path: root/src/mongo/db/field_ref.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 <boost/optional.hpp>
#include <iosfwd>
#include <set>
#include <string>
#include <vector>

#include "mongo/base/string_data.h"

namespace mongo {

/**
 * A FieldPath represents a path in a document, starting from the root. The path
 * is made of "field parts" separated by dots. The class provides an efficient means to
 * "split" the dotted fields in its parts, but no validation is done.
 *
 * Any field part may be replaced, after the "original" field reference was parsed. Any
 * part can be accessed through a StringData object.
 *
 * The class is not thread safe.
 */
class FieldRef {
public:
    /**
     * Helper class for appending to a FieldRef for the duration of the current scope and then
     * restoring the FieldRef at the end of the scope.
     */
    class FieldRefTempAppend {
    public:
        FieldRefTempAppend(FieldRef& fieldRef, StringData part) : _fieldRef(fieldRef) {
            _fieldRef.appendPart(part);
        }

        ~FieldRefTempAppend() {
            _fieldRef.removeLastPart();
        }

    private:
        FieldRef& _fieldRef;
    };

    /**
     * Returns true if the argument is a numeric string which is eligible to act as the key name for
     * an element in a BSON array; in other words, the string matches the regex ^(0|[1-9]+[0-9]*)$.
     */
    static bool isNumericPathComponentStrict(StringData component);

    /**
     * Similar to the function above except strings that contain leading zero's are considered
     * numeric. For instance, the above function would return false for an input "01" however this
     * function will return true.
     */
    static bool isNumericPathComponentLenient(StringData component);

    FieldRef() = default;

    explicit FieldRef(StringData path);

    /**
     * Field parts accessed through getPart() calls no longer would be valid, after the
     * destructor ran.
     */
    ~FieldRef() {}

    /**
     * Builds a field path out of each field part in 'dottedField'.
     */
    void parse(StringData dottedField);

    /**
     * Sets the 'i-th' field part to point to 'part'. Assumes i < size(). Behavior is
     * undefined otherwise.
     */
    void setPart(size_t i, StringData part);

    /**
     * Adds a new field to the end of the path, increasing its size by 1.
     */
    void appendPart(StringData part);

    /**
     * Removes the last part from the path, decreasing its size by 1. Has no effect on a
     * FieldRef with size 0.
     */
    void removeLastPart();

    /**
     * Returns the 'i-th' field part. Assumes i < size(). Behavior is undefined otherwise.
     */
    StringData getPart(size_t i) const;

    /**
     * Returns true when 'this' FieldRef is a prefix of 'other'. Equality is not considered
     * a prefix.
     */
    bool isPrefixOf(const FieldRef& other) const;

    /**
     * Returns true if 'this' FieldRef is a prefix of 'other', or if both paths are identical.
     */
    bool isPrefixOfOrEqualTo(const FieldRef& other) const;

    /**
     * Returns the number of field parts in the prefix that 'this' and 'other' share.
     */
    size_t commonPrefixSize(const FieldRef& other) const;

    /**
     * Returns true if the specified path component is a numeric string which is eligible to act as
     * the key name for an element in a BSON array; in other words, the fieldname matches the regex
     * ^(0|[1-9]+[0-9]*)$.
     */
    bool isNumericPathComponentStrict(size_t i) const;

    /**
     * Returns true if this FieldRef has any numeric path components.
     */
    bool hasNumericPathComponents() const;

    /**
     * Returns the positions of all numeric path components, starting from the given position.
     */
    std::set<size_t> getNumericPathComponents(size_t startPart = 0) const;

    /**
     * Returns a StringData of the full dotted field in its current state (i.e., some parts may
     * have been replaced since the parse() call).
     */
    StringData dottedField(size_t offsetFromStart = 0) const;

    /**
     * Returns a StringData of parts of the dotted field from startPart to endPart in its
     * current state (i.e., some parts may have been replaced since the parse() call).
     */
    StringData dottedSubstring(size_t startPart, size_t endPart) const;

    /**
     * Compares the full dotted path represented by this FieldRef to other
     */
    bool equalsDottedField(StringData other) const;

