1 //===- FuzzedDataProvider.h - Utility header for fuzz targets ---*- C++ -* ===//
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //===----------------------------------------------------------------------===//
8 // A single header library providing an utility class to break up an array of
9 // bytes. Whenever run on the same input, provides the same output, as long as
10 // its methods are called in the same order, with the same arguments.
11 //===----------------------------------------------------------------------===//
13 #ifndef LLVM_FUZZER_FUZZED_DATA_PROVIDER_H_
14 #define LLVM_FUZZER_FUZZED_DATA_PROVIDER_H_
21 #include <initializer_list>
23 #include <type_traits>
27 // In addition to the comments below, the API is also briefly documented at
28 // https://github.com/google/fuzzing/blob/master/docs/split-inputs.md#fuzzed-data-provider
29 class FuzzedDataProvider {
31 // |data| is an array of length |size| that the FuzzedDataProvider wraps to
32 // provide more granular access. |data| must outlive the FuzzedDataProvider.
33 FuzzedDataProvider(const uint8_t *data, size_t size)
34 : data_ptr_(data), remaining_bytes_(size) {}
35 ~FuzzedDataProvider() = default;
37 // Returns a std::vector containing |num_bytes| of input data. If fewer than
38 // |num_bytes| of data remain, returns a shorter std::vector containing all
39 // of the data that's left. Can be used with any byte sized type, such as
40 // char, unsigned char, uint8_t, etc.
41 template <typename T> std::vector<T> ConsumeBytes(size_t num_bytes) {
42 num_bytes = std::min(num_bytes, remaining_bytes_);
43 return ConsumeBytes<T>(num_bytes, num_bytes);
46 // Similar to |ConsumeBytes|, but also appends the terminator value at the end
47 // of the resulting vector. Useful, when a mutable null-terminated C-string is
48 // needed, for example. But that is a rare case. Better avoid it, if possible,
49 // and prefer using |ConsumeBytes| or |ConsumeBytesAsString| methods.
51 std::vector<T> ConsumeBytesWithTerminator(size_t num_bytes,
53 num_bytes = std::min(num_bytes, remaining_bytes_);
54 std::vector<T> result = ConsumeBytes<T>(num_bytes + 1, num_bytes);
55 result.back() = terminator;
59 // Returns a std::string containing |num_bytes| of input data. Using this and
60 // |.c_str()| on the resulting string is the best way to get an immutable
61 // null-terminated C string. If fewer than |num_bytes| of data remain, returns
62 // a shorter std::string containing all of the data that's left.
63 std::string ConsumeBytesAsString(size_t num_bytes) {
64 static_assert(sizeof(std::string::value_type) == sizeof(uint8_t),
65 "ConsumeBytesAsString cannot convert the data to a string.");
67 num_bytes = std::min(num_bytes, remaining_bytes_);
69 reinterpret_cast<const std::string::value_type *>(data_ptr_),
75 // Returns a number in the range [min, max] by consuming bytes from the
76 // input data. The value might not be uniformly distributed in the given
77 // range. If there's no input data left, always returns |min|. |min| must
78 // be less than or equal to |max|.
79 template <typename T> T ConsumeIntegralInRange(T min, T max) {
80 static_assert(std::is_integral<T>::value, "An integral type is required.");
81 static_assert(sizeof(T) <= sizeof(uint64_t), "Unsupported integral type.");
86 // Use the biggest type possible to hold the range and the result.
87 uint64_t range = static_cast<uint64_t>(max) - min;
91 while (offset < sizeof(T) * CHAR_BIT && (range >> offset) > 0 &&
92 remaining_bytes_ != 0) {
93 // Pull bytes off the end of the seed data. Experimentally, this seems to
94 // allow the fuzzer to more easily explore the input space. This makes
95 // sense, since it works by modifying inputs that caused new code to run,
96 // and this data is often used to encode length of data read by
97 // |ConsumeBytes|. Separating out read lengths makes it easier modify the
98 // contents of the data that is actually read.
