Shamelessly copy Josiah

source/lib/json/tests/thirdparty/Fuzzer/test/CustomCrossOverTest.cpp

@@ -0,0 +1,63 @@
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+
+// Simple test for a cutom mutator.
+#include <assert.h>
+#include <cstddef>
+#include <cstdint>
+#include <cstdlib>
+#include <iostream>
+#include <random>
+#include <string.h>
+
+#include "FuzzerInterface.h"
+
+static const char *Separator = "-_^_-";
+static const char *Target = "012-_^_-abc";
+
+static volatile int sink;
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
+  assert(Data);
+  std::string Str(reinterpret_cast<const char *>(Data), Size);
+
+  // Ensure that two different elements exist in the corpus.
+  if (Size && Data[0] == '0') sink++;
+  if (Size && Data[0] == 'a') sink--;
+
+  if (Str.find(Target) != std::string::npos) {
+    std::cout << "BINGO; Found the target, exiting\n";
+    exit(1);
+  }
+  return 0;
+}
+
+extern "C" size_t LLVMFuzzerCustomCrossOver(const uint8_t *Data1, size_t Size1,
+                                            const uint8_t *Data2, size_t Size2,
+                                            uint8_t *Out, size_t MaxOutSize,
+                                            unsigned int Seed) {
+  static bool Printed;
+  static size_t SeparatorLen = strlen(Separator);
+
+  if (!Printed) {
+    std::cerr << "In LLVMFuzzerCustomCrossover\n";
+    Printed = true;
+  }
+
+  std::mt19937 R(Seed);
+
+  size_t Offset1 = 0;
+  size_t Len1 = R() % (Size1 - Offset1);
+  size_t Offset2 = 0;
+  size_t Len2 = R() % (Size2 - Offset2);
+  size_t Size = Len1 + Len2 + SeparatorLen;
+
+  if (Size > MaxOutSize)
+    return 0;
+
+  memcpy(Out, Data1 + Offset1, Len1);
+  memcpy(Out + Len1, Separator, SeparatorLen);
+  memcpy(Out + Len1 + SeparatorLen, Data2 + Offset2, Len2);
+
+  return Len1 + Len2 + SeparatorLen;
+}