(typeid(*genericRCPtr) == typeid(const RCDecimal));
        const RCDecimal* decPtr = static_cast<const RCDecimal*>(genericRCPtr);
        return decPtr->decimalValue;
    }

    // Document is incomplete here so this can't be inline
    Document getDocument() const;

    BSONType bsonType() const {
        return BSONType(type);
    }

    BinDataType binDataType() const {
        dassert(type == BinData);
        return BinDataType(binSubType);
    }

    void zero() {
        memset(this, 0, sizeof(*this));
    }

    // Byte-for-byte identical
    bool identical(const ValueStorage& other) const {
        return (i64[0] == other.i64[0] && i64[1] == other.i64[1]);
    }

    void verifyRefCountingIfShould() const;

    // This data is public because this should only be used by Value which would be a friend
    union {
#pragma pack(1)
        struct {
            // byte 1
            signed char type;

            // byte 2
            struct {
                bool refCounter : 1;  // true if we need to refCount
                bool shortStr : 1;    // true if we are using short strings
                // reservedFlags: 6;
            };

            // bytes 3-16;
            union {
                unsigned char oid[12];

                struct {
                    char shortStrSize;  // TODO Consider moving into flags union (4 bits)
                    char shortStrStorage[16 /*total bytes*/ - 3 /*offset*/ - 1 /*NUL byte*/];
                    union {
                        char nulTerminator;
                    };
                };

                struct {
                    union {
                        unsigned char binSubType;
                        char pad[6];
                        char stringCache[6];  // TODO copy first few bytes of strings in here
                    };
                    union {  // 8 bytes long and 8-byte aligned
                        // There should be no pointers to non-const data
                        const RefCountable* genericRCPtr;

                        double doubleValue;
                        bool boolValue;
                        int intValue;
                        long long longValue;
                        unsigned long long timestampValue;
                        long long dateValue;
                    };
                };
            };
        };
#pragma pack()

        // covers the whole ValueStorage
        long long i64[2];

        // Forces the ValueStorage type to have at least pointer alignment. Can't use alignas on the
        // type since that causes issues on MSVC.
        void* forcePointerAlignment;
    };
};
MONGO_STATIC_ASSERT(sizeof(ValueStorage) == 16);
MONGO_STATIC_ASSERT(alignof(ValueStorage) >= alignof(void*));
}