URLRequest fuzzer.

net/base/fuzzed_data_provider.cc

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "net/base/fuzzed_data_provider.h"
+
+#include <algorithm>
+#include <limits>
+
+#include "base/logging.h"
+
+namespace net {
+
+FuzzedDataProvider::FuzzedDataProvider(const uint8_t* data, size_t size)
+    : remaining_data_(reinterpret_cast<const char*>(data), size) {}
+
+FuzzedDataProvider::~FuzzedDataProvider() {}
+
+base::StringPiece FuzzedDataProvider::ConsumeBytes(size_t length) {
+  length = std::min(length, remaining_data_.length());
+  base::StringPiece result(remaining_data_.data(), length);
+  remaining_data_ = remaining_data_.substr(length);
+  return result;
+}
+
+uint32_t FuzzedDataProvider::ConsumeValueInRange(uint32_t min, uint32_t max) {
+  CHECK_LE(min, max);
+
+  uint32_t range = max - min;
+  uint32_t offset = 0;
+  uint32_t result = 0;
+
+  while ((range >> offset) > 0 && !remaining_data_.empty()) {
+    // 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.
+    uint8_t next_byte = remaining_data_.data()[remaining_data_.length() - 1];
+    result = (result << 8) | next_byte;
+    remaining_data_ = remaining_data_.substr(0, remaining_data_.length() - 1);
+    offset += 8;
+  }
+
+  // Avoid division by 0, in the case |range + 1| results in overflow.
+  if (range == std::numeric_limits<uint32_t>::max())
+    return result;
+
+  return min + result % (range + 1);
+}
+
+uint32_t FuzzedDataProvider::ConsumeBits(size_t num_bits) {
+  CHECK_NE(0u, num_bits);
+  CHECK_LE(num_bits, 32u);
+
+  if (num_bits == 32)
+    return ConsumeValueInRange(0, std::numeric_limits<uint32_t>::max());
+  return ConsumeValueInRange(0, (1 << num_bits) - 1);
+}
+
+bool FuzzedDataProvider::ConsumeBool() {
+  // Double negation so this returns false once there's no more data.
+  return !!ConsumeBits(1);
+}
+
+}  // namespace net