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// Copyright 2018 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#ifndef BYTE_STREAM_H_
#define BYTE_STREAM_H_
#include <algorithm>
#include <cstddef>
#include <cstdint>
#include <limits>
#include <string>
// Wrapper for fuzzer input strings that helps consume and interpret the data
// as a sequence of values, such as strings and PODs.
class ByteStream {
public:
// Does not take ownership of data.
ByteStream(const uint8_t* data, size_t size)
: data_(data), size_(size), position_(0) {}
ByteStream(const ByteStream&) = delete;
ByteStream& operator=(const ByteStream&) = delete;
// Returns a string. Strings are obtained from the byte stream by reading a
// size_t N followed by N char elements. If there are fewer than N bytes left
// in the stream, this returns as many bytes as are available.
std::string GetNextString();
// The following GetNext{integer type} functions all return the next
// sizeof(integer type) bytes in the stream or 0 if there is insufficient
// capacity.
size_t GetNextSizeT() { return ConsumeCopyOrDefault<size_t>(0); }
int GetNextInt() { return ConsumeCopyOrDefault<int>(0); }
uint8_t GetNextUint8() { return ConsumeCopyOrDefault<uint8_t>(0); }
int64_t GetNextInt64() { return ConsumeCopyOrDefault<int64_t>(0); }
// Returns an integer in the range [0,n) for n > 0 and consumes up to
// sizeof(int) bytes. For n<=0, returns 0 and consumes 0 bytes.
int GetNextInt(int n);
// The remaining capacity of the ByteStream.
size_t capacity() const { return size_ - position_; }
// Returns data_ + position_ and then advances position_ by requested bytes.
//
// This is the canonical way for the class to request regions of memory
// or to advance the position by requested bytes. This operation is unchecked
// for maintaining that position_ <= size_. Requesting 0 bytes always
// succeeds.
const uint8_t* UncheckedConsume(size_t requested) {
const uint8_t* region = data_ + position_;
position_ += requested;
return region;
}
private:
// Directly initialize T by copying sizeof(T) bytes into results if there is
// sufficient capacity in the stream. If there is not sufficient capacity
// result is unmodified.
template <class T>
void ConsumeBytesByCopy(T* result) {
constexpr size_t type_size = sizeof(T);
if (type_size <= capacity()) {
const uint8_t* region = UncheckedConsume(type_size);
memcpy(static_cast<void*>(result), region, type_size);
} else {
// Consume the remainder of data_.
UncheckedConsume(capacity());
}
}
// A helper function for using ConsumeBytesByCopy and returning a default
// value `t` if there is insufficient capacity to read a full `T`. T should
// probably be a primitive type.
template <class T>
T ConsumeCopyOrDefault(T t) {
ConsumeBytesByCopy(&t);
return t;
}
const uint8_t* data_;
const size_t size_;
size_t position_;
};
inline std::string ByteStream::GetNextString() {
const size_t requested_size = GetNextSizeT();
const size_t consumed_size = std::min(requested_size, capacity());
const uint8_t* selection = UncheckedConsume(consumed_size);
return std::string(reinterpret_cast<const char*>(selection), consumed_size);
}
inline int ByteStream::GetNextInt(int n) {
if (n <= 0) {
return 0;
}
// We grab as few bytes as possible as n will often be fixed.
int selection = 0;
if (n <= std::numeric_limits<uint8_t>::max()) {
selection = static_cast<int>(GetNextUint8());
} else if (n <= std::numeric_limits<uint16_t>::max()) {
selection = ConsumeCopyOrDefault<uint16_t>(0);
} else {
selection = GetNextInt();
}
// Take the absolute value of selection w/o undefined behavior.
// If selection is INT_MIN, return 0.
if (selection == std::numeric_limits<int>::min()) {
selection = 0;
} else if (selection < 0) {
selection = -selection;
}
return selection % n;
}
#endif // BYTE_STREAM_H_
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