URLRequest fuzzer.

net/base/fuzzed_data_provider.h

+// 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.
+
+#ifndef NET_BASE_FUZZED_DATA_PROVIDER_H
+#define NET_BASE_FUZZED_DATA_PROVIDER_H
+
+#include <stdint.h>
+
+#include "base/macros.h"
+#include "base/strings/string_piece.h"
+
+namespace net {
+
+// Utility class to break up fuzzer input for multiple consumers. 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.
+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);
+  ~FuzzedDataProvider();
+
+  // Returns a StringPiece containing |length| bytes of the input data. If fewer
+  // than that many bytes remain, returns a shorter StringPiece containing all
+  // of the data that's left. The data pointed at by the returned StringPiece
+  // must not be used after the FuzzedDataProvider is destroyed.
+  base::StringPiece ConsumeBytes(size_t bytes);

[eroman, 2016/04/28 18:32:33]

FYI: In some follow-up changes I am reviewing, another useful API that has
emerged is something along the lines of:

  base::StringPiece ConsumeRemainingBytes()
  size_t num_remaining_bytes();

For instance I suggested this in
https://codereview.chromium.org/1929703003/#msg5, and I know Charles was
thinking similarly in
https://codereview.chromium.org/1919013003/diff/80001/net/base/fuzzed_data_pr...

[Charlie Harrison, 2016/04/28 18:37:42]

Yeah I was actually planning on adding this method now that this class dispenses
StringPieces.

[mmenke, 2016/04/28 18:38:29]

I was thinking I'd probably need something like that at some point, too.

Another thing that I was thinking may be useful is:

base::StringPiece ConsumeLine();

Which just consumes bytes up to the next LF, for fuzzing things that don't
expect to contain LFs that can be of arbitrary length (URLs, maybe?).  Less
finicky than separating out length and data into separate fields, too.

Or could make it contain a character / list of characters to stop at, like
strtok.

[eroman, 2016/04/28 18:45:48]

sgtm

+
+  // Returns a value from |min| to |max| inclusive, extracting a value from the
+  // input data in some unspecified manner. Value may 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|.
+  uint32_t ConsumeValueInRange(uint32_t min, uint32_t max);
+
+  // Returns a value with the specified number of bits of data. Returns 0 if
+  // there's no input data left. |num_bits| must non-zero, and at most 32.
+  // Basically the same as ConsumeValueInRange((1 << num_bits) - 1);
+  uint32_t ConsumeBits(size_t num_bits);
+
+  // Same as ConsumeBits(1), but returns a bool. Returns false when there's no
+  // data remaining.
+  bool ConsumeBool();
+
+ private:
+  base::StringPiece remaining_data_;
+
+  DISALLOW_COPY_AND_ASSIGN(FuzzedDataProvider);
+};
+
+}  // namespace net
+
+#endif  // NET_BASE_FUZZED_DATA_PROVIDER_H