100 result = (result << CHAR_BIT) | data_ptr_[remaining_bytes_];
104 // Avoid division by 0, in case |range + 1| results in overflow.
105 if (range != std::numeric_limits<decltype(range)>::max())
106 result = result % (range + 1);
108 return static_cast<T>(min + result);
111 // Returns a std::string of length from 0 to |max_length|. When it runs out of
112 // input data, returns what remains of the input. Designed to be more stable
113 // with respect to a fuzzer inserting characters than just picking a random
114 // length and then consuming that many bytes with |ConsumeBytes|.
115 std::string ConsumeRandomLengthString(size_t max_length) {
116 // Reads bytes from the start of |data_ptr_|. Maps "\\" to "\", and maps "\"
117 // followed by anything else to the end of the string. As a result of this
118 // logic, a fuzzer can insert characters into the string, and the string
119 // will be lengthened to include those new characters, resulting in a more
120 // stable fuzzer than picking the length of a string independently from
121 // picking its contents.
124 // Reserve the anticipated capaticity to prevent several reallocations.
125 result.reserve(std::min(max_length, remaining_bytes_));
126 for (size_t i = 0; i < max_length && remaining_bytes_ != 0; ++i) {
127 char next = ConvertUnsignedToSigned<char>(data_ptr_[0]);
129 if (next == '\\' && remaining_bytes_ != 0) {
130 next = ConvertUnsignedToSigned<char>(data_ptr_[0]);
138 result.shrink_to_fit();
142 // Returns a std::vector containing all remaining bytes of the input data.
143 template <typename T> std::vector<T> ConsumeRemainingBytes() {
144 return ConsumeBytes<T>(remaining_bytes_);
147 // Returns a std::string containing all remaining bytes of the input data.
148 // Prefer using |ConsumeRemainingBytes| unless you actually need a std::string
150 std::string ConsumeRemainingBytesAsString() {
151 return ConsumeBytesAsString(remaining_bytes_);
154 // Returns a number in the range [Type's min, Type's max]. The value might
155 // not be uniformly distributed in the given range. If there's no input data
156 // left, always returns |min|.
157 template <typename T> T ConsumeIntegral() {
158 return ConsumeIntegralInRange(std::numeric_limits<T>::min(),
159 std::numeric_limits<T>::max());
162 // Reads one byte and returns a bool, or false when no data remains.
163 bool ConsumeBool() { return 1 & ConsumeIntegral<uint8_t>(); }
165 // Returns a copy of the value selected from the given fixed-size |array|.
166 template <typename T, size_t size>
167 T PickValueInArray(const T (&array)[size]) {
168 static_assert(size > 0, "The array must be non empty.");
169 return array[ConsumeIntegralInRange<size_t>(0, size - 1)];
172 template <typename T>
173 T PickValueInArray(std::initializer_list<const T> list) {
174 // TODO(Dor1s): switch to static_assert once C++14 is allowed.
178 return *(list.begin() + ConsumeIntegralInRange<size_t>(0, list.size() - 1));
181 // Returns an enum value. The enum must start at 0 and be contiguous. It must
182 // also contain |kMaxValue| aliased to its largest (inclusive) value. Such as:
183 // enum class Foo { SomeValue, OtherValue, kMaxValue = OtherValue };
184 template <typename T> T ConsumeEnum() {
185 static_assert(std::is_enum<T>::value, "|T| must be an enum type.");
186 return static_cast<T>(ConsumeIntegralInRange<uint32_t>(
187 0, static_cast<uint32_t>(T::kMaxValue)));
190 // Returns a floating point number in the range [0.0, 1.0]. If there's no
191 // input data left, always returns 0.
192 template <typename T> T ConsumeProbability() {
193 static_assert(std::is_floating_point<T>::value,
194 "A floating point type is required.");
196 // Use different integral types for different floating point types in order
197 // to provide better density of the resulting values.
