libFuzzer fuzzer that dumps its input to stdout to get a sense of the effect of a given dictionary file (fuzzer argument "-dict=FILE")

show_libfuzzer_input.cxx

// Copyright (c) 2025 Sebastian Pipping <[email protected]>
// Licensed under the MIT license

#include <cctype> // isprint(3)
#include <cstdint>
#include <cstdio>      // putchar(3), printf(3)
#include <sys/param.h> // MIN(3)

static const unsigned int MAX_LEN = 30;

extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
  printf("[%19zd] \"", Size);

  for (size_t i = 0; i < MIN(Size, MAX_LEN); i++) {
    const uint8_t ch = Data[i];
    switch (ch) {
    case '\0':
      printf("\\0");
      break;
    case '"':
      printf("\\\"");
      break;
    case '\\':
      printf("\\\\");
      break;
    default:
      if (isprint(ch)) {
        putchar(ch);
      } else {
        printf("\\x%X", ch);
      }
    }
  }

  printf("\"");

  if (Size > MAX_LEN) {
    printf(" [..]");
  }

  printf("\n");

  return 0;
}