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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 <limits.h>
+#include <stddef.h>
+#include <stdint.h>
+
+#include <algorithm>
+#include <cstring>
+#include <initializer_list>
+#include <string>
+#include <type_traits>
+#include <utility>
+#include <vector>
+
+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_);
+  }
+
+  // Prefer using |ConsumeRemainingBytes| unless you actually need a std::string
+  // object.
+  // Returns a std::vector containing all remaining bytes of the input data.
+  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 a value selected from a 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) {
+    // static_assert(list.size() > 0, "The array must be non empty.");
+    return *(list.begin() + ConsumeIntegralInRange<size_t>(0, list.size() - 1));
+  }
+
+  // Return 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)));
+  }
+
+  // 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_