toxcore/testing/fuzzing/fuzz_support.h

/* SPDX-License-Identifier: GPL-3.0-or-later
 * Copyright © 2021 The TokTok team.
 */

#ifndef C_TOXCORE_TESTING_FUZZING_FUZZ_SUPPORT_H
#define C_TOXCORE_TESTING_FUZZING_FUZZ_SUPPORT_H

#include <cstdint>
#include <cstdlib>

struct Fuzz_Data {
    const uint8_t *data;
    std::size_t size;

    uint8_t consume1() {
        const uint8_t val = data[0];
        ++data;
        --size;
        return val;
    }

    const uint8_t *consume(std::size_t count) {
        const uint8_t *val = data;
        data += count;
        size -= count;
        return val;
    }
};

/** @brief Consumes 1 byte of the fuzzer input or returns if no data available.
 *
 * This advances the fuzzer input data by 1 byte and consumes that byte in the
 * declaration.
 *
 * @example
 * @code
 * CONSUME1_OR_RETURN(const uint8_t one_byte, input);
 * @endcode
 */
#define CONSUME1_OR_RETURN(DECL, INPUT) \
    if (INPUT.size < 1) {     \
        return;               \
    }                         \
    DECL = INPUT.consume1()

/** @brief Consumes SIZE bytes of the fuzzer input or returns if not enough data available.
 *
 * This advances the fuzzer input data by SIZE byte and consumes those bytes in
 * the declaration. If less than SIZE bytes are available in the fuzzer input,
 * this macro returns from the enclosing function.
 *
 * @example
 * @code
 * CONSUME_OR_RETURN(const uint8_t *ten_bytes, input, 10);
 * @endcode
 */
#define CONSUME_OR_RETURN(DECL, INPUT, SIZE) \
    if (INPUT.size < SIZE) {       \
        return;                    \
    }                              \
    DECL = INPUT.consume(SIZE)

inline void fuzz_select_target(uint8_t selector, Fuzz_Data input)
{
    // The selector selected no function, so we do nothing and rely on the
    // fuzzer to come up with a better selector.
}

template<typename Arg, typename ...Args>
void fuzz_select_target(uint8_t selector, Fuzz_Data input, Arg fn, Args ...args)
{
    if (selector == sizeof...(Args)) {
        return fn(input);
    }
    return fuzz_select_target(selector - 1, input, args...);
}

template<typename ...Args>
void fuzz_select_target(const uint8_t *data, std::size_t size, Args ...args)
{
    Fuzz_Data input{data, size};

    CONSUME1_OR_RETURN(uint8_t selector, input);
    return fuzz_select_target(selector, input, args...);
}

#endif // C_TOXCORE_TESTING_FUZZING_FUZZ_SUPPORT_H