    /**
     * Return 0 if 'this' is equal to 'other' lexicographically, -1 if is it less than or
     * +1 if it is greater than.
     */
    int compare(const FieldRef& other) const;

    /**
     * Resets the internal state. See note in parse() call.
     */
    void clear();

    //
    // accessors
    //

    /**
     * Returns the number of parts in this FieldRef.
     */
    size_t numParts() const {
        return _size;
    }

    bool empty() const {
        return numParts() == 0;
    }

    StringData operator[](int index) const {
        return getPart(index);
    }

private:
    // Dotted fields are most often not longer than four parts. We use a mixed structure
    // here that will not require any extra memory allocation when that is the case. And
    // handle larger dotted fields if it is. The idea is not to penalize the common case
    // with allocations.
    static const size_t kReserveAhead = 4;

    // In order to make FieldRef copyable, we use a StringData-like type that stores an offset and
    // length into the backing string. StringData, in constrast, holds const char* pointers that
    // would have to be updated to point into the new string on copy.
    struct StringView {
        // Constructs an empty StringView.
        StringView() = default;

        StringView(std::size_t offset, std::size_t len) : offset(offset), len(len){};

        StringData toStringData(const std::string& viewInto) const {
            return {viewInto.c_str() + offset, len};
        };

        std::size_t offset = 0;
        std::size_t len = 0;
    };

    /** Converts the field part index to the variable part equivalent */
    size_t getIndex(size_t i) const {
        return i - kReserveAhead;
    }

    /**
     * Returns the new number of parts after appending 'part' to this field path. This is
     * private, because it is only intended for use by the parse function.
     */
    size_t appendParsedPart(StringView part);

    /**
     * Re-assemble _dotted from components, including any replacements in _replacements,
     * and update the StringData components in _fixed and _variable to refer to the parts
     * of the new _dotted. This is used to make the storage for the current value of this
     * FieldRef contiguous so it can be returned as a StringData from the dottedField
     * method above.
     */
    void reserialize() const;

    // number of field parts stored
    size_t _size = 0u;

    // Number of field parts in the cached dotted name (_dotted).
    mutable size_t _cachedSize = 0u;

    // First 'kReservedAhead' field components. Each component is either a StringView backed by the
    // _dotted string or boost::none to indicate that getPart() should read the string from the
    // _replacements list.
    mutable boost::optional<StringView> _fixed[kReserveAhead];

    // Remaining field components. Each non-none element is a view backed by '_dotted'. (See comment
    // above _fixed.)
    mutable std::vector<boost::optional<StringView>> _variable;

    /**
     * Cached copy of the complete dotted name string. The StringView objects in "_fixed" and
     * "_variable" reference this string.
     */
    mutable std::string _dotted;

    /**
     * String storage for path parts that have been replaced with setPart() or added with
     * appendPart() since the lasted time "_dotted" was materialized.
     */
    mutable std::vector<std::string> _replacements;
};

inline bool operator==(const FieldRef& lhs, const FieldRef& rhs) {
    return lhs.compare(rhs) == 0;
}

inline bool operator!=(const FieldRef& lhs, const FieldRef& rhs) {
    return lhs.compare(rhs) != 0;
}

inline bool operator<(const FieldRef& lhs, const FieldRef& rhs) {
    return lhs.compare(rhs) < 0;
}

inline bool operator<=(const FieldRef& lhs, const FieldRef& rhs) {
    return lhs.compare(rhs) <= 0;
}

inline bool operator>(const FieldRef& lhs, const FieldRef& rhs) {
    return lhs.compare(rhs) > 0;
}

inline bool operator>=(const FieldRef& lhs, const FieldRef& rhs) {
    return lhs.compare(rhs) >= 0;
}

inline FieldRef operator+(const FieldRef& lhs, const FieldRef& rhs) {
    FieldRef result = lhs;
    for (size_t i = 0; i < rhs.numParts(); ++i) {
        result.appendPart(rhs.getPart(i));
    }
    return result;
}

std::ostream& operator<<(std::ostream& stream, const FieldRef& value);

}  // namespace mongo