src/core/common/heap_string.hpp

/*
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 *     names of its contributors may be used to endorse or promote products
 *     derived from this software without specific prior written permission.
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 */

/**
 * @file
 *   This file includes definitions for `Heap::String` (a heap allocated string).
 */

#ifndef HEAP_STRING_HPP_
#define HEAP_STRING_HPP_

#include "openthread-core-config.h"

#include "common/equatable.hpp"
#include "common/error.hpp"
#include "common/heap.hpp"

namespace ot {
namespace Heap {

/**
 * This class represents a heap allocated string.
 *
 * The buffer to store the string is allocated from heap and is manged by the `Heap::String` class itself, e.g., it may
 * be reused and/or freed and reallocated when the string is set. The `Heap::String` destructor will always free the
 * allocated buffer.
 *
 */
class String : public Unequatable<String>
{
public:
    /**
     * This constructor initializes the `String` as null (or empty).
     *
     */
    String(void)
        : mStringBuffer(nullptr)
    {
    }

    /**
     * This is the move constructor for `String`.
     *
     * `String` is non-copyable (copy constructor is deleted) but move constructor is provided to allow it to to be
     * used as return type (return by value) from functions/methods (which will then use move semantics).
     *
     */
    String(String &&aString)
        : mStringBuffer(aString.mStringBuffer)
    {
        aString.mStringBuffer = nullptr;
    }

    /**
     * This is the destructor for `HealString` object
     *
     */
    ~String(void) { Free(); }

    /**
     * This method indicates whether or not the `String` is null (i.e., it was never successfully set or it was
     * freed).
     *
     * @retval TRUE  The `String` is null.
     * @retval FALSE The `String` is not null.
     *
     */
    bool IsNull(void) const { return (mStringBuffer == nullptr); }

    /**
     * This method returns the `String` as a C string.
     *
     * @returns A pointer to C string buffer or `nullptr` if the `String` is null (never set or freed).
     *
     */
    const char *AsCString(void) const { return mStringBuffer; }

    /**
     * This method sets the string from a given C string.
     *
     * @param[in] aCString   A pointer to c string buffer. Can be `nullptr` which then frees the `String`.
     *
     * @retval kErrorNone     Successfully set the string.
     * @retval kErrorNoBufs   Failed to allocate buffer for string.
     *
     */
    Error Set(const char *aCString);

    /**
     * This method sets the string from another `String`.
     *
     * @param[in] aString   The other `String` to set from.
     *
     * @retval kErrorNone     Successfully set the string.
     * @retval kErrorNoBufs   Failed to allocate buffer for string.
     *
     */
    Error Set(const String &aString) { return Set(aString.AsCString()); }

    /**
     * This method sets the string from another `String`.
     *
     * @param[in] aString     The other `String` to set from (rvalue reference using move semantics).
     *
     * @retval kErrorNone     Successfully set the string.
     * @retval kErrorNoBufs   Failed to allocate buffer for string.
     *
     */
    Error Set(String &&aString);

    /**
     * This method frees any buffer allocated by the `String`.
     *
     * The `String` destructor will automatically call `Free()`. This method allows caller to free buffer
     * explicitly.
     *
     */
    void Free(void);

    /**
     * This method overloads operator `==` to evaluate whether or not the `String` is equal to a given C string.
     *
     * @param[in]  aCString  A C string to compare with. Can be `nullptr` which then checks if `String` is null.
     *
     * @retval TRUE   If the two strings are equal.
     * @retval FALSE  If the two strings are not equal.
     *
     */
    bool operator==(const char *aCString) const;

    /**
     * This method overloads operator `!=` to evaluate whether or not the `String` is unequal to a given C string.
     *
     * @param[in]  aCString  A C string to compare with. Can be `nullptr` which then checks if `String` is not null.
     *
     * @retval TRUE   If the two strings are not equal.
     * @retval FALSE  If the two strings are equal.
     *
     */
    bool operator!=(const char *aCString) const { return !(*this == aCString); }

    /**
     * This method overloads operator `==` to evaluate whether or not two `String` are equal.
     *
     * @param[in]  aString  The other string to compare with.
     *
     * @retval TRUE   If the two strings are equal.
     * @retval FALSE  If the two strings are not equal.
     *
     */
    bool operator==(const String &aString) const { return (*this == aString.AsCString()); }

    String(const String &) = delete;
    String &operator=(const String &) = delete;

private:
    char *mStringBuffer;
};

} // namespace Heap
} // namespace ot

#endif // HEAP_STRING_HPP_