199 typename std::conditional<(sizeof(T) <= sizeof(uint32_t)), uint32_t,
202 T result = static_cast<T>(ConsumeIntegral<IntegralType>());
203 result /= static_cast<T>(std::numeric_limits<IntegralType>::max());
207 // Returns a floating point value in the range [Type's lowest, Type's max] by
208 // consuming bytes from the input data. If there's no input data left, always
209 // returns approximately 0.
210 template <typename T> T ConsumeFloatingPoint() {
211 return ConsumeFloatingPointInRange<T>(std::numeric_limits<T>::lowest(),
212 std::numeric_limits<T>::max());
215 // Returns a floating point value in the given range by consuming bytes from
216 // the input data. If there's no input data left, returns |min|. Note that
217 // |min| must be less than or equal to |max|.
218 template <typename T> T ConsumeFloatingPointInRange(T min, T max) {
224 constexpr T zero(.0);
225 if (max > zero && min < zero && max > min + std::numeric_limits<T>::max()) {
226 // The diff |max - min| would overflow the given floating point type. Use
227 // the half of the diff as the range and consume a bool to decide whether
228 // the result is in the first of the second part of the diff.
229 range = (max / 2.0) - (min / 2.0);
237 return result + range * ConsumeProbability<T>();
240 // Reports the remaining bytes available for fuzzed input.
241 size_t remaining_bytes() { return remaining_bytes_; }
244 FuzzedDataProvider(const FuzzedDataProvider &) = delete;
245 FuzzedDataProvider &operator=(const FuzzedDataProvider &) = delete;
247 void Advance(size_t num_bytes) {
248 if (num_bytes > remaining_bytes_)
251 data_ptr_ += num_bytes;
252 remaining_bytes_ -= num_bytes;
255 template <typename T>
256 std::vector<T> ConsumeBytes(size_t size, size_t num_bytes_to_consume) {
257 static_assert(sizeof(T) == sizeof(uint8_t), "Incompatible data type.");
259 // The point of using the size-based constructor below is to increase the
260 // odds of having a vector object with capacity being equal to the length.
261 // That part is always implementation specific, but at least both libc++ and
262 // libstdc++ allocate the requested number of bytes in that constructor,
263 // which seems to be a natural choice for other implementations as well.
264 // To increase the odds even more, we also call |shrink_to_fit| below.
265 std::vector<T> result(size);
267 if (num_bytes_to_consume != 0)
272 std::memcpy(result.data(), data_ptr_, num_bytes_to_consume);
273 Advance(num_bytes_to_consume);
275 // Even though |shrink_to_fit| is also implementation specific, we expect it
276 // to provide an additional assurance in case vector's constructor allocated
277 // a buffer which is larger than the actual amount of data we put inside it.
278 result.shrink_to_fit();
282 template <typename TS, typename TU> TS ConvertUnsignedToSigned(TU value) {
283 static_assert(sizeof(TS) == sizeof(TU), "Incompatible data types.");
284 static_assert(!std::numeric_limits<TU>::is_signed,
285 "Source type must be unsigned.");
287 // TODO(Dor1s): change to `if constexpr` once C++17 becomes mainstream.
288 if (std::numeric_limits<TS>::is_modulo)
289 return static_cast<TS>(value);
291 // Avoid using implementation-defined unsigned to signer conversions.
292 // To learn more, see https://stackoverflow.com/questions/13150449.
293 if (value <= std::numeric_limits<TS>::max()) {
294 return static_cast<TS>(value);
296 constexpr auto TS_min = std::numeric_limits<TS>::min();
297 return TS_min + static_cast<char>(value - TS_min);
301 const uint8_t *data_ptr_;
302 size_t remaining_bytes_;
305 #endif // LLVM_FUZZER_FUZZED_DATA_PROVIDER_H_