Add base32_fuzzer for base32::Base32Encode()

Change-Id: Ib2a9cf2b39eb758d120cff562c385d17a6d5c526
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1861139
Commit-Queue: Daniel Hosseinian <dhoss@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#708075}

components/base32/BUILD.gn

@@ -2,6 +2,8 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//testing/libfuzzer/fuzzer_test.gni")
+
 static_library("base32") {
   sources = [
     "base32.cc",
@@ -38,3 +40,15 @@ source_set("unit_tests") {
     "//testing/gtest",
   ]
 }
+
+fuzzer_test("base32_fuzzer") {
+  sources = [
+    "base32_fuzzer.cc",
+  ]
+
+  deps = [
+    ":base32",
+    ":base32_test_util",
+    "//base",
+  ]
+}

components/base32/base32_fuzzer.cc

+// Copyright 2019 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 <stddef.h>
+#include <stdint.h>
+
+#include <limits>
+
+#include "base/logging.h"
+#include "base/stl_util.h"
+#include "components/base32/base32.h"
+#include "components/base32/base32_test_util.h"
+
+base32::Base32EncodePolicy GetBase32EncodePolicyFromUint8(uint8_t value) {
+  // Dummy switch to detect changes to the enum definition.
+  switch (base32::Base32EncodePolicy()) {
+    case base32::Base32EncodePolicy::INCLUDE_PADDING:
+    case base32::Base32EncodePolicy::OMIT_PADDING:
+      break;
+  }
+
+  return (value % 2) == 0 ? base32::Base32EncodePolicy::INCLUDE_PADDING
+                          : base32::Base32EncodePolicy::OMIT_PADDING;
+}
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
+  if (size < 2 || size > std::numeric_limits<size_t>::max() / 5)
+    return 0;
+
+  const base32::Base32EncodePolicy encode_policy =
+      GetBase32EncodePolicyFromUint8(data[0]);
+  const base::StringPiece string_piece_input(
+      reinterpret_cast<const char*>(data + 1), size - 1);
+  std::string encoded_string =
+      base32::Base32Encode(string_piece_input, encode_policy);
+  std::string decoded_string = base32::Base32Decode(encoded_string);
+
+  CHECK_EQ(string_piece_input, decoded_string);
+  return 0;
+}