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+//===- FuzzedDataProvider.h - Utility header for fuzz targets ---*- C++ -* ===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+// A single header library providing an utility class to break up an array of
+// bytes. Whenever run on the same input, provides the same output, as long as
+// its methods are called in the same order, with the same arguments.
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_FUZZER_FUZZED_DATA_PROVIDER_H_
+#define LLVM_FUZZER_FUZZED_DATA_PROVIDER_H_
+
+#include <algorithm>
+#include <climits>
+#include <cstddef>
+#include <cstdint>
+#include <cstring>
+#include <initializer_list>
+#include <string>
+#include <type_traits>
+#include <utility>
+#include <vector>
+
+// In addition to the comments below, the API is also briefly documented at
+// https://github.com/google/fuzzing/blob/master/docs/split-inputs.md#fuzzed-data-provider
+class FuzzedDataProvider {
+ public:
+ // |data| is an array of length |size| that the FuzzedDataProvider wraps to
+ // provide more granular access. |data| must outlive the FuzzedDataProvider.
+ FuzzedDataProvider(const uint8_t *data, size_t size)
+ : data_ptr_(data), remaining_bytes_(size) {}
+ ~FuzzedDataProvider() = default;
+
+ // Returns a std::vector containing |num_bytes| of input data. If fewer than
+ // |num_bytes| of data remain, returns a shorter std::vector containing all
+ // of the data that's left. Can be used with any byte sized type, such as
+ // char, unsigned char, uint8_t, etc.
+ template <typename T> std::vector<T> ConsumeBytes(size_t num_bytes) {
+ num_bytes = std::min(num_bytes, remaining_bytes_);
+ return ConsumeBytes<T>(num_bytes, num_bytes);
+ }
+
+ // Similar to |ConsumeBytes|, but also appends the terminator value at the end
+ // of the resulting vector. Useful, when a mutable null-terminated C-string is
+ // needed, for example. But that is a rare case. Better avoid it, if possible,
+ // and prefer using |ConsumeBytes| or |ConsumeBytesAsString| methods.
+ template <typename T>
+ std::vector<T> ConsumeBytesWithTerminator(size_t num_bytes,
+ T terminator = 0) {
+ num_bytes = std::min(num_bytes, remaining_bytes_);
+ std::vector<T> result = ConsumeBytes<T>(num_bytes + 1, num_bytes);
+ result.back() = terminator;
+ return result;
+ }
+
+ // Returns a std::string containing |num_bytes| of input data. Using this and
+ // |.c_str()| on the resulting string is the best way to get an immutable
+ // null-terminated C string. If fewer than |num_bytes| of data remain, returns
+ // a shorter std::string containing all of the data that's left.
+ std::string ConsumeBytesAsString(size_t num_bytes) {
+ static_assert(sizeof(std::string::value_type) == sizeof(uint8_t),
+ "ConsumeBytesAsString cannot convert the data to a string.");
+
+ num_bytes = std::min(num_bytes, remaining_bytes_);
+ std::string result(
+ reinterpret_cast<const std::string::value_type *>(data_ptr_),
+ num_bytes);
+ Advance(num_bytes);
+ return result;
+ }
+
+ // Returns a number in the range [min, max] by consuming bytes from the
+ // input data. The value might not be uniformly distributed in the given
+ // range. If there's no input data left, always returns |min|. |min| must
+ // be less than or equal to |max|.
+ template <typename T> T ConsumeIntegralInRange(T min, T max) {
+ static_assert(std::is_integral<T>::value, "An integral type is required.");
+ static_assert(sizeof(T) <= sizeof(uint64_t), "Unsupported integral type.");
+
+ if (min > max)
+ abort();
+
+ // Use the biggest type possible to hold the range and the result.
+ uint64_t range = static_cast<uint64_t>(max) - min;
+ uint64_t result = 0;
+ size_t offset = 0;
+
+ while (offset < sizeof(T) * CHAR_BIT && (range >> offset) > 0 &&
+ remaining_bytes_ != 0) {
+ // Pull bytes off the end of the seed data. Experimentally, this seems to
+ // allow the fuzzer to more easily explore the input space. This makes
+ // sense, since it works by modifying inputs that caused new code to run,
+ // and this data is often used to encode length of data read by
+ // |ConsumeBytes|. Separating out read lengths makes it easier modify the
+ // contents of the data that is actually read.
+ --remaining_bytes_;
+ result = (result << CHAR_BIT) | data_ptr_[remaining_bytes_];
+ offset += CHAR_BIT;
+ }
+
+ // Avoid division by 0, in case |range + 1| results in overflow.
+ if (range != std::numeric_limits<decltype(range)>::max())
+ result = result % (range + 1);
+
+ return static_cast<T>(min + result);
+ }
+
+ // Returns a std::string of length from 0 to |max_length|. When it runs out of
+ // input data, returns what remains of the input. Designed to be more stable
+ // with respect to a fuzzer inserting characters than just picking a random
+ // length and then consuming that many bytes with |ConsumeBytes|.
+ std::string ConsumeRandomLengthString(size_t max_length) {
+ // Reads bytes from the start of |data_ptr_|. Maps "\\" to "\", and maps "\"
+ // followed by anything else to the end of the string. As a result of this
+ // logic, a fuzzer can insert characters into the string, and the string
+ // will be lengthened to include those new characters, resulting in a more
+ // stable fuzzer than picking the length of a string independently from
+ // picking its contents.
+ std::string result;
+
+ // Reserve the anticipated capaticity to prevent several reallocations.
+ result.reserve(std::min(max_length, remaining_bytes_));
+ for (size_t i = 0; i < max_length && remaining_bytes_ != 0; ++i) {
+ char next = ConvertUnsignedToSigned<char>(data_ptr_[0]);
+ Advance(1);
+ if (next == '\\' && remaining_bytes_ != 0) {
+ next = ConvertUnsignedToSigned<char>(data_ptr_[0]);
+ Advance(1);
+ if (next != '\\')
+ break;
+ }
+ result += next;
+ }
+
+ result.shrink_to_fit();
+ return result;
+ }
+
+ // Returns a std::vector containing all remaining bytes of the input data.
+ template <typename T> std::vector<T> ConsumeRemainingBytes() {
+ return ConsumeBytes<T>(remaining_bytes_);
+ }
+
+ // Returns a std::string containing all remaining bytes of the input data.
+ // Prefer using |ConsumeRemainingBytes| unless you actually need a std::string
+ // object.
+ std::string ConsumeRemainingBytesAsString() {
+ return ConsumeBytesAsString(remaining_bytes_);
+ }
+
+ // Returns a number in the range [Type's min, Type's max]. The value might
+ // not be uniformly distributed in the given range. If there's no input data
+ // left, always returns |min|.
+ template <typename T> T ConsumeIntegral() {
+ return ConsumeIntegralInRange(std::numeric_limits<T>::min(),
+ std::numeric_limits<T>::max());
+ }
+
+ // Reads one byte and returns a bool, or false when no data remains.
+ bool ConsumeBool() { return 1 & ConsumeIntegral<uint8_t>(); }
+
+ // Returns a copy of the value selected from the given fixed-size |array|.
+ template <typename T, size_t size>
+ T PickValueInArray(const T (&array)[size]) {
+ static_assert(size > 0, "The array must be non empty.");
+ return array[ConsumeIntegralInRange<size_t>(0, size - 1)];
+ }
+
+ template <typename T>
+ T PickValueInArray(std::initializer_list<const T> list) {
+ // TODO(Dor1s): switch to static_assert once C++14 is allowed.
+ if (!list.size())
+ abort();
+
+ return *(list.begin() + ConsumeIntegralInRange<size_t>(0, list.size() - 1));
+ }
+
+ // Returns an enum value. The enum must start at 0 and be contiguous. It must
+ // also contain |kMaxValue| aliased to its largest (inclusive) value. Such as:
+ // enum class Foo { SomeValue, OtherValue, kMaxValue = OtherValue };
+ template <typename T> T ConsumeEnum() {
+ static_assert(std::is_enum<T>::value, "|T| must be an enum type.");
+ return static_cast<T>(ConsumeIntegralInRange<uint32_t>(
+ 0, static_cast<uint32_t>(T::kMaxValue)));
+ }
+
+ // Returns a floating point number in the range [0.0, 1.0]. If there's no
+ // input data left, always returns 0.
+ template <typename T> T ConsumeProbability() {
+ static_assert(std::is_floating_point<T>::value,
+ "A floating point type is required.");
+
+ // Use different integral types for different floating point types in order
+ // to provide better density of the resulting values.
+ using IntegralType =
+ typename std::conditional<(sizeof(T) <= sizeof(uint32_t)), uint32_t,
+ uint64_t>::type;
+
+ T result = static_cast<T>(ConsumeIntegral<IntegralType>());
+ result /= static_cast<T>(std::numeric_limits<IntegralType>::max());
+ return result;
+ }
+
+ // Returns a floating point value in the range [Type's lowest, Type's max] by
+ // consuming bytes from the input data. If there's no input data left, always
+ // returns approximately 0.
+ template <typename T> T ConsumeFloatingPoint() {
+ return ConsumeFloatingPointInRange<T>(std::numeric_limits<T>::lowest(),
+ std::numeric_limits<T>::max());
+ }
+
+ // Returns a floating point value in the given range by consuming bytes from
+ // the input data. If there's no input data left, returns |min|. Note that
+ // |min| must be less than or equal to |max|.
+ template <typename T> T ConsumeFloatingPointInRange(T min, T max) {
+ if (min > max)
+ abort();
+
+ T range = .0;
+ T result = min;
+ constexpr T zero(.0);
+ if (max > zero && min < zero && max > min + std::numeric_limits<T>::max()) {
+ // The diff |max - min| would overflow the given floating point type. Use
+ // the half of the diff as the range and consume a bool to decide whether
+ // the result is in the first of the second part of the diff.
+ range = (max / 2.0) - (min / 2.0);
+ if (ConsumeBool()) {
+ result += range;
+ }
+ } else {
+ range = max - min;
+ }
+
+ return result + range * ConsumeProbability<T>();
+ }
+
+ // Reports the remaining bytes available for fuzzed input.
+ size_t remaining_bytes() { return remaining_bytes_; }
+
+ private:
+ FuzzedDataProvider(const FuzzedDataProvider &) = delete;
+ FuzzedDataProvider &operator=(const FuzzedDataProvider &) = delete;
+
+ void Advance(size_t num_bytes) {
+ if (num_bytes > remaining_bytes_)
+ abort();
+
+ data_ptr_ += num_bytes;
+ remaining_bytes_ -= num_bytes;
+ }
+
+ template <typename T>
+ std::vector<T> ConsumeBytes(size_t size, size_t num_bytes_to_consume) {
+ static_assert(sizeof(T) == sizeof(uint8_t), "Incompatible data type.");
+
+ // The point of using the size-based constructor below is to increase the
+ // odds of having a vector object with capacity being equal to the length.
+ // That part is always implementation specific, but at least both libc++ and
+ // libstdc++ allocate the requested number of bytes in that constructor,
+ // which seems to be a natural choice for other implementations as well.
+ // To increase the odds even more, we also call |shrink_to_fit| below.
+ std::vector<T> result(size);
+ std::memcpy(result.data(), data_ptr_, num_bytes_to_consume);
+ Advance(num_bytes_to_consume);
+
+ // Even though |shrink_to_fit| is also implementation specific, we expect it
+ // to provide an additional assurance in case vector's constructor allocated
+ // a buffer which is larger than the actual amount of data we put inside it.
+ result.shrink_to_fit();
+ return result;
+ }
+
+ template <typename TS, typename TU> TS ConvertUnsignedToSigned(TU value) {
+ static_assert(sizeof(TS) == sizeof(TU), "Incompatible data types.");
+ static_assert(!std::numeric_limits<TU>::is_signed,
+ "Source type must be unsigned.");
+
+ // TODO(Dor1s): change to `if constexpr` once C++17 becomes mainstream.
+ if (std::numeric_limits<TS>::is_modulo)
+ return static_cast<TS>(value);
+
+ // Avoid using implementation-defined unsigned to signer conversions.
+ // To learn more, see https://stackoverflow.com/questions/13150449.
+ if (value <= std::numeric_limits<TS>::max()) {
+ return static_cast<TS>(value);
+ } else {
+ constexpr auto TS_min = std::numeric_limits<TS>::min();
+ return TS_min + static_cast<char>(value - TS_min);
+ }
+ }
+
+ const uint8_t *data_ptr_;
+ size_t remaining_bytes_;
+};
+
+#endif // LLVM_FUZZER_FUZZED_DATA_PROVIDER